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SID 5 Research Project Final Report

NoteIn line with the Freedom of Information Act 2000, Defra aims to place the results of its completed research projects in the public domain wherever possible. The SID 5 (Research Project Final Report) is designed to capture the information on the results and outputs of Defra-funded research in a format that is easily publishable through the Defra website. A SID 5 must be completed for all projects.

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Project identification

1. Defra Project code BD1458

2. Project title

A Literature Review and Gap Analysis of Grassland Restoration Research in the UK and Europe

3. Contractororganisation(s)

Dr Richard PywellNERC centre for Ecology and HydrologyMonks WoodAbbots RiptonHUNTINGDONPE28 2LS

54. Total Defra project costs £ 50,000(agreed fixed price)

5. Project: start date............. 01/12/05

end date................. 31/05/06

SID 5 (Rev. 3/06) Page 1 of 45

6. It is Defra’s intention to publish this form. Please confirm your agreement to do so...................................................................................YES NO (a) When preparing SID 5s contractors should bear in mind that Defra intends that they be made public. They

should be written in a clear and concise manner and represent a full account of the research project which someone not closely associated with the project can follow.Defra recognises that in a small minority of cases there may be information, such as intellectual property or commercially confidential data, used in or generated by the research project, which should not be disclosed. In these cases, such information should be detailed in a separate annex (not to be published) so that the SID 5 can be placed in the public domain. Where it is impossible to complete the Final Report without including references to any sensitive or confidential data, the information should be included and section (b) completed. NB: only in exceptional circumstances will Defra expect contractors to give a "No" answer.In all cases, reasons for withholding information must be fully in line with exemptions under the Environmental Information Regulations or the Freedom of Information Act 2000.

(b) If you have answered NO, please explain why the Final report should not be released into public domain

Executive Summary7. The executive summary must not exceed 2 sides in total of A4 and should be understandable to the

intelligent non-scientist. It should cover the main objectives, methods and findings of the research, together with any other significant events and options for new work.

1. Productive, species-poor grasslands are the dominant land cover type in the UK by area. They are therefore an important component of the agri-environment schemes. Intensive management associated with these habitats has strongly negative effects on a wide range of taxa.

2. A literature review and gap analysis was undertaken to provide a background for increasing the cost-effectiveness and reliability of prescriptions to enhance the botanical diversity of these species-poor, structurally uniform grasslands.

3. There are currently no clearly defined targets for the enhancement of biodiversity for this extensive resource of species-poor grasslands managed under the agri-environment schemes.

4. Different taxa exploit grassland habitats at a range of scales, so in the absence of clear targets, it would be advisable to aim for moderate increases in diversity at the largest possible (landscape) scale by large numbers of farmers.

5. Widely implemented prescriptions for grassland diversification are currently simplistic and low cost, but unlikely to result in large benefits for biodiversity in the short term. More interventionist approaches are highly effective, but they can only be implemented at a small number of sites for reasons of cost and practicality.

6. The future research challenge is therefore to develop whole a farm systems approach to the restoration of biodiversity. This should couple a greater understanding of the underlying ecological mechanisms limiting restoration to the existing framework of low intensity pastoral farming practices encouraged under the agri-environment schemes to facilitate and accelerate the natural processes of colonisation and establishment of desirable species across the field, farm and landscape.

7. Research into the mechanisms of dispersal and colonisation by desirable species, and how these might be manipulated by extensive management practices, is therefore the 8. Other critical gaps in the scientific knowledge are: (i) techniques (including phased introduction) to improve the establishment and persistence of poor-performing species and therefore avoid uniformity of restored grassland communities; (ii) the effects of soil structural degradation on biodiversity enhancement and methods to overcome this constraint.

9. A more limited amount of research is required to develop and refine practical ‘restoration tools’ for promising approaches to grassland diversification, including the use of


functional species, such as parasitic plants.10. Some basic research is also required to determine the potential impacts of wide scale

and repeated introductions of non-local genotypes and agricultural varieties in seed mixtures on native patterns of genetic diversity and associated taxa.

11. A considerable amount of research has provided practical solutions to overcoming seed limitation at the field scale, including seed sowing and green hay. Future research should focus on low-cost alternative approaches to the large-scale sowing of complex and costly seed mixtures, including encouraging dispersal and colonisation.

12. Recent research on productive grasslands and arable field margins suggests that, provided appropriate management is implemented, it is possible to achieve and sustain modest increases in botanical diversity despite relatively high soil fertility.

13. Grassland management activities are the key to the enhancement of grassland biodiversity at the large scale. Future research should concentrate on the effects of management activities on seed dispersal and microsite creation.

14. Ongoing research should answer many of the applied questions relating to the effects on soil microbial communities on the restoration process.

Project Report to Defra8. As a guide this report should be no longer than 20 sides of A4. This report is to provide Defra with

details of the outputs of the research project for internal purposes; to meet the terms of the contract; and to allow Defra to publish details of the outputs to meet Environmental Information Regulation or Freedom of Information obligations. This short report to Defra does not preclude contractors from also seeking to publish a full, formal scientific report/paper in an appropriate scientific or other journal/publication. Indeed, Defra actively encourages such publications as part of the contract terms. The report to Defra should include: the scientific objectives as set out in the contract; the extent to which the objectives set out in the contract have been met; details of methods used and the results obtained, including statistical analysis (if appropriate); a discussion of the results and their reliability; the main implications of the findings; possible future work; and any action resulting from the research (e.g. IP, Knowledge Transfer).


1. Introduction

Centuries of low intensity pastoral farming have resulted in the development and maintenance of highly diverse temperate grassland ecosystems across northwest Europe which are of high conservation value (Poschlod & Wallis-DeVries 2002). Agricultural intensification, especially in the second half of the twentieth century, has caused the loss of much of this resource either through conversion to arable land, or through degradation caused by methods aimed at increasing grassland productivity (re-seeding, drainage and increased inputs of fertilizers and pesticides). Enhanced grassland productivity has supported a significant intensification of management practices, including earlier repeated cutting for silage and increased stocking rates (Hopkins & Hopkins 1994). As a result, most of the grassland in the UK has been replaced by species-poor, structurally uniform and intensively managed swards which are now the dominant land cover type, covering approximately 59,000 km2 (24%) (Fuller et al. 2002). It is estimated that as little as 50,000 to 100,000 ha of unimproved, semi-natural grasslands now remain in lowland England and Wales (reviewed by Blackstock et al. 1999).There is a growing body of evidence that intensive management associated with improved grassland has a strongly negative effect on a wide range of taxa (reviewed by Vickery et al. 1999; 2001): including broad-leaved plants and fine-leaved grasses (Kirkham et al. 1996; Defra projects BD1425, BD1435); bumblebees (BD1617; Carvell et al. 2001); butterflies (Asher et al. 2001; Léon-Cortés et al. 2000); phytophagous and granivorous ground-beetles and leaf-hoppers, caterpillars and sawfly larvae (BD1435).

One of the key aims of recent conservation policy across Europe is the re-instatement of low intensity farming systems to benefit biodiversity. Improved and semi-improved grasslands are therefore a particularly important component of the UK agri-environment schemes, with over 4,925 km2 currently under agreement in the ESA and Countryside Stewardship schemes alone (Carey et al. 2002; Carey et al. 2005). However, the results of recent monitoring and research suggest that the botanical diversity of these grasslands often remains low despite management prescriptions aimed at diversification (Carey et al. 2000; Kleijn & Sutherland 2003; Mountford et al. 1996). In order to understand the reasons for this it is important to consider the main above- and below-ground limitations on ecological restoration (Mortimer, Hollier & Brown 1998; Bakker & Berendse 1999), and develop practical techniques to overcome them (reviewed by Walker et al. 2004).

The aim of this project was to provide an overview of the key limitations on the restoration of botanical diversity to species-poor grassland and suggest research questions that will ultimately result in an increase in the cost-effectiveness and reliability of agri-environment scheme prescriptions. This was achieved through a workshop consultation with key stakeholders and a literature review of UK and European research to provide a comprehensive, evidence-based summary of the current knowledge (and lack of knowledge) of:1) the key processes constraining the restoration of grassland diversity;2) the most cost-effective and reliable means of overcoming these limitations within modern farming systems;3) the future research priorities to meet current and future agri-environment scheme and UKBAP policy objectives for the restoration of species-rich grasslands.

The enhancement and restoration of faunal diversity to grasslands has been the subject of several recent reviews (e.g. Morris 2000; Vickery et al. 2001; Steffan-Dewenter & Tscharntke 2002) and it therefore not considered here.

2. Policy requirements for grassland diversification

The UK Biodiversity Action Plan (UKBAP) requires the restoration of 2000 ha of various types of high quality species-rich grassland before 2010 (Anon. 1998). However, there are currently no clearly defined targets for the enhancement of biodiversity on the very extensive resource of species-poor grasslands managed under the agri-environment schemes. Different taxa are known to exploit grassland habitats at a wide range of scales (reviewed by Vickery et al. 2001; Tscharntke et al. 2005), so in the absence of clear targets, it would be advisable to aim for at least moderate increases in diversity and habitat heterogeneity at the largest possible (landscape) scale by large numbers of farmers. Widely implemented prescriptions for grassland diversification under the agri-environment schemes are currently simplistic and low cost (e.g. nil or low inputs of fertiliser (EK2, EK3); Defra 2005). However, previous monitoring and research would suggest that these are unlikely to result in large benefits for biodiversity in the short term. Conversely, Defra-funded research into more interventionist approaches to diversification, including sowing complex seed mixtures and topsoil stripping, has concluded that whilst these are highly effective, they can only be implemented at a small number of sites for reasons of cost and practicality. Future research therefore needs to develop a whole farm systems approach to the restoration of biodiversity. This would seek to couple a greater understanding of underlying ecological mechanisms to the existing framework of low intensity pastoral farming practices of

BD1458 Draft Final ReportNERC Centre for Ecology and Hydrology

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grazing and late hay cutting encouraged under the agri-environment schemes in order to facilitate and accelerate the natural processes of colonisation and establishment of desirable species and communities across the farm and landscape. This will also need to address other key issues, such as resource protection and socio-economic barriers to uptake and implementation of these policies, including the role of farmer attitude and training, and critically, the potential impacts on farm livelihoods.

3. Theoretical framework: key ecological processes in grassland diversification

It is most informative to think of the process of grassland diversification in terms of community ecology and the theory of assembly rules (Diamond 1975). Studies of plant communities following some form of disturbance have identified the following factors as key determinants of the trajectories of community assembly: 1) Rate and sequence of propagule arrival; 2) Resource supply; and 3) Biotic interactions (see reviews and papers in Weiher & Keddy 1999). While there has been much debate among ecologists about the precise mechanisms of community assembly, recent years have seen increasing consensus and a movement away from over-emphasis on particular mechanisms (e.g. Weiher & Keddy 1999; Grime 2001; Bullock et al. 2002). In general plant community assembly involves a sequences of processes that often interact (see Fig. 1). In restoration the starting point may comprise a range of initial states, from a bare substrate to a pre-existing vegetation (e.g. species-poor grassland). New species can potentially colonise through the seed bank, dispersal from other vegetation, or addition by humans. These seeds require appropriate microsites where local conditions allow germination and establishment. These plants must then survive, complete their life-cycles and reproduce to provide propagules (seeds, clonal material, etc) for the next generation. Persistence of these new populations and change in pre-existing populations (the initial community) is controlled by a range of factors, listed below (Fig. 1). More general understanding of how restored communities assemble in response to these factors is available through analysis of species’ traits. Traits such as life-cycle, seed size, plant growth rate, etc allow species to be grouped into functional types. In this way, while individual species have idiosyncratic responses to these factors, their grouping into functional types illustrates general patterns in the assembly of restored communities and allows greater predictability (BD1433; Pywell et al. 2003; Fukami et al. 2005).

The factors which govern community assembly can be summarised under the following headings and these will form the structure of this review. 1) Resource supply: Soil physical characteristics, fertility, pH and hydrology; Gap and microsite limitation; Soil microbial communities2) Biotic interactions: Resource competition; Parasites; Herbivores; Management; Genetic provenance3) Rate and sequence of propagule arrival: Seed and dispersal limitation; Successional stage.


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Fig. 1. Key processes in the assembly of grassland communities during restoration

4. Methodology

4.1 LITERATURE SEARCHES

This review was primarily based on a comprehensive search of the scientific literature on the theory and practice of grassland restoration. This was undertaken using Web of Science (http://www.isinet.com/), Google Scholar (http://scholar.google.com/) and the Defra science and research reports web site. Web of Science searches were undertaken using the terms ‘grassland SAME diver* AND one of the factors controlling community assembly (Section 3)’ and ‘grassland SAME restor* AND …..’ Google searches used the term 'grassland AND .... with restoration or restored.’

4.2 STAKEHOLDER CONSULATION

A structured questionnaire was completed by 21 people directly involved in grassland restoration policy, research and practice in the UK and Europe (Appendix 1), including representatives from Defra, RDS, English nature, research scientists and the wildflower seed industry (full list of attendees given in Appendix 2). In this they were asked to prioritise the relative importance of various biotic and abiotic factors affecting grassland restoration (Section 3) and to give an assessment of the current state of scientific knowledge relating to each factor (nil, poor, moderate, good). This group also attended a workshop held in March 2006 which provided an opportunity to discuss ongoing and recently completed research, and to assess priorities for future theoretical and applied research requirements.


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State 3:Target Plant Community(desirable sp.)

State 2: Intermediate

Plant Community

(desirable + undesirable sp.)

State 1:Initial Plant Community

(undesirable sp.)

1. Colonisation

Rate & sequence of propagule arrival

3. Establishment

Resource supply

4. Regeneration

Dispersal from local / regional sp. pool

Seed bank

Seed addition

2. Germination

Target / desirable species

Biotic interactionsSoil physical properties, hydrology, fertility & pH

Gap & microsite limitation

Soil microbial communities

Successional stage

Resource competition

Parasites

Herbivores

Genetic provenance

Management

http://scholar.google.com/

5. Results

5.1 LITERATURE SEARCHESSearches using both Web of Science and Google Scholar with either search terms yielded a broadly similar pattern of results. Factors important in grassland diversification with the greatest numbers of ISI publications (>50) were grazing and cutting management, soil fertility and pH, soil microbial communities, and seed mixtures and seed bank (Fig. 2). Factors with a moderate to low number of publications (20-30) were dispersal, genetic provenance, parasitic plants and herbivory. Finally, areas with few publications (<20) included gaps and microsites, hydrology, soil compaction, soil pathogens and plant traits.

Fig. 2. Results of Web of Science search of ISI publications 1970 to present using the search term ‘grassland SAME diver* AND……..’

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5.2 STAKEHOLDER CONSULTATION

When interpreting the results of the questionnaire it is important to understand that the sample of experts questioned was relatively small (21) and there will be a degree of uncontrolled bias in the results which reflects personal research interests and preferences. Nevertheless, results suggested that soil fertility, dispersal, gaps and microsites, and seed limitation were the most important factors controlling grassland diversification (Fig. 3a). Soil compaction, hydrology and parasitic plants were also judged to be important, whereas, soil microbial communities, genetic provenance and herbivory were considered to be of lesser importance.

Factors for which the current scientific knowledge was considered to be moderate to good included grazing and cutting management, soil fertility, seed limitation and hydrology (Fig. 3b). Factors judged to have moderate to poor knowledge were gaps and microsites, dispersal, soil compaction and parasitic plants. Finally, factors thought to currently have a poor knowledge base were genetic provenance, soil microbial communities and herbivory.

It was concluded from the questionnaire that important factors controlling grassland diversification that currently have a poor scientific knowledge base were: dispersal, gap and microsite limitation, soil compaction and parasitic plants (Fig. 3a,b). As expected, the key discussion points and research priorities that emerged from the workshop broadly concurred with the results of the questionnaire (summarised in Appendix 3).


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In the remaining sections of the report we will provide a synopsis of the current state of knowledge of each factor identified as important in the process of grassland diversification, and for each we will recommend future research priorities.

Fig. 3. Results of structured questionnaire completed by panel of experts to determine opinion of (a) import factors for grassland diversification; (b) Current state of knowledge.


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6. Soil physical and chemical parameters

6.1 CURRENT KNOWLEDGE

6.1.1 Soil physical parametersCompaction and other structural degradation of grassland soils may inhibit the full potential of biodiversity enhancement for many wet grassland agri-environment schemes (reviewed by BD1307). High rates of soil compaction were recorded for 30% of the grassland sites in England and Wales following the wet winter of 2000 (Holman et al. 2003). Overstocking, or grazing when the soil is too wet, leads to poaching and compaction (Vallentine 1990). Lowland pastures where grass growth starts early in the year and persists later are especially vulnerable because stock may be kept on the land at the wettest point in the hydrological cycle. Vehicle passage also results in soil surface deformation and compaction (Chambers & Garwood 2000). A replicated experiment on freely-drained chalk grassland found that single and multiple passes of a 4 tonne wheeled vehicle, and multiple passes of a 1 tonne vehicle resulted in significant soil compaction and resultant damage to the grassland community which persisted for at least 3 years (Hirst et al. 2003). Such compaction can alter local hydrology, soil nutrient status and decomposition of litter (Voorhees et al. 1989; Alakukku & Elonen 1995), in addition to restricting root penetration and growth (Agnew & Carrow 1985; Braunack & Williams 1993). Modified site conditions caused by soil compaction, altered hydrology and the availability of propagules all affect grassland re-establishment (Shaw & Diersing 1990; Jones & Bagley 1998).

The remediation of soil compaction occurs naturally through biotic agents (e.g. soil fauna and plant root growth) and abiotic agents (such as the action of frost heave). Estimates have been made for the recovery of soils from compaction in desert systems that range between 80 and 140 years (Knapp 1992; Webb & Wilshire 1980). It is likely that in less dry environments, where microbial populations are higher, recovery rates will be more rapid (Belnap 1995). It is possible to accelerate the process of soil re-structuring by physical means, including the exclusion of livestock (Beebe et al. 2002), mechanical aeration (Martin & Chambers 2002) and soil ripping (Yates, Hobbs & Atkins 2000). Moreover, there is evidence from arid agriculture that deep rooted plant species can be used to improve soil structure (the ‘primer-plant concept’) (reviewed by Yunusa & Newton 2003). The rate of natural recovery from compaction and these approaches to remediation require further testing in the context of wet grassland restoration in the UK.

6.1.2 Soil hydrologyHydrological regime (flood duration and water-table) is one of the most important environmental variables controlling plant community composition in wet grasslands (BD0209; BD1310; BD1321; Boutin & Keddy 1993; Grevilliot et al. 1998). Indeed, hydrological niche separation has been proposed as the primary mechanism of co-existence in these species rich communities (Silvertown et al. 1999). The water regime requirements of many wet grassland species (99) and communities (9) in the UK is now well understood (BD1310; BD1321). Hydrological regime has been shown to have a potentially greater influence on wet grassland community re-assembly under restoration than seed mixture composition (Gilbert, Gowing & Bullock 2003). It is therefore extremely important to select appropriate species for the achievable hydrological conditions, or to have full control over the water regime during restoration.

There is a growing body of research into wet grassland restoration by re-instatement of appropriate hydrological conditions (rewetting) (Oomes 1992; Oomes, Olff & Altena 1996) in order to decrease nitrogen mineralization and productivity (Myers et al. 1982). Other studies have emphasised the additional importance of water quality in the restoration of oligotrophic fen meadow communities (van Duren et al. 1998). However, the re-assembly of wet grassland communities following rewetting has typically been slow due to lack of available seed sources (Bakker & Berendse 1999; Section 9).

6.1.3 Soil chemical parametersGrasslands of high conservation value are typically associated with soils of low nutrient status (Vermeer & Berendse 1983; Fuller 1987; Marrs 1993; Smith 1993). This follows the humpback model of plant community structure that predicts species richness will decline with increasing nutrient availability and biomass due to competitive exclusion by species capable of rapid resource capture and biomass accumulation (Al-Mufti et al. 1977; Grime 1979). A survey of 281 permanent, mostly mesotrophic grasslands across Europe found that low levels of soil phosphorus (P) were correlated with high levels of plant species richness (Janssens et al. 1998). A survey of a broader range of lowland grassland types in England revealed a more complex relationship, with other soil properties, such as pH and wetness, being important determinants of plant diversity for some grassland types (Critchley et al. 2002). Finally, the famous Park Grass Experiment has shown that addition of P reduced species richness of the grassland, but the biggest negative effect was when P and nitrogen (N) fertilisers were applied together (Crawley et al. 2005). This also confirmed the importance of pH in controlling the availability of major nutrients.


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High residual soil fertility and altered pH resulting from intensive farming may therefore place severe constraints on the enhancement and long-term maintenance of plant species diversity (Marrs 1993; Pywell, Webb & Putwain 1994). However, recent research as shown that it possible to restore and maintain moderate levels of plant species richness to productive grasslands and fertile arable land with high concentrations of P provided appropriate management is implemented (BD1404; BD1425; BD1624; Pywell et al. 2002a; Pywell et al. in press).

Techniques to reduce soil fertility have been reviewed by Marrs (1993). Grazing alone is unlikely to decrease soil nutrients in the medium term. Bullock et al. (2001) found heavy vs. light sheep grazing following cessation of fertilizer inputs had no effect on the major soil nutrients over 12 years. Reduction of soil nutrients through herbage removal as hay or silage alone is also likely to take many years. Only 1% of total P and exchangeable potassium (K), and 2.5% of total N were removed annually from soil nutrient pools by this method, but this exceeded the off-take by grazing animals alone (Bakker 1987). However, more frequent cutting removes more nutrients and generally hastens reversion of vegetation composition (e.g. Olff & Bakker 1991; Hayes & Sackville Hamilton 2001). It has been calculated to take 25 years of cutting 2-3 times per year to reduce soil P in highly improved grasslands to levels equivalent to those of unimproved grasslands (BD1425; Tallowin et al. 2002). However, additions of 250 kg N/ha and 100 kg K/ha accelerated P off-take and reduced time to reach equivalence to 12 years. Hay cutting followed by aftermath (and sometimes spring) grazing has generally been more successful than either cutting or grazing alone (Hayes et al. 2000; Smith et al. 2000; Hayes & Sackville Hamilton 2001). Such management has been shown to accelerate reductions in residual soil fertility as well as optimise conditions for the colonisation and establishment of target species.

Continuous cereal cropping failed to reduce significantly soil P or pH prior to heathland restoration (Marrs et al. 1998). Deep cultivation to dilute fertile topsoil with less fertile subsoil caused only a short-term (<4 years) reduction in P and K on shallow arable soils undergoing reversion to species-rich grassland (BD1404; Pywell et al. 2002a). Topsoil removal has been shown to be effective in reducing soil fertility and plant competition in some instances (e.g. Pegtel et al. 1996; Tallowin & Smith 2001; Holzel & Otte 2003). However, this approach significantly reduced N but not P concentrations when applied to two highly productive grassland sites in lowland England (BD1425; Pywell et al. in press). This approach to nutrient reduction is only applicable at the small scale for reasons of cost and practicality (Pywell et al. 2002b)

6.2 RESEARCH QUESTIONS

Both the workshop and the questionnaire were in agreement that soil compaction, hydrology and fertility were all potentially important factors controlling grassland diversification. However, the scientific knowledge base was judged to be moderate to good for hydrology and soil fertility, whereas it was thought to be poor for soil compaction and degradation. The literature search generally concurred with this view, but there were few published papers on hydrology. This apparent disparity can be explained by a considerable amount of very recent Defra-funded research on this topic which reported in 2005 (BD1310; BD1321). Future research should address the following:

1) Surveys of the extent and magnitude of soil structural degradation in grasslands managed within the agri-environment schemes.

2) Effects of structural degradation on factors such as (i) re-wetting characteristics of the soil; (ii) soil processes such as mineralisation; (iii) soil macrofauna; (iv) plant community assembly and (v) the utilisation of wet grassland habitats by birds assemblages. Research should specifically focus on clay and peat soils undergoing wet grassland restoration.

3) Field experiments to determine the effectiveness of large-scale techniques to re-structure degraded soils prior to restoration. This should consider (i) physical remediation using mechanical aeration, cultivation and ripping, (ii) biological remediation using deep-rooted plant species, and (iii) a combination of both techniques.

4) Research across a wide range of sites and conditions into the potential of using intensive management in the early phases of restoration to mitigate the impact of high residual soil fertility on grassland community re-assembly. This would follow on from the findings of recent Defra research on the diversification of highly productive grasslands (BD1425; Pywell et al. in press).


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7. Soil microbial communities


7.1.1 Role of soil microbes in promoting plant diversityThere is increasing evidence that soil microbial communities play a critical role in the regulation and maintenance of above-ground plant biodiversity through their control of essential ecosystem functions, such as nutrient recycling (van der Heijden et al. 1998; Hartnett & Wilson 1999; Bardgett 2005). It is well known that fungal dominated soils typically support extensive arbuscular mycorrhizal fungal (AMF) networks that enable slower-growing plants to exploit resources that would otherwise be unavailable to them, thereby enhancing their relative abundance within the community (van der Heijden et al. 1998; Hartnett & Wilson 1999). These soils retain large amounts of N in their microbial biomass which is released at a slower rate with a high proportion in an organic form, favouring slower growing species over fast-growing species (Bardgett 2005). In contrast, bacteria dominated soils have fast cycles and low microbial retention of N released predominantly as inorganic N which favours fast growing species.

7.1.2 Soil microbial response to grassland managementExtensively managed, species-rich grasslands have fungal-dominated soil microbial communities with elevated fungal growth (mycorrhizae and decomposer) and a high fungal-to-bacterial biomass ratio as measured by phospholipid fatty acid analysis (PLFA) (Frostegård & Bååth 1996) (Table 1). Intensive grassland management invariably leads to bacterial-dominance of the microbial community. However, this shift in fungal-bacterial ratios resulting from management change has still only been confirmed for a sub-set of grassland types. Defra project BD1451 is currently undertaking a comprehensive survey of soil microbial community attributes across the full range of management intensity and different climatic and topographic conditions. Such information would also provide an indication of how factors such as variation in soil organic matter quality, pH and soil moisture status, and vegetation diversity relate to changes in soil microbial communities.

Table 1. Summary of previous studies on microbial responses to grassland management (adapted from BD1451).

Grassland system Methodology

Response of microbial community

Reference

Complete range of grassland types in the UK including calcareous and wet grasslands

PLFA Ongoing BD1451

Comparison of long-term organic and conventional grassland systems in lowland Mid Wales.

PLFA Total microbial biomass and fungal:bacterial biomass ratio significantly greater in organic than fertilised grassland soils.

Yeates et al. (1997)

Different intensities of long-term grassland management in Devon, SE England.

PLFA Total microbial biomass and fungal: bacterial biomass ratio significantly greater in long-term unfertilised than fertilised grasslands (280 kg N ha-1 an-1)

Bardgett et al. (1999)

Adjacent fertilised and unfertilised meadows in northern England and Wales.

PLFA, Ergosterol analysis

Total microbial biomass, fungal biomass and fungal:bacterial biomass ratio consistently greater in unfertilised than adjacent fertilised upland meadows.

Donnison et al. (2000)

Productive upland grasslands under extensive management (3 yrs) in South Wales.

PLFA Cessation of fertiliser applications and liming resulted in significant increase in the soil fungal:bacterial biomass ratio

Bardgett & Leemans (1995)

Gradient of meadow management from MG6-to-MG3 in Yorkshire Dales

PLFA Total fungal biomass and the fungal:bacterial biomass ratio twice as high in unmodified/slightly modified meadows than intensively managed grasslands

Bardgett & McAlister (1999)

A range of sites across upland UK with a each having a gradient of management

PLFA Intensive management led to shift from fungal-to-bacterial dominance

Grayston et al (2001)


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intensity from unimproved-to-semi-improved-to improved grasslands

in microbial community across all sites and environmental conditions

Colt Park restoration experiment, Yorkshire

PLFA Experimental treatments associated with traditional management and seed introduction enhance fungal:bacterial ratio

Smith et al. (2003)

Alpine meadows across a N-S transect in the European Alps

PLFA Elevated fungal-to-bacterial biomass ratio associated with traditionally managed, high diversity meadow

Zeller et al. (2000)

7.1.3 Effect of plant species on soil microbial communitiesDifferent plant species can affect soil microbial communities by altering the quality and quantity of resources returned to the soil via root exudates and plant litter (Cadisch 1996; Quested et al 2002; 2003). It has been hypothesised that plant species with particular ecophysiological traits may act as important drivers of change in soil microbial communities (Smith et al. 2003; Bardgett et al. 2006). In addition, parasitic plants, such as Rhinanthus sp., have the capability to indirectly influence this process by limiting the growth of other species within the community (Section 12). Certain forb species have been shown to significantly enhance fungal growth compared with fast-growing grasses which enhance bacterial growth (‘soil conditioning’) (Grayston et al. 1998; Innes, Hobbs & Bardgett 2004). Moreover, some grasslands species grow better in soils that have been conditioned by other species relative to their own soil (negative feedback), whereas fast growing grasses, performed better in their own soil (positive feedback). This has important implication for grassland community assembly at the small scale since it suggests that species showing negative feedback may facilitate sward enhancement, whereas those showing positive feedback will retain dominance.

7.1.4 Reversing detrimental changes in soil microbial communitiesShifts in microbial community structure resulting from intensive management are reversible over long time-scales through the implementation of extensive management regimes aimed at restoring botanical diversity (Smith et al. 2003). Inoculation of productive grassland and ex-arable land in the early stages of restoration with fungal-dominate soil failed to alter the soil microbial community (BD1425; Pywell et al. in press; Hedlund 2002). BD1451 is investigating the use of ‘facilitator’ species to enhance the quantity and quality of litter entering the soil and promote decomposer fungi. Novel stable isotope (N15) approaches (Streeter, Bol & Bardgett 2000) will test whether elevated fungal biomass resulting from the presence of facilitator species directly influence the uptake of limiting resources (nitrogen) by slower-growing species.

7.1.5 The role of soil pathogens in determining vegetation developmentWhile the decomposer and mycorrhizal communities are the focus of much attention, the role of soil pathogens in affecting plant diversity has been less studied. Particular soil fungi and bacteria which have pathogenicity towards a plant species can build up locally in the presence of that species and cause plant death or reduced competitive ability (Wardle et al. 2004). This effect can outweigh beneficial impacts of mutualistic microbes, so that soil sterilization as a positive effect on plant growth (Olff et al. 2000). Within a grassland, this may drive a small-scale shifting mosaic of plant abundance as pathogens build up locally (Olff et al. 2000), but can also lead to individual species decline throughout a particular community (Bezemer et al. 2006). It is thought that diversity in the soil pathogen community might lead to increased plant diversity (Westover & Bever 2001; Wardle et al 2004), but equally, specific soil pathogens may limit the establishment of certain species (van der Putten 2003).

7.2 RESEARCH QUESTIONSThere have been a considerable number of published studies on grassland soil microbial communities in recent years (Fig. 2). Also, many of the remaining applied research questions are currently being addressed in Defra project BD1451. Interestingly, stakeholders at the workshop thought that current knowledge of this topic was poor, yet it was considered of lesser importance in controlling grassland diversification. This apparent disparity between the literature search and the consultation may be explained by the absence of soil microbial ecologists from the workshop (2 were invited but could not attend). Given the amount of ongoing research, only one topic is considered to be important:

1) Understanding of the role of the complete soil microbial community in plant community development is lacking. To what extent do fungal and bacterial pathogens limit the establishment of certain species, or conversely, drive species co-existence?


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8. Species considerations for grassland diversification


8.1.1 Performance in restorationA recent study of the performance of 13 grasses and 45 forbs sown in 25 grassland restoration experiments found that many desirable species performed poorly during the establishment phase (years 1-4) (BD1433; Pywell et al. 2003). Analysis of ecophysiological traits found these species were habitat specialists associated with infertile soils and those exhibiting the stress-tolerator life history strategy (Grime 1979) (e.g. Succisa pratensis, Sanguisorba officinalis and Thymus polytrichus). Forb species with good performance were strong competitors with the capability of clonal growth, habitat generalists and species characteristic of fertile grasslands (e.g. Leucanthemum vulgare, Achillea millefolium and Rumex acetosa). Furthermore, many of these species performed increasingly well with time, suggesting that restored grasslands rapidly develop into closed, productive communities, where opportunities for seedling recruitment are increasingly rare. Restored grasslands therefore lacked characteristic species which are constant components of the species-rich target communities described by the National Vegetation Classification (e.g. MG4, U1, CG3) (Rodwell 1992). This could lead to a uniformity of restored grasslands across Britain, thus harming, or at least diminishing, the potential benefits of habitat restoration for national and regional biodiversity.

8.1.2 Genetic provenanceIn the last 40 years non-native and non-local genotypes have increasingly been used to restore and re-create species-rich grasslands for conservation, amenity and landscape purposes. This has led to growing concern over potential impacts on native patterns of genetic diversity both in the UK (Akeroyd 1994a; Akeroyd 1994b; Gilbert and Anderson 1998; Moore 2000; Jones 2001; Sackville Hamilton 2001) and Europe (Mennema 1984). Some early attempts at restoration involved the introduction of robust non-native subspecies from central and eastern Europe (e.g. Anthyllis vulneraria subsp. polyphylla), but this practice has largely ceased. Current prescriptions for the restoration under the agri-environment schemes require the introduction of native plant species as seed. This primarily comes from two sources: 1) commercially produced seed of native genotypes which originate from a small number of semi-natural populations which are seldom close to the recipient site or from the same habitat type (non-local genotypes); and 2) agricultural cultivars or varieties of native species which have been selectively bred for characteristics such as productivity and livestock feed value (i.e. forage grasses and legumes). These may have originated from populations in the UK or elsewhere in Europe. These agricultural varieties are much cheaper and more readily available than native seed, and have therefore been used as a major component of seed mixtures. Over 20,000 tonnes of seed of agricultural varieties is sown each year in the UK compared with only 20-30 tonnes of native provenance seed (BD1447). The potential risks of repeated and large-scale introduction of non-local genotypes, including agricultural varieties of British native species, to native genetic plant diversity are not well understood (Biodiversity Research Working Group 2000; Wilkinson 2001) and urgently require further research. These can be summarised as follows:

8.1.2.1 Reduced likelihood of survival on the receptor siteThe restricted number of donor sites and habitat types used for seed harvesting and the unconscious selection of certain genotypes during multiplication suggest that commercial wildflower material will only carry a small proportion of the genetic diversity available in native populations (Hufford & Mazer 2003). Although the consequences of this are difficult to predict and may be genotype dependent, some species may exhibit reduced fitness due to increased relatedness or poor adaptation within the population (inbreeding depression) (Vergeer et al. 2004; Luijten et al. 2002). This may reduce the likelihood of survival on the receptor site. A recent study of germination performance of four species from five difference provenances found large differences in germination between provenances both in growth chambers and in the field (Bischoff et al. 2006). Local provenance genotypes did not generally exhibit greater germination compared with non-local genotypes. This could have important implications for the success of restoration.

8.1.2.2 Reduced value of the restored vegetation for other organisms Physiological and phenological differences between local and non-local genotypes, and agricultural cultivars may have potentially damaging effects on species in the same or higher trophic levels. For example, variations in plant defences (e.g. cyanogenesis) have been shown to affect herbivory in legume species (e.g. Compton et al. 1983; Compton & Jones 1985; Keller et al. 1999). Equivalent differences in phenological traits (e.g. flowering time, pollen and nectar production and quality) between native and agricultural genotypes can have potentially large impacts on native pollinators (Carvell et al. in press) and mutualists.

8.1.2.3 Direct threats to genetic diversity of native populations

Genetic swamping, either due to a numerical or fitness advantage of the introduced genotype or as a result of hybridisation, is potentially one of the most significant threats to native genetic variation. However, recent


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studies are contradictory making it difficult to generalise about the potential outcomes of genetic exchange following habitat restoration (Bonnemaison & Jones 1984; Anttila et al. 2000; Chambers et al. 1999). They do suggest that local genotypes may perform better under semi-natural conditions and that fitness will decline with increasing ecological or geographic distance during introduction (e.g. Barratt et al. 1999; Jones & Hayes 1999; Joshi et al. 2001; Smith et al. 2005). However, these local advantages may be ruled out where conditions at the recipient site are extreme (e.g. highly disturbed, fertile agricultural soils) (Jones 1990). Under these conditions non-local genotypes may perform better without posing a significant threat to local genotypes which occur nearby (i.e. in nutrient-poor, semi-natural swards).

Hybridisation between genotypes may lead to fitness advantages as a result of hybrid vigour (heterosis) in the first generation (F1) (e.g. Luijten et al. 2002; Vergeer et al. 2004), although this has usually been followed by overall declines in fitness in the longer term (outbreeding depression) thereby potentially reducing the fitness of introgressed native populations following re-creation (Keller et al. 2000).


8.2.1 Performance in restorationThe literature search suggested that plant performance and the potential to generalise findings using trait analyses are under-researched. Indeed, with the exception of BD1433 (Pywell et al. 2003), there has been no systematic assessment of the performance of species in grassland diversification restoration schemes, and no research into the abiotic and biotic factors influencing performance. Future research should consider the following:

1) Since this study there have been a large number of grassland restoration experiments (e.g. BD1425; BD1444; BD1624). Analysis of data from these would enable performance indices to be calculated for a greater range of plant species sown under a wider variety of environmental conditions.

2) The performance of species in BD1433 were analysed in terms of response to environmental and biotic factors (‘response traits’), including resource availability, soil nutrients and disturbance. Future analysis should include the traits that determine the effects of plants on ecosystem functions (‘effects traits’), including nutrient cycling, productivity, pollinator webs and invertebrate food webs. This will give valuable insights into the mechanisms by which plant introduction as part of restoration can affect ecosystem function (e.g. Rhinanthus sp., Bardgett et al. 2006). It will also predict how the establishment of different plant species may affect associated invertebrate and pollinator assemblages.

3) Most critically, research is urgently required to improve the establishment and persistence of the poor-performing species and therefore avoid uniformity of restored grassland communities. This should include: (i) analysis of the increasing numbers of long-term restoration experiments to calculate species performance beyond year 4 of restoration and give critical insights into abiotic and biotic constraints on the establishment and persistence of poor performing species; using this information (ii) field trials should then be used to develop practical techniques to re-create these conditions in restored grassland communities; (iii) this may require the creation of specific microhabitats and the ‘phased introduction’ of species several years after restoration when both the plant community is more stable and the environmental conditions are more favourable for establishment (e.g. fertility has declined or suitable microsites are available).

8.2.1 Genetic provenanceThe literature search would suggest that genetic provenance is also a comparatively under-researched factor in grassland diversification. The consultation confirmed that this factor was poorly understood, but was considered of lesser importance in restoration. In the absence of a sound knowledge base and given the sheer scale of seed introduction as part of the agri-environment schemes, the precautionary principle would dictate that some very basic research is required in the following areas:

1) Effects of commercial seed production on genetic diversity: simple comparative studies are required to investigate the effects of commercial harvesting and production techniques on the genetic diversity of seed populations sown in habitat restoration. This will compare the genetic diversity of commercial seed stocks with those of natural populations. It will determine the maximum number of generations a crop can be harvested before shifts in genetic variation are likely to take place. It will use common garden experiments and morphological measurements to determine if commercial seed production selects for specific traits, such as greater seed production and earlier flowering.

2) Degree of genetic differentiation between local and non-local populations: large-scale surveys are required to quantify selectively neutral variation within and between populations over both large geographic (regional) and ecological (habitat) distances for commonly sown species. Trait


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comparisons between pairs of species (e.g. inbreeding vs. cross, annual vs. perennial) would provide powerful generality especially where species-pairs were phylogenetically constrained (i.e. from the same family or genus).

3) Performance of different genotypes in restoration: common garden experiments and reciprocal transplant are required to measure how different genotypes of species perform in a common environment. These will provide and assessment of adaptive variation within widespread species, and therefore highlight where variation might be lost (or enhanced) through gene-flow and introgression with non-local genotypes.

4) Effects of hybridisation on fitness of offspring: simple crossing experiments should be undertaken under controlled and field conditions to determine the impacts of hybridisation and introgression between different genotypes on fitness of hybrid offspring for a small number of ‘model’ species.

5) Effects on other taxa: detailed observations are required to examine how genetic provenance might affect biotic interactions and ecosystem functions. This would include differences in the quality of food resources (e.g. pollen and nectar, plant tissues); feeding behaviour and performance of herbivores and pollinators; and the incidence of pests and pathogens on genotypes from different provenances.

9. Seed limitation


9.1.1 Natural regenerationIt is widely recognised that the re-assembly of diverse grassland communities is primarily limited by a lack of propagules of desirable species (Walker et al. 2004). It has been calculated that over 80% of the component species of diverse grassland communities have short-lived or transient seed banks (Pywell unpub. data). They are therefore poorly adapted to the frequent disturbance associated with intensive grassland management (Bakker et al. 1996, Hirst et al. 2003) and tend to be replaced by annual and weedy species (BD1401-4; BD0206; BD1504; Graham & Hutchings, 1988; Hutchings & Booth, 1996a; McDonald et al., 1996; Bekker et al., 1997; Manchester 2002). This constraint is exacerbated by severe dispersal limitation in highly fragmented and intensively managed landscapes where traditional farming practices that formerly transported grassland species between sites have largely ceased (Section 10; Strykstra et al. 1997; Poschlod et al. 1998; Bullock et al. 2002). Much recent research has focused on developing and refining techniques to overcome this constraint which are applicable at the field scale. These can be classified into five basic approaches:

9.1.2 Seed mixturesSowing seed mixtures of ecologically adapted grasses and forbs onto a suitably prepared seed bed on ex-arable land or into gaps created in productive grassland swards (Section 11) is the most widely used and practical means of overcoming this constraint (e.g. BD1401-4; BD1425; BD1431; Wells, Cox & Frost 1989; Hopkins et al. 1999; McKenzie & Peel 1999; Pywell et al. 2002; Pywell et al. in press). Several studies have highlighted the superior performance of complex species-rich mixtures in facilitating grassland re-assembly compared with simple mixtures of generalist grasses (BD1401-4; van der Putten et al. 2000; Mortimer et al. 2002; Pywell et al. 2002). Indeed, there is increasing evidence that sowing simple mixtures of fine-leaved, generalist grasses at high rates may impede the assembly of desirable plant communities through lack of microsites for colonisation in the later stages of restoration (Section 11) and increased competition for resources. However, the high cost of complex seed mixtures, and the limited availability of rare species and their poor performance in restoration (Pywell et al. 2003) currently precludes the complete re-assembly of species-rich grassland communities at the large scale. Costs can be reduced by the use of lower sowing rates. After two years there was no significant difference in the richness of chalk grassland species between treatments sown at 4, 10, and 40 kg ha-1 (Stevenson, Bullock & Ward 1995). However, high sowing rates were more effective in suppressing weedy species in the early stages of restoration. Finally, several studies have demonstrated the practicality of collecting seed of rare species by brush or vacuum harvesting (BD1444; Stevenson, Ward & Pywell 1997), but this has proved costly and time-consuming.

9.1.3 Traditional made hayTraditional made hay from species-rich grasslands has variable composition, but has been found to contain large numbers of seed (450,000 seeds per 21 kg bale) of up to 17 grasses and 24 forbs (BD0206; Wells, Frost & Bell 1986). However, seed of generalist grasses are typically dominant (Wells et al. 1986; Smith et al. 1996; Manchester 2002), probably reflecting the late summer hay cut and the loss of species in the hay-


15

making process. Grassland communities resulting from hay addition have therefore tended to be grass-dominated and species-poor (BD0206; Wells et al. 1986; Manchester 2002).

9.1.4 Green hayIn marked contrast, fresh cut green hay has been found to contain a higher proportion of seed of desirable forb species (BD1414; BD1444). Application of fresh cut vegetation has proved to be a cost-effective and practical means of successfully restoring species-rich grassland and heathland communities on ex-arable land (Jones, Trueman & Millet 1995; Pywell et al. 1995; BD1444) and improved grassland at the field scale (BD1444). The time of hay cutting has a critical effect on the seed content and multiple cuts are required to collect seed of a high proportion of component species (BD1444; Pywell unpub. data).

9.1.5 Plug plantsRe-assembly of species-rich communities from seed is a slow and potentially uncertain process. Introduction of container-grown seedlings or adult plants avoids the risks associated with seedling establishment, particularly where species have seed dormancy mechanisms and are vulnerable to competition (Boyce 1995; Hopkins et al. 1999). It is also a means of introducing mid- to late-successional species which perform poorly in restoration schemes (Section 8; Pywell et al. 2003). However, despite high initial survival rates in most studies (reviewed by Barratt 1999), subsequent losses, and limited dispersal, has led some authors to question its utility for large-scale restoration (Hopkins et al. 1999).

9.1.6 Soil and turf transplantsThe inoculation of sown swards with soil and turf transplants from species-rich grassland donor sites has also been shown to increase species diversity by between 3 and 6 species per plot (BD1431; van der Putten et al. 2000; Mortimer et al. 2002). It is also effective in introducing rare and desirable species (BD1425; Pywell et al. in press). However, this technique is costly, unsuitable for large-scale restoration, and results in damage to the donor site (Pywell et al. 1995).

9.2 RESEARCH QUESTIONSThe consultation considered that seed limitation was one of the key constraints on grassland diversification. The large number of ISI journal papers concerned with the use of seed in grassland restoration would suggest this topic has been thoroughly researched. This view was confirmed by the results of the questionnaire. The remaining research questions relate to the development of low-cost alternative approaches to the large-scale sowing of complex and costly seed mixtures, including encouraging dispersal and colonisation (Section 10):

1) The potential for natural regeneration of species-rich grassland communities requires testing over a wide range of sites and conditions, including distance from donor sites and management history. Detailed mechanistic studies are needed to determine what might limit this process and techniques to accelerate colonisation (Sections 11 & 12). Such information would underpin guidelines for targeting sites where natural regeneration is more appropriate than seed introduction.

2) Further research is required into the composition, sowing rate and management of species-poor seed mixtures in order to increase their permeability to invasion by desirable species in the later stages of restoration.

10. Dispersal limitation

10.1 CURRENT KNOWLEDGE The facilitation and acceleration of natural re-colonisation by locally adapted genotypes of desirable plant species is likely to be a more cost-effective, appropriate and sustainable means of restoring ecological diversity to grassland communities at the whole farm or landscape scale than conventional restoration by sowing commercial wildflower species. This is especially true where the one-off seed-sowing described in Section 9 may not lead to successful establishment. Dispersal from nearby sources will be a continuous process, meaning that poor-performing species will continue to arrive at the site in the latter stages of restoration when conditions for their establishment and survival might be more suitable. However, several factors are thought to limit the potential for natural colonisation of species-poor, intensively managed grassland communities, namely:

absence of species from the grassland community, as well as the local and regional species pools (Bullock et al. 1994a; Pywell & Putwain, 1996);

limited dispersal ability of many species by natural means (Bullock & Clarke 2000, Coulson et al. 2000); and


16

lack of suitable microsites for seedling establishment (Section 11; Bullock et al. 1994b; Bullock 2000)

Earlier debate about the relative importance of these processes, especially in relation to habitat restoration, has resolved into an overview which sees each of these processes as limiting steps in colonisation by new species (Turnbull et al. 2000, Bullock et al. 2002). Many species are both dispersal and microsite limited (Turnbull et al. 2000). Here we consider dispersal limitation with microsites considered in Section 11.

10.1.1 Evidence for dispersal limitationEvidence for dispersal limitation during restoration and succession comes from a number of approaches. In many cases restored communities comprise species which were sown or were already in the seed bank or vegetation. Colonisation by other desirable species (i.e. components of the target vegetation) can be very rare and indeed constrains further development of the community towards the target (BD1401-4; BD1431; Manchester et al. 1994; Bullock et al. 2001; Bischoff 2002; Donath et al. 2003). However, a number of studies have shown that proximity to source populations, for example nature reserves, allows colonisation by some species (Matlack 1994; McClanahan 1996; Brunet & von Oheimb 1998; Bullock et al. 2002). The distances over which species can colonise depends on the specific dispersal abilities, so that studies have shown that: bird-dispersed species colonise faster than wind-dispersers (grassland; Yao et al. 1999), water-dispersers faster than animal dispersers (saltmarsh: Chang et al. 2005), or good wind dispersers (with plumes) better than poor wind-dispersers (grassland: Soons et al. 2005). Dispersal among habitat patches may have been frequent in past landscapes. However, habitat loss and fragmentation mean that there are fewer and smaller sources of seeds in the landscape and these sources will, on average, be further away than previously (Herben et al. 2006). This reduction in the ‘connectivity’ of landscapes could mean many restoration sites are too isolated from any sources for natural colonisation to take place (Soons et al. 2005).

10.1.2 Dispersal distancesWe know little about the distances over which plant species can effectively disperse over landscapes. A recent study suggested natural colonisation of restored grasslands may only be effective if sources are less than a kilometre away (Novak & Konvicka 2006). The mean dispersal distances of many grassland species are very low, at most a few metres (Verkaar et al. 1983; Willson et al. 1993), but the maximum dispersal distances can be very high (Greene & Calogeropoulos 2002). It is hard to measure these maxima (Bullock & Clarke 2000), but models suggest wind or animal dispersal may take herbaceous species a few kilometres (Soons et al. 2004; Mouissie et al. 2005). There is some evidence that traditional farm management practices can be important in enhancing seed dispersal distances. Mowing machinery (Strykstra et al.1997), hay-making (Coulson et al. 2001, Bullock et al. 2003), vehicle tyres (Hodkinson & Thompson 1997), dung (Pakeman et al. 1998) and coats of livestock (Fischer et al. 1996; Mouissie et al. 2005) can transport seed both within and between sites, and species differ in the degree to which they are dispersed by these means The widespread loss of farming practices that formerly transported grassland species between sites (e.g. shepherding, folding, hay-strewing) may mean that the isolation caused by habitat fragmentation is exacerbated by the loss of seed transport processes (Strykstra et al. 1997; Poschlod et al. 1998).

10.1.3 Poor understanding of dispersalWe are only beginning to understand and quantify the vectors and processes of seed dispersal at landscape scales or to determine practical methods to overcome isolation effects. While individual measurement of dispersal distances is complicated, some recent developments could aid such studies. There are now very good comparative data on relative dispersal abilities by animals, wind and other vectors (www.leda-traitbase.org) which should allow the use of model species from which generic conclusions can be drawn. Approaches to model seed dispersal mechanistically are available for wind-dispersed and animal-dispersed seeds (Soons et al. 2004; Katul et al 2005; Mouissie et al. 2005) and these should allow predictions about dispersal at the landscape scale in some cases. For other mechanisms, there are now good strategies for gathering relevant dispersal information efficiently (Bullock et al. 2006). It is now relatively simple to construct landscape-scale simulation models of dispersal and colonisation processes (e.g. Herben et al. 2006), which can allow scenario testing of practices aimed at enhancing species movement into restoration sites.

10.2 RESEARCH QUESTIONSThe consultation concluded that dispersal limitation was the key constraint to large-scale grassland diversification under the agri-environment schemes. The current scientific knowledge base for this factor is poor, both in terms of ISI publications and the findings of the questionnaire. Applied mechanistic research is therefore urgently required in the following areas:

1) Detailed measurements to quantify the vectors and processes responsible for seed dispersal at the field, farm and landscape scale for a range of upland and lowland farming systems. This will include dispersal by livestock, machinery, and other farm practices, such as manure spreading.


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http://www.leda-traitbase.org/

http://www.leda-traitbase.org/

2) Examine the relative importance of dispersal vs. microsite limitation in the process of grassland community re-assembly.

3) Develop and test practical, cost-effective means of facilitating seed dispersal and colonisation by adapting existing farm management practices. This would require quantification of these processes and incorporation in farm-scale models.

11. Gap and microsite limitation


11.1.1 GapsA high proportion of seed added to species-poor grassland sites during restoration invariably fails to germinate and establish (BD1404; Pywell et al. 2002; Zeiter et al. 2006; BD 1425; Pywell et al. in press). The reasons for failure tend to be described as ‘microsite limitation’, meaning that the abiotic and biotic conditions necessary for seedling emergence and/or survival are rare or absent (Bullock 2002). An analysis of the traits of species used in grassland restorations (BD1433; Pywell et al. 2003) showed that species which establish well at the recruitment stage tend to have high seed viability and germinate in the autumn rather than during active grass growth in the spring. This confirms that one of the major limitation on seedling establishment in temperate grasslands is the presence of gaps (Bullock 2002).

In regions where abiotic conditions are extreme, such as arid or montane zones, gaps cans be detrimental to seedling establishment as surrounding vegetation can protect seedlings from water or cold stress. However, Bullock (2002) showed a general trend for temperate regions is that gaps enhance seedling establishment of most species. For this reason seedling establishment in arable reversion sites is generally better than in established grasslands (BD1404), and soil disturbance by harrowing, scarification, stripping, etc leads to enhanced establishment in productive grasslands (BD1425; Pywell et al. in press; Poschlod & Biewer 2005). Grazing creates gaps which allow seedling establishment (Bullock 2000). Trait analyses to showed that the diversification of a grassland by heavy grazing was facilitated more by gap creation than by selective grazing or changed competition (Bullock et al. 2001). However, heavy grazing (‘hoof and tooth’) was less effective than mechanical disturbance (harrowing or scarification) in facilitating seedling establishment in fertile grasslands (BD 1425; Pywell et al. in press). This may reflect the small size and short longevity of gaps created by grazing compared with mechanical disturbance.

Gaps may vary in size and the abiotic (soil nutrients, soil moisture) and biotic (remaining canopy) conditions, depending on the mechanism by which they are created (Bullock 2002). Dung (Malo & Suarez 1995), grazing (Bullock et al. 1995), scarification (Pywell et al. in press) and mowing machinery (Coulson et al. 2000) all create gaps which enhance seedling establishment. However, the type of gap may affect seedling establishment; dung may enhance initial emergence but cause high seedling mortality through toxicity (Malo & Suarez 1995). Similarly, soil disturbance associated with strip seeding (rotovation) may result in enhanced nutrient mineralization and excessive competition for light (Hopkins et al. 1998). While it is clear that gaps enhance seedling establishment, the role of a range of gap creation mechanisms in allowing a diversity of species to establish is less well understood. Gap size is known to be important. Some species, especially those with larger seeds, can establish in smaller gaps than others (Bullock 2002). Therefore, a range of gap sizes in a grassland will lead to a greater diversity of establishing species (Bullock et al. 1995).

A further issue is the role of gap creation in the long term maintenance of species richness. Initial disturbance, by scarification, soil stripping, etc, may enhance early establishment. However, poor seedling establishment is the major bottleneck in the persistence of many grassland plants (Bullock et al. 1994b; Jongejans et al. 2006). Continued regeneration of introduced and desirable species may require repeated gap creation and re-introduction. This can be by heavy grazing at appropriate times of year, especially autumn (Bullock et al. 2001), hay-cutting (Coulson et al. 2000), the use of hemi-parasites (Section 12) or light harrowing and scarification. However, an explanation for the relatively poor performance of non-clonal species in grassland restorations (BD1433; Pywell et al. 2003) is that conditions for seedling recruitment are not maintained in many restorations. Further research is required into simple techniques to overcome this limitation on the long-term restoration of botanical diversity.

11.1.2 Other microsite variablesThere is some, albeit limited, evidence that certain grassland species need more than simply a gap in order to establish. Certain species establish poorly even when sown following intensive disturbance, such as Thymus polytrichus, Succisa pratensis and Helianthemum nummularium (BD1404; Pywell et al. 2002; BD1433; Pywell et al. 2003). A possible explanation is that they have more precise microsite requirements.


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For example, some Helianthemum, Thymus and Viola species are associated with nests of Lasius flavus ants (King 1977). This may be due to requirements for hot, well-drained microsites. Conversely, Succisa pratensis requires wet soils for germination which is enhanced by a moderate canopy cover (Isselstein et al. 2002). Certain species have very specific germination requirements which may severely limit their ability to colonise new sites. For example, Pulsatilla vulgaris grows on well-grazed, sunny sites but requires low disturbance and moist soil for germination (Wells & Barling 1971). Very little is known however, about specific requirements of such species, or how these might be provided during the restoration process (Section 8).

11.2 RESEARCH QUESTIONSBoth dispersal limitation and the lack of suitable microsites for establishment are key constraints to large-scale grassland diversification under the agri-environment schemes. Importantly, there has been little research on this topic relating to grassland restoration. Research is therefore urgently required in the following areas:

1) Investigate the density, and spatial and temporal pattern of different sized gaps created by management activities (cutting, grazing, dung mechanical), and their role in the recruitment of a range of grassland species.

2) Measure the particular microsite requirements of species which perform poorly in restoration (Section 8) and determine how these requirements might be met by adapting farming practices.

3) Consider the importance of continued gap creation at different stages of restoration as a significant factor in causing the decline of certain species following initial recruitment. Develop practical methods by which disturbance might be continued without damaging the developing grassland.

4) Develop and test simple techniques for overcoming both dispersal and microsite limitation, for example by the use of free-ranging livestock to disperse seed and create gaps. Such systems of grazing would require livestock to have open access to both species-rich ‘donor’ grasslands and species-poor ‘recipient’ grasslands to facilitate seed transport.

12. Parasitic plants

12.1 CURRENT KNOWLEDGEIt is well known that parasitic plants can have a dramatic effect on the performance of their host species. Moreover, there is increasing evidence that they can act as major drivers of both above-ground and below-ground processes in temperate grassland ecosystems (Thomas, Renaud & Gue´gan 2005). Rhinanthus species (particularly R. minor, R. angustifolius and R. alectorolophus) are the most widespread and common parasitic plants found in European grasslands (Ter Borg 1985).

12.1.1 Effects of Rhinanthus on host speciesBoth R. minor and R. angustifolius have negative effects on the growth and fecundity of parasitized plants (Ter Borg & Bastiaans 1973; Gibson & Watkinson 1991; Seel & Press 1996), which are greater than simple competitive effects (Matthies 1995). Rhinanthus species are known to parasitize a wide range of hosts, with at least 50 species for R. minor and 17 for R. alectorolophus (Gibson & Watkinson 1989). These include important and potentially dominant species of grasslands, for example R. minor selects Lolium perenne, Holcus lanatus, Dactylis glomerata, Agrostis sp. and Trifolium repens (Gibson & Watkinson 1989), and R. angustifolius selects A. stolonifera and L. perenne (Ter Borg & Bastiaans 1973). Selection of particular host species appears to vary among sites and over time, and does not seem to be related to dominance or nutrient status of the host (Gibson & Watkinson 1989).

12.1.2 Effects of Rhinanthus on grassland communitiesThis selective reduction in the growth of host species will influence directly the productivity and structure of plant communities, and indirectly increase the competitive status of non-host species. Most field studies have focused on species-rich, low productivity grasslands which naturally contain Rhinanthus species. These have provided three types of evidence for community effects (Table 2; reviewed by Bullock & Pywell 2005): 1) Correlation studies, comparing community variables (e.g. biomass, species number) between patches with naturally occurring populations of Rhinanthus with differing densities. However, these correlations do not imply causation and community structure may not be directly related to parasite abundance but to other factors that affect the pattern of Rhinanthus occurrence, such as local productivity (Ter Borg & Bastiaans 1973). Experimental manipulations are therefore more informative. 2) Removal experiments: involve elimination of Rhinanthus from plots and comparison of community structure with controls after a recovery period. These have the slight weakness that the community is recovering from a disturbance (plant removal), not just the exclusion of the parasite. Finally, less common, but most informative, are 3) Addition


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experiments, where areas with no Rhinanthus (within grasslands containing the parasite) are sown with the species and compared with controls after a period of establishment. All three approaches give generally similar results for three different Rhinanthus species (R. minor, R. angustifolius, R. alectorolophus) and across a wide range of grassland types and geographic regions (Table 2). Rhinanthus presence always decreases the total dry biomass of the vegetation per unit area (i.e. yield), where biomass is measured. This supports the suggestion by Matthies (1995) that Rhinanthus, in common with other hemiparasites, utilizes nutrients inefficiently. Where biomass is broken down into species groups, grass biomass, and sometimes legume biomass, is decreased, but other forbs remain unaffected.

In contrast, presence of Rhinanthus has resulted in increases in plant species richness at some sites and decreases at others. An explanation may be found in the so-called hump-back model by which species richness increases with productivity to a non-zero mode and then declines (Grime 1979, Waide, et al. 1999). The effect of Rhinanthus on species number may depend on the productivity of the system in relation to this mode. If introduced to highly fertile sites (to the right of the mode) Rhinanthus should always increase species number since it reduces the competitiveness of the few dominant species.

12.1.3 Effects of Rhinanthus on below-ground processes A recent study concluded that Rhinanthus minor was a major driver of soil decomposition processes through its ability to change patterns of root growth and exudation (Bardgett et al. 2006). Introduction of the parasite increased the trend towards bacterial dominance in the soil microbial community. This was accompanied by a 174% increase in the rate of nutrient cycling (N mineralization) and increased the availability of mineral N relative to dissolved organic N. This might be expected to promote the dominance of competitive, fast-growing grasses (Section 7) and result in increased productivity and reduced diversity. However, the ability of the parasite to suppress the growth of these competitive species meant that this effect was not detected. This may explain the comparatively greater effectiveness of Rhinanthus in enhancing diversity in productive grasslands.

12.1.4 Use of Rhinanthus as a restoration tool

Rhinanthus has a number of attributes which make it a potentially useful tool for the diversification of productive grassland (Bullock & Pywell 2005): 1) it is commonly associated with the target vegetation type (species-rich grasslands); 2) seed is relatively low cost and easily harvested for restoration projects, 3) it reduces the vigour of competitive species and allows establishment and persistence of target species; 4) it can colonise rapidly and persist in fertile grasslands; 5) excessive population size (which can lead to weed problems or extreme declines in yield for the farmer) can be controlled readily by commonly-used management practices.

To date three studies have successfully used Rhinanthus to facilitate the diversification of productive grasslands (Table 3). Pywell et al. (2004) sowed R. minor into a species-poor grassland and greatly increased the number and abundance of target forbs from seed added two years later. BD1425 compared the effectiveness of power harrowing and scarification of fertile grassland to establish a mixture of oversown species both with and without Rhinanthus addition. Sowing the hemiparasite was found to enhance the beneficial effects of harrowing and significantly increased the richness and frequency of sown forbs (>20%) (Pywell et al. in press). The relatively high additional cost of Rhinanthus seed (£288 ha-1) could be reduced to £12-60 ha-1 if lower rates were used as in Pywell et al. (2004). Finally, the presence of the parasite in experimental grasslands established in mesocosms was associated with a significant increase in the cover of forbs and overall diversity (Bardgett et al. 2006). This was primarily due to the suppression of the competitive grass Lolium perenne and the increased abundance of the desirable species Geranium sylvaticum and Ranunculus acris. However, Rhinanthus addition was found to have few beneficial effects on species-rich grassland restoration on ex-arable land (Table 3). This maybe because exposure through lack of vegetation cover inhibits some species when re-creating grassland on arable soils (Pywell, et al. 2002) and so reducing biomass at this early stage may be detrimental.

12.2 RESEARCH QUESTIONSThere have been relatively few published studies of the use of parasitic plants as a tool for grassland diversification, the exceptions being Pywell et al. (2004) and Bullock & Pywell (2005). There was a strong consensus at the workshop that parasitic plants, especially Rhinanthus sp., could act a major drivers of both above-ground and below-ground processes in temperate grassland ecosystems and could be manipulated to accelerate grassland diversification. More research is required to understand the process by which the


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parasite enhances diversity and to develop and refine practical prescriptions or tools which utilise Rhinanthus to facilitate grassland diversification at the field- and farm-scale within the agri-environment schemes:

1) Simple multi-site experiments are required to test the generality of the effect of Rhinanthus on above- and below- ground processes across a wide range of grasslands with different soil types, species composition, geographical location and management regimes. This work should consider the most appropriate time to introduce Rhinanthus for restoration (Phased introduction) so that the parasite has maximum effect on above- and below-ground processes.

2) More detailed experiments at a smaller number of sites are required to determine the appropriate sowing rates and target densities for Rhinanthus required to enhance botanical diversity. This should consider different methods of introduction and management to best facilitate population growth and spread of Rhinanthus. It should also consider the best methods to keep populations at appropriate levels in the long-term to achieve a balance between diversity and agronomic productivity.

3) Mechanistic studies are required to identify the precise ecological processes by which Rhinanthus enhances diversity in restored grasslands. The role of the hemiparasite in gap creation and reduction of competitive advantage need to be quantified, together with the effects on seedling establishment and survival at the established phase.

4) Future research needs to consider how simple, low cost approaches to restoration, such as Rhinanthus addition and scarification, might be combined and applied strategically over large areas. The ecology of Rhinanthus probably make it an especially effective means of diversifying large areas of grassland under traditional late summer hay cutting management. In contrast, scarification by harrowing alone would be more suitable to continuously grazed pasture systems. Research also needs to consider the extent to which management practices can be used to accelerate the dispersal seed added to these large restored areas.


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Table 2. A summary of studies of the effects of Rhinanthus species on community variables in species-rich grasslands in which Rhinanthus occurs naturally. Studies are of three types; correlation, removal experiments and addition experiments (see text). Note that the total biomass includes Rhinanthus. *Species number data were taken from Table 4 in Mizianty (1975) and analysed (see text).

Rhinanthus species Vegetation Region Variables measured Effects of higher Rhinanthus abundance Reference1) Correlation studiesR. minor 18 species-rich

grasslandsEngland Species number 6-36% decrease in species number Gibson & Watkinson

(1992)R. minor Species-rich flood

meadowEngland Total biomass 60% decrease in total biomass Davies et al (1997)

R. alectorolophus 4 species-rich calcareous grasslands

Italy Grass, legume & forb biomass

8-43% decrease in total biomass45-72% decrease in grass biomass

Davies et al (1997)

2) Removal experimentsR. angustifolius Species-rich

grasslandNetherlands Grass, legume, forb,

lower plant biomass6-60% decrease in total biomass60-90% decrease in legume biomass30-85% decrease in grass biomass

ter Borg & Bastiaans (1973)

R. angustifolius Species-rich meadow

Poland Total biomassSpecies number*

28% decrease in total biomass10% increase in species number*

Mizianty (1975)

R. minor Species-rich flood meadow

England Grass, legume & forb biomass

36-73% decrease in total biomass≤79% decrease in grass biomass

Davies et al (1997)

R. minor 4 species-rich sand dunes

England Species richnessDiversity indices

Decreased Simpson’s and Shannon-Wiener diversity Gibson & Watkinson (1992)

3) Addition experimentsR. angustifolius Floodplain

meadowsRussia Grass, legume & forb

biomass25-30% decrease in total biomass35-60% decrease in legume biomass

Rabotnov (1959)

R. angustifolius Species-rich meadow

Poland Total biomassSpecies number*

25% decrease in total biomass Mizianty (1975)


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Table 3. A summary of studies of the effects of Rhinanthus species on community variables in restored grasslands. Rhinanthus species were not previously present and were added as seed in experimental contrasts which comprised no Rhinanthus vs Rhinanthus added, and in some cases different sowing rates of Rhinanthus.

Rhinanthus species

Vegetation Region Rhinanthus sowing rate - seeds m-2

Maximum Rhinanthus density (after years)

Variables measured

Effects of higher Rhinanthus abundance

Reference

R. minor Arable field margin sown with 3 grasses, 17 forbs

England 12–96* 20–33%† (2 yrs)

Total biomass None Pywell et al. (1999)

R. minor Ex-arable field sown with 5 grasses, 6 forbs

England 600-1000 177-375 m-2 ‡ (1 yr)

Grass & forb biomassSpecies number

21-44% decrease in total biomass30-54% decrease in forb biomass84-87% decrease in grass biomassincrease in species number (by 1)

Westbury & Dunnett (2000)

R. alectorolophus Experimental grassland sown with ≤48 species

Switzerland 800 130 m-2 ‡ (1 yr)

Grass, legume & forb coverTotal biomass

8% decrease in total cover18-22% decrease in grass cover38% increase in cover of weed (unsown) species

Joshi et al. (2000)

R. minor Species-poor grassland, previously fertilised and grazed. Now unfertilised and hay cut. 10 forb species sown.

England 3-75* 60-90%† (4 yrs)

Sward heightFrequency of sown species

52-67% decrease in sward height60% increase in number of sown speciesIncreased frequency in 7 of 10 sown species

Pywell et al. (2004)

R. minor Experimental grassland sown with 6 grasses, 5 forbs

England 0, 30 or 60 0, 30 or 60 m-2

(1 yr)Forb coverSpecies diversityBiomass excluding Rhinanthus

35% reduction in total biomass excluding Rhinanthus17% increase in forb cover10-28% increase in species diversity

Bardgett et al. 2006

R. minor Species-poor grassland, previously fertilised and grazed. Now unfertilised and hay cut. Sown with 4 grasses, 15 forbs.

England 72* 1250 m-2 †(4 yrs)

Grass & forb biomassForb species number

55% decrease in grass biomass45% increase in forb species number

Pywell et al. (in press)

* Calculated from kg.ha-1, assuming 300 seeds g-1. † Mean percentage occupied of 25 cells per 1m2 quadrat. ‡ Plant density.


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13. Invertebrate herbivory

13.1 CURRENT KNOWLEDGELarge vertebrate herbivores are particularly influential on grassland plant communities because of the amount they eat and the disturbance they cause (see Section 14; reviewed by Olff & Richie 1998). However, the activities of above- and below-ground invertebrate herbivores can also have subtle, but highly significant effects on grassland communities (e.g. Bentley et al. 1980; Brown & Gange 1989; Rees & Brown 1992). In particular molluscs (slugs and snails) can have a major influence on the composition and biomass of temperate grassland communities (Oliveira Silva 1992; Hanley et al. 1995a; 1996; Hulmes 1994). Many slug species show distinct preferences for feeding on particular plant species and avoidance of others (Scheidel & Bruelheide 1999). Mollusc herbivory is likely to affect grassland community dynamics directly through preferential elimination of seedlings of certain species, and indirectly through changes to adult plant performance, e.g. leaf area, height, which may alter competitive interactions between species. Molluscs have been shown to prefer seedlings rather than mature plants and they prefer forbs to grasses (Cottam 1986; Drizo & Harper 1980; Hanley et al. 1995b). The selective influence they exert on plant populations is therefore greater than the biomass they consume because they can prevent plants from establishing and becoming adult (Hanley & Fenner 1997; Rodriguez & Brown 1998). Indeed, grazing by molluscs during the vulnerable seedling stage has marked negative effects on seedling recruitment and species composition in grassland communities created by seeding (Buschmann et al. 2005) and gaps created in grasslands (e.g. Hanley et al. 1996; Clear Hill & Silvertown 1997). It follows that mollusc herbivory can have an important influence on the success of field-scale restoration of species-rich plant communities (Frank 2003). Pywell et al. (in press; BD1425) showed that a reduction in mollusc grazing by adding molluscicide resulted in significant beneficial effects on the richness and abundance of the species introduced to two productive grasslands which lasted for several years. The greater negative effects of mollusc grazing on forbs compared with grasses reflects the differences in their morphology and palatability. However, the positive effects of field-scale molluscicide application on plant communities must be considered in the light of the potentially damaging effects of the pesticide on non-target species, such as small mammals and birds (e.g. Shore et al. 1997).

13.2 RESEARCH QUESTIONSThe consultation concluded that whilst invertebrate herbivory could have important damaging effects on restored grassland communities, there were well researched and effective treatments to control the pest species although these did have potentially detriment effects on non-target species. Research now needs to focus on how mollusc herbivory might interact with other constraints on restoration, particularly gap and microsite limitation (Section 11).

14. Management

14.1 CURRENT KNOWLEDGE The reinstatement of extensive cutting and grazing regimes, following the cessation of fertiliser inputs, can cause measurable changes in the productivity and composition of formerly improved swards (Bakker 1989).

14.1.1 CuttingCutting is a useful management tool for grassland diversification because it immediately removes the shading effect of tall, competitive species and opens up the sward for colonisation. Cutting and removal of herbage also provides a useful agronomic return and reduces nutrient pools. Declines in productivity with hay cutting in the absence of fertiliser inputs are variable between sites, depending on factors such as soil type and fertility. Some studies show rapid declines in yields to 4 tonne/ha (Hayes et al. 2000; Hayes & Sackville Hamilton, 2001), other suggest more gradual declines (Smith et al. 2000), or initial decline then increase due to increased atmospheric N deposition (Berendse et al. 1992). Sward productivity of <4 to 6 tonne/ha is required to sustain high species coexistence (Oomes 1992). In a few cases rapid diversification has followed the decline in productivity. For example, at Trawsgoed in west Wales extensively managed plots had between 5–15 species (per 4 m2) more than fertilised controls after 8 years (Hayes & Sackville Hamilton 2001). However, in most studies only modest increases in species richness were recorded due to severe seed-limitation (e.g. 1 species per 4 m2 per 4 years: Bakker 1987; Olff & Bakker 1991; Berendse et al. 1992) and the persistent effects of fertiliser applications on competitive interactions (e.g. 1 species per m 2

per year: Mountford et al. 1996). As a consequence, major shifts between grassland community types have not been recorded under this management. For example, it has been estimated to take 70–90 years for fertilised plots in the Park Grass Experiment to revert to Cynosurus cristatus–Centaurea nigra grassland


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(MG5) (Dodd et al. 1994). Similarly, restoration of upland hay-meadows (MG3) may take over 20 years using extensive management alone (assuming a linear increase in species-richness) (Smith et al. 2002).

14.1.2 Grazing Grazing management is an essential tool for both the conservation and restoration of biodiversity in temperate grassland ecosystems (Crofts & Jefferson 1999). Grazing may affect the population and community ecology of grassland plants through a variety of mechanisms (Duffey et al. 1974; Bullock & Marriott 2000). Direct effects include: 1) creation of vegetation gaps for seedling germination and recruitment; 2) damage by defoliation, trampling and dung and urine deposition; and 3) localised pulses of nutrients resulting from dung and urine allowing greater survival and growth. Defoliation will also have important indirect affects through the alteration of the intensity of competition for resources and relative competitive abilities of other grassland species (Bullock 1996). Grazing will have an important influence on invertebrate communities by changing the quantity and phenology of food resources and refuges, and by creating sward heterogeneity and micro-topographical features (reviewed by Morris 2000; see also BD1445). However, these effects are outside the scope of this review. The magnitude of grazing effects on grassland composition and structure will depend on factors such as the timing, duration and intensity of grazing, together with the species and breed of livestock used.

Until recently there has been a paucity of long-term experimental data on the effects of grazing on the composition of temperate grasslands. Most studies concur that perennial grassland communities respond slowly to different grazing intensities (e.g. BD1425; Smith & Ruston, 1994; Smith et al. 2000; Bullock et al. 2001; Pywell et al. in press), and the abundance of forb species generally increases under heavier grazing, but there is little evidence of treatment effects through the colonisation of new species. Recent research has examined the impacts of different intensities of continuous cattle grazing (severe, moderate, lenient) on the floral and faunal diversity of species-rich neutral grassland (BD1440 (‘SUSGRAZ’); Tallowin, Rook & Rutter 2005)). Between 2000 and 2004 botanical diversity declined significantly across all grazing treatments by 0.5 to 2.5 species per 25m2. Declines were lowest under the lenient grazing regime. There was a corresponding increase in Ellenberg fertility (N) score across all grazing regimes which was linked to increased cover of competitive species, such as Lolium perenne. Under severe and moderate grazing regimes there was a significant decline in positive indicator species and an increase in the abundance of pernicious weeds, such as Cirsium spp. Key factors causing the decline in botanical diversity were thought to be dispersal limitation, constraints on species establishment due to an accumulation of litter and increased cover of competitive species. Similar studies in species-poor grassland (BD1449) have found that continuous, severe grazing by sheep or cattle results in a conflicting increase in both pernicious weeds and forb diversity. It was concluded that grazing management alone may not be sufficient to deliver all the biodiversity objectives for grassland habitats. Finally, a number of studies have shown significant variation in grazing behaviour between breeds of livestock (e.g. Newborn et al. 1993; WallisDeVries 1994; Osoro et al. 1999), with some suggestion that more traditional breeds will graze less preferentially and include less digestible plant species in their diet. However, there have been relatively few studies of the biodiversity outcomes of these differences in grazing behaviour, or their potential as a tool for grassland diversification. Also, there is evidence that these observed breed effects may be confounded with the effect of previous experience and rearing conditions. An ongoing study (BD1443 (‘BEFORBIO’)) aims to separated true breed effects from the effects of early experience. This has been achieved by cross-fostering calves from a traditional breed (North Devons) with cows from a commercial breed (Hereford/Friesian × Simmental). In the first year the North Devon cows and calves will graze unimproved species-rich grassland while the Hereford/Friesian cows and calves graze improved grassland. In the second year all calves will graze species-rich grassland and their influence of vegetation composition and structure will be evaluated.

14.1.3 Interaction between cutting and grazingThere is increasing evidence of positive interactions between cutting and aftermath grazing management as a tool for the diversification of improved grasslands (BD1425; Hayes et al. 2000; Smith et al. 2000; Hayes & Sackville Hamilton 2001). In upland hay meadows undergoing diversification the most positive vegetation response was in plots managed by late July hay cutting and autumn grazing (Smith et al. 2000). This may reflect the removal of competition by cutting and the creation of suitable microsites for germination by autumn and spring grazing. In contrast, hay cutting without aftermath grazing has been shown to favour coarse grasses, whereas grazing alone encourages the establishment of undesirable weed species (Hayes & Sackville Hamilton 2001).

14.1.4 Farm yard manure


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The application of moderate amounts of farmyard manure (FYM) is part of traditional meadow management and is associated with the maintenance of high species richness in mesotrophic hay meadow communities (BD1415; Smith et al. 2002). Recent Defra-funded research (BD1415) concluded that 5 years of FYM application to unimproved and improved grassland sites resulted in only small changes in the botanical and soil microbial communities. However, another study showed that FYM addition to a semi-improved upland hay meadow resulted in major increases in hay yield and an increased the proportion of species associated with fertile conditions (BD1439). The precise mechanisms for these effects is poorly understood. Preliminary studies suggest that seed digestion by cattle, particularly exposure to acidified pepsin, has negative effects on the germination capacity of some meadow species (Edwards, Younger & Chaudhry 2002). It was concluded that dispersal of seed by FYM application was therefore of limited value for the conservation or re-introduction of many species. However, FYM application creates gaps and microsites suitable for germination of desirable species (R.Pywell unpub. data). Further research is required to determine what role these might play in grassland diversification (Section 12).


The workshop concluded that management practices (cutting, grazing, FYM) were all potentially very important factors influencing the diversification of grassland composition and structure. However, the literature search and questionnaire confirmed that a considerable amount of research has been undertaken to address this topic in recent years (e.g. BD1440 (‘SUSGRAZ’); BD1443 (‘BEFORBIO’); BD1445 (‘FORBIOBEN’)). Key gaps in the knowledge relate to the effects of management practices on other constraints on grassland restoration, namely dispersal and microsite limitation. There is also an important requirement to devise practical management regimes which deliver biodiversity objectives and are economically viable within the framework of the agri-environment schemes:

1) Research is required into the use of individual management practices and mixtures of different practices for the maintenance and restoration of grassland biodiversity. This should consider the following: i) cutting, ii) grazing (single species vs mixed species; traditional vs commercial breeds) and iii) FYM application. Studies should examine the effects of the timing of management actions in a given year, combinations of management and the rotation of different actions between years (‘static vs dynamic’) on grassland composition, structure and agronomic productivity.

2) Integrated research between agronomists, ecologists and social scientists is required to develop the findings from 1) above into practical whole-farm grassland management systems which deliver biodiversity objectives and are economically viable within the framework of the agri-environment schemes.

3) Research is required into management regimes which resolve the conflict between lenient grazing to control undesirable species and the negative impacts of this grassland diversity.

4) Detailed studies are required of how different management regimes in 1) above influence ecological process critical for grassland diversification, e.g. gap and microsite creation (Section 11).

5) Detailed measurements are required of the role of management practices in dispersal of seeds at different scales (Section 10).

15. Conclusions and recommendations

It was concluded that the combination of literature review and stakeholder consultation was an effective means of providing a comprehensive, evidence-based summary of the current knowledge (and lack of knowledge) of grassland diversification. On this basis the review made the following recommendations:

1) Clearly defined targets are required for the enhancement of biodiversity for the very extensive resource of species-poor grasslands managed under the agri-environment schemes.

2) In the absence of clear targets, it would be advisable to aim for at least moderate increases in diversity and habitat heterogeneity at the largest possible (landscape) scale by large numbers of farmers.

3) Multi-disciplinary research is therefore required to develop a whole farm systems approach to the restoration of biodiversity. This will require a greater understanding of underlying ecological mechanisms coupled to the existing framework of low intensity pastoral farming practices encouraged under the agri-environment schemes to facilitate the natural processes of colonisation and establishment of desirable species across the field, farm and landscape.


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4) This should also consider other key issues, such as resource protection and socio-economic barriers to uptake and implementation of these policies, including the role of farmer attitude and training, and critically, the potential impacts on farm livelihoods.

5) There has been a considerable amount of applied research into grassland diversification, particularly to address seed limitation, management, fertility and soil microbial communities.

6) The top priority for future research are the mechanisms of dispersal and colonisation by desirable species, and how these might be manipulated by extensive management practices.

7) Other important gaps in the scientific knowledge are: (i) techniques (including phased introduction) to improve the establishment and persistence of poor-performing species and therefore avoid uniformity of restored grassland communities; (ii) the effects of soil structural degradation on biodiversity enhancement and methods to overcome this constraint.

8) A more limited amount of research is required to develop and refine practical ‘restoration tools’ for promising approaches to grassland diversification, including the use of functional species, such as parasitic plants.

9) Some basic research is also required to determine the potential impacts of wide scale and repeated introductions of non-local genotypes and agricultural varieties in seed mixtures on native patterns of genetic diversity and associated taxa.

10) A considerable amount of research has provided practical solutions to overcoming seed limitation at the field scale, including seed sowing and green hay. Future research should focus on low-cost alternative approaches to the large-scale sowing of complex and costly seed mixtures, including encouraging dispersal and colonisation.

11) Recent research on productive grasslands and arable field margins suggests that, provided appropriate management is implemented, it is possible to achieve and sustain modest increases in botanical diversity despite relatively high soil fertility.

12) Grassland management activities are the key to the enhancement of grassland biodiversity at the large scale. Future research should concentrate on the effects of management activities on seed dispersal and microsite creation.

13) Ongoing research will answer most of the applied questions relating to the effects on soil microbial communities on the restoration process.


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References to published material9. This section should be used to record links (hypertext links where possible) or references to other

published material generated by, or relating to this project.

16. References

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Akeroyd, J. R. (1994a). Some problems with introduced plants. The Common Ground of Wild and Cultivated Plants. A. Perry and R. Gwynn Ellis. Cardiff, National Museum of Wales: 31-40.

Akeroyd, J. R. (1994b). Seeds of Destruction? Non-native Wildflower Seed and British Floral Biodiversity. London, Plantlife.

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Al-Mufti, M. M., Sydes, C. L., Furness, S. B., Grime, J. P. & Band S. R. (1977) A Quantitative Analysis of Shoot Phenology and Dominance in Herbaceous Vegetation. Journal of Ecology, 65, 759-791.

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Bakker, J.P, Bakker, E.S, Rosen, E., Verweij, G.L. & Bekker, R.M. (1996) Soil Seed Bank Composition along a Gradient from Dry Alvar Grassland to Juniperus Shrubland, Journal of Vegetation Science, 7, 165-176.

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Bakker, J.P. (1989) Nature Management by Grazing and Cutting. Kluwer, Dordrecht.Bakker, J.P. (1993) Nature management in Dutch grasslands. In: R.J. Haggar and S. Peel (eds) Grassland Management

and Nature Conservation, pp 115-124, Occasional Symposium of the British Grasslands Society, 28, Reading, UK.Bakker, JP (1987) Restoration of species rich grassland after a period of fertilizer application. In: Disturbance in

Grasslands (eds J. van Andel et al.), pp. 185-200. Junk, Dordrecht.Bardgett, R. D., R. D. Lovell, P. J. Hobbs & S. C. Jarvis (1999) Seasonal changes in soil microbial communities along a

fertility gradient of temperate grasslands. Soil Biology and Biochemistry 31: 1021–2030.Bardgett, R.D. & Leemans, D.K. (1995) The short-term effects of cessation of fertiliser applications, liming, and grazing on

microbial biomass and activity in a reseeded upland grassland soil, Biology and Fertility of Soils, 19, 148 – 154.Bardgett, R.D. & McAlister, E. (1999) The measurement of soil fungal:bacterial biomass ratios as an indicator of ecosystem

self-regulation in temperate meadow grasslands. Biology and Fertility of Soils, 29, 282 – 290.Bardgett, R.D. (2005) The Biology of Soil: A Community and Ecosystem Approach. 256 pp. Oxford University Press,

Oxford.Bardgett, R.D., Smith, R.S., Shiel, R.S., Peacock, S., Simkin, J.M., Quirk, H. & Hobbs, P.J. (2006) Parasitic plants

indirectly regulate below-ground properties in grassland ecosystems. Nature 439, 969-972.Barratt, D. R., K. J. Walker, et al. (1999). Variation in the responses of intraspecific variants of wet grassland species to

manipulated water levels. Watsonia 22: 317-328.Barratt, D.R. (1999) Habitat diversification using plug-plants: realising a growing potential? A review of the current

situation in the UK. Journal of Practical Ecology and Conservation, 3, 11–22.Beebe, J., Everett, R., Scherer, G. & Davis, C. (2002) Effect of fertilizer applications and grazing exclusion on species

composition and biomass in wet meadow restoration in eastern Washington. United States Department of Agriculture Forest Service, Research Paper PNW-RP-542.

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Appendix 1: Questionnaire completed by policy makers, practitioners and research scientists involved in grassland restoration


36

FACTORS INFLUENCING GRASSLAND DIVERSIFICATION

Rank importance (1=highest) avoid ties

Rate current level of knowledge 0=nil 1=poor 2=moderate 3=good

Possible solutions (e.g. sow seed mix, turf removal)

How often tested? 0=none 1=rarely 2=occasionally 3=frequently

How effective? 0=not tested/not effective 1=low 2=moderate 3=high

Comment on key process for successful restoration

Soil physical characteristics

Soil nutrients / pH Hydrology Soil microbes Mycorrhizal fungi Seed limitation Seed bank / dispersal


37








Genetic provenance Gap / microsite limitation

Initial plant community Competition Hemiparasites Invertebrate herbivores Vertebrate herbivores (non-domestic)


38








Pollinators & other mutualists

Management: grazing Management: cutting Other factors


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Appendix 2:

List of attendees at Grassland Diversification Workshop held in London on 2 March 2006

Name Organisation Area of interestRichard Brand-Hardy Defra (NRRA) PolicyMark Baylis Defra (CURE) PolicyAndrew Cooke RDS / Natural England PolicySteve Peel RDS / Natural England EcologistMark Stevenson RDS / Natural England EcologistMorwenna Christian RDS / Natural England EcologistVicky Robinson RDS / Natural England EcologistAlistair Helliwell RDS / Natural England EcologistJohn Martin RDS / Natural England EcologistRichard Jefferson English Nature / natural England EcologistClare Pinches English Nature / natural England EcologistProf. Val Brown Defra Grassland AU advisor Research scientistNigel Critchley ADAS Research scientistDr. Richard Pywell CEH Research scientistDr. James Bullock CEH Research scientistDr. Matt Heard CEH Research scientistJerry Tallowin IGER Research scientistProf. Jan Bakker University of Groningen Research scientistDr. Roger Smith University of Newcastle Research scientistDr. Simon Mortimer University of Reading Research scientistDonald MacIntyre Flora Locale Wildflower seed industry


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Appendix 3:

Discussion Points from Defra Grassland Diversification Workshop, 2 March 2006

Seed Limitation

Key Limitations

If soil is incorrect- it doesn’t matter what seed is used

Overridden if species already present

The seed bank is not so important- usually impoverished

Need clear idea of which species are missing

How do we define target?- NVC- Functional diversity- General neutral grassland- Providing resources for other trophic levels

Timescales for targets- Do we put in all species at the beginning?

Succession theory- Connell Slatyer - Create general community- Enhance landscape dispersal to create specialised community

Restoring of processes to allow community to develop

Facilitate dispersal- restore functional infrastructure at landscape scale

Role of historical distribution data- to allow targeting of appropriate species- to identify what has gone wrong

Some species are more important than others- function- some drive succession- when to introduce (phased sowing)

Practical aspect- how to move from intermediates to target

Can we define functional groups that we want in a restored grassland?

Aim of restoration to create a ‘fully functioning system’ – maintaining all trophic groups- in the long-term.

Matching restored site with local targets

Understanding is needed of ecology of difficult species- What limits them? -biotic

-abiotic etc.

Over- eagerness to introduce all species at start, need to condition site first- over several years

Can we develop indicators (microbes?) to tell us which stage of succession we are at?- Use certain species to drive succession?- Do others slow succession (oxeye daisy?)

Lower sowing rates may be possible


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RDS monitoring suggest difficult to move from low to moderate diversity but probably due to poor targeting- how to target?

- how do we know when to move onto next stages of restoration- tool kit.

May draw different conclusions from monitoring versus experiments- lack of control of conditions under monitoring

Resource Competition

Do microbes drive ecosystem change or are they just responding?

Are there tight feedbacks between microbes and vegetation?

Are microbes an indicator of change?

Is the way the microbial community breaks down litter an important factor in vegetation development? e.g.- rate of nitrogen release.

Do some plants, by the quality of their litter, drive the development of soil qualities?- What is the role of microbes in this?

Are soil microbes poor dispersers?

High soil fungal ratios are associated with good quality soils.

Is FYM a useful soil primer?

Importance of gap creation by different species and processes.

Role of initial disturbance- Herbicide/ scarification- but this is not restoring a process- Grazing, hemiparasites = restoring a process

Leaving sites to develop versus accelerating change

Argument that moderately fertile grasslands can get to moderate diversity simply by seed addition, gap creation and hay making- but are they sustainable?

Hay making is better than grazing for dealing with high nutrients

Need for long- term experiments to understand whether restored communities are sustained

Idea to collate data from different studies to pinpoint best management methods

Use existing long- term experiments and add new treatments to test key factors- disturbance- seed- FYM

Need to do experiments at farm-scale to see how processes act within the farm system.

Analysis of existing traditionally managed farms to identify processes acting at farm- scale.

How can we diversify grasslands which are grazed not cut? – reduce spring grazing to decrease nutrient input.

Mixture of hay cutting alternating with grazing over years to allow regeneration from seed.

Importance of time of hay cut- need to understand flowering phenology.


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Methods to reduce soil nutrients under grazing- need to soil strip or intensive hay removal over several years.

Different novel combinations of management changing over years to create a range of conditions.

RESEARCH QUESTIONS

1) Seed limitation

- Phased sowing

- Mechanism of dispersal at- large- scale~ farm – animals- small-scale ~ field

2) Seed provenance

- Effect of provenance on species performance

- Relative importance of geography, genetic, ecological distance

- Is there a genuine impact on other species?

3) Resource competition

- What are the rates of soil nutrient depletion and how do we accelerate them?

- Importance of soil organic matter and phenology of nutrient availability – impacts on plants.

- Link between low P and N mineralization.

- Spatial and temporal mechanisms of action of FYM- FYM as a soil addition

- Mechanisms of Rhinanthus impacts on vegetation- gaps versus competition- generality of effects in relation to 3 stages of vegetation change

- Gap creation- herbicide use to open up sward and over-sowing.

- How red clover influences litter inputs and soil structure.

- Microbial inoculation in relation to stages of the community, time of year (dispersal ability of microbes).

- Influencing microbes- FYM, soil, (carbon storage).

- Soils as carbon pools- how do we do it?

- Timing of grazing and interaction with hay cutting- timing within year, rotation among years.

- Refining scarification as a technique.

- How to cope with declines in the national herd and how to replace the processes they provide.

- Invertebrate populations in recreated grasslands- how does management affect them

- Are we recreating species interactions- with pollinators, seed predators

- Function of hay cut systems in whole landscapesBD1458 Draft Final Report

NERC Centre for Ecology and Hydrology43

- transient resource or critical resource.

- Are cultivated varieties sufficient resources for bumblebees etc.- changed phenology- importance of co-evolution

- Control of undesirable species- e.g. thistle, reconcile with desirable species

- Autecology of desirable/ poor species - link to traits

- Analyse functional diversity of restored grasslands

- Targeting sites - initial plant community, nutrient conditions- can we refine how this is done- microbial communities - plants present- landscape context

- Soil physical state as a limit to botanical development

- Impact of key plant species or soil characteristics- structure, nutrients

- Long-term stability/ sustainability of grasslands- address with mechanistic studies

- Can we construct a model as a framework for grassland functioning?

- Practical obstacles for diversification


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