January 2018 Vol 112 No.1 www.rfs.org.uk 53 Features A cross the UK trees are facing serious challenges from the increasing impact of tree pests and diseases (see Figure 1). The IPCC Fourth Assessment Report (IPCC, 2007) asserts that the global surface temperature is likely to increase by 2.4-6.4° by the end of the 21st century, and in spite of initiatives set in train to limit average global temperature increase a rise of at least 2° seems inevitable. In combination, these expose our native and forest trees to increasing environmental stresses. These projected global average temperatures have not been experienced since before the onset of the quaternary ice ages. These changes will occur within the economic lifespan of trees established over the next decade and well within their biological lifetimes. This article is the first in a short series of four that explores the important need to establish forest resilience in British woods and forests in the face of environmental change. Later articles will explore the establishment of resilience in recently planted forests dominated by stands of non-native spruce and other conifers outlining the implications for forest planning and management; why tree species diversity, especially those valued for timber production, is so limited in north western Europe and the implications of this in the development of more resilient forests in the future. The final article will explore the implications of forest resilience for policy and practice, and an outline proposal for a forest policy framework for addressing woodland conservation and forest management will be presented, with suggested approaches for ancient woodland, existing forests and to new afforestation. The four articles are intended to provide an outline rationale that will allow forest managers to increase forest resilience in ways best suited to their location and the character of the woods in their charge. The cumulative numbers of new tree pathogens and insect pests identified in the UK shown over time since 1900. The total accumulated number of pathogens and pests are also shown. Reproduced with kind permission of Dr Joan Webber, Forest Research, Alice Holt Research Station. (Freer-Smith & Webber, 2015) Forest Resilience in British Forests, Woods & Plantations - the ecological components Jonathan Spencer begins a new four part series on how we can increase resilience, starting with a look at woodland ecology.
Transcript
January 2018 Vol 112 No.1 www.rfs.org.uk 53
Features
Across the UK trees are facing serious challenges fromthe increasing impact of tree pests and diseases (seeFigure 1). The IPCC Fourth Assessment Report (IPCC,
2007) asserts that the global surface temperature is likely toincrease by 2.4-6.4° by the end of the 21st century, and inspite of initiatives set in train to limit average globaltemperature increase a rise of at least 2° seems inevitable. Incombination, these expose our native and forest trees toincreasing environmental stresses.
These projected global average temperatures have notbeen experienced since before the onset of the quaternaryice ages. These changes will occurwithin the economic lifespan of treesestablished over the next decadeand well within their biologicallifetimes. This article is the first in ashort series of four that explores theimportant need to establish forestresilience in British woods andforests in the face of environmentalchange. Later articles will explore theestablishment of resilience inrecently planted forests dominatedby stands of non-native spruce andother conifers outlining theimplications for forest planning andmanagement; why tree speciesdiversity, especially those valued fortimber production, is so limited innorth western Europe and theimplications of this in thedevelopment of more resilient forests
in the future. The final article will explore the implications offorest resilience for policy and practice, and an outlineproposal for a forest policy framework for addressingwoodland conservation and forest management will bepresented, with suggested approaches for ancientwoodland, existing forests and to new afforestation.
The four articles are intended to provide an outlinerationale that will allow forest managers to increase forestresilience in ways best suited to their location and thecharacter of the woods in their charge.
The cumulative numbers of new tree pathogens and insect pests identified in the UK shownover time since 1900. The total accumulated number of pathogens and pests are also shown.
Reproduced with kind permission of Dr Joan Webber, Forest Research, Alice Holt Research Station. (Freer-Smith & Webber, 2015)
Forest Resilience in BritishForests, Woods & Plantations- the ecological components Jonathan Spencer begins a new four part series on how we canincrease resilience, starting with a look at woodland ecology.
Lesley Trotter
Text Box
Copyright: The Royal Forestry Society - click to visit website.
54 www.rfs.org.uk Quartely Journal of Forestry54 www.rfs.org.uk Quarterly Journal of Forestry
FeaturesThe ecological components of forest resilienceForests have many unique properties, related to their highrates of primary productivity and their high levels ofassociated biodiversity. Complex interactions between plantsand fungi, between trees, shrubs and other plants for lightand water, the interdependent development of forest soils,forest composition and forest history, and the extremelyefficient mechanisms within forests for securing andcirculating nutrients from forest soils, all drive these highlevels of productivity and biodiversity. In addition, theprocesses within forest soils driven by fungi and other micro-organisms, in a rather bewildering array of species andprocesses, support tree disease resistance and forestresilience (Kimmins, 2004; Moore et al., 2011).
Definitions of resilienceForest resilience is a term widely used in discussions onforest adaptation to climate change but it is not a widelyunderstood term. Some useful definitions are presented
below:“Resilience is the capacity of a forest to withstand or
absorb external pressures and return, over time, to its predisturbance state.” (Holling, 1973; Walker and Salt, 2006)
An alternative more dynamic perspective sees resilience as:“The capacity of the forest to continue to provide most, or
all, of the ecosystem services, even if the composition andstructure are permanently altered by disturbances.”
(CBD Technical Series No.43, 2009)And very technically:
“Resilience is an emergent property of ecosystems that isconferred at multiple scales by genes, species, functionalgroups of species and processes within the system.”
(Gunderson, 2000; Drever et al., 2006)
Each definition has some value and can be used indifferent situations. All, however, have an underlyingmessage that resilience is dependent on biodiversity; in thegenetic variation of forest trees, tree species diversity or thestructural diversity of forest stands, underpinned by forestsoil biodiversity below ground and forest biodiversity aboveground. All the available scientific evidence strongly supportsthe conclusion that the capacity of forests to resist oraccommodate change, or recover from disturbance, isdependent on biodiversity at multiple scales (CBD TechnicalSeries No.43, 2009).
Some forest types are resilient without being resistant.Pine forests are not resistant to fire and readily burn, but areresilient in that they also readily return over time to theiroriginal structure and composition. Indeed, many species insuch forests depend on such disturbance for germinationand natural regeneration to occur; fire in pine forests is aclassic example. These forests are adapted to severedisturbances. By contrast, other forests are resistant tochange but lack resilience once significant disruptive changehas been wrought. Some ancient woodland treecommunities fall into this category.
Measures taken to enhance forest resilience (throughenhancing species, age and structural diversity andsupporting the development of forest soils) essentially movesimplified stands towards conditions found in more naturalforests. Measures that promote forest resilience are widelyregarded as promoting nature conservation and biodiversityaims alongside a wider array of other ecosystem servicebenefits (Gamfeldt et al., 2013).
Forest resilience then is the capacity of a forest to absorb
Offer the complete range of wood log boilers
Two complete ranges Angus Super and Angus Orligno 200
Output range 18kW, 25kW, 40kW, 60kW, 80kW, 96kW and 130kW
Products fully MCS certified
Grants available under Renewable Heat Incentive
92% Heat Efficiency
Significantly reduce heating costs
Incorporate into existing heating system
www.ecoangus.co.uk 01934 862642
January 2018 Vol 112 No.1 www.rfs.org.uk 55
Ecological Components of Forest Resilience
or withstand impacts and disturbances, both physical (in theform of weather events, droughts, frosts and floods etc.), andbiotic (such as outbreaks of disease or insect outbreaks),and return over time to something like its pre-disturbancestate. A ‘resilient’ forest ecosystem is able to maintain its‘identity’ in terms of its taxonomic composition, structure,ecological functions and process rates (CBD TechnicalSeries No.43, 2009).
From a utilitarian perspective forest resilience can also beconsidered as the capacity of a forest to continue to providemost or all of its current suite of ecosystem goods andservices whilst absorbing external impacts and recovering toa condition something like its original pre-disturbance state,where it can continue to deliver the same or similar range andquantity of goods and services (the ecosystem servicesderived from the natural capital asset, the forest itself).
The components of forest resilienceThe resilience of a forest ecosystem is fundamentallydetermined by its biological and ecological components.These are listed below:l The diversity of tree species and of other species in the
forest ecosystem (including and especially micro-organisms in the soil and forest litter).
l The genetic variation within species.l The wider regional pool of species and ecosystems from
which genetic material can flow.l …and hence the extent, condition and character of the
surrounding landscape.
For forest managers resilience in forests valued for theproduction of timber and other wood products should relyon:l Intact functioning forest soils that drive nutrient and water
cycling.l Genetic variation within tree species.l Tree species diversity within forests or stands.l Structural diversity within and between stands.
Forest soilsAs with vascular plants, fungal diversity develops throughtime and forests established on non-forest vegetation ornewly disturbed soils take time to develop a maturecomplement of forest fungi and other micro-organisms.Different tree species influence soil formation and createvarying conditions for the soil biota that perform key functionsof nutrient extraction from underlying rocks. Mixed stands of
conifers and broadleaves in temperate forests consistentlysupport more diverse and efficient forest soils with regard tonutrient extraction and tree performance (Humphrey et al.,2003).
Bialowieza Forest, Poland. Mixed mature old growth stands of oak,lime, hornbeam and aspen; wetter hollows and sumps support
stands of Norway spruce and alder. Mixed stands can provide fortall and well formed timber trees under a range of silviculturalinterventions, including in this instance long established non
The role of arbuscular mycorrhizal fungi in resilienceThe role of mycorrhizal fungi in the health and performanceof trees has long been appreciated (Killham, 1994). Their rolein supporting forest resilience is mediated through severalimportant and interacting mechanisms.
Firstly, mycorrhizal fungi grow at higher water potentialsthan tree roots, potentially supporting plants at times ofdrought stress. This is coupled with extensive and pervasivehyphal networks giving access to deeper and less accessibleground water than might otherwise be available (Moore et al.,2011).
Secondly, mycorrhizal fungi have several strategies tocombat pathogen attack (Moore et al., 2011) by:l Excreting of anti-fungal and anti-bacterial substances.
(80% of Tricholoma species produce antibiotics, andBoletus and Clitocybe are known to produce anti-fungalsubstances.)
l Stimulating the growth of other soil micro-organisms,which themselves inhibit or limit pathogen growth.
l Stimulating the plant itself to produce antibiotics underthe control of the mycorrhizal fungus.
l Providing structural protection of the root and rootlets bytheir thick fungal sheaths. This mechanical barrier giveseffective protection because plant pathogens needaccess to plant tissue to infect it; they cannot usuallyinfect other fungal tissue.Arbuscular mycorrhizae have been of proven
effectiveness in reducing the effects of pathogenic pests
such as root nematodes (Moore et al., 2011, p.407). In part,this may be mediated through the plant’s own response tomycorrhizal infections, with a thickening of cell walls or theproduction of phytoalexins, which may lead to animprovement in resistance to pathogens and soil pests.
Mycorrhizal fungi supply the tree with access to keyminerals (phosphates, magnesium, calcium, potassium andother important trace elements), along with nitrogen in theform of nitrates. In exchange, the tree supplies the funguswith products of photosynthesis. When soil nutrients are inplentiful supply the trees reduce investment in theirassociation with fungi, which may lead to issues of pathogenvulnerability when artificial fertilisers are used in forest standsto promote growth.
Effects of climate change on forests and forest soilsThe effects of climate change on forest soils areunprecedented and unpredictable. Such evidence as there ispoints to major disruption of established energy and materialflows and to a long period of readjustment. Tree speciescomposition, forest productivity, litter decomposition, wateravailability and nutrient cycling will act together to determinethe response of forest soils to climate change (Lukac andGodbold, 2011). Increases in soil temperature will raise therate of organic matter decomposition and nutrient releasethrough enhanced microbial and chemical activity. Higherrates of water loss can also be expected. Cold climateforests, which typically have large root systems and fastermetabolisms to utilise the much shorter period of summeractivity, can rapidly increase their activity as a short termreaction to soil warming. Root mortality may increase with anincrease in soil temperature. Water stressed roots are alsolikely to have shorter life spans and higher mortality. Severehot spells, likely to be accompanied by drought, will imposesignificant mortality on fine roots and the impact may be feltfor much of the subsequent growing period. The adoption offorest management practices that maintain forest shade andavoid exposure of forest soils to sun and drying winds arelikely to be effective mitigation measures.
In broadleaved forests the presence of hornbeam, lime,ash and birch litter promotes earthworm activity (Rackham,1980; Stewart, 2004). In upland forests birch, rowan andaspen similarly enhance earthworm activity and abundance.The activity of earthworms promotes drainage in soilsotherwise prone to waterlogging. They also improve treeperformance by encouraging deeper rooting and enhanced
Ash regeneration, West Woods, near Winchester, Hampshire.Adoption of natural regeneration allows for the extensive
reassembly of genetic variation from existing parent geneticmaterial and, provided deer and other herbivores are controlled,overcomes erratic but important events such as insect outbreaks
or incidents of drought. (Photo: Jonathan Spencer)
Features
January 2018 Vol 112 No.1 www.rfs.org.uk 57
mycorrhizal activity (which are greatly inhibited bywaterlogged anaerobic soils). This may be particularlyimportant in monocultural stands (of beech or oak forexample) that have a strong tendency to create mor soils withlittle or no earthworm activity leading to gleyed poorly aeratedsoils on heavy clays.
The presence of broadleaved litter also promotes thebreakdown of the superficial conifer litter horizon (the needlelitter makes for a cold and unaerated layer inhibitingbreakdown and incorporation into the soil), improvingdrainage and reversing gleying. A key role of nativebroadleaves within such forests will be to restore andmaintain forest soils and to re-establish deeper moreextensive networks of fungal hyphae connecting forest treesto subsoil and underlying rock. Of note here may be theobservation that in native North American forests, the finerroot masses of spruces and other conifers are confined to adepth of about 30cm below the surface, while those ofbroadleaved associates such as aspen can be found up to ametre depth (Startsev et al., 2007).
The role of mycorrhizal fungi in carbon sequestration in forest soilsTrees contribute up to 20% of their photosynthate to theirmycorrhizal fungi (Moore et al., 2011); a symbiotic trade-offsupporting the extensive hyphal network deep into subsoiland bedrock, securing mineralised elements and makingthem biologically mobile and accessible to trees. Thesehyphal networks are constantly growing and retracting in theirsearch for essential nutrients and the energy required issupplied by the tree in exchange. A great deal of the carbonsupplied is used in creating the stiff glomalin hyphal sheathsof the mycorrhizal fungi (Treseder and Turner, 2007). Thelongevity of hyphae may be as short as two weeks and rarelyextends beyond six months or so, and the glomalin is shed in
large quantities as the hyphae extend and contract in searchof materials. Designed to protect the fungus from the attacksof other fungal species, the glomalin is highly resistant todecay and as a result, when shed into the soil, remains forconsiderable periods of time, resisting utilisation by otherelements of the soil biota. Its residency time, particularly inthe deeper, colder soil horizons reached by broadleavedtrees such as aspen, can be very prolonged. It is this longresidency time coupled with the high rate of production andshedding of glomalin into the deeper, colder, less biologicallyactive lower horizons that leads to the accumulation of soilcarbon in maturing forest soils. The process is greatlyenhanced by the presence in quantity of minor broadleavedtrees amongst the conifer stands, such as birch, aspen,maples and others.
Corsican pine plantation, Thetford Forest, Norfolk. The reliance onone timber crop species, planted in monocultural stands of even
age and spacing, led eventually to their comprehensive demise inthe face of Dothistroma needle blight. The forest is now beingreplaced with varied planted species and associated naturalregeneration, established within the forest conditions of the
retained heavily thinned Dothistroma stricken stands. (Photo: Jonathan Spencer)
Ecological Components of Forest Resilience
Tree and forest composition; functional diversity and forest productivityIn establishing tree diversity, and hence forest resilience,there is a need to ensure that within forest stands there aretrees that can act in a complementary fashion that sustainfunction and performance.
For example, by having a small number of shade tolerantspecies capable of performing below the canopy ofemergent timber trees (e.g. hornbeam or lime in temperateoak woods, or western hemlock and red cedar in northernspruce forests), a far higher percentage of the available lightis captured throughout the life history of the stand, andnutrients in soils more efficiently captured from throughoutthe soil column. This can be complemented by a smallnumber of faster growing early successional tree species(such as birch) that rapidly establish forest conditions andexploit the light and space created within well-lit conditionsfollowing harvest, windblow or heavy thinning operations.Aspen or alder perform a similar function on wetter soils.Most temperate forests consist of two or more tall emergents
(usually timber producing species; a product of their evolvedtall structure and competitive apical dominance), alongside asmall number of shade tolerant understorey species and twoor more early pioneers. This complementarity is reflected inprimary production; biomass production in stands with fivetree species can be up to 54% higher than stands with onlyone species (Gamfeldt et al., 2013). Sites monitored in theForest of Bowland (Lancashire) support this view. Mixedstands of spruce and pine have clearly shown suchinteractions (Mason and Connolly, 2013) with the enhancedperformance of both tree species attributed to mycorrhizalinteractions and efficiency of exploiting available nutrients.
Early succession species have a key ecological role inrapidly re-establishing forest conditions followingdisturbance or forest operations, supporting soil mycorrhizaefollowing felling, leaf fall restoring forest soils, and theprovision of shade over exposed soils and drying outotherwise waterlogged prone soils. Rapid regrowth fromroots, stumps and suckers of various tree species perform asimilar function, rapidly restoring forests conditions, andcreating cooler, better aerated soils favoured by mycorrhizalfungi (waterlogging and anaerobic soils following soilcompaction or rising water tables seriously hinders soilfungal activity).
Identifying such groups of complementary species andunderstanding their comparative ecological roles within theforest (and their relevance to sustainable production) is thecurrent challenge. In a project aimed at embedding forestresilience within forest management, Forest Research arepursuing the development of ‘forest development types’ astemplates for natural and ‘naturalistic’ stands for use acrossthe UK (Jens Haufe, Gary Kerr, Forest Research, pers.comm.).
Tree genetics and variationTrees are amongst the most genetically diverse of allorganisms (Hamrick and Godt, 1990). It is this geneticvariation, both within and between natural populations ofmost tree species, alongside the diversity of micro-organisms in forest soils, that drives both forest productivityand is the foundation of forest resilience.
Because individual trees can live for such considerablelengths of time, and forest stands mature and change overdecades to centuries, there is a general perception that treesare at a severe disadvantage in terms of responsiveness toenvironmental change. However, trees in forest communitiesare not simply dependent on their generational ‘turnover’
time to respond adaptively to events. Most trees mature andset seed at an early age (at about 20 years in most species,although in small amounts until later in the life of the tree) andthe inherently high levels of genetic diversity that characterisemost species, coupled with the ability of many to persistvegetatively for very long periods of time and to produceprodigious numbers of offspring when conditions allow,means that new associations of trees and new combinationsof genes can arise over comparatively short periods of time.They are in effect, very responsive to change as populationsof trees, and very resistant to change as individuals. Theycan certainly respond within the timescales of forestmanagement operations and can rapidly recombineextensive existing genetic variation and express it in a verywide range of phenotypes in response to environmentalchange.
Most gene flow in trees occurs over a few hundredmetres, but often with a significant component from outsidethe wood or forest. Over time gene flow in trees can occurover large distances, particularly for wind pollinated or winddispersed species. Consequently, gene flow in trees is more
than sufficient to prevent loss of diversity through chance inwidespread forest trees and there is little clear differentiationbetween British populations of common species. Themajority of our tree species are outcrossing, which maintainshigh levels of genetic variation.
Most climate scenarios present change in terms of meanchanges to parameters, such as temperature or rainfall(Broadmeadow and Ray, 2005), but it is likely to be extremeweather events such as droughts or floods, and the arrival ofnovel pests and pathogens that present the real challengesand have the biggest impact. The retention of forest levelgenetic variation will provide adaptiveness over the life cycleof individual trees, and the ability to address a number ofeventualities. The adoption of natural regeneration orregrowth will be a key component in the management ofresilient forests that allows for both the conservation and theexpression of genetic variation in the face of changingcircumstances.
Wider forest species diversityOther species are also critical to forest function andresilience. Species that facilitate pollination (hoverflies, forexample), seed dispersal (wild boar, small mammals, jays),nutrient cycling and soil aeration (notably earthworms andmoles) all contribute significantly and in concert to thefunctioning of forest ecosystems and the health of the treeswithin them. Many insect species, notably wood ants in manynorthern forests, and parasitic wasps in all forest types, playcritical roles in suppressing the impact of tree insect pests.Insect diversity, supported by tree species diversity andstructural variation, introduces competitive and interactivepressures on insects regarded as forest pests.
A useful concept is that of ‘functional groups’;assemblages of species that perform similar functional roleswithin a forest (primary production in trees, pollination by
Table 1. Forestry species in England. Five species ofbroadleaves make up 77% of total volume and sixspecies of conifer make up 89% of total volume. Measure: % representation in England; standing volume (m3 over bark). (Forestry Commission, 2012)
Broadleaved % total Conifer % totalspecies standing species standing
crop crop
Oak 32% Scots pine 22%Ash 14% Sitka spruce 21%Beech 14% Larches 15%Sycamore 11% Corsican pine 12%Birch 6% Norway spruce 10%Other (total) 23% Douglas fir 9%
Other conifers 11%
Ecological Components of Forest Resilience
60 www.rfs.org.uk Quartely Journal of Forestry60 www.rfs.org.uk Quarterly Journal of Forestry
range of insects, decomposition in soils etc.) and henceprovide a level of resilience through redundancy.Redundancy describes the diversity of species involved inperforming similar tasks, and that perform differently undervarying environmental conditions (in soils these conditionsmight vary throughout the day, the season or between years).Species that appear on casual inspection to have limitedroles may come to the fore under changing or extremeconditions, buffering the forest ecosystem fromenvironmental change and disturbance. This ‘redundancy’ ofspecies generates the ability of a forest to respond swiftly tochanging conditions as they occur (Verhayen et al., 2016).This variable response has been termed ‘functional responsediversity’ and is critical to ecosystem resilience (Elmqvist etal., 2003).
The need for forest resilienceWhy are the components of resilience of such importancenow? For the past century the Forestry Commission andmany others have been steadily increasing the area of forestand woodland in England. Forest cover now constitutessome 10% of the country. However, much of this is of veryrecent origin, with most consisting of first or secondgeneration near monocultural plantations on former openground. The underlying soils are now fast becoming ‘forest’soils, with a rapidly developing forest soil biota and withmany of the early problems confronting foresters inestablishing trees in challenging open conditions nowreplaced with problems associated with managing trees inforest conditions; deer and other herbivores, competitionfrom forest vegetation and shade from competing trees.
Conversely, the soils, originally depleted of key nutrientsor prone to waterlogging, and made available to forestry asof small value to agriculture, are now far more capable of
accruing and retaining plant nutrients than they were at thetime of establishment. Paradoxically though, their capacity tosupport future harvests of trees could be compromised bycontinuous extraction of forest products that threatens tosignificantly reduce forest productivity (Kimmins, 2004).Increased risks from novel pests and diseases, and site levelstresses from a changing climate, are now adding to thoseresulting from past timber harvests, nutrient depletion or soilcompaction from the use of heavy machinery. We remaindependent on a very small number of tree species for themajority of our forest production, which works againstaccelerating tree species diversity in UK woodlands (Table 1).
Alongside all these changes there has been a significantshift in the appreciation of what woodlands provide forsociety; functions beyond simple timber production, mostnotably in water quality, flood regulation and carbonsequestration, through to cultural meaning, enjoyment andrecreation. These valuable goods and services arethreatened by environmental change and novel biologicalthreats. The climate that our woods and plantations willmature in will be very different from the more or less steadystate conditions assumed by those drafting forest policythroughout the 20th century. Managing forest composition toaddress climate change is a challenge that will varyconsiderably from forest to forest and from location tolocation. However, the underlying biological realities remainmuch the same.
The adoption of resilience measures in British woods andforests requires a new framework for thinking about forestmanagement; a rationale that accommodates present needsbut addresses concerns for continued performance of ourforests for the next and subsequent generations. Thisrequires us to think differently about tree speciesassemblages, forest management practices and the
Features
Premium Solution for Tree Protection
Advancing growth
VITICULTURE FRUITFORESTRY
For Forestry sales contact: www.tubex.com/distributorsalso for Technical Support contact: Simon Place: 07734 856101
supporting forest ecosystem. These will be examined furtherin the later articles in this short series.
AcknowledgementsI should like to thank Alison Field, James Simpson, MarkBroadmeadow and Gary Kerr for their help andencouragement in the drafting of this article, and to Dr FreiaBladon for help in its drafting and the preparation of Fig.1.Thanks are also due Emmanuel College Cambridge and theDerek Brewer Visiting Fellowship, and the ConservationScience Group at Cambridge University whose support in thepreparation of these articles in spring 2017 was invaluable.
ReferencesBroadmeadow, M.S.J. & Ray, D. (2005) Climate Change and British
Woodland. Research Note. Forestry Commission. Edinburgh.Convention of Biological Diversity (CBD) & UNEP (2009) Forest Resilience,
Biodiversity, and Climate Change. A synthesis of thebiodiversity/resilience/stability relationship in forest ecosystems. CBDTechnical series No. 43.
Drever, C.R., Peterson, G., Messier, C., Bergeron, Y. & Flannigan, M.D. (2006)Can forest management based on natural disturbances maintainecological resilience? Can. Journ. For. Res., 36:2285-2299.
Elmqvist, T., Folke, C., Nystrom, M., Peterson, G., Bengston, J., Walker, B. &Norberg, J. (2003) Response diversity and ecosystem resilience. Front.Ecol. Environ., 1:488-494.
Forestry Commission (2012) National Forest Inventory: preliminary estimatesof quantities of broadleaved species in British woodlands with a specialfocus on ash; standing timber volume for coniferous trees in Britain.Available at: http://www.forestry.gov.uk/inventory
Freer-Smith, P.H. & Webber, J.F. (2015) Tree pests and diseases: the threatto biodiversity and the delivery of ecosystem services. Biodiversity andConservation doi: 10.1007/s10531-015-1019-0
Gamfeldt, L., Snäll, T., Bagchi, R., Jonsson, M., Gustafsson, L., Kjellander, P.,Ruiz-Jaen, M.C., Fröberg, M., Stendahl, J., Philipson, C.D., Mikusi�ski,G., Andersson, E., Westerlund, B., Andrén, H., Moberg, F., Moen J. &Bengtsson, J. (2013) Higher levels of multiple ecosystem services arefound in forests with more tree species. Nature Communications, 4,Article number: 1340.
Gunderson, L. (2000) Ecological resilience: in theory and application. Ann.Rev. Ecol. Syst., 31:425-439.
Holling, C.S. (1973) Resilience and stability in ecosystems. Ann.Rev.Ecol.Syst., 4:1-23.
Humphrey, J.W. Ferris, R., Newton, A. & Peace, A. (2003) The value of coniferplantations as a habitat for macrofungi, in J.W. Humphrey, R. Ferris &C.P. Quine (eds) Biodiversity in Britain’s Planted Forests. ForestryCommission, Edinburgh.
IPCC (2007) Climate Change 2007: Synthesis Report. Contribution ofWorking Groups I, II and III to the Fourth Assessment Report of theIntergovernmental Panel on Climate Change [Core Writing Team,Pachauri, R.K and Reisinger, A. (eds.)]. IPCC, Geneva, Switzerland,104pp.
Killham, K. (1994) Soil Ecology. Cambridge University Press.Kimmins, J.P. (2004) Forest Ecology. A foundation for sustainable forest
management and environmental ethics in forestry. Third Edition.University of British Colombia.
Lukac, M. & Godbold,D.L. (2011) Soil Ecology in Northern Forests.
Cambridge University Press.Mason, W.L. & Connolly, T. (2013) Mixtures with spruce species can be more
productive than monocultures; evidence from the Gisburn experiment inBritain. Forestry; doi: 101093/forestry/cpt042
Moore, D., Robson, G.D. & Trinci, P.J. (2011) 21st Century Guidebook toFungi. Cambridge University Press.
Rackham, O. (1980) Ancient Woodland. Edward Arnold.Startsev, N., Lieffers, V.J. & Landhäusser, S.M. (2007) Impact of aspen litter
on forest floor development in conifer dominated stands. Centre forEnhanced Forest Management, Department of Renewable Resources,University of Alberta. Research Note 07/2007.
Stewart, A. (2004) The Earth Moved; on the remarkable achievements ofEarthworms. Algonquin Books.
Treseder, K. & Turner, K. (2007) Glomalin in Ecosystems. Soil ScienceSociety of America, 71(4):1257-1266.
Verhayen, K. & 27 others (2016) Contributions of a global network of treediversity experiments to sustainable forest plantations. Ambio, 45:29-41
Walker, B. & Salt, D. (2006) Resilience thinking; sustaining ecosystems andpeople in a changing world. Island Press, Washington, DC, USA.
Jonathan William Spencer is Head of Planning &Environment for Forest Enterprise England, with wideprofessional interests in the history and ecology ofwoods and forests, the conservation of their historicalcharacter and wildlife, and in forest resilience,silviculture and management.
Forest Enterprise, Forestry Commission England, 620Bristol Business Park, Bristol BS16 1EJ
