Environmental Change in Peri-Urban Areas and Human and Ecosystem Health
Ian Douglas*School of Environment and Development, University of Manchester
AbstractRapidly changing peri-urban areas have great ecological and human land-usediversity. Contrasting habitats abound. However, little is known about the waythat the biodiversity of a whole urban area depends on the variety of habitats andthe linkages, migration and dispersal patterns between them. Great opportunitiesexist for extending these concepts in both the rapidly expanding manufacturingand commercial cities of Latin America and Asia and into some of the poorestperi-urban environments. To take these opportunities requires understanding ofthe diverse pressures on peri-urban ecosystems and their consequences for bothecosystem and human health. For some people, peri-urban areas are healthy andthe scene of good living standards; for others, they offer a survival opportunity.The complex ecology of urban and peri-urban areas is constantly being disruptedlocally by the injection of new species or new types and concentration of chemicalsinto specific habitats through human activity. Each change alters ecosystem health.The ecosystem health and human mental and physical health consequences of theinterplay between economy, society, land and ecosystems in peri-urban areas providea wonderful opportunity for innovative thinking in applied science, particularlyfor public health medicine, geography and human ecology.
Introduction
Peri-urban areas are fringe zones around cities where new urban land usesand activities are being imposed on a rural landscape. They are impermanent,in that as cities grow, their peri-urban areas move outwards. They aresocially diverse, in that they are likely to contain the homes of traditionalrural people, wealthy urban people and pockets of poor people (Douglas2007), be they in trailer parks on the edges of North American cities orin squatter settlements on the fringes of southern African cities (Figure 1).They are also biologically diverse, in that they are likely to contain remnantsof natural vegetation and farmland, new gardens and also waste or brownfieldland, the latter providing sites for the deliberate or accidental colonisationby invasive and exotic species.
While economic, cultural, political and legal variations between cities willproduce contrasts between the precise character of their peri-urban areas,
this article explores trends that affect both human health and ecosystemhealth that are likely to be common to most, if not all, peri-urban areas.
A global-scale analysis of the consequences of change in peri-urban areasat the global scale involves cutting across several frontiers. By definition,it considers the interplay of the urban with the rural. It also investigates boththe biophysical and the social, cultural and economic consequences of land-use change and associated human and other organic activity. Furthermore,it involves the legacies of the past with the conditions and drivers of thepresent. In addition, it examines a wide range of contrasts in affluence andpoverty, necessarily emphasising conditions associated with deprivation on
Fig. 1. Housing contrasts in peri-urban Rosario, Argentina: (A) squatter settlement and peri-urban agriculture; (B) gated upper class housing estate.
some occasions and those associated with the over consumption of affluenceon the other. Too often, these contrasts are not recognised because enquiriesare associated with specific places, societies or relatively narrow sets ofphenomena. However, all the situations mentioned above impinge onone another and on both global society and the global environment.
The article draws on experiences and reports to develop commonalitiesfrom a wide range of contrasting and conflicting views of the world.Collectively, these views point to the need to think laterally about the issuesraised and about how relevant they are from London to Lusaka, New Yorkto Nairobi, and São Paulo to Shanghai. In particular, when human health isbeing discussed, it is important to recognise that in the peri-urban areas ofalmost all cities we can now find evidence of both the traditional diseasesof poverty, such as dysentery and cholera, and the modern diseases of affluence,such as heart disease and stress. Just as obesity is beginning to concern manynewly affluent communities in Asia (Seidell 2000), so the re-emergenceof rickets in some European industrial towns (Lawson and Thomas 1999)and in Australia (Robinson et al. 2006) is worrying health agencies.
The Value of Healthy Peri-Urban Emerging Ecosystems
Ecosystems are naturally dynamic entities. Fundamental to the concept ofan ecosystem is the idea that living organisms are continually engaged ina set of relationships with every other element making up the environmentin which they exist. The structure and functioning of the ecosystem changein response to a change in any one of those elements. Change in ecosystemsis constant but most undisturbed ecosystems absorb successive changes andretain their overall structure and function. For example, even after eventslike major cyclones, coastal mangroves and coral reefs can recover andregain their characteristic form (Nyström and Folke 2001). The speed withwhich an ecosystem returns to an equilibrium point following a pertur-bation is termed its resilience (Society for Ecological Restoration Science& Policy Working Group 2004). The faster the perturbed system returnsfrom its initial displacement back to the equilibrium point, the shorter itsrecovery time, and the greater its resilience is said to be (DeAngelis 1980).However, biological diversity appears to enhance the resilience of ecosystems(Elmqvist et al. 2003). The contrasted land cover conditions in peri-urbanareas often favour biodiversity and enhance the opportunities for a diver-sity of responses to environmental change among species contributing tothe same ecosystem function. This response diversity is critical to resilience andis particularly important for ecosystem renewal and reorganisation followingchange (Elmqvist et al. 2003). Peri-urban zones may thus have conditionsthat are highly favourable for the production of essential ecosystem servicesthat are fundamental for both the natural world and human existence.
People have created human ecosystems, such as urban areas, where natureis manipulated and resources from other areas are used to adapt the
environment to the needs of human life. On the edges of these urban humanecosystems are the peri-urban areas where the conversion of natural andagricultural ecosystems to urban forms takes place. In the process, ecosystemsare modified, adapted, altered, destroyed and replaced. Opportunities arecreated for invasive species and deliberate introductions. The land-usemosaic created by these processes has been called a ‘hybrid landscape’ (partold rural, part new urban). The term ‘hybrid’ has been used in landscapeecology in two senses: one being the bringing together of the naturallandscape with a people-made landscape (Golley 1987), and the other interms of combining two place-making processes (Quayle and van der Lieck1997) in terms of the formal urban structures such as streets and plannedopen-spaces, and the informal uses of land, such as squatter settlements,illegal dumping and informal recreation areas. The two types of processgive the hybrid landscape greater diversity of land cover, human activityand biota than fully urbanised or totally rural areas. These landscapes providegreat opportunities for managing and restoring ecosystems and improvingthe quality of human life. To take these opportunities requires understandingof the diverse pressures on peri-urban ecosystems and their consequencesfor both ecosystem and human health.
Peri-urban areas are the transition zones, or interaction zones, whereurban and rural activities are juxtaposed, and landscape features are subjectto rapid modifications, induced by human activities (Douglas 2006). Whilethey may contain relicts of old rural ecosystems and some protectednatural areas, they are generally places of rapid ecosystem change, sometimesdeliberate and sometimes spontaneous. Great ecological diversity existsin peri-urban areas, but much of it is short-lived, as the growth of citiesdrives the peri-urban area outwards, almost relentlessly, save where thereare strict green-belt regulations or extensive protected areas. The resultingdiversity of land cover types reflects the differing values of various groupsconcerned with peri-urban areas:
• For the poor: places where it is easier to build shelters and to occupyland for agriculture;
• For industry: sources of materials essential for urban life: water, brick-clays,sand and gravel, limestone, fuel-wood and timber;
• For the middle class: a place for houses in a rural setting, with bothformal and informal recreational facilities;
• For local government: sites for landfills, waste dumps, peripheral freeways,airports or noisy and toxic industries;
• For conservationists: the site of valuable protected areas, forested hills,preserved woodlands, important wetlands or mangroves, and major coastalecosystems; and
• For education and human well-being: the place where many urbanpeople make their first contacts with major areas of natural vegetationand biodiversity (Douglas 2006).
For all these groups, peri-urban areas are zones of opportunity, hopeand expectation, yet the values may often be in conflict at the local leveland may have wider implications in terms of national development andglobal environmental change. While local values and stakeholder interestsare important, there are wider biodiversity values in emerging urban andperi-urban ecosystems (di Castri and Younes 1996). Much of the discussionon such values has been built around detailed recording in individualgardens (Owen 1991), remnant woodlands, ponds (Wood and Barker 2000)or local nature reserves. For example, in a stratified sample of 61 urban,domestic gardens in Sheffield, UK, the entire garden flora contained1166 species, of which 30% were native and 70% alien. The garden floracontained 146 plant families, which included 72% of the native, naturalisedor recurrent casual families recorded in the wild in Britain and Ireland(Smith et al. 2006). The assemblages of individual small patches of variedlymanaged peri-urban land together have a great biodiversity that is constantlyboth receiving additions and suffering losses, because of the rapid changein land cover, patch by patch. These changes create opportunities for newecosystems to emerge.
Emerging ecosystems (or novel ecosystems) result when species occurin combinations and relative abundances that have not occurred previouslywithin a given biome (Hobbs et al. 2006). Many possibilities arise foremerging ecosystems in rapidly changing peri-urban areas. However,little is known about the way that the biodiversity of a whole urban areadepends on the variety of habitats and the linkages, migration and dispersalpatterns between them. Great opportunities exist for extending theseconcepts in both the rapidly expanding manufacturing and commercialcities of Latin America and Asia and into some of the poorest peri-urbanenvironments. There are differences in how urban ecosystems are interpretedin these continents; for some the peri-urban green area can be theremnants of a natural forest, such at the Mata Atlantica around São Paulo,Brazil (Victor et al. 2004; Figure 2); for others it has to be a newly plantedand carefully maintained urban forest, such as the Olympic Forest beingestablished for the periphery of the Olympic Games area for Beijing 2008(Li et al. 2005).
The concept of health, both in terms of individual people and individualorganisms and in terms of human and ecological communities, is funda-mental in evaluating the cumulative impacts of environmental change. Everyorganism responds to its genetic make-up, to the behaviour of other similarorganisms and to the surrounding environment and all the processes inthat environment. In a way, an organism is a highly sensitive indicator ofthe state of the environment. Given a set of healthy organisms, we shouldhave a healthy ecosystem. Ecosystem health is broadly defined as the stateor condition wherein ecosystem function is not compromised by humanactivity (Rapport 2002a). It is a concept used in promoting sustainabilityand in ensuring that ecosystem services are maintained (Haskell et al. 1992).
Thus, the health of organisms and of ecosystems tells us a great deal aboutenvironmental quality, providing we can unpick the complex series ofprocesses and forces working in a particular environment. Good environmentsalso help human society. Areas of natural vegetation both within and onthe fringes of cities bring social and health benefits to people (Barker andBox 1998). Both mental and physical health can be improved by gentleexercise in such areas (Douglas 2005a).
This article appraises our understanding of both how these highlydynamic peri-urban zones impact on human health and well-being andhow they influence on the character of relict natural and rural ecosystems aswell as providing opportunities for emerging ecosystems. Before analysingthe effects of change, the various main types of peri-urban environmentwill be examined and the nature of the processes likely to influence humanand ecosystem health will be discussed.
URBAN GROWTH AND PERI-URBAN AREAS
To introduce the diversity of peri-urban landscapes and the impacts ofthe differing human expectations and activities, this section addresses theconsequences of the six sets of values outlined above, those of the poor,industry, the middle class, local government, conservation, and educationand well-being.
Over much of the world peri-urban areas contain two types of informalsettlements occupied by poor people. One is an area of direct urbanimpact that experiences the immediate impacts of land demands fromurban growth, pollution, minerals extraction and waste dumping, and the
Fig. 2. Part of the Mata Atlântica peri-urban forest near São Paulo, Brazil.
other is a wider market-influenced zone in which urban demands distortagricultural production and resource use (Simon et al. 2006). All thesettlements tend to lack organised drainage and efficient waste disposal.The majority of settlements are in the areas of direct urban impact, but theircharacter may vary considerably, from the highly crowded settlements ofmajor cities such as Nairobi and Bogota, to more spacious settlementswith room for vegetable gardens. The latter may be in hazardous placeswhere people do not build, such as on river flood plains. Elsewherecultivation takes place among settlements in the outer peri-urban area.These peri-urban agricultural zones provide important ecosystem servicesfor the poor, whose health depends on achieving adequate nutrition.
The health of the urban poor in informal settlements is subject to manyrisks, from the lack of adequate sanitation, from industrial pollution, fromthe type of work they do, from lack of access to medical services and fromenvironmental hazards, be they the abundance of habitats for diseasevectors, or the contamination of their peri-urban crops by industrialpollutants in the air or in irrigation water. Many are exposed to hazardoussubstances because they live by collecting and sorting waste, particularlyin Indian cities, where the recycling of waste in the informal sector ishighly organised (Huysman 1994; Figure 3). In such situations, there is acritical peri-urban human ecology where healthy crop plants and healthyhuman life go hand in hand. The extent to which human and other urbanwastes can be safely used to boost peri-urban crop yields remains poorlyunderstood.
For industry, peri-urban areas have long been the most convenientplaces from which to source raw materials and to locate new factories.Virtually, all cities have expanded across areas where aggregates and brickclays were extracted decades or centuries ago, from the clay pits of theTuileries in Paris (Douglas 1983), to the rock quarries of Central Park,
Fig. 3. Recycling by the poor in Ahmedabad, Gujarat, India: materials sorted by individual‘ragpickers’ around their dwellings.
New York (Schnadelbach 2001) and the former tin mines around KualaLumpur (Douglas 2005b). Yet, peri-urban quarrying and sand and gravelextraction are still to be found, from the gravel pits in the Vale of St.Albans, north of London, to the gravel extraction from river beds outsidemany Asian cities. Industry is increasingly seeking peripheral locations formajor new industrial installations, be it the science parks at Cambridge orthe new manufacturing industries around the towns of the Pearl RiverDelta (Sit and Yang 1998). At the same time, some peri-urban areas arecharacterised by industrial decline, as in the ‘rust belt’ zones of NorthAmerica (Teaford 1994) and Europe (Bennett et al. 2000). This changingperi-urban landscape is thus not simply the replacement of rural land usesby urban land uses, but also involves readjustments of urban uses byredevelopment and through neglect. Industrial decline creates opportunitiesfor plants and animals to become re-established and for other species toinvade and for informal land uses to occur in temporarily derelict land.
For the middle class, the dream is often a house in a rural setting,with golf courses and other recreational facilities, and easy access to bothcountryside and the city centre. For many, the reality is urban sprawl, thelow-density expansion of large urban areas driven by land values, and freemarket developers, without planning controls, mainly into the surroundingagricultural areas (European Environment Agency 2006). Urban sprawl iswell defined by the US National Trust for Historic Preservation, RuralHeritage Program: ‘Sprawl is dispersed, low-density development that isgenerally located at the fringe of an existing settlement and over largeareas of previously rural landscape. It is characterized by segregated landuses and dominated by the automobile’ (Gillham 2002, 4). Urban sprawlis driven by three key factors: a growing population, rising incomes andfalling commuting costs. In addition, greater affluence among sectors ofthe urban population means that living space per person is increasing inmany urban areas (an increase in 30 years from 27 to 40 m2 per person inthe city of Erlangen, Germany, for example; Brueckner 2000). Urbangrowth occurring purely in response to these fundamental forces is notsocially undesirable. However, three market failures may distort the balanceof agricultural and rural land uses: the failure to account for the benefitsof open space, excessive commuting because of a failure to account forthe social costs of congestion, and failure to make new development payfor the infrastructure costs it generates (Brueckner 2000). Generally, suchlow-density, residential environments offer an excellent standard of livingand are healthy places, to the extent that they have good sanitation andavoid the traditional diseases associated with poverty. However, they indirectlycontribute to the high level of transportation-related greenhouse gasemissions, to intensification of the urban heat island, and to the moderndiseases of affluence such as heart disease and stress. Their social costsinclude the traffic accidents associated with high vehicle use and longstraight roads, encouraging high speeds (Ewing et al. 2003), the increased
excess deaths during heat waves (Patz et al. 2005), increased levels ofozone in outer suburbs (Civerolo et al. 2007), higher noise levels leadingto interrupted sleep, and increased levels of road rage and aggressivebehaviour (Graham 2005).
Although thought to be characteristic of North America, Europe andother wealthy regions, sprawl is fast becoming a feature of peri-urbanareas in Latin America and Asia (Table 1). Here too, greater affluence israising living space per person (from 6 to 12 m2 per person in Beijing,China, for example) with increasing demands for land for open space forboth private and public recreation (Li et al. 2005; Figure 4).
Land for handling waste is a significant element in urban planning. Forlocal government, peri-urban areas have always been sites for landfills,waste dumps, peripheral freeways, airports or noisy and toxic industries.Landfills may be changed into country parks or golf courses over time, whilethe uncontrolled waste dumps outside Asian and African cities (Figure 5)provide livelihoods for thousands of ragpickers, some of whom havesurvived that way for generations (Appadurai 2001). Waste is a resourcethat is sorted, reworked and traded by millions of urban and peri-urbanpeople around the world.
Peripheral freeways themselves become foci for new economic activities,such as retail parks close to intersections. Eventually, these lead to theevolution of ‘edge nodes’, with restaurants, hotels, retail shopping,manufacturing, warehousing and offices. Usually, such complexes are built
Table 1. Indicators of urban sprawl from Latin America and Asia.
City and country Indicator Change Source
Quito, Ecuador Urban area 18,254 out of 253,666 ha converted to urban use in 1980–1986
Murray (1997)
Beijing, China Urban area 99.8 km2 in 1949, 373 km2 in 1985 and 488.1 km2 in 1997
Lu (1999)
Beijing, China Arable land 5967 km2 in 1953 to 3423 km2 in 1997
Lu (1999)
Udupi, Mangalore, India
Population and urban land increase
54% population growth and 146% developed land increase, 1972–1999
Sudhira et al. (2003)
Delhi, India Population and urban land increase
46.31% population growth and 122% developed land increase, 1991–2001
Fig. 4. Urban Sprawl in the USA and China: (A) part of Las Vegas, Nevada; (B) part of ChaoyanNew Town, Chongqing, an area that has paid particular attention to greenspaces aroundfactories and residences.
Fig. 5. Uncontrolled waste dumping at a peri-urban informal settlement near Lusaka, Zambia.
at densities too low for the effective provision of public transport, but highenough to cause traffic gridlock (Hayden 2003). These ‘edge nodes’ or‘edge cities’ are typified by Tyson’s Corner, VA, USA (Short et al. 2007).Once a quiet area located some 30 km west of Washington, DC, Tyson’sCorner grew rapidly in the 1980s and 1990s, largely as a consequence ofhighway construction. By 2006, the area had more than 2.3 million m2
of office space and 0.37 million m2 of retail space. Almost 110,000 peopleworked in the immediate area. It became the 12th largest business districtin the USA (Short et al. 2007). As they are focal points for both privatecars and lorry movements, such developments almost inevitably affecttraffic flows, aggravating the impacts of traffic generally associated withsprawl. Furthermore, the concentrations of vehicles and other activitieslead to increased local water pollution, affecting both surface streams andground water with consequent impacts on aquatic ecosystems (Kaufmanand Marsh 1997).
For conservationists, the green spaces on the edge of cities becomeincreasingly valuable with the passage of time. From such protected areasas Epping Forest and Burnham Beeches in peri-urban London (Fitter 1945)to the Mata Atlantica greenbelt around São Paulo (Victor et al. 2004), tothe salt marshes, mangroves and coral reefs juxtaposed to expandingcoastal cities, there are major conservation debates and conflicts. From theenormous efforts to bring sufficient water back into the everglades (Davisand Ogden 1994) to the re-creation of mangroves around Shenzhen insouthern China (Ren et al. 2008; Figure 6), great efforts are being madeto ensure that urban people can have access to natural areas. These greenspaces bring multiple benefits, often protecting water supply catchments,preserving biodiversity, providing wildlife habitats, absorbing CO2, reducingheat island effects, providing potential sources of wood and offering variedrecreational opportunities.
For education and human well-being, peri-urban areas are of highrecreational value, often having formal playing fields, golf courses and placesfor informal recreation. In many circumstances, they also may includeimportant human heritage sites, such as significant religious buildings,industrial structures and many historic sites. But they are also places ofescape, especially at weekends for urban people wishing to escape the cityand enjoy natural areas. For many children, their first encounters withnature are in peri-urban areas, when they see frogs or fish in a river,glimpse deer in a woodland or encounter a snake in a forest.
These examples of the varied values of peri-urban areas indicate thecomplex of inter-fingered, overlapping human interests that are found onthe edges of urban areas. The contrast between the old and the new is tobe set against the patches of rapid change, where former rice fields areburied with new housing estates, dairy pastures are bisected by newhighways and abandoned industrial buildings are converted into apartments.Change brings advantages to some peri-urban people, but means problems
for others, especially for the people in informal settlements whose homesmay be cleared at short notice so that new buildings can be provided forthe more prosperous.
These changes mean constant introductions, both deliberate and accidental,of new species that affect both ecosystem and human health. They alsoinvolve major biogeochemical changes, not only in the shifts of naturalmaterials but also in the introduction of hundreds of new chemicalcompounds, from the pharmaceuticals helping people and their livestockto the food additives and cleaning agents that find their way into domesticwaste streams. These new conditions, coupled with the changes to atmosphere
Fig. 6. Views of the restored mangroves adjacent to the city of Shenzhen, China: (A) view ofthe canopy of the mangrove woodland; (B) close up of the water level.
and soils, produce new living conditions for all organisms and raise issuesof their resilience to change. Such impacts require an examination of bothhuman and ecosystem health in peri-urban environments.
HUMAN HEALTH IN PERI-URBAN AREAS
Health refers to the ability of an individual to feel well and be strong,to be adequately nourished and free from disease. It is a state of goodfunctioning and balance on the spiritual, social, mental, emotional,perceptional and physical level: the opposite to disease. Thus, health impliesa freedom from disease as well as a feeling of well-being and an absenceof mental stress. Key health issues in the peri-urban transition zoneinclude communicable diseases (e.g. malaria), non-communicable diseases(e.g. poisoning), injuries, malnutrition and psycho-social disorders. Theycan be classified as traditional and modern diseases. Most of the traditionaldiseases are communicable or related to undernutrition, and are generallyimmediate and localised. The modern diseases are mainly non-communicableor linked to injury, overnutrition or psycho-social disorders. They tend tobe delayed in occurrence and to have complex, interrelated causes. Thechange from high prevalence rate of traditional diseases to occurrence ofmodern diseases with social and economic development is known as thehealth-risk transition (Birley and Lock 1998).
Malaria is a major problem in informal settlements in peri-urban areaslacking adequate water supply and sanitation, wherever open, standingwater is colonised by the mosquitoes carrying the disease. The frequencyof illness and the abundance of malaria mosquitoes vary from one part ofthe peri-urban transition zone to another depending on the mobility ofthe human population, the abundance of breeding sites for mosquitoesand the quality of housing and services. Increased availability of mosquitonets has helped many people, but in some areas DDT spraying has beenre-introduced, despite the hazards associated with it (Shiff 2002). In India,however, industrial malaria is a particular problem, as many industrialcomplexes are situated in peri-urban areas (Sharma 1966). Its control requiresa combination of biological and environmental methods that are preferableto chemical control, such as DDT. Habitats for malarial mosquitoes arechanging, both because of local actions and as a consequence of globalclimate change. Warmer summers in temperate latitudes may bring malariaback to peri-urban areas where it has not been seen for centuries. Formany tropical areas, increased drought will cause more people to attemptto store water that, if not covered, could become breeding grounds formosquitoes. Tropical peri-urban areas could experience more frequentflooding, creating many more temporary pools that persist for longer,again giving opportunities to mosquitoes.
Filariasis and dengue fever are also widespread in tropical peri-urbanareas. The breeding sites of their vectors depend on solid and/or liquid
waste disposal systems. Smoke and dust from industry also lead to bronchialdiseases. For example, in the peri-urban zone around Aligarh, India, villagersreported breathlessness because of smoke pollution, and were affected byfly ash particles (Singh and Asgher 2005).
Many tropical peri-urban zones supply locally grown food for the poor.However, there are many health hazards in peri-urban agricultural pro-duction and potentially in the food from such cultivation. The hazardsinclude airborne contaminants, particularly from industries, polluted irrigationwater, and the use of human and animal wastes as fertilisers. Industrialpollution may reduce crop yields (Agrawal et al. 2003; Wahid et al. 2001),while the residues on the leaves of plants grown close to roads and toindustrial emission sources pose health problems for those who eat them.Children, in particular, may ingest lead from vegetables as well as fromsoil and dust (Finster et al. 2004; Nabulo et al. 2006).
Fertiliser handling in peri-urban agriculture has its own problems.Farmers on the Jos Plateau, Nigeria, have little knowledge of how to usefertilisers effectively, merely using whatever they can obtain and applyingit without reference to any instructions (Harris et al. 2006). This behaviourproduces health risks for those handling the chemicals and risk of con-tamination of water supplies that could have a major impact in a denselypopulated peri-urban area. The use of raw domestic sewage for vegetablecultivation in the suburbs of the capital city of Asmara, Eritrea, has leadto heavy contamination of vegetables by faecal coliforms as well as withGiardia cysts (Srikanth and Naik 2004). Dietary intake of raw salads (lettuce,cabbage) grown on the raw sewage appears to be a causative factor ofGiardiasis in both the farming community as well as in peri-urban settlementsaround Asmara (Srikanth and Naik 2004). On the other hand, peri-urbancommunities around Kumasi, Ghana, have successfully experimented withhousehold-composting strategies to improve sanitation and provide organicfertiliser (Adam-Bradford et al. 2006). New technologies are being developedto minimise the possible harmful effects of using human wastes inagriculture through better composting at the local scale (Belevi andBaumgartner 2003). Many international aid agencies have recognised thepotential of using human wastes in peri-urban agriculture, but despitetechnologies being available, appropriate funds to set up schemes and toprovide both capacity building and appropriate maintenance of facilitiesare often lacking. Thus, the health risks remain.
Much disease is associated with waste in peri-urban areas, not just amongthose who collect and sort waste for a living, but also among residentsin settlements where waste is simply dumped or piled up. For example,residents in part of the Bani-Zaid district of Aleppo, Syria, were dumpingwaste in a courtyard area where children were playing. Elsewhere, contractorsleft waste in peripheral dumps where it became scattered by stray dogs,goats, scavengers and children (Hammal et al. 2005). Vermin live in the wastedumps and help to spread disease. In poor settlements around Aleppo,
leishmaniasis (‘Aleppo boil’) is frequently found, especially where there areopen sewers. Rodents harbour the disease, whose pathogen Leishmaniatropica is spread by the female sandfly. Ideally, people would be protectedby window screening and netting, things that are not often available tothe poor in informal settlements (Hammal et al. 2005).
The cooking fuels used by the peri-urban poor may influence theoccurrence of respiratory diseases. Household cooking on an open firemay be the largest single occupational health problem in the world forwomen (Smith 1993). Their babies and young children are also exposedto the smoke for much of the day. Biomass fuel smoke can lead to acuterespiratory disease in children and to chronic obstructive lung disease inadults, while the eyes can be affected by the smoke and heat from fires(Bruce et al. 1998). Stoves at floor level often cause injuries, particularlyburns to children, and are risky in terms of food hygiene (Birley and Lock1998). Respiratory diseases have long been associated with industrial airpollution especially during the 19th and early 20th centuries in Europeand North America. While the smoke from coal burning has largely beeneliminated from those regions, it still occurs in many Asian countries.Thus, the ambient air in peri-urban areas downwind of industrial zonesmay create ill-health or aggravate conditions associated with smoke fromhousehold fuel use (Bruce et al. 2000). For individuals, additional com-plications are introduced by cigarette smoking that adds to the risk of lungdisease. Unravelling the roles of these three factors in any individual caseis difficult. In some peri-urban households, all three types of pollution willaffect whole families, but particularly the women doing the cooking andtheir young children.
Access to health services is a major factor in avoiding sickness. Manyperi-urban residential areas, whether poor slums or wealthy suburbs, haveinadequate health care facilities and long journeys have to be made toclinics and hospitals, the best of which tend to still be close to city centres.One reason why health care facilities in Khayelitsha, the large, expanding,poverty-ridden, peri-urban settlement east of Cape Town, South Africa,were regarded as inadequate was that nearly half the women interviewedhad to travel for more than half an hour to reach the health services(Hoffman et al. 1997). Improvements to local health conditions would requirethe provision of basic infrastructural services and new social developmentpolicies. For the extremely poor here, the health services would have tobe free or extremely cheap.
New health hazards are continually evolving because of the dozens ofnew manufactured chemical compounds entering the environment everymonth. Relatively, little is known about the occurrence and origin (e.g.new household products, surface-active agents, plasticisers) of endocrine-disrupting chemicals in the peri-urban environment, particularly thosein effluents or solid wastes. Poor conditions for the disposal of malecontraceptives and the contraceptive pill lead to harmful effects such as
the ingestion by cattle, effects on humans (e.g. rag pickers), slow rates ofbiodegradation, drain blockage, high costs for screen-cleaning in waste-watertreatment plants. Hormones from oral contraceptive pills excreted in urineaffect aquatic food chains, particularly fish, and thus can enter the humandiet (Ehiri and Birley 2002).
Overall, the health problems of poor peri-urban settlements are complexand reflect the interactions between social and environmental conditionsand the institutional structures, or lack of them, in individual settlements.The environmental conditions work to perpetuate poverty through suchthings as poor housing, limited awareness of risks, lack of employmentopportunities with those that have jobs often working in hazardous con-ditions, inadequate health care, poor sanitation, low access to clean water,air pollution, accumulations of waste, poor drainage and exposure to rawsewage (Hammal et al. 2005). The vulnerability of the people is heightenedby the superimposition of climatic and geophysical hazards on the risksassociated with their environmental conditions. A major case may be madefor giving the peri-urban (and urban and rural) poor priority in adaptationto climate change (Douglas et al. 2007).
While the catalogue of poor conditions leading to ill-health in poorsettlements is a matter of great concern, there is also strong evidence ofill-health associated with urban sprawl in affluent peri-urban areas. Becauseareas of peri-urban sprawl usually have wide, long streets that encourageexcessive speed, they tend to have more traffic fatalities, especially forpedestrians, than do compact urban areas (Ewing et al. 2003). The risk ofbeing killed when hit by a vehicle is greater the faster it is travelling (85%at 65 km/hr and 5% at 32 km/hr). Environmental injustice also occurs.In the USA, people from minority communities are more susceptible toinjuries in car crashes and pedestrian accidents. Residents of poor areasbisected by major commuter highways are particularly vulnerable, especiallyif they have to negotiate roads without footpaths or pedestrian crossings(Ewing et al. 2000).
Air and water pollution also create health risks in sprawl areas. Highvehicle use in spread-out peri-urban residential areas is a major cause ofoccasional hazardous air pollution levels (Frumkin et al. 2004; Figure 7).As mentioned above, the emissions and built-up surfaces in urban andperi-urban areas also contribute to the ‘urban heat island effect’. This canmake city temperatures 6–8 °C higher than surrounding rural areas, raisingthe number of deaths during exceptional heat waves. Motor vehicles,especially those with petrol engines, are also a significant source of polycyclicaromatic hydrocarbon emissions (Marr et al. 1999). Motor vehicle trafficgrowth has been linked to increased polycyclic aromatic hydrocarbonconcentrations in peri-urban lake sediments in the USA (Van Metre 2000)and consequent impacts on the aquatic food chain. Such increases can alsohave impacts on both surface and groundwater supplies, leading to highertreatment costs and higher water charges.
While the modern garden suburbs helped to reduce the occurrenceof traditional diseases, such as rickets, the lifestyles in motor car-dependenturban sprawl are highly conducive to modern, non-communicable diseasesthrough obesity, inactivity, depression and loss of community. In large,single land-use, peri-urban sprawl areas the likelihood of obesity ishigher, regardless of gender and ethnicity. In Atlanta, USA, every additionalhour per day spent in a car was associated with a 6% increase in thelikelihood of obesity (Frank et al. 2004). However, well-designed andplanned suburban areas, with mixed land uses and features encouragingwalking or cycling, can reduce trends towards obesity and favour betterhuman health (Frank et al. 2005). Many people in areas of sprawl canmake choices that reduce their peri-urban health risks. Not all are ableto do so, their residential choices being constrained by the state of thehousing markets and their ability to buy or rent property on the locationsof their first choice.
For the poor, in deprived, unhealthy, informal settlements, there is evenless choice. They cannot escape the imposition of environmental changescaused by public or private agencies that have the power to build newfacilities close to their dwellings. Thus, for some, peri-urban areas are healthyand the scene of good living standards. For others living in poverty, theyoffer survival opportunities, if they can find work and grow some of theirown food. For many groups, both in affluent and poverty-stricken areas,they are full of risks to health, whether due to people’s own behaviour orto that of others. The plants, animals and microbes of peri-urban areas areequally subject to the disturbances and threats of the changing dynamicsof these hybrid landscapes.
Fig. 7. Early morning smog over Salt Lake City, UT, USA.
Ecosystem health refers to the situation in which ecosystem functions arenot compromised by human activity. From an ecological standpoint,healthy ecosystems are characterised by an absence of distress syndrome,by their resilience to disturbance and by their characteristic productivityand structure (Rapport 2002a). Healthy ecosystems are able to supplynatural services like water, food, fibre, fuel and genetic resources. A healthyecosystem is stable and sustainable, actively maintaining its organisationand autonomy over time and is resilient to stress (Costanza et al. 1992).Rapport et al. (1998) defined ecological health in terms of ecosystemvigour, organisation and resilience (Table 2), as well as the absence of ecosystemstress. Resilience emphasises the essential ecosystem functions and lifesupport systems, which are key elements of ecological sustainability. Transforma-tion of ecosystems under stress, from healthy to pathological conditions, isoften irreversible, even when the initial stress factors are removed. This canaffect human health because the breakdown of ecosystems under stress isoften conducive to an increase in human pathogens, recycling toxic sub-stances, reduced yields and compromised food supplies, scarcity of potablewater, and air pollution (Rapport 2002b). With all the consequences ofdiverse forms of changing land use and modifications of biogeochemicalcycles for ecosystems, ecosystem health is a particularly acute problemfor peri-urban areas. While the protection of some areas may enhanceecosystem recovery, activities in others are leading to irreversible impactson ecosystem health.
While many people have developed indicators of ecosystem health,questions have been raised about their value in managing ecosystems (Niemiand McDonald 2004). Ecosystem restoration is a goal of much peri-urbanland management, but it needs specific indicators of the factors that arecritical for a particular ecosystem at a given time. Indicators need to betuned to the problem at hand and be capable of indicating improvementor otherwise of ecosystem state in response to restoration efforts (Harrisand Hobbs 2001). In examining peri-urban areas, it is important to identifythe processes that are assisting restoration of ecosystems and thus whichare reducing ecosystem health.
Table 2. Indicators of ecosystem health (after Rapport et al. 1998).
• Vigour: refers to activity or rate of processes (e.g. primary production)• Organisation: refers to diversity and the number of interactions between system
components. Healthy ecosystems have complexity of structure (both physically and biologically) whereas unhealthy ecosystems often lack complex organisation
• Resilience: refers to a system’s capacity to maintain structure and function in the presence of stress. Healthy ecosystems have the ability to ‘bounce back’ after a disturbance, unhealthy ones often do not
Being a complex mosaic of land cover types, peri-urban areas mayhave significant open space reserves and green spaces that are prominentzones for the protection of biodiversity. However, to some extent,organisms colonise virtually all parts of peri-urban areas. From the plantsthat establish themselves on the walls of derelict and poorly maintainedbuildings, to the self-seeded vegetation of disused railways tracks oralong canals, and the exotic plants deliberately brought into gardens, butwhich spread to a host of other spaces in and around cities, biodiversityabounds (Kirkpatrick and Bridle 2007; Zagorski et al. 2004). Then, thereare a host of animals and birds that have adapted to life in and aroundurban areas, from feral cats and dogs to kangaroos on Australian peri-urbangolf courses (as at Anglesea, Victoria) (Whitley 2007); or from rats in sewers,pigeons in city squares to mosquitoes in the choked drains of the world’sworst slums. A vision of ecosystem health in peri-urban areas has toencompass this great diversity.
Nevertheless, there are fundamental contrasts in the relative dynamismof ecosystems between city centres, inner suburbs, outer suburbs andperi-urban areas. In the heart of large cites, small patches of land maychange character as new prestige buildings are built, or as redevelopmentsees new apartment buildings created. However, here, most green spacesare jealously protected and seldom changed. Few green spaces are builton, few new roads are created, few new plants are introduced, save intothe decorative indoor gardens of ever more imposing hotel atriums andoffice reception areas. Perhaps the trend to green roofs, roof gardens andpavement cafés with shrubs may add greater diversity to the heart of thecity. Similarly, the only time the inner suburbs see change is when onebuilding replaces another, or when a huge regeneration scheme clearsold houses for new developments. Most of these areas stay unchangedfor decades. In the outer suburbs, more land-use change occurs, as olderbuildings are replaced with new structures, usually with a loss of gardensand other open spaces and increases in paved and roofed impermeableareas and apartments replace single family dwellings and retail and officebuildings get larger. However, in the peri-urban areas, with the devel-opment of both greenfield and brownfield sites, change can be affectinglarge areas simultaneously. Here, nature is uprooted, plants are removed,others are imported and new species are introduced or invade. Thegreen spaces that are left, or which are created in the developmentprocess, will be valued for their potential biodiversity and their ecosystemservices.
With concerns about urban flash flooding rising as a result of possibleincreased storminess due to global warming, the role of peri-urban greenspaces, both among buildings and along streams and rivers, becomesincreasingly important (Ashley and Saul 2007). In new developments, greenroofs and green spaces can provide storm runoff detention (Getter andRowe 2006; Oberndorfer et al. 2007). Ideally, surface runoff pathways should
encourage detention of water, infiltration and flow rate reduction. Inpractice, most urban drainage evacuates the water as quickly as possible.Debris and contaminants are thus swept quickly into rivers, damaging peri-urban aquatic ecosystems. Campaigns to restore river channels to morenatural conditions (Kondolf and Micheli 1995) and to daylight culvertedstreams (Pinkham 2000) are showing how peri-urban green space can beused to improve aquatic ecosystem health, just as its recreational use helpsto improve human health (Figure 8).
The transient nature of the peri-urban ecosystems has to be re-emphasised.It is the interface where urban and rural activities meet. The peri-urban
Fig. 8. Former urbanised stream serving many water mills, now developed into an attractiveriver valley corridor: the Water of Leith, Edinburgh, Scotland.
ecosystem mosaic is affected by the material and energy flows demanded byboth cities and countryside. Even in Europe, some policies for agriculturalland create new activities for urban people in land designated for agriculture.For example, the ‘set-aside’ policies of the European Union have encouragedsome farmers to develop land for golf courses (Robinson and Lind 1999).Already 5300 golf courses in Europe occupy 250,000 ha of land with plansfor more facilities to be built before 2010. Yet, these new golf coursespresent opportunities for biodiversity (Stubbs 1996) and nurturing resiliencein the overall landscape. Seasonal wetlands on golf courses increase amphibianbiodiversity (Scott et al. 2003, 2008). Golf courses have the potentialto function as corridors and buffer zones for biodiversity between ruraland built-up areas and to provide habitats for pollinators and species thatcontrol pests.
The great pace of change also creates demands for earth resources, forfossil fuels, water, building land, but especially aggregates and brick-makingclays, and for land for disposal of wastes. Frequently, toxic industries are alsolocated in peri-urban zones, so that there is a high risk of contaminationfrom industrial chemicals and toxic substances. In the past, urban and peri-urban vegetation was eliminated by implementation of smoke control ordersand building taller chimneys. The taller chimneys alleviated the problemin their immediate vicinity but sent the pollutants higher into the air(Woodin 1989). The sulfur dioxide fell as dilute sulfuric acid in distantupland forested areas, creating the acid problem, forest die-back and lakeacidification (Mannion 1999). This, in turn, required correction by theaddition of lime to lakes, involving further quarrying and release of dustto the atmosphere (Olem 1991). Countless other examples of this issue of‘problem shifting’ or ‘problem displacement’ (Christoff 1996) can be foundin peri-urban areas. The complex ecology of urban and peri-urban areasis constantly being disrupted locally by the injection of new species ornew types and concentration of chemicals into specific habitats throughhuman activity. Each change alters ecosystem health.
Despite these problems, it is important to emphasise the role of peri-urbangreen space in adapting to climate change. The ecological performance ofcities depends critically on the amount of vegetation cover, especially oftrees, in the urban environment (Whitford et al. 2001). Urban and peri-urbantrees have the potential to help reduce the levels of atmospheric carbon.Wide variations in CO2 uptake per km2 occur due to the size and densityof trees (Jo and McPherson 1995). Trees also modify the hydrological regimeand reduce the urban heat island effect (Douglas 1983). Healthy peri-urbanecosystems, particularly those with trees, could play a small global role incarbon uptake, but a more significant local role in counteracting risingtemperatures, modifying the water regime and reducing local pollutioneffects. This role of trees indicates the value of classifying peri-urbanland in terms of its ecosystem characteristics, as a variety of habitats, orland cover types.
Urban habitats are extremely varied and offer a wide variety of opportunitiesfor vegetation to become established, for the protection of naturalvegetation and the establishment and maintenance of gardens and otherplanted landscapes. For planning and restoration purposes, it is useful tointroduce a form of classification that can aid the analysis of peri-urbanecosystems. Urban habitats have been sub-divided in terms of vegetationtypes (Shimwell 1983), types of biotic zone (Dorney 1979), urban ecosystem(Duvigneaud 1974) and urban land use types (Douglas 1983) (Table 3).For an analysis of urban vegetation and other ground cover, Lindley et al.(2006) use ‘urban morphology units’ which combine different types of builtenvironment with forms of open spaces, including gardens. They emphasisethe role of green space within the different morphology units in order toapply knowledge of the ground cover to adaptation to climate change.
A classic view (Marren 2002) is that there are two main kinds of wildlifehabitat in urban areas. One is based on built structures: roofs and streets,railway sidings and canal banks, urban parks and churchyards, and derelictland. The other comprises the remnants of the countryside caught up inthe growth of the city, the pieces of woodland, wetland and even farmlandthat are now surrounded by urban growth. However, today so muchreclamation of old mining, quarrying and derelict industrial land has goneon that many of the key wildlife areas are now as much created by humanendeavour as the buildings and roads to the urban area. In central London,close to Kings Cross Station, an old coal yard has been converted into anecology park, with a large pond and reed beds fringed by willow andbirch trees and has become a haven for both wading birds and peopletaking a break from city routines (Goode 1986). Emerging ecosystems inurban and peri-urban areas may include some relict rural systems, forexample, the small and somewhat degraded Bukit Nanas in Kuala Lumpur(Hai 1977; Southwick and Cadigan 1972), and the larger and species richBukit Timah in Singapore (Turner and Corlett 1996). They also includeexamples of combinations of adventitious exploiters and colonisers of thebuilt environment (for example in Brussels; Godefroid 2001) and deliberatelycreated ecosystems, through land reclamation with natural colonisation(Millard 2000), or the making of parks and gardens (Goode 1989).
Impacts of Urban Activities on Ecosystem Health
The human impacts on urban and peri-urban ecosystems can be dividedinto a three-dimensional set of spatial and temporal effects. There are thedirect on-site effects, such as the clearance of vegetation and removal ofsoil during construction, or the bringing in of new soil and deliberateplanting of vegetation. There are the indirect on-site effects, such as thedisturbance of nesting sites and the modifications of drainage that affect
Table 3. Types of urban and peri-urban land cover and ecological condition.
Habitat type (Douglas 1983)
Habitat type used in Iowa Nature Mapping
Substrate type used in urban LTER, USA
Biotic zone (after Dorney 1979)
Type of urban ecosystem (after Duvigneaud 1974)
Urban vegetation type (Shimwell 1983)
Paved roofed, densely urban complexes devoid of vegetation and water bodies
Urban high-density commercial/industrial
Asphalt +/– concrete Cliff/organic detritus
Anthropogenic Pioneer, open communities of rocks, walls, roofs, pavements and other metalled or trodden surfaces, dominated by cryptograms or other specifically adapted rock plants (lithophytes)
Suburban mosaic of houses, roads, gardens and mature trees
Peripheral Rank, perennial, tall grass and tall herb (usually > 70 cm) communities of embankments, road verges, abandoned sewage beds and damp swamp and marsh margins
Landscaped parks and open spaces
Urban maintained parkland
Grass + water +/– sandy soil
Mown grassland
Anthropogenic and modified natural
Managed, mown grasslands and weedy, perennial herb grass communities
Derelict land construction sites
Abiotic weed complex
Urbanophile Therophyte-dominated communities of derelict brick-rubble, cinder and fuel-ash tips, etc. (includes communities with large number, or even mostly, perennials)
the survival of particular plants and animals. In addition, off-site effectsoccur, such as the disposal of cleared material to another site, or the washoff of eroded soil from the construction site into a nearby wetland ofstream, or the blowing of dust onto nearby plants and food crops. However,not all the impacts are so immediate. Sometimes, earthworks on a slopecreate instability that only becomes apparent later when heavy rains saturatethe soil and substrate and cause part of the slope to fail producing a smalllandslide or earth movement that displaces trees and other plants.
The off-site shift of indirect impacts, such as the fallout of pollutantsor the degradation of downstream aquatic habitats, has important effectson peri-urban agricultural production, on air quality, on water pollutionand soil contamination. Metal contamination of urban and peri-urbansoils, for example, is affected by three groups of factors (Thornton 1991).First, individual pollutants may be dispersed over a wide area from diffusesources such as vehicle emissions, or may be locally concentrated from apoint source, such as emissions from a chimney or waste pipe. Second,dispersion may occur in gaseous, particulate, liquid or large solid form.Third, over time, emissions may be continuous and regulated, as from alicensed factory chimney or point source discharge to a stream, or fromuncontrolled, accidental or illegal emissions or dumping (Thornton 1991).
To these impacts from work and living at home must be added thosedue to recreation. All urban and peri-urban ecosystems, but particularlygrasslands, are likely to suffer from trampling as people move through suchareas (Ash 1991). The initial effect of trampling is an increase in perennialspecies capable of withstanding the pressure, for example, rosette speciessuch as daisy (Bellis perennis) and plantain (Plantago major) and species suchwhite clover that root at stem nodes. More persistent trampling leads tooccasional, dry period, bare patches that can be colonised by annuals suchas Poa annua, the introduced pineapple weed (Maticaria matricoides), knotweedand pearlworts. These perennials die out if the trampling becomes moresevere the final stage is bare earth.
Many effects are moderated or reduced by deliberate human inter-ventions. The public is willing to campaign for and to pay for protectionand improvement of parts of the peri-urban landscape. From Local NatureReserves in the UK to UNESCO Biosphere Reserves adjacent to majorcities in Latin America and Asia, there are examples of ecosystem healthbeing enhanced or maintained by good management and protection (Shafer2008). Management may constrain access to protect sensitive areas, confiningvisitors to footpaths. Deliberate feeding of birds, or provision of nestingareas, can enhance species diversity. Selective removal of invasive weeds canincrease plant diversity. Beneficial human activity often requires constantmaintenance and good supervision of the sites involved.
The adverse pressures on peri-urban vegetation are well illustrated bychanges to woodlands on the eastern slopes of the Sierra de las Cruces to thewest of Mexico City (García-Romero 2001). The temperate and sub-humid
highly disturbed oak woodlands on the dry and inhospitable low piedmont(below 2500 m) have been greatly affected by the creation of illegalsettlements, infrastructure construction and waste dumping. These activitieshave led to the destruction of the original forest communities and colonisationand dispersal of low-value species (plants common in the adjacent urbanand agricultural areas). Thus, the remaining oak woodlands are confinedto steep-sided ravines that retain more moisture than the surrounding slopes.As the urban growth and activity advances up the mountains, human useof the land becomes consolidated and the original vegetation retreats.Readily dispersed neophytes colonise these disturbed areas. Eventually, thereis a lowering of species richness on the mountains.
Similar pressures exist around smaller cities, including Canberra, Australia,where the invasion of environmental weeds and other exotic species(including feral animals) (particularly in the peri-urban areas) into theremaining fragmented native grasslands is a serious threat to biodiversity(Environment Commissioner 1997). Bushwalking, camping and off-roadvehicle driving are also changing ecosystems. Generally, residentialdevelopment on the urban fringe in affluent areas leads to reducedsurvival and reproduction of native species near homes. Native speciesrichness often drops with increased residential densities. Exotic species,some human-adapted native species and species from early successionalstages often increase with such sprawl-type development. These relationshipsare sometimes non-linear, with sharp thresholds in biodiversity response(Hansen et al. 2005).
Aquatic ecosystem health in peri-urban areas can be degraded byrunoff from buildings and roads. Generally, urban streams contain manyfewer individuals of most species (especially invertebrates) than ruralstreams, although certain tolerant, adaptable species will be present ingreater numbers (Bernhardt and Palamer 2007). The parallel decrease inspecies richness can be attributed to the effects of urbanisation, particularlythe effects of storm water input and piping of stream water (Roy et al.2005). Peri-urban areas provide an opportunity to determine when thischange in species abundance occurs. In a peri-urban residential area closeto Auckland, New Zealand, inflows of stormwater cause degradationwhen the impervious surface exceeded 12% of the total catchment area(Herald 2003). However, in terms of resilience, there is positive news,in that the native fish, banded kokopu, was found in headwater streamsabove the sprawl areas. To reach these headwaters, this fish, which returnsto the sea for part of its life cycle, must pass through the degraded waterand habitat of the lower and middle reaches of these catchments, includingsignificant lengths of lined or culverted channel. On one stream, thebanded kokopu were swimming through 0.4 km of culverted channelto reach the catchment headwaters.
Stream ecosystem function changes with peri-urban change. Near Atlanta,Georgia, the amount of fine benthic organic matter decreases as the urbanised
area grows, leading to a reduction in both NH4 and soluble reactive Puptake velocities (Meyer et al. 2005). Ecosystem metabolism was notcorrelated with extent of urbanisation. While the breakdown rate of Acerbarbatum leaves was positively correlated, nutrient uptake velocities werenegatively correlated. Such problems can be tackled by programmes of streamenhancement. Often enhancement activities change riparian vegetationand bank conditions, as well as substrate composition, instream organic matterand variability of instream velocities. When this was done near Christchurch,New Zealand, there were only small changes to the invertebrate community,with subtle shifts in overall abundance, species evenness and diversity(Suren and McMurtie 2005). The invertebrates did not respond stronglyto enhancement activities. Caddis flies and mayflies did not reappear atthe enhanced sites. This illustrates a dilemma of ecosystem manipulation:can restoration to an ideal previous condition be realistically expected? Orshould some new state be expected generally? Perhaps if the key factorsthat potentially limit invertebrate communities are identified, the enhancementpotential of streams could be better assessed. This would allow managersto identify sites where recovery of biological communities is possible, andthose where it is not (Suren and McMurtie 2005). Aquatic ecosystemhealth is greatly affected by changes in the sources of runoff to streams.One changing source is the gradual exposure through time of the wastedeposits from former industrial activities. This can release many heavymetals and hydrocarbon compounds to streams. These waste and industrialresidual substrates are a particular issue of re-establishing green areas in theperi-urban environment.
The Importance of the Substrate and Landform Stability
The materials on which organisms live affect ecosystem health in urbanand peri-urban areas through nutrient availability, water availability andthe nature of the habitat (Ash 1991). If a built-up area is considered as abiogeochemical complex, it will be found to have a huge chemical diversitywith varied opportunities for colonisation by microbes, bacteria, plants andinvertebrates. The types of building material (brick, concrete or wood) offerdiffering challenges to the colonising insects. However, once decay begins,the colonisation is rapid, as plants exploiting any crack in concrete surfacesin the humid tropics show (Mishra et al. 1999). Severe deficiencies innutrients or water, or both, usually favour the lower plants, especiallywhere there is no depth of loose material to act as a soil. Mosses, lichensand liverworts can survive drought and high temperatures and gain enoughmoisture and nutrients from rainfall and runoff to survive on roofs, wallsand pavements more readily than higher plants.
In terms of ecosystem health and biodiversity, the important factor onderelict land is not the actual composition of the substrate but the variabilityof it (Elias and Chadwick 1979). A variety of substrates will produce a
greater diversity than a homogenous substrate. Acidity or alkalinity havemarked impacts, but soil depth, seasonal moisture characteristics andsubstrate bulk density, are all important influences on the vegetation. Forexample, a rubble substrate at different depths and particle size can influencethe vegetation community above it, with distinct communities emergingon crushed, uncrushed and granular rubble (Gilbert 1989).
The acid sulfate soils that underlie many coastal plains in SoutheastAsia, Australia and elsewhere can prove highly problematic both whendrained for agriculture (White et al. 1997) and when opened up for urbandevelopment (Lam 1992; Waltham 2005). Drained, sulfidic sedimentsoxidise and produce highly acidic discharge (pH < 4) with significant impactson estuarine ecosystems, especially in the release of iron and aluminium.This poses major problems for peri-urban agriculture, especially whenfertilisers are derived from urban sources such as animal wastes and woodash that may contain relatively high concentrations of metals (Hedlund et al.2003). Such soils are often overlain by peat which shrinks of drainage.Across sites worldwide, peat originally 5–10 m thick is about 50–65% ofthe fall in water level on first drainage and 20–30% of the fall on subsequentstages of renewed drainage (Waltham 2005). Such alluvial areas can alsohave groundwaters affected by arsenic. For example, in the Mekong delta,aquifers usually contain groundwaters of no more than 10 μg/L, althoughscattered anomalous areas of 10–30 μg/L are also quite common (Stangeret al. 2005). The most serious, but possibly ephemeral arsenic anomaliesof up to 600 μg/L are associated with iron and organic-rich flood-plainsediments subject to very large flood-related fluctuations in water level,resulting in transient arsenopyrite dissolution under oxidising conditions.In managing these areas, water control, drain spacing and drain depth arecritical factors in regulating the export of acidity into coastal streams(White et al. 1997).
A good example of extreme alkalinity leading to biodiversity occurredat St. Helens in Merseyside, England, where wastes from the glass industrywere deposited behind 15 m high bunds, several hectares in extent (Ash1991). Originally alkaline, they are now largely dominated by tall fescue(Festuca arundinacea) with a locally unusual population of broomrape(Orobbanche minor). The highly alkaline (pH > 10) water escaping from thebase of the banks supports saline areas colonised by sea poa (Puccinelliadistans). In many other cases, the diversity of substrates has permitted thesurvival and invasion of rare plants of conservation significance (Hollidayand Johnson 1979). While such extreme peri-urban environments mayprovide opportunities for new assemblages of plants and animals, they aregenerally inhospitable and a more normal policy with such contaminatedland is to remove the contamination and to provide some form of moreneutral soil-forming material to cover it. Such a decision is typical of theissues confronting management of the urban fringe (Clark 1999): in whatway should it be managed?
Unplanned and Unmanaged Urban and Peri-Urban Ecosystems
The global shift in heavy industry and in the sources of minerals has leftareas of what is usually considered as industrial wasteland, but what arereally zones of ecological and social opportunity. The classic NorthwesternEuropean derelict coal-mining landscape of waste tips was left to the workof natural processes in the first half of the 20th century. Some becameeroded and gullied, others were colonised by herbs and grasses and, ifundisturbed, eventually by trees. The opportunities for plants varied withlocal seed bank (Skousen et al. 1994), with the actual succession on individualwaste tips depending on the substrate, topography, local climate and airquality, and the pH of the spoil (Hall 1957). Erosion may hinder plantcolonisation. Some communities, such as grass-heath, require 50 years ormore to become established. The uneven invasion of abandoned miningsites (Ashby 1984) often produces irregular islands or patches of vegetationcomprising plants found on nearby undisturbed areas (Bramble and Ashley1955). Such micro-sites initially become colonised by plant propagules,forming small patches of vegetation. These grow and few new patches areformed. Eventually, the patches coalesce as the remaining unvegetatedareas decrease in size (Game et al. 1982). Local micro-habitat factors maybe important. For example, individual fallen logs may provide shade,better moisture and shelter for specific such as ferns (Skousen et al. 1994).Sites with favourable substrates, having a high pH and low acidity, experiencerapid invasion of the herbaceous layer that so covered the ground thatthere was little opportunity for tree development. On more acid soils,favourable micro-sites are colonised by acid-tolerant grasses and tree speciesfrom the surrounding forest.
Worked out peri-urban sand and gravel pits provide other opportunities(Gill et al. 2007) for plants and wildlife. Contrasts in the water depth,steepness of pit walls and banks and surrounding materials producevariations in the succession and colonising species. For example, those tothe south of Loch Lomond, near Glasgow, UK, often act as a refuge foronce common arable weeds that are no longer readily found in the areaas so few fields are under the plough. They shelter less common speciessuch as Verbascum thraspus, Resela luteola and Perentucellia viscosa (Mitchell2001). Water-filled gravel pits left to natural succession initially attractshingle nesting birds such as the ringed plover, oyster catcher and commontern. As the banks of pebbles gradually become covered by a successionof willow, alder, birch and broom, scrubland birds, such as sedge warbler,garden warbler and lesser redpoll, occur (Ratcliffe 1974).
Some abandoned degraded lands, however, change little, persisting asscars on the landscape. The expected normal succession from open fieldto woodland does not occur, as found by Robinson and Handel (1993)on landfills in the New York metropolitan area. This could have beenbecause birds had nowhere to perch on these sites and so did not carry
many seeds on to the sites. However, once 18 species of tree had beenplanted as an experiment, birds started to come into them. After a year,there were 50 tree species on the site. Birds and animals brought in 20 ofthe new species, the wind nine and the other three were probably in soilof the nursery root balls of the planted trees (Robinson and Handel 1993).Such observations suggest that regeneration is enhanced by appropriateplanting, that local seed banks are important, and that understanding thedynamics of the local flora and fauna is necessary. The opportunity toengage in innovative ecosystem management exists.
Restoration of Degraded Urban and Peri-Urban Ecosystems
In the preliminary planting for the restoration of abandoned coal minesites, the species chosen influence both the nature and rate of subsequentnatural plant colonisation of the sites (Holl et al. 2001). While accessibilityto the local seed bank in undisturbed areas is clearly important, any soilstockpiled during mining may be a valuable seed source. Sometimes, thesoil from a newly opened mining area is used to help recolonisation of arecently abandoned mine site. Certain ground cover species hinder theestablishment of planted seedlings and those from seeds dispersed fromadjacent undisturbed areas. In the eastern USA, there is increasing interestin encouraging hardwoods that have a high commercial value (Holl 2002).In the UK, the planting of ‘urban forests’ in peri-urban areas betweenindustrial towns is characterised by a variety of hardwoods of both amenityand long-term commercial potential (England Forestry Forum 2005). Thediversity so created produces a great variety of canopy architecture andfood sources, allows native herbaceous species to grow favouring bird life(Karr 1968), and leads to varied invertebrate communities. In short, thereclamation of abandoned land requires the balancing of short-tem legaland planning requirements with long-term ecological succession and socialneeds. Successful work in temperate latitudes can see plant communitieson abandoned sites developing into ecosystems that resemble hardwoodforests within 30 years (Holl et al. 2001).
Such activity in peri-urban areas often involves intense public interestand sometimes direct action by civil society organisations. Ecosystem healththus becomes a directly valued good, to be argued for and protected.London’s largest wetland, Rainham Marshes adjoining the River Thamesis recognised as one of the nation’s most important wildlife habitatsforming part of Inner Thames Marshes Site of Special Scientific Interest.The site is home to water voles and birds such as teal and redshank. Along battle over the conservation status of this area was fought in the1980s and 1990s (Harrison and Burgess 1994). Without official permission,some local residents blocked drains and flooded the area. Birds quicklymoved into the area, indicating that its conservation value could berestored through good management. The Royal Society for the Protection
of Birds acquired some of the land thanks to the UK government’s landfilltax credit scheme and set about creating shallow pools, ditches and wetgrassland (Marren 2002).
Not all attempts to restore old industrial land are ecologically fullysuccessful. Many aspects of planning, planting and maintenance have tobe carefully integrated to ensure success. At the former steelworks site atTinsley Park, east of Sheffield, UK, ecologists planned a natural lookingmosaic of grassland and scrub, with heath on higher ground and a chainof ponds in the valley (Marren 2002). Despite the planning, sowing of amixture of grass and native wildflower seeds did not go well and the areabecome dominated by a tall fodder variety of bird’s foot trefoil. Many ofthe planted broad-leaved trees died from lack of maintenance. The survivingalders were largely planted in the wrong place. The restoration ecology wasunsatisfactory, even though the local authority was pleased with the newgreen space (Gilbert and Anderson 1998).
Particular problems arise, and will become even more important in thefuture, in the restoration of peri-urban derelict industrial and miningland in tropical countries. The rapid urban and industrial growth in suchcountries is creating landscape restoration problems for the future. However,mineral resource exploitation has occurred throughout the world forcenturies and worked out mining areas abound in the tropics. It is impor-tant to look at examples of what happens in those environments if somerestoration is carried out. A good example of the problems arises in therestoration of former tin mining land in Indonesia and Malaysia. Fewstudies have examined how a minimal restoration effort may still achievepositive ecological results (Passell 2000). One hundred and fifty years ofalluvial tin mining has left large areas of disturbed ground worked byhydraulic pumps and sand dredges of low fertility and little agriculturalpotential. On tin mine tailings around Kuala Lumpur, Malaysia, unstablesand piles were only colonised by pioneer species and the areas did notprogress towards a forest succession. On the other hand, former slimeponds had a succession from pioneer species, to Phragmites spp. after 3years, followed by shrubs and a forest with species normally found inlowland secondary forests after 12 years (Palaniappan 1974). Few tin minetailings restoration efforts in Indonesia and Malaysia in the last 100 yearswent beyond minimal land regrading and the planting of species such asAcacia mangium. On the Indonesian island of Bangka, 3 years after minetailings restoration, significant increases in the numbers and varieties of thecommon, widespread birds of the natural secondary forest had occurred(Passell 2000). This indicates that even rudimentary restoration producespositive increases in bird species numbers and diversity. Ecosystem healthgains can be high and eventually stability is achieved. Low-cost, basicrestoration methods are helpful and a great improvement over neglect ofthe abandoned mine sites. They can be designed to encourage specifictypes of invasion by creating particular micro-habitats.
Derelict land from former mining and heavy industrial activities is nolonger confined to the old coalfields of Europe and North America. Forexample, massive land restoration works are taking place around Mengoutou,west of Beijing, China (Wang et al. 2007) and industrial dereliction canbe found from São Paulo to Manchuria. Differing approaches are adoptedto these opportunities for restoring ecosystems, or creating new plant andanimal communities. All the interventions result in natural ecologicalresponses. The emerging new biotic assemblages affect key interactionsand processes, such as plant–animal interactions, microbial communitiesbreaking down organic matter in soils, and the impacts and reaction tochanging soil acidity or alkalinity. Knowledge of the ability of an area torecover naturally is important in deciding on restoration interventions. Asin the examples on minimal reclamation of mine land sites and landfills,the crucial role of some initial planting, the creation of some ‘syntheticvegetation’ (Bridgewater 1990) or the rehabilitation of selected attributes(Cairns 1990) may be pivotal. In one extreme, the restored landscape maybe almost a highly managed, highly labour intensive, virtually urban,formal parkland. On the other extreme, it can be a highly biodiverse wildassemblage of invasive and native local species. The latter may enjoy thegreater ecosystem health.
When planning restoration or management, goals have to be set, butnot necessarily in restoring what might have existed in the past (Hobbsand Harris 2001), but in creating something that will withstand and adaptto the human impacts and environmental changes of the future. Goals fora particular site have to balance the ecological potential for restoration withsocial and cultural uses of, and desires for, the site. Stakeholder expectationsand interests have to be understood and incorporated into the goalformulation process. Ecological constraints and opportunities have to beset into local and national social and political priorities, not the least ofwhich are the funding mechanisms for restoration and maintenance.
CONSEQUENCES OF MULTI-PURPOSE LAND-USE MANAGEMENT
Increasingly, pressures on urban green spaces are so great that they areinevitably subject to multiple uses. Ecosystem resilience is put to the test,and ecosystem health is threatened, in many popular natural areas on theedges of cities. Singapore’s Bukit Timah rain forest reserve (Turner andCorlett 1996) has high tree diversity, helps to protect the island’s watersupply catchment, houses troupes of monkeys and many bird species, andattracts thousands of visitors (Figure 9). It provides a psychological escapefrom the hectic, order, regulated, densely built-up urban landscape.
Peri-urban floodplains provide excellent examples of these pressures.The Nairobi river floodplain in Kenya has much peri-urban agriculture,provides a key recreation area, is affected by markets and slum housingthat spill on to its margins, is used in part by people who collect and sort
waste and yet has to evacuate urban floodwaters effectively (Freeman1991). In Manchester, UK, the floodplain of the Mersey River (Kidd andShaw 2000) still has some agriculture; many golf courses and playing fields;peri-urban woodlands, areas for informal recreation; public footpaths; andlakes in former gravel pits that include notable bird sanctuaries, yet providefor water-skiing, sailing and canoeing, while having sufficient capacity to actas diversionary flood basins. The multi-lane ring road around Manchesteroccupies part of the floodplain for 10 km. Careful management of thepublic areas as water parks provides for many societal needs, includinga variety of outdoor recreation that helps to improve human health, yetsupports a variety of terrestrial and aquatic habitats whose bird populationssuggest good ecosystem health.
Much work in Europe has examined the restoration of ecosystemhealth on degraded floodplains to provide flood protection, wildlife habitatsand recreational opportunities. For example, work on the lower Seine Riverin France, seeks to find (i) the appropriate scale for restoration, (ii) the besttools to measure ecosystem function and the impact of management and(iii) how to choose the best management targets (rehabilitation, conservation,restoration) (Poudevigne et al. 2002). The biogeochemical cycles that affectwater quality, and the local biodiversity (plant communities, avifauna,amphibians) are closely related to each other and to the habitat quality (atlocal and landscape scales) of the riverine system. Restoration strategiesfor these species-rich habitats and their healthy ecosystem functions requirethe integrated study of the ecosystem at different scales (Poudevigneet al. 2002).
Appropriate vegetation has to be used in restoring riparian forest bufferstrips along urban floodplains as it will influence fish and wildlife populations
Fig. 9. The interior of the rainforest at the Bukit Timah Nature Reserve, Singapore.
through its effects on temperature, habitat, food resources and water quality.Native trees and shrubs typical of the riparian area that are well adaptedto the riparian environment may support many species of native wildlife.Trees that are especially beneficial to the aquatic community are those withstrong root systems that tend to grow over water, are long-lived, grow tall,and provide large, dense crowns for shade (Higgins 1996). The buffer stripwidth will depend on the particular site and the species in question. Forexample, some animals, particularly ‘edge species’, may require only narrowbuffers (8 m or less) to meet their needs, while others like large mammalsand certain birds require a buffer of 30–100 m (Croonquist and Brooks1991; Keller et al. 1993). In managing peri-urban areas for wildlife, theneeds of the animal for food, shelter and certain environmental conditions(e.g. cool, moist environments for certain amphibians) will be as importantas creating a particular buffer width (Naiman et al. 2005). As yet, there islittle work on whether or not such strategies have produced viable, healthy,stable ecosystems. Even if such knowledge were available there would remaina need to produce the research information that planners really need.Ecologists should be more active in the process in providing ecologicalinsights for plans, a proper and simple biodiversity valuation methodshould be developed, more research on the function on ecological corridorsshould be conducted, and biodiversity monitoring of implemented planningprojects should be developed (Yli-Pelkonen and Niemelä 2006).
Conclusions
Peri-urban areas are the transition zone, or interaction zone, where urbanand rural activities are juxtaposed, and landscape features are subject torapid modifications, induced by human activities. This inter-fingering ofrelict rural and advancing urban creates an ecological, social and economicdiversity that juxtaposes situations that are both healthy and potentiallyunhealthy for their human inhabitants and for all the other animals, plantsand microbes that live and survive in these hybrid landscapes. Globally,the great variety of peri-urban situations makes the transfer of solutionsdifficult. The human health problems associated with urban sprawl inaffluent areas are beginning to be seen in the rapidly expanding industrialcities of Asia. In some countries, the new affluence rests uncomfortablyagainst peri-urban poverty in informal settlements. The very industriesthat are bringing prosperity may also be causing greater ill-health to thepoor, just as 19th-century industrialisation did in Europe. The economicglobalisation that has so changed the location of manufacturing industryhas these significant consequences for public health and ecosystem health.At the same time, the increasing affluence, reflected in the increased numberof motor vehicles, has aggravated climate change. It has also had someconsequences for the dynamics of the earth’s surface, such as reservoirassociated earthquakes and construction-induced landslides (Douglas 2005c).
As a consequence, the vulnerability of peri-urban people to geophysicalhazards such as floods and mass movements has grown. Each geophysicalevent disrupts peri-urban ecosystem health and can affect human mentaland physical health. These health consequences of the interplay betweeneconomy, society, land and ecosystems provide a wonderful opportunityfor innovative thinking in applied science, particularly for public healthmedicine, geography and human ecology. At the same time, they offer bigchallenges to policymakers at both local and national levels as the planningjurisdictions at the urban fringe often overlap between municipal andrural. Deciding on whether there should be urban containment, greenbelts, industrial expansion or freedom for the poor to develop peri-urbanagriculture remains a difficult and contested arena.
At the same time, attention has to be given to ecosystem health, particularlyfor the ecosystem services that are so important for adapting to climatechange by alleviating urban heat island conditions and modifying the localclimate and playing their role in sustainable urban drainage systems. Theyalso play a role in human well-being, especially relief from urban stress andencouraging physical recreation. However, there are also fundamental aspectsof ecosystem dynamics that can be elucidated by analysing the developmentof new assemblages of organisms on both managed and abandoned peri-urban open spaces. The diversity of peri-urban habitats, from relict ruralsystems to neglected derelict land and managed parks and gardens offersopportunities for basic ecological science. Particularly, attractive is the wayecosystem health in peri-urban areas is constantly being disrupted locallyby the injection of new species or new types and concentrations ofchemicals into specific habitats through human activity. Other impacts ofhuman activity include use of, and physical changes to, habitats by economicand recreational activities. Analysis of the diversity of substrates and theireffects on ecosystem development, the role of local seed sources, andmoisture and nutrient availability has already given new ideas on how toreclaim derelict land (Robinson and Handel 2000). Often, minimal reclamationwork, such as the planting of fast growing trees to provide perches for birds,greatly accelerates the emergence of new ecosystems (Robinson and Handel1993). Most restored sites that rely largely on dispersal from neighbouringseed sources eventually taken on the characteristics of the surroundingnatural or secondary vegetation.
Nevertheless, relatively little is known about the way the biodiversityand ecosystem health of extensive peri-urban areas depends on the varietyof habitats and the linkages, migration and dispersal patterns betweenthem. Knowledge of ecosystem resilience is important in deciding onrestoration interventions. When planning ecological restoration or the habitatimprovements, goals for a particular site have to balance the ecologicalpotential for restoration with social and cultural uses of, and desires for,the site. Enhancement of biodiversity in peri-urban ecosystems can havea positive impact on the quality of life and education of urban dwellers.
Such local education can help change attitudes and thus facilitate thepreservation of biodiversity in natural ecosystems nationally and globally.Stakeholder involvement is important, partly because ecosystem healthcontributes to human health, but also because there are so many differentpotential uses of any public land on the urban fringe. Stakeholder expectationsand interests have to be understood and incorporated into the planningprocess and local people have to be involved in the management process.Peri-urban areas are a crucial part of the urban scene, but they are oftenmarginal concerns in urban management and planning. Their rapid changesand their crucial health issues make them a key area for sound environ-mental management and improvement of human living conditions andecosystem integrity.
Acknowledgements
This article reflects experiences gained while the author was Chairmanof the Scientific Advisory Committee of the Scientific Committee onProblems of the Environment Project on Peri-Urban Environmental Change.I am grateful to all those who took part in that project, to the ScopeSecretariat and to the International Council for Science for funding theproject. I wish to thank the editor and two anonymous referees for theirconstructive advice.
Short Biography
Ian Douglas is Emeritus Professor of Physical Geography at the Universityof Manchester, Manchester, UK. He has had 45 years of research experiencerelating to changes to the hydrologic and geomorphic systems in tropicalrain forests, mainly in Australia and Malaysia, and to the biophysicalchanges in the urban environment, especially in relation the materialsflows, urban hydrology and flooding, and urban geomorphology. He isTreasurer of the Scientific Committee on Problems of the Environmentof the International Council for Science (www.icsu-scope.org). He is onthe editorial boards of Catena, Geographical Research, and Land Degradationand Development.
Note
* Correspondence address: Ian Douglas, School of Environment and Development, Universityof Manchester, Oxford Road, Manchester M13 9PL, UK. E-mail: [email protected].
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