S. Murray
Sharon Murray is currently completing her Ph.D. in the Department of Environmental science, Policy and Management at the university of California, Berkeley, USA.
Consideration of the opportunities for and challenges to the management of trees and forests in urban and pert-urban areas of developing countries for positive environmental impacts.
At the revel of individual urban sites, vegetation can have a significant microclimatic impact
The assessment and management of forest influences in the context of urban zones require an understanding of the special biophysical and social challenges presented by these systems.
As a starting point, it is useful to consider metropolitan areas along a landscape gradient from urban centre to rural hinterland (Bradley, 1984). There is a significant spatial variability at different locations along this gradient and it is reflected in diverse biophysical and morphological forest characteristics, including: the type and amount of vegetation present; the degree of fragmentation of the landscape; the amount and location of human-constructed elements, including buildings, paved surfaces and infrastructure; and the characteristics and functioning of individual ecosystem elements such as soil, water and biota.
The continuum of environments encountered (which will not necessarily be strictly linear in space) can be conveniently classified for urban forest management purposes according to characteristics of vegetative cover and human land use. These will often parallel existing urban land-use categories, for example city centre business, medium-density urban residential, commercial corridors, low-density suburban residential/commercial and former urban agricultural zone with new housing development. Other zoning may also be appropriate, for example an urban riparian zone which traverses several of the other urban land-use categories listed above or pert-urban zones of a rural appearance which experience intense environmental impacts from nearby urban centres.
Forest influences along the urban-rural gradient
An estimate of current forest influences on the environment and a projection of potential urban forest influences that may be possible through human management must pay as much attention to understanding the "influences" of the city on the forest as to those of the forest on the city. The environmental impacts of forest vegetation in the city centre, for example, may be important locally, but the generally fewer trees present and the large percentage of exotic species that may not be adapted to local resource limitations as well as the environmental stresses associated with extensive paved surfaces, vehicles, industrial and domestic activity and built structures often limit the extent of forest influences generated in such locations.
On the other hand, the less urbanized or human-modified portions of pert-urban forests generally have a greater potential to exert "influences" on other components of the urban ecosystem. The typically larger quantity of biomass and land area covered by vegetation, the greater space available for planting new trees and the relatively less intense human activity to which the area is subject permits a greater possibility for significant forest influences originating in these zones. Of course, in all points along the gradient, influences are not only a function of "how much" vegetation is present but can vary drastically depending on the particular species of tree planted in a given site and the extent of management applied to the vegetation.
Most of the detailed scientific studies available on urban and pert-urban forest influences have been carried out in the cities of industrialized countries and suggest predictable amounts and types of influence experienced along the above-mentioned gradients at different levels of urban impact. For example:
· The more forested outlying zones and large parks within the city centre are a few degrees cooler than the urban "heat islands" of contiguous built-up areas. The dampening effect on ambient temperature is due to both shading and evapotranspiration by urban trees (Akbari et al., 1992).· Urban and pert-urban trees and other vegetation can mitigate air pollution by absorbing gaseous compounds and intercepting air-borne particulate matter (McPherson, Nowak and Rowntree, 1994).
· At the level of individual urban sites, there are significant local micro-climatic impacts of vegetation, including influences on daily and seasonal temperature fluctuations, wind speed and frost protection, depending on plant type and location (McPherson, 1993; Akbari et al., 1992).
· Trees and other urban forest vegetation facilitate soil water infiltration and lower surface runoff in built-up central urban districts as well as outlying zones, and they are an important mediator in urban hydrological cycles (Loucks, 1993).
· Soil development, nutrient cycling and soil texture can be enhanced by urban and pert-urban trees. These influences may be diminished in more urbanized sectors, owing to the removal of dead biomass from surfaces and changed physical soil conditions (Craul, 1985; Loucks, 1993), but litter decomposition rates; may actually be higher in other central zones because of changed chemical soil conditions resulting from pollution (Pouyat, 1990).
Particular challenges and opportunities in developing countries
In the developing world at present there are few scientific accounts of forest influences in metropolitan areas and there is a great need for further detailed investigation. Some of the environmental influences of trees identified in industrialized countries are likely to exist in developing country cities as well, given that similar construction technologies, urban planning approaches and engineering designs have been used (Gilbert and Gugler, 1992). However, the urban spatial dynamics in these growing metropolises differ enough from cities of the industrialized world to warrant a modified model. Following are some frequently encountered differences in urban spatial development and human interaction patterns with urban vegetation in developing countries, including their possible impacts on forest influences:
· In most countries of the developing world, the particularly high pace of demographic and spatial urban expansion since the middle of this century (Dogan and Kasarda, 1988) has resulted in the intensive and extensive disturbance of pre-existing vegetation in metropolitan areas. It may also disrupt or discourage efforts to introduce tree planting in peri-urban zones, since trees often require longer establishment periods than accelerated urbanization pressures can accommodate.· In many cities (e.g. Calcutta in India) there is a high population and settlement density extending from the city centre throughout the immediate pert-urban zone (Berry and Kasarda, 1977; Gilbert and Gugler, 1992).This often includes the presence of numerous spontaneous housing settlements which are frequently constructed with a minimal provision of public services and insufficient official control on precarious building sites without proper engineering (e.g. in Rio de Janeiro in Brazil and Lima in Peru). Such an urban density gradient contrasts significantly with cities in industrialized countries, which tend to have much lower-density land uses in suburban areas. The continuous high-density settlement pattern implies a high rate of land disturbance, a greater rate of removal of original vegetation and less area available for new tree planting in these outlying areas.
· At the same time, in some cities (especially in Latin America and Africa) there is a high degree of urban land speculation, coupled with relatively ineffective land-use controls, which creates a rapidly expanding zone Of low-density fragmented urban land use in highly spread out former urban areas (Vennetier, 1989; Violich and Daughters, 1987). While such a development pattern is generally detrimental to pre-existing forest cover, the persistence of large areas of peri-urban "open space" or "vacant lots" may also provide opportunities for the establishment of both interim and permanent new forests. These forest stands, integrally woven into the metropolitan landscape, can be the source of locally important forest influences.
· The continued use of wood (fuelwood and charcoal) as a major energy source in many urban areas of developing countries places elevated pressures on forest resources throughout metropolitan areas and may significantly reduce peri-urban forest influences. At the same time, demand for this resource has also encouraged the development of peri-urban forest plantations for the provision of urban fuelwood in many cities (e.g. Delhi in India and Dakar in Senegal), with mixed results (Hardoy, Mitlin and Satterthwaite, 1992; Vennetier, 1989).
There are two critical problem areas frequently encountered in the social management of urban and pert-urban forests which are of great relevance to forest influences. The first pertains to the framework of urban issues in which the management of forest influences is situated, while the second deals with the related question of the variety of individuals and groups who are currently or potentially involved in decisions that have a bearing on urban woody vegetation.
The urban forestry issue framework
An examination of how urban forest environmental influences fit into the broader picture of city management may begin from the perspective of forest management itself. Additional insights can be gained by considering a more comprehensive set of urban management concerns.
All tree planting and management cities is done with a human value and objective in mind, i.e. to provide: what: people want from their forests and trees It is thus not surprising that the relatively ecological term "forest influences" (referring to the interaction between the forest and the other components of the environment) is rarely even used in the urban forestry literature and is often translated or replaced by the more anthropocentric concept of "environmental service benefits" of forest cover.
Environmental service benefits refer here to those produced by natural processes without human intervention, but which have widespread effects on humans as a result of the forest system's interaction with the hydrological, atmospheric and terrestrial components of the biophysical environment. In cities, these effects are almost always stated in a value-laden way as "benefits". In other words, forest environmental influences only "exist" for many urban managers to the extent that they result in the provision of positive environmental services for people.
Of course, the real interface of forest and other ecosystem components in urban areas does not always align so neatly with people's definitions of strictly positive effects. Some of the biophysical environmental "influences" of the urban forest in fact have negative impacts on humans, for example they may constitute a fire hazard near human settlements or else utilize scarce water resources. Management may therefore have to be geared towards altering urban forest structure and composition to minimize adverse impacts on people, and in all cases it must incorporate an understanding of the complex interplay of the benefits and costs of all forest influences vis-à-vis human needs and priorities at a variety of different scales.
Reconciling environmental services, commodity production and amenity benefits
Environmental service benefits must be considered alongside two other classes of human benefits of urban and pert-urban forest cover, i.e. commodity and amenity benefits. Commodity benefits consist of extractable goods produced in the forest system for human use, including food products, medicinal plants, timber and fuelwood. Amenity benefits are psychological, social, cultural, political or economic functions of urban and peri-urban forests and are experienced by humans in generally intangible or nonmaterial ways.
These different classes of human benefits can be in conflict and competition, or they may be assigned different levels of value in different locations, under different types of landownership or tenure or among different social groups along the urban-rural gradient. For example, tree planting in the central city public park of Santiago in Chile focuses on amenity functions, including shade and beautification, while fruit-trees for commodity food production are a priority in many home gardens in poor urban neighbourhoods in Kampala in Uganda. Throughout the Sahel, state-supported fuelwood plantations at city edges focus on commodity benefits whereas the declared protected greenbelt of Quito in Ecuador was originally established for the positive "environmental service" benefits of slope stabilization and natural disaster prevention (Egziabher et al., 1994; Hoffman, 1983; Vennetier, 1989; Moore et al., 1984).
Sometimes one objective can be in direct conflict with another. For example, fuelwood cutting has deforested huge areas around Delhi and many other cities, eliminating the potential for amenity uses of these forest stands (e.g. recreation and aesthetics) as well as reducing environmental service benefits such as soil stabilization and erosion prevention (Hardoy, Mitlin and Satterthwaite, 1992). In the same way, legally "protecting" forests around cities, such as that around Quito mentioned above, can help optimize the environmental service benefits of forest influences but will also produce adverse impacts on local residents who draw on those forests for commodity products (Moore et al., 1984). Urban forestry professionals need to be alert to this and identify potential opportunities for coupling objectives related to forest influences with other higher-priority forestry goals.
Forest influences and broader urban development priorities
Given the dynamics that are currently driving the human management of space in nearly every city in the world, activities specifically directed towards forest management are only one element (and usually a minor one) in determining how woody vegetation is actually manipulated by humans. In much general urban research dealing with spatial dynamics and major land management issues in urban and peri-urban zones in Africa, Asia and Latin America, most of the concerns described are not at all directly related to forest management and may even be in conflict with forest development and conservation objectives. For example:
· Concerns with urban housing shortages dominate much of the discussion. The spread of spontaneous, illegal housing settlements is one of the most frequently researched phenomena in the field of urban studies in the developing world and affects numerous cities in Latin America, Africa, Asia and the Near East (Mendizabel de Finot, 1990; Hardoy, Mitlin and Satterthwaite, 1992; United Nations Centre for Human Settlement, 1989).· Distorted land markets and the general lack of land-use planning and zoning guiding "orderly" urban development are likewise very frequently cited on all continents. Rampant land speculation throughout Latin America and ineffective municipal controls on city growth in Delhi and in Lagos, Nigeria, are examples of these issues (Vennetier, 1989; Dogan and Kasarda, 1988; Hardoy, Mitlin and Satterthwaite, 1992; Anthony, 1979; Farvacque and McAuslan, 1992; Mabogunje, 1992).
· Problems related to primary productive sector activities are also commonly discussed, including changes in agricultural production patterns owing to urbanization. Severe losses of peri-urban agricultural lands through urban expansion have been reported in Jakarta, Indonesia, in Buenos Aires, Argentina, in several Colombian cities and in cities of many African countries (Hardoy, Mitlin and Satterthwaite, 1992; Gutman, 1987 Egziabher et al., 1994).
· To a lesser extent, urban industrial location issues and associated environmental impacts are mentioned, for example severe downstream water contamination in Dakar in Senegal and in Alexandria in Egypt and peri-urban air pollution in southwestern China (Hardoy, Mitlin and Satterthwaite, 1992; Vennetier, 1989).
The dominant attention and resources of urban planners, other city personnel, city politicians, development agencies and local citizen activists are devoted to meeting what are considered more basic health, safety and welfare needs of the population; urban forestry efforts are accorded low priority on the urban management agenda in virtually every one of these countries.
In response to this reality, municipal forest managers must understand which overall urban management issues are considered a public priority in their cities and they must be proactive in establishing necessary linkages with these priority sectors within the local government. This includes building personal and professional bridges with the relevant staff and political leaders and effectively communicating the potential advantages of coordination with forestry projects in the cost-effective provision of city services.
Examples of municipally sponsored infrastructure or basic service projects which are fully integrated with urban forestry activities are rare in developing countries, but many innovative examples of such projects are now in place in cities of Europe and North America. The types of linkages which have been promoted include forest cover protection of peri-urban city watersheds, vegetation employed in managing storm water runoff and projects employing forests and other vegetation to absorb and process treated urban waste water or urban composting of solid waste.
In many cities of developing countries, current activities in small-scale domestic urban agriculture both incorporate tree planting and promote urban waste recycling as well as having great potential to be expanded as the basis for such a multi-objective integrated urban management strategy. The application of human waste to pert-urban agricultural lands, for example, may be modified and technologically improved for implementation in many urban locations and it could be an excellent supply of water and nutrients for urban and peri-urban forest areas (Egziabher et al., 1994; Smit and Nasr, 1992) [Ed. note: see also the article by Braatz and Kandiah].
In addition to identifying opportunities for coordinated action, the direct engagement of urban foresters with other municipal sectors will help forestry professionals pinpoint potential conflicts surrounding actions early enough to make changes or to identify areas of urban forestry activity that may be best avoided or postponed because of insurmountable physical or socio-political constraints.
Finally, since strong leadership and advocacy on the part of local political leaders is critical to promote intersectoral coordination, a collaborative relationship with politicians and community leaders is another key factor in the success of urban forestry.
These linkages should not remain the unique responsibility of urban foresters. It is equally incumbent on urban planners and other city personnel to broaden their professional perspective and increase their awareness of the impacts of all urban management activities on the biophysical ecosystem, including forest resources. There are signs that municipal administrations throughout the developing world are becoming more cognizant of general urban environmental quality (Hardoy, Mitlin and Satterthwaite, 1992), but non-forestry professionals still have a long way to go to become more educated about the role of trees and other woody vegetation in ecosystem functioning in cities.
Management of urban trees requires the collaboration of foresters and city planners
In sum, the urban area must be considered in systemic terms by all municipal professionals, both those specifically focused on woody vegetation and those involved in urban development and the provision of services in more general terms. This requires involving both professional education and political mobilization, and will not come easily or quickly. From a pragmatic standpoint, given the current stage of development of urban forestry in most countries, it is the urban forester or parks professional who still has most to gain from pursuing and cultivating such cross-sectoral relationships and linkages in order to advocate and improve the environmental service and other benefits of forest cover. The burden will thus largely be on this set of professionals at least to begin the work of coordination.
Expanded participation in the decision-making process
The previous section of this article discussed the need to broaden professional integration at the level of local government activity, i.e. among municipal employees. However, the political pressure and resources for many types of urban activity often originate outside government offices entirely: in other levels of government, neighbourhood groups, housing developers, local grassroots environmental organizations, private businesses, international aid agencies or a combination of the above. It is therefore essential to involve a wider constituency in the discussions and action regarding urban and pert-urban forest resources.
In some cases, the initiative for broader participation may emerge from municipal employees themselves. For example, the urban forestry programme in Guatemala City was transformed in the early 1990s from an inefficient governmental unit into an action-oriented, innovative work team under the leadership of an inspired Parks Department director and a supportive city government (Pokorny de Marcet, 1992).
In other instances, the leadership in promoting and protecting urban forest resources may come from outside the city government. In the case of Santiago de Guayaquil in Ecuador, for example, where the municipal government has long been constrained by administrative and management problems, an inspired executive of a local cement company spearheaded and financed an extensive metropolitan greening programme, including the establishment of a nature reserve, a tree nursery and a citywide "Adopt-a-Tree" campaign. Important collaborations were established with a local environmental organization and other national and international organizations.
In all cases, expanding the pool of interested parties will require a conciliation of conflicting values and needs, both those concerning urban vegetation itself and those involving all urban space and functions which may influence the urban and peri-urban forest resource.
"Natural" resources of all kinds are at the centre of the rural development professional worldview. At present, the urban development perspective is understandably people-oriented but, at times, seems to exist in a universe without a natural environment at all. Urban professionals and activists must take the first step of acknowledging and embracing the linkages between the products and services they desire as well as the natural ecosystems which ultimately sustain them, including forests. This will require a two-way communication and education process whereby urban planners, infrastructure managers and service providers discover the importance of and recognize the interrelationships between what they do and the health and productivity of the urban and pert-urban forest system. At the same time, urban foresters and urban green space and recreation managers must recognize that the success or failure of their work is determined largely outside the domain of technical or social forestry management and thus place their forest centred activities squarely within the framework of broader urban management concerns.
Finally, both sets of municipal actors (urban foresters and urban planners or managers) must further acknowledge that, in complex urban systems, much action impacting the urban natural environment and the other services they provide occurs at the individual, household, neighbourhood or regional level without any direct control by city officials at all. Thus, other actors at various levels of government as well as in the private sector and civil society must be invited to become involved in the management of urban land and natural resources and in determining the policies and programmes that guide the human inhabitants of those biophysical systems.
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