Overstory #87 - Urban Forestry
Urban Forestry
Although trees have been an important part of human settlements throughout history, only recently has their full value to urban dwellers been recognized. Trees and green spaces play an important role in improving city living conditions. In the past, urban forestry in developed countries was considered almost exclusively on the basis of its aesthetic merits. Now, a closer look is being given to the environmental services and quantifiable economic benefits they provide. This article discusses the role of trees in and around densely populated areas.
Introduction
Urban forestry has as its objective the cultivation and management of trees for their present and potential contribution to the environmental, social, and economic well-being of urban society. Urban forestry is a merging of arboriculture, ornamental horticulture and forest management. It is closely related to landscape architecture and park management. In its broadest sense, urban forestry embraces a multifaceted managerial system that includes municipal watersheds, wildlife habitats, outdoor recreation opportunities, landscape design, recycling of municipal wastes, tree care and the production of wood as a raw material.
Urban forestry includes activities carried out in the city centre, suburban areas and the "urban fringe" or interface area with rural lands. Forestry activities can differ significantly according to the zone. In central areas, the potential for significant new urban forestry efforts are relatively limited in most cities. Here, it is mainly an issue of maintaining or replacing trees planted long ago.
In the suburban areas, more scope exists for tree-planting, as the availability of land is greater than in the city centre. The land is more likely to be privately owned than in the peri-urban or fringe area and the people more settled, thereby having a greater vested interest in tree protection and care.
There are many differences between the management of trees in an urban environment and "traditional" rural forestry. In many cities, trees are a minor part of the landscape, particularly in the centre. Cities present harsh conditions for tree growth. Even in those which have large tree cover in their central urban area and/or suburban areas, management is complicated by the fragmentation of green space. The objectives of tree-planting, the location, the configuration of planting and the management of the trees in urban areas differ from those in rural areas. Socioeconomic conditions and requirements can be quite different and more variable in a city than in the countryside. In addition, the availability of technical information on which management decisions or urban/peri-urban forestry can be based is still limited, particularly in developing countries (Kuchelmeister, 1991).
Urban Forestry Through History
The planting of trees in human settlements and as an integral part of landscape architecture is not new; it has its roots in ancient Chinese, western Asian and Greek civilizations (Jellicoe, 1985). A number of ancient cities had highly developed parks, gardens and other green spaces - the most notable being Babylon, "the mother city of gardens," dating back more than 3,000 years. The Assyrian civilization and, much later, the classical Persian and Greek civilizations arising in the fifth century BC, also had such a tradition, based on amenity as well as cultural and religious beliefs. In Europe in the seventeenth and eighteenth centuries, municipal and crown forests were managed for recreational hunting. Later, the elite developed urban gardens and parks as visual amenities in many European cities, particularly Italy, France, Austria and England. The practice of urban amenity plantings subsequently spread to colonies in Africa and Asia. Spanish colonization introduced into Latin America the concepts of interior patios in houses and public plazas in urban centres. Throughout history, the planting and management of trees and forests has been based much more on aesthetic and spiritual values than on utilitarian benefits.
The Value of Urban Forests
The list of goods and services that urban forestry can provide is impressive. Trees and green spaces help keep cities cool, act as natural filters and noise absorbers; improve microclimates and protect and improve the quality of natural resources, including soil, water, vegetation and wildlife. Trees contribute significantly to the aesthetic appeal of cities, thereby helping to maintain the psychological health of their inhabitants. Beyond ecological and aesthetic benefits, urban forestry has a role in helping resource-poor populations meet basic needs, particularly but not exclusively in developing countries.
Tangible Benefits
Beyond their aesthetic and ecological value, trees can contribute to the satisfaction of energy requirements as well as the daily food requirements of urban dwellers, particularly in the case of the poorest elements of society.
• Food production Urban agriculture is common in many cities in Asia, Latin America and Africa (Yeung, 1987; Sanyal, 1985; Streiffeler, 1987; Ninez, 1985; Skinner, 1981). Who and how many people practice it as well as what form it takes differ greatly from place to place. It is most often practiced in the urban fringe area by low-income families but, in places such as Africa and the Pacific Islands, urban agriculture is widespread within cities. Although in most places the emphasis is not on the production of staple foods, through the production of vegetables, fruits and condiments, urban agriculture can contribute to the improvement of the nutritional value and variety of city dwellers' diets.
Fruit-trees are often an important component of urban home gardens. In some places, trees are planted to help supplement fuelwood and fodder needs and even to provide raw materials for handicrafts. The role of agroforestry in improving productivity and diversifying production should be examined - it is a field that should become much more important in the future.
In many developing countries, particularly in Africa and Latin America, about half the low- and moderate-income households moving into cities will be headed by women. Urban agroforestry will not only be important to household nutrition but may offer a source of income while allowing women to stay at home.
• Fuelwood Wood fuel provides between 25 and 90 percent of urban household energy supplies; it is particularly important as a source of energy in smaller urban centres in developing countries, especially in dry zones (Kuchelmeister, 1998). Poor urban households spend a significant proportion of their cash income in obtaining wood energy. If the urban poor population continues to grow, an increase in the consumption of traded wood fuel is likely to be a consequence. Under favourable circumstances, fuelwood from non-rural forests and agroforestry systems can contribute significantly to fuelwood supply.
• Timber Availability of an adequate timber supply is a problem for a growing number of households in developing countries. Principle sources of timber in urban areas are plantations, street trees, shelterbelts or windbreaks and greenbelts, parks and gardens. In many cities timber harvesting is combined with intensive outdoor recreation activities. Systematic planting of street trees for timber production is widely practised in China and Malaysia (Webb, 1998). Some cities in industrialized countries offset the costs of tree care through harvesting of trees.
Environmental Services
As a result of the predominance of concrete buildings, asphalt and metal as well as the concentration of transport systems and industrial activities in and around urban areas, the median temperature is higher (the "heat island" effect), the air is drier and often polluted, rainfall is less efficiently absorbed and the environment is generally noisier than in a rural setting.
• Cleaning the air One of the major problems in urban areas is poor air quality. Plants help remove pollutants from the air in three ways: absorption by the leaves or the soil surface; deposition of particulates and aerosols on leaf surfaces; and fallout of particulates on the leeward (downwind) side of the vegetation because of the slowing of air movement.
Research on the removal of airborne pollutants by vegetation shows that plants are effective sinks for pollution. Trees absorb sulfur dioxide very efficiently. Keller (1979) has quantified an 85 percent reduction in lead behind a shelter-belt of trees. Soil effectively absorbs gaseous pollutants, including carbon monoxide, sulfur dioxide, nitrogen oxides, ozone and hydrocarbons. Trees intercept dust: a belt of trees measuring 30 meters in width has been found to intercept almost all dust in the air. Trees also often mask fumes and disagreeable odours by replacing them with more pleasing scents or by actually absorbing them. Trees also help to increase the relative humidity of urban air through evapotranspiration.
• Modifying temperature extremes Trees, shrubs and other vegetation help to control temperature extremes in urban environments by modifying solar radiation. The shade of one large tree may reduce the temperature of a given building to the same extent as would 15 air conditioners at 4000 British thermal units (BTU), i.e. 4220 kJ, in a similar but unshaded building. Energy saving through tree-planting around houses ranges from 10 to 50 percent for cooling and from 4 to 22 percent for heating (NAA/ISA, 1991).
• Noise reduction Noise is often referred to as invisible pollution. Excessive noise levels in most major cities contribute to both physical and psychological damage. Trees can help both by absorbing and refracting or dissipating noise such as that produced by the heavy vehicular traffic which characterizes urban areas.
• Water use, reuse and conservation Urban forests can help in the protection of urban water supply, wastewater treatment systems and storm water management. Most poor cities face significant wastewater treatment challenges and could integrate stabilization ponds into park systems and reuse wastewater for urban forestry. Reusing city wastewater not only recharges aquifers but also reduces the demand exerted on scarce water reserves. The greatest potential of wastewater reuse is in arid zones in developing countries (Braatz, 1994; Kuchelmeister, 1998).
Protection of the suburban and rural areas that serve as the source of cities' water is a traditional urban forestry linkage, but to be successful such projects must be integrated into urban planning.
• Soil conservation Trees and forests are a means of soil conservation, preventing landslides in fragile ecosystems with steep terrain, little vegetation and harsh seasonal rains, and thus protecting people's lives and homes.
• Biodiversity Green areas have a vital role in urban biodiversity. Suburban wetlands can be some of the most productive natural ecosystems and can provide important habitats for fauna. Incorporating green areas in networks will improve biological conservation and biodiversity; greenbelts and greenways (linear parks) can serve as biological corridors (IUCN, 1994).
Social Benefits
• Improving the aesthetic quality of urban areas It is the aesthetic and recreational value of trees, forests and parks that is most directly identified by most urban dwellers, in developed and developing countries alike. Trees fulfill certain psychological, social and cultural needs of the urban dweller (Dwyer, Schroeder and Gobster, 1991). They play a very important social role in easing tensions and improving psychological health; people simply feel better living around trees. One study has demonstrated that hospital patients placed in rooms with windows facing trees heal faster and require shorter hospital stays (Ulrich, 1990). When appropriately selected and placed, trees are effective in screening out undesirable views and ensuring privacy while permitting free visual access to the rest of the landscape. Parks provide easily accessible recreational opportunities for people.
• Health Parks and green areas provide opportunities for healthy physical activity. In addition, the passive benefit to physical and mental health of an urban landscape with trees has been documented in industrialized countries (Ulrich, 1984); enjoyment of green areas may help people to relax or may give them fresh energy.
Improving air quality through the planting of vegetation certainly has an impact on health, with such obvious benefits as decreased incidence of respiratory illnesses. Urban forests can also contribute to food security, as discussed above.
• Employment Tree planting and especially urban agroforestry systems can be labour intensive and provide work opportunities which may be especially important in poorer cities. In wealthier countries arboriculture is a significant business. Urban forests and green areas also provide opportunities for many kinds of formal and informal enterprise related to recreation.
• Education Urban forests are increasingly appreciated in environmental education. A number of cities both in industrialized and developing countries have botanical gardens, zoos, nature trails and visitor information centres that can inform people about flora and fauna. Easily accessible trees and woodlands provide a vital facility for both formal and informal learning.
• Recreation Urban forests greatly enhance outdoor recreation. Lower income residents tend to frequent city parks more than wealthier citizens do because they lack the financial means and leisure time to reach more distant recreation sites. To be useful to low income people, forests and green areas must be within an affordable traveling distance and must have the amenities that people desire.
• Community building and property value improvement Public involvement with trees in towns can help strengthen neighbourhood communities by providing people with an opportunity to work together for the benefit of the local environment (NUFU, 1998).
Studies have shown an increase in house prices where property is associated with urban trees, for example up to 5 percent in Hong Kong (Webb, 1998) and in the Finnish town of Salo (Tyrvainen, 1999) and up to 18 percent in the United States (Morales, Micha and Weber, 1983). In Singapore and Kuala Lumpur it has been recognized that a tree-rich urban landscape is an important attraction for new businesses and investors (Kuchelmeister, 1998).
References
Braatz, S. 1994. Urban forestry in developing countries: status and issues. In: C. Kollin, J. Mahon & L. Frame, (eds). Growing greener communities. Proceedings of the sixth National Urban Forest Conference, Minneapolis, Minnesota, USA, 14-18 September 1993, p. 85-88. American Forests, Washington, DC.
Dwyer, J.F., Schroeder, H.W. & Gobster, P.H. 1991. The significance of urban trees and forests: toward a deeper understanding of values. J. Arboriculture, 17(10): 276-284.
FAO. 1989. Arid zone forestry: a guide for field technicians. FAO Conservation Guide No. 20. FAO, Rome.
IUCN. 1994. Putting plans into action. Report of Metropolitan Open Space Systems (MOSS) International Conference, Durban, South Africa, 9-11 February.
Jellicoe, G.A. 1985. The search for a paradise garden. In IFLA Yearbook 1985/86, p. 6-33. International Federation of Landscape Architects, Versailles.
Keller, T. 1979. The possibilities of using plants to alleviate the effects of motor vehicles. TRRL Symposium Report 513 DOE/DT.
Kuchelmeister, G. 1991. Urban and peri-urban multipurpose forestry in development cooperation - experience, deficits and recommendations. Funded by the Commission of the European Communities, Illertissen, Germany. (Unpubl. final report)
Kuchelmeister, G. 1998. Urban forestry in the Asia-Pacific Region - status and prospects. Asia-Pacific Forestry Sector Outlook Study Working Paper Series No. 44. Rome, FAO. (Also available at: )
Morales, D.J., Micha, F.R. & Weber, R.C. 1983. Two methods of evaluating trees on residential sites. Journal of Arboriculture, 9(1): 21-24.
NAA/ISA. 1991. The importance of large tree maintenance in mitigating global climate change. National Arborist Association, Amherst, USA.
Ninez, V. 1985. Working a half potential: constructure analysis of home garden programmes in the Lima slums with suggestions for an alternative approach. Food Nutr. Bull., 7(3): 8-14.
NUFU. 1998. Trees matter. The benefits of trees & woods in towns. National Urban Forest Unit, London.
Sanyal, B. 1985. Urban agriculture: who cultivates and why? A case study of Lusaka, Zambia. Food Nutr. Bull. 7(3): 15-24.
Skinner, G.W. 1981. Vegetable supply and marketing in Chinese cities. In D.L. Plucknett & H.L. Beemer, Jr, eds. Vegetable farming systems in China. Westview Press, Boulder, Colorado.
Streiffeler, F. 1987. Improving urban agriculture in Africa: a social perspective. Food Nutr. Bull. 9(2): 8-13.
Tyrvainen, L. 1999. Monetary valuation of urban forest amenities in Finland. Doctoral dissertation. Research Paper No. 739. Finnish Forest Research Institute, Vantaa, Finland.
Ulrich, R.S. 1984. View through a window may influence recovery from surgery. Science, 224: 420-421.
Ulrich, R.S. 1990. The role of trees in wellbeing and health. In P.D. Rodbell. ed. Proc. Fourth Urban Forestry Conference, St Louis, Missouri, 15-19 October 1990.
Yeung, Y. 1987. Examples of urban agriculture in Asia. Food Nutr. Bull., 9(2): 14-23.
Original Source
This article is excerpted from:
Kuchelmeister, G. and S. Braatz. 1993. Urban Forestry Revisited. Unasylva 173, Vol. 44:13-18. FAO, Rome. Web site:
Some material in "The Value of Urban Forests" was originally published in: Kuchelmeister, G. 2000. Trees for the urban millennium – urban forestry update, Unasylva 200, Vol. 51:49-55. FAO, Rome. Web site:
About the Authors
Guido Kuchelmeister is an independent consultant specializing in agroforestry and urban forestry issues. With more than 18 years experience, he has worked internationally with many organizations including FAO (Food and Agriculture Organization); GTZ (German Agency for Technical Cooperation) and ADB (Asian Development Bank). He is Coordinator of the TREE CITY Initiative in Illertissen, Germany. Web site:
Susan Braatz is a Forestry Sector Analyst and coordinator for State of the World's Forests (SOFO) in the Forestry Department of FAO, Rome.