What are the environmental costs and benefits of urban forests?
Tree planting programs are being implemented in many cities because of their potentially beneficial effects on local and global climate. Trees remove greenhouse gases from the atmosphere which can mitigate global warming, and may have a cooling effect on local temperatures through shading and the evaporation of water. However, the direct uptake of greenhouse gases by urban trees is very small compared to total greenhouse gas emissions from vehicles and energy generation in cities. In addition, urban trees have potential maintenance and environmental costs that include fuel usage, fertilizer application and associated pollutant emissions, and irrigation the latter being particularly significant in semi-arid regions facing water shortages such as southern California. In fact, planting trees in semi-arid environments provides both environmental costs and benefits. There have been very few direct, comprehensive studies of these tradeoffs in urban forests, as most measurements of tree proce
