Trees can have a profound effect on the local environment in which they are planted. They do this by moderating the local climate, protecting water and soil and decreasing air and noise pollution. The effect trees have on local climate is important in all areas but even more so in urban areas. Due to the absorption of solar energy by the overwhelming amounts of paved and concrete surfaces and the quick drainage of water away from the surface the urban area becomes warmer and forms what is called a "heat island". Trees can help curve this phenomenon. Trees through evapotranspiration put huge amounts of water into the atmosphere. As water is evaporated from the leaves of the trees it draws heat energy from the air around the tree thus cooling it. Although trees have a cooling effect on the surrounding air their ability to shade surfaces and people has a more profound impact. By preventing the warming effect of solar radiation on surfaces, building and even people, trees prevent heat transfer thus keeping it cool. Large deciduous trees can be planted on the south and west sides of a building to shade it from the sun and in turn keeping it cooler. Also by planting a deciduous tree, during the winter when solar warming is wanted the tree will not have leaves and wont shade building.
The Kentucky Coffee Tree is almost ideal for this situation but many others will be very effective. A dense tree such as a conifer can also be planted on the north/ northwest side of building to provide a windbreak and prevent heat loss.
Trees can also protect local water and soil. Urban areas are predominantly impervious surfaces which accelerate water velocity due to runoff and snowmelt. Trees can slow these runoff velocities and in turn prevent erosion. Trees can also absorb some rainfall which aids in the process. The roots and litter of trees also hold soils together and provide habitats for organisms which aid in soil preservation. Trees along waterways can also decrease erosion during high velocity times. It has been shown that trees can filter some types of pollution out of the runoff.
Controlling air pollution is also a factor that trees have a moderate effect on. Trees can remove particulate matter and gases from the air. Dust and other particles get caught in the leaves and structure of the tree and are washed to the ground by rain. Trees absorb many gaseous pollutants such as chlorine, ozone, fluorine, sulfur dioxide and peroxyacetylnitrate (PAN) (massarbor). These chemicals can also prove to be damaging to the trees. Trees also remove large amounts of carbon dioxide which is very beneficial considering it is directly related to global warming and the green house effect. When planted in tight rows or groves trees can also provide as a noise barrier. When used in conjunction with barriers or berms they can reduce even more noise pollution from roads and other nuisances. Trees are an investment not only in the present but also in the future. Once a tree is planted it can live for many decades and its beauty and presence can be enjoyed by many. However all too often the lack of planning and lack of knowledge result in misinformed tree selections which can lead to infirm trees or damage to surrounding infrastructure. There are many factors that first must be considered before a tree should be planted. This holds true in any circumstance but it is vital in an urban environment. The planting site and a trees characteristics and tolerances will play a major role in the type of tree planted, its health and longevity.