Most trees and shrubs in cities or communities are planted to provide beauty or shade. Woody plants also serve many other purposes. These benefits of trees can be grouped into social, communal, environmental, and economic categories.
Social Benefits – We like trees around us because they make life more pleasant. Most of us respond to the presence of trees beyond simply observing their beauty. We feel serene, peaceful, restful, and tranquil in a grove of trees. We are “at home” amongst trees. Hospital patients have been shown to recover from surgery more quickly when their hospital room offered a view of trees. The strong ties between people and trees are most evident in the resistance of community residents to removing trees to widen streets. The stature, strength, and endurance of trees give them a cathedral-like quality. We often become personally attached to trees that we or those we love have planted.
Communal Benefits – Because trees occupy considerable space, planning is required if both you and your neighbors are to benefit and to be satisfied with the long term results. City trees often serve several architectural and engineering functions. They provide privacy, emphasize views, or screen out objectionable views. They reduce glare and reflection. They direct pedestrian traffic. They provide background to and soften, complement, or enhance architecture.
Environmental Benefits – Trees alter the environment in which we live by moderating climate, improving air quality, conserving water, and harboring wildlife. Climate control is obtained by moderating the effects of sun, wind, and rain. Radiant energy from the sun is absorbed or deflected by leaves on deciduous trees in the summer. We are cooler when we stand in the shade of trees and are not exposed to direct sunlight. In winter, we value the sun’s radiant energy. Therefore, we should plant only small or deciduous trees on the south sides of homes.
Wind speed and direction can be affected by trees. The downward fall of rain, sleet, and hail is initially absorbed or deflected by trees, which provides protection for people, pets, and buildings. Trees intercept water, store some of it, and reduce storm runoff and the possibility of flooding. Temperature in the vicinity of trees is cooler than that away from trees. By using trees in the cities, we are able to moderate the heat-island effect caused by pavement and buildings in commercial areas.
Air quality can be improved as leaves filter the air we breathe by removing dust and other particulates. Leaves absorb carbon monoxide from the air to form carbohydrates that are used in the plant’s structure and function. In this process, leaves also absorb other air pollutants – such as ozone, carbon monoxide, and sulfur dioxide – and give off oxygen. By planting trees and shrubs, we return to and connect with a more natural, less artificial environment. Birds and other wildlife are attracted to the area. The natural cycles of plant growth, reproduction, and decomposition are again present, both above and below ground. Natural harmony is restored to the urban environment.
Economic Benefits – Individual trees and shrubs have value, but the variability of species, size, condition, and function makes determining their economic value difficult. The economic benefits of trees can be both direct and indirect. Direct economic benefits are usually associated with energy costs. Air-conditioning costs are lower in a tree-shaded home. Heating costs are reduced when a home has a windbreak. Trees increase in value from the time they are planted until they mature. The savings in energy costs and the increase in property value directly benefit each home owner.
The indirect economic benefits of trees are even greater. Lowered electricity bills are paid by customers when power companies are able to use less water in their cooling towers, build fewer new facilities to meet peak demands, use reduced amounts of fossil fuel in their furnaces, and use fewer measures to control air pollution. Communities also can save money if fewer facilities must be built to control storm water in the region.
ISA – International Society of Arboriculture