Appraisers often call on other experts for consultation in some of these areas. Monetary value can also be assigned to some of the benefits trees bring to the urban environment. As mentioned earlier, sewage treatment costs could be cut by applying treated effluent to trees and other landscape plantings. Irrigating with recycled waste water reduces the need for costly evaporation ponds and sewage lagoons, as well as the dumping of municipal wastes into rivers, lakes and oceans. And, water-loving species could serve as natural water pumps for areas with high water tables.
Trees can cut energy costs, too.
Trees shade buildings and pavement, which reduces the temperatures in and around buildings. By cutting air-conditioning costs, trees indirectly reduce carbon dioxide emissions equivalent to fifteen times the amount the tree alone could absorb. Three well placed trees can cut air-conditioning costs by ten to fifteen percent. For every ton of new wood that grows, about 1.8 tons of carbon dioxide is removed from the air and 1 .3 tons of oxygen is produced. Reducing carbon dioxide through tree planting costs about 0.3 to 1.3 cents per pound.