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Carbon Sink
Mature trees act as a significant means of carbon sequestration. For every ton of new wood that grows, about 1.5 tons of CO2 are removed from the air and 1.07 tons of life-giving oxygen are produced.[1]
Climate Control
Climate control is obtained by moderating the effects of sun, wind, and rain. Trees have demonstrated the ability to reduce heating and cooling costs and counteract the "heat island" effect in urban environments. Trees also act as shields against wind and snow. Dew and frost are less common under trees because less radiant energy is released from the soil in those areas at night. Urban areas with little vegetation can experience temperatures of up to seven degrees higher than those with tree cover. This translates into significantly higher energy costs to cool buildings. Properly planted trees can cut heating and cooling costs by as much as 12 percent and reduce overall power demand[2]. The larger the tree, the greater the cooling, therefore the roof planter enables design teams to maximise the positive climate effects of rooftop planting.
Trees, through their shade and transpiration, provide natural "low-tech" cooling that means less need for engineered solutions. The Arbor Day Foundation states that the overall effect of the shade created by planting a healthy tree is equivalent to 10 room-size air conditioners running 20 hours a day![3]
Air Quality
Air quality can be improved through the use of trees, shrubs, and turf. Leaves filter the air we breathe by removing dust and other particulates. A mature tree absorbs between 55-110 kgs per year of small particles and gases, like carbon-dioxide, which are released into the air by automobiles and industrial facilities[4].
Leaves absorb carbon dioxide 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, nitrogen oxide and sulphur dioxide, which cause respiratory problems - and give off oxygen. A single tree produces nearly three-quarters of the oxygen required for one person; and a canopy of trees in an urban environment can slash smog levels up to six percent[5].
Large trees have a greater benefit in terms of reducing pollution than small trees.
Water Conservation
Trees help reduce storm water runoff, saving the high costs of drainage ditches, storm sewers, and other "engineered solutions" to storm water management. Trees intercept water, store some of it, and reduce storm runoff and the possibility of flooding. As a source control mechanism in the Sustainable Urban Drainage System green roofs can help reduce flash floods as a consequence of intense rainfall events. This will become increasingly important as a consequence of climate change.
Biodiversity
Trees provide a natural habitat that supports a wide variety of wildlife flora and fauna. Larger trees such as those supported by the rooftop tree planter will attract a greater variety of birds and other wildlife to the area.
Aesthetic Benefits
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 provide background to and soften, complement, or enhance architecture. Trees also add colour and seasonal interest.
Noise Pollution
Noise pollution is an often overlooked problem. Excessive or unwanted sound has negative physical and psychological effects. Noise can come from many sources, especially roads and highways. Trees can play an important role in deadening unwanted noise. Sound waves are absorbed by a tree's leaves, branches, and twigs. Greenery provides 'white noise' reducing the effects of man-made sounds. The growing medium tends to block lower sound frequencies whilst the plants block higher frequencies.
Properly placed screens of trees and shrubs significantly decrease noise pollution along busy thoroughfares and intersections.
[1] USDA Forest Service: http://www.treelink.org/docs/29_reasons.phtml
[2] Scenic America: http://www.scenic.org/tree/environmental
[3] US Department of Agriculture
[4] Scenic America: http://www.scenic.org/tree/environmental
[5] Scenic America: http://www.scenic.org/tree/environmental
