The evidence from a 5-year investigation shows that the tree coverage in U.S. urban areas is constantly reducing at a rate of 708.2 km2 which is equivalent to a loss of 36 million trees, annually.
According to David Nowak, lead author of the study and senior US Forest Service scientist, human activities do not account for the entire forest loss. Natural disasters, including fires, tornadoes, hurricanes or even plant diseases have resulted in reducing the tree cover.
Nevertheless, Mr. Nowak emphasizes the fact that imprudent infrastructure development has impacted the phenomenon. "We see the tree cover being swapped out for impervious cover, which means when we look at the photographs, what was there is now replaced with a parking lot or a building," he stated.
Tree cover is crucial especially in urban environments where concrete buildings tend to absorb vast amounts of solar heat dramatically increasing the temperature. Another study has proved that trees can reduce the temperature in cities by 10 degrees Fahrenheit creating a beneficial cooling effect. This effect is noticeable to the scale of a single block. "Every time we put a road down, we put a building and we cut a tree or add a tree, it not only affects that site, it affects the region," Mr. Nowak added.
A tree network established in an urban environment is a challenging task to accomplish. Planting trees all over the city is not a viable solution as it would hamper everyday life. "You don't want a tree in the middle of a baseball field. It's very difficult to play sports if you have trees in the way. Or trees in the middle of freeways," Mr. Nowak, commented. For this reason, communities should design and establish tree canopies that will be preserved by official organizations. In order for the canopy to provide its full cooling benefit, it should exceed 40% of the total area of interest.
The most beneficial effects the trees provide are:
- 96% protection from UV radiation
- Heat reduction also associated with a reduction in energy emissions
- Air pollution reduction
- They act as water filters improving its quality
- Flood control as their routes absorb water from rainfalls
- They benefit mental and physical health
- Sound deflection which leads to noise reduction
- Aesthetics improvement