Microclimates and Trees
There isn’t much one can do about the climate. If you live in a desert, the climate is virtually certain to remain hot and dry during your lifetime. That doesn’t apply to microclimates, however. While climate affects an entire region, a microclimate is local. The term “microclimate” refers to atmospheric conditions that are different in one area from those in surrounding areas. It can mean areas as small as a few square feet (meters) or it can refer to larger areas of many square miles (kilometers). That means that there can be microclimates under trees. This makes sense if you think about sitting under trees in the heat of a summer afternoon. The microclimate is decidedly different than when you’re in full sun.
Do Trees Change Microclimates?
The relationship between microclimates and trees is a real one. Trees have been found to alter microclimates and even create specific ones under trees. The extent of these modifications varies depending on the characteristics of a tree’s canopy and leaves. Microclimates that affect human comfort include environmental variables like solar radiation, air temperature, surface temperatures, humidity, and wind speed. Trees in cities have been shown to modify these factors in a variety of ways. One of the reasons homeowners plant trees is to provide shade during hot summers. The air under a shade tree is obviously cooler than outside the shady area, since the tree’s canopy blocks the sun’s rays. That’s not the only way trees change microclimates.
How Do Trees Affect Microclimates?
Trees can block sunrays from anything within their shade. That prevents solar radiation from heating the surrounding buildings and surfaces as well as cools the area. Microclimates under trees are altered in other ways too. Trees cool the air by the evaporation of moisture from their leaves and branches. In this way, street trees function as natural air conditioners in the neighborhood. Trees also provide a warming effect on a microclimate. Trees, especially evergreens, can block the chilly winter winds that blow down a street, slowing the wind speed and warming the air. Certain tree species are better at providing cooling and wind-blocking benefits, something to consider when selecting street trees for a particular area.
