Wind is air in motion.
Wind is air moving from a place that has higher pressure to one that has lower pressure. Let’s say that you blow up a balloon but don’t tie a knot at the open end. Air comes out because the pressure inside the balloon is higher than the pressure outside the balloon. Air molecules will spread out, spacing themselves far apart if they have room. The places with more air molecules have higher pressure. The areas with fewer air molecules have lower pressure. As you let the air out of the balloon, air whooshes into the area with lower pressure. That’s wind. Sometimes wind is just a light breeze and other times it is strong enough to blow the roofs off buildings. For example, thunderstorms can create high winds including microbursts and tornadoes. Another kind of wind is the prevailing wind that comes from a particular direction on a more seasonal timescale.
Winds impact trees.
Different strengths of wind have varying impacts on trees. The most obvious being downed trees and broken branches from damaging winds from extreme events such as hurricanes or tornadoes. Even though these extreme events can cause loss of lives and property, these events play an important ecological role in forests. Natural disturbances such as wind damage are actually beneficial for the forests because fallen trees open up the canopy, allowing more sunlight which leads to more diverse types and ages of vegetation. Windblown branches or fallen trees can also provide additional habitat for wildlife. Even gentle breezes and prevailing winds impact trees through transpiration, growth rate, and even the shape of the trees. Winds enhance the transpiration rate leading trees to lose water and heat that they need for growth.
Trees reduce wind speed.
It is common to use trees as windbreaks near buildings to block the wind to reduce energy costs such as heating a house in the winter. A windbreak is usually formed by planting a combination of shrubs and trees in relation to the prevailing wind direction. For example, most windbreaks in the Northern Hemisphere are planted north or northwest of a house or building because the prevailing wind comes from the west. This would be opposite in the Southern Hemisphere. Other benefits include preventing snowdrifts across driveways, noise buffer, privacy, as well as to protect livestock such as cattle on farms.
Wind also varies with altitude (height). In this activity, students learn that the lowest wind speeds occur closest to the ground when trees block most, if not all, of the wind. Higher wind speeds are found at the top of the tree (canopy-level) while the highest wind speeds occur above the tree line (above canopy-level) due to no blockage.
Deforestation impacts local climates
While we often think of climate as a non-biological factor that influences ecosystems, changes in the structure and distribution of living organisms in an ecosystem can, in fact, have profound climate effects both regionally and globally. Changes in vegetation affect regional atmospheric phenomena, including rainfall and evapotranspiration as well as convection and winds. It is well documented that vegetative changes due to human activity have consequences for local climate. For example, deforestation leads to higher wind speeds and therefore more soil moisture loss and wind erosion. In addition, deforestation increases the albedo (reflectivity) of the land surface, further reducing local rainfall.
This activity was developed at UCAR as part of the Project LEARN and includes graphics created by the COMET Program.