Forest managers—and forestland owners who manage their land with the advice of forest managers—have a wide variety of management methods at their disposal. Each method entails a set of options and actions intended to achieve a particular set of goals. These actions can range from doing nothing at all to cutting down all, or nearly all, the trees. Shelterwood cutting is a method that is more or less midway between these two extremes. It involves cutting some trees while leaving others, for a time, to help shelter new growth. This practice has many possible advantages and disadvantages.
Any time loggers go into a forest to remove even one tree, it's likely to cause at least some collateral damage to the remaining trees. As more logging activity goes on and more machinery is brought in, the more impact there will likely be. Tree damage can result from logging equipment—like skidders that haul the logs out of the woods—scuffing trees, while falling trees can also break limbs or scuff remaining trees. This kind of damage can degrade the value of those remaining trees in future harvests.
Soil naturally has a certain balance of soil particles and air spaces within a given volume. Those spaces between and among the particles provide pathways for oxygen and water to infiltrate the soil. Heavy logging machinery running in the woods can compact the soil, causing the particles to be squeezed together and the spaces between them to be reduced. This in turn interferes with air and water movement into the soil, depriving tree roots and other plants' roots of oxygen and water. As with other impacts, soil compaction can be mild, moderate or severe.
Opening a forest stand up to the elements by conducting a shelterwood cut can expose the remaining trees to stresses that they would not have otherwise experience. Wind is one important factor, as valuable trees that remain after the initial shelterwood cut are more vulnerable to being blown over because simply don’t have the protection that was provided by the previously intact stand.
In addition to soil compaction, operating logging machinery in the woods and dragging logs on the ground (called "skidding" in the logging trade) can expose the soil to the erosive forces of rain and running water. Without the soil-binding effects of the many roots that stabilized the soil prior to the disturbance, rain and the resulting runoff can carry soil away. This degrades the ability of the site to support trees and other plant growth. A further disadvantageous consequence of soil erosion is siltation, which is the deposition of eroded soil into watercourses. This displaced soil can choke waterways, and sometimes almost literally choke aquatic organisms by interfering with gill function.
In many areas, non-native plant species have become problematic. Some can be very invasive, but oftentimes they don't really get a foothold until there's a disturbance. A logging operation like a shelterwood cutting can provide that disturbance, opening the way for exotic plants to occupy the site. This may well be at the expense of the new generation of desirable trees or other vegetation that foresters managing the site might have intended.