Science News 13/01/2011

Local roll off vegetation removal

Landowners should also control who removes the trees. Certainly contractors can remove trees that offer no risk of damaging surrounding trees. However, an arborist skilled at tree removal should remove any trees that may damage surrounding trees that are to be retained after construction.

The removal of vegetation during construction can cause minor or dramatic changes in the environment of the remaining trees, depending on the size and extent of the removal. At the one extreme, the environment of a very open, sparsely wooded residential lot would be changed little by the removal of a single tree to allow home construction. In contrast, on a heavily wooded property, the removal of a substantial number of trees to allow construction of a commercial building and the thinning of the remaining trees to develop a lawn and parking area would dramatically change many elements of the remaining trees' environment. Different species of trees tolerate this type of disturbance differently.

The Appendix identifies the relative tolerance of different tree species to construction activities, which include the environmental changes that can occur when surrounding vegetation is reduced or eliminated. Some species of trees, such as many oaks, hickories, and green ash, tolerate this type of disturbance well, while other species, including sugar maple, American beech, and white ash, do not. Many of the thinner-barked species, such as the beeches and maples, will develop dead, splitting areas of bark if their trunks, which previously were shaded, are suddenly exposed to direct sunlight as the result of the removal of surrounding trees.

One of the best examples of the disastrous consequences that can result from ignoring the differences among tree species in their tolerance to construction and clearing disturbances was a country club that built its club house and parking lot within a wooded area and thinned the woods, leaving the larger, and then beautiful, white ash towering over the parking lot. Within a year the ash were showing signs of decline, and within 10 years they were all gone. White ash and many other species will not tolerate that type of environmental change once the trees are established in a natural stand. When selecting trees to retain following construction in a well-wooded area, to the extent possible, select healthy, vigorous trees of species that are better at tolerating the new environment. Select as well for trees that can tolerate the activities associated with the construction of the site, including the thinning and/or removal of other vegetation.

Another potential impact of reducing the number of trees on a well-treed property can be a dramatic change in the vegetation growing under the trees. The forest understory is very much influenced by the degree of shade provided by the trees. When trees are removed, resulting in additional light and other changes in the understory environment, plants better suited to the new, more exposed environment often replace those that grew in the more shaded environment. This may or may not be desirable, depending on the owner's objectives. Certainly the owner wanting to establish grass under the trees will need to manage the tree densities to allow sufficient light for the grass to grow. In contrast, the owner intending to retain the natural character of the woods and enjoy the many woodland wildflowers will be dismayed to discover the woodland overrun with honeysuckle or other plants that thrive in the increased sunlight that resulted from thinning some of the trees.

di S. C.