Plant community classification is a way of understanding something of the underlying order to vegetation. What can we tell about the past, present, and future of a particular place by observing plants? How many species live together in one place and how did they come to be there? How is this assemblage of plants similar or different from others? How have plants and other organisms coevolved? These and many other questions are addressed by plant community ecologists.
Most of the southern two-thirds of Pennsylvania was covered historically by oak-dominated mesophytic forests, sometimes referred to as Appalachian Oak Forest. This forest type was characterized by red and white oaks, American Chestnut, hickories, and tuliptree. The northern third of the state was covered by mixed hardwood/hemlock/white pine forests characterized by beech, birches, black cherry, and sugar maple with either, or both, hemlock and/or white pine. In southwestern Pennsylvania, the forests were dominated by beech, basswood, and sugar maple.
As lumbering, pests and diseases, and ecological imbalances swept across Pennsylvania, the character of the forests changed forever. American chestnut, once the most common forest trees in the state, was devastated by chestnut blight. Gypsy moth has reduced the importance of oaks in many forests by preferentially feeding on them. Hemlock wooly adelgid is killing our state tree. The extreme overabundance of deer is preventing the regeneration of many tree species.
These influences have resulted in forest communities that are very different than those seen by the first Europeans to arrive here. Many species remain and others have arrived and made themselves at home. It's often difficult to recognize, define, and categorize the forests we see today. Most forests exist as mosaics of intergrading types making it hard to draw boundaries.
Evolution is in the process of sorting things out. One thing is clear, the forests of Pennsylvania's future will look considerably different from those of the past. However, as botanists, we are always interested in learning more about the fundamental nature of groups of living things.