Pennsylvania’s forests have been subjected to a constantly evolving set of anthropogenic
drivers that changed their composition, structure, and dynamics over the last several centuries.
These drivers include timber harvesting, fire management, herbivore pressure (e.g., by near
extirpation followed by overabundance of white-tailed deer), introduced insects and pathogens,
and climate change. Effects of some of these drivers are relatively immediately apparent, such as
when introduced pathogens cause die-offs of host tree species; others may take decades or
centuries to emerge. In response to anthropogenic climate change, forests are expected to change
much more gradually over time as changes in precipitation and temperature affect their
regeneration, growth, and subsequent composition. However, the rate of regeneration and
successional mosaic of the landscape will depend heavily on the intensity and frequency of
disturbance related to these other drivers. Some of these disturbance factors are likely to increase
as a direct result of climate change.