In 1995, Hurricane Opal toppled trees throughout the South, including parts of the southern Appalachians. Wind is a common canopy disturbance in upland oak-hickory forests, but little has been reported on naturally formed large gaps of more than six trees where a partial canopy remains.
With Erik Berg, SRS researchers Stanley Zarnoch and Henry McNab observed and modeled tree survivorship in and around 12 large gaps created by the hurricane. The scientists monitored the sites for 20 years. Many survivorship studies only last for five years or so, which may not be long enough to understand survivorship dynamics.
For the first nine years of the study, seedlings of species rated intermediate in shade tolerance, such as the red oaks, were more likely to survive farther from the center of the gap. But by year 20, this relationship had reversed: survivorship was higher towards gap centers. This change in seedling survivorship was largely related to changes in light received below the forest canopy and midstory.
The seedlings’ shade intolerance (yellow poplar) or tolerance (red maple) did not affect survivorship by position from gap center at any time. In general, trees that were taller to begin with were more likely to survive.