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This is the first report of a long-term project begun in 1996 to study the development of regeneration on Pennsylvania Bureau of Forestry lands before and after harvest. Specific objectives are to: 1) develop or identify criteria for regeneration success following harvest; 2) provide a continuing assessment of regeneration and forest renewal following timber harvest; 3) determine the pre-existing stand and site conditions necessary for the successful renewal of harvested stands; and 4) refine and develop treatments for enhancing regeneration where regeneration has failed or where conditions indicate that success is uncertain.
After five years of data collection, we have developed an extensive database of pre-existing stand conditions and stand development patterns following harvest in 53 forest stands in southcentral, central, and northcentral Pennsylvania. Approximately 75% of the stands were predominantly oak in composition before harvest; the remainder were “northern hardwoods” stands dominated typically by red maple, sugar maple, black cherry, and beech. In a minority (15) of the stands measured, the state of advance regeneration and other stand characteristics indicated to the managing forester that stand regeneration would be successful, and no special treatments were applied to assist the regeneration process. In the remainder, a variety of special treatments (primarily fencing or fencing and herbicide in combination) were applied to mitigate inhibiting factors (e.g., deer and competition, respectively). In each stand, before harvest or treatment, we measured vegetation and site characteristics on a grid of 0.001- and 0.05-acre plots. Plot centers are permanently marked and their exact locations determined with a global positioning system, and each plot is remeasured periodically after harvest to assess the progress of regeneration. Results to date are based on initial measurements in all stands plus remeasurements in 33 stands one year after harvest (or in some cases treatment prior to harvest).
Regeneration of oaks in particular is of overriding concern because of the importance of this group and because poor regeneration and replacement by other species are widespread phenomena. Guidelines for oak regeneration that are widely used in the Midwest are based on the number and size of advance regeneration seedlings and the expected contribution from stump sprouts. Application of these guidelines to our stands suggests that no oak-dominated stands in our study will be oak-dominated in the next generation, and that most will have less than 10% oak stocking. However, it remains to be seen whether these guidelines apply to Pennsylvania conditions. In the “average oak stand” in our study, chestnut oak (ca. 3000 seedlings/acre), northern red oak (2150 seedlings/acre), and white oak (800 seedlings/acre) are the most abundant oak species in the regeneration cohort before harvest, but red maple (21,000 seedlings/acre) is the most abundant tree species. One year after harvest (or treatment), the number of oak seedlings in most stands is about the same or higher as before harvest, but red maple seedling density declines to just under 15,000 per acre.
Not surprisingly, both biotic (especially the kinds of canopy trees over the plot) and abiotic factors (especially slope, aspect, and angle of horizon) are correlated with the presence and abundance of advance oak regeneration. For reasons that may relate in part to the occurrence of the parent seed source, chestnut oak seedlings are more abundant on slopes, while red oak and white oak are more abundant on relatively flat sites. Oak regeneration appears to be favored on southern aspects and by topography with low horizons to the east and west (minimal shading).
Typically, non-treatment stands have more oak seedlings than fenced stands, even in post-treatment assessments. Furthermore, the density of oak regeneration increased between the first and second measurements in all non-treatment stands, but it decreased in about half of the fenced stands. Hence, fencing immediately after harvest has not significantly enhanced the abundance of oak regeneration in most stands (there are one or two notable exceptions), and we are encouraging foresters to erect fences at least three years in advance of harvest to accumulate oak seedlings in the advance regeneration cohort. As expected, oak regeneration is larger following harvest or treatment at most locations, especially non-treated locations. Stems larger than two feet tall were almost completely absent in the pre-harvest assessments, but are moderately abundant in the majority of the stands one year after harvest or treatment. Even advance regeneration oak seedlings less than six inches tall, expected to contribute negligibly stand regeneration based on Midwest guidelines, appear to be surviving and growing so far. However, these trends are very preliminary; data from the third year after harvest will provide more reliable results.
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