Preliminary results of planting small gaps as a strategy for restoring longleaf pine forests

Background/Question/Methods

At Horseshoe Bend National Military Park in Alabama, the National Park Service (NPS) is pursuing ecological restoration. Fire was excluded for 75+ years and past agriculture occurred on a portion of the ~800 ha site. Historical records suggest that uplands were once open-canopied forests dominated by longleaf pine (Pinus palustris). Most longleaf were removed prior to 1930 and fire exclusion resulted in loblolly pine and native hardwoods encroaching from down-slope, moist areas. Ongoing efforts include reintroducing fire, minimizing encroaching hardwood species, and decreasing accumulated duff and litter. There is also a need to plant longleaf pine because the site lacks a sufficient seed source. The NPS hopes to reintroduce longleaf without dramatic, sudden visual changes to the landscape that surrounds a historically significant battleground. Traditional approaches to re-establishing most pine species include mechanical and/or chemical treatments to clear and prepare sites for tree planting. In an effort to meet NPS objectives and also successfully plant longleaf, we established trial small-scale gaps (< 0.2 ha each). Questions include: 1) are small-sized gaps adequate to provide sufficient light for seedling survival and growth and 2) are there unexpected consequences related to planting in small patches embedded in a mixed pine-hardwood forest?

Results/Conclusions

Over a two-year period the areas of twenty existing natural gaps were expanded and planted with containerized longleaf. Monitoring 2 and 3 years post-planting indicates that almost 75% of seedlings (~1450/2000) survived and that ~80% of those experienced small or moderate amounts of growth. Although we anticipated seedling mortality, we assumed that the primary cause would be related to shading; however this may not be the case. There is evidence that uprooting or other damage by mammals may be responsible for almost 70% of the lost seedlings. Compared to native longleaf pine stands, the matrix of mixed pines and hardwoods surrounding the small planting gaps is expected to support higher densities of white-tailed deer (Odocoileus virginianus) and perhaps some species of small mammals, although there was no indication of activity by feral hogs (Sus scrofa). Planted longleaf pine seedlings embedded in mixed-pine and hardwoods may be vulnerable to damage by vertebrates. Monitoring continues in an effort to determine if mammal damage decreases with seedling age and/or if low light compromises growth over time. It is hoped that restoration of natural forest structure can eventually be successful without creating sudden, dramatic changes in the landscape appearance and so meet NPS goals.