Effects of mechanized pine straw raking on population densities of longleaf pine seedlings

摘要

Longleaf pine communities occupy a small fraction of their original extent in the southeastern United States and are in great need of restoration and conservation management. Recent anthropogenic disturbances, such as pine straw raking, may interfere with seedling survival and, hence, restoration efforts. We examined the effects of mechanized straw raking on longleaf pine (Pinus palustris Mill.) seedlings (pre-grass stage, or <3-yr-old) in natural, fire-maintained plant communities in Croatan National Forest, North Carolina, by testing the effects of number of rakings (0-4 times during a 2-yr period (1992-1994)) and community type (pine-turkey oak, dry savanna, and mesic savanna) on seedling densities in 1-mpo quadrats. Despite initial differences in densities of seedlings among communities, analyses of variance did not detect significant differences among communities as averaged over time and raking treatment. Both raked and unraked quadrats exhibited declines in seedling density during the study, but the declines were greater for raked quadrats. After 2yr, initial densities were, on average, reduced by 34% in unraked quadrats and by 47%, 63%, 78%, and 77% in quadrats raked one, two, three, and four times, respectively. In quadrats raked four times, censuses performed after each raking indicated significant declines in densities in response to all but the first raking. Raking either injures pine seedlings directly and/or modifies microsite conditions in ways unfavorable for seedling survival. Having established a link between raking and mortality, we now recommend additional work to reveal the causal mechanisms. Land management decisions should accommodate the potential adverse effects of mechanized raking on pine regeneration.