Longleaf pine establishment affects site restoration potential through changes in vegetation, fuels, and fire behavior

Background/Question/Methods

Longleaf pine once dominated large areas of the southeastern US including a broad spectrum of sites from extremely xeric to poorly drained.  Most of this fire-dependent system has been lost to development, and the remaining areas are much altered.  Restoring this ecosystem ultimately requires the establishment of longleaf pine. Successful longleaf establishment requires site preparation methods designed to reduce competition and/or to improve the distribution of resources in favor of planted seedlings, especially on wetter sites where competition can rapidly overtop seedlings.  But site preparation can adversely affect desired ground layer vegetation, and possibly alter the restoration potential by changing prescribed fire behavior.  We installed an experiment at Camp Lejeune, NC to test the effects of selected site preparation methods on plant community composition and subsequent fire behavior.  Eight treatments included combinations of chopping (C) or herbicides (H) to reduce competition and bedding (B), mounding (M), and flat (F) treatments to vary planting sites: F, CF, HF, CM, HM, CB, HB, and CHB. Analyses of variances tested for short-term (1-3 years) treatment effects on vegetation, fuels, and fire behavior.

Results/Conclusions

For all treatments ground cover was lowest the first season after planting trees (range: 19.9%, CHB – 73.1%, F) and increased through time. There were significant treatment effects on cover in all years, but by year 3 the F plots differed only from the HM and HB plots. Planting site changes resulted in no differences by year 3, but an herbicide effect on vegetation cover persisted.  The effects on species richness were similar to cover results.  Treatment effects of species groups (large and small graminoids, shrubs, vines, ferns, and forbs) varied by year and group.  Notably, the small graminoid group increased while shrubs decreased with herbicide treatments.  Effects on common species were analyzed. Of woody species only Vaccinium tenellum responded negatively to both site altering (B, M) and H treatments. A weedy large grass Andropogon capillipes increased with disturbance while ecologically conservative Aristida stricta decreased. Bedding resulted in reduced maximum fire temperatures and fuel consumption compared to F plots; M plots were intermediate.  Our study documents short term changes in vegetation, but more importantly shows the potential for longer term and cumulative impacts as a result of spatially disrupting fires that are necessary for restoration and maintenance. Flat planting or mounding which creates discontinuous fire breaks may provide conditions for ensuring restoration success.