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Keywords:

  • sandhill, Pinus palustris, longleaf pine, hardwoods, restoration, vegetation, prescribed fire, hexazinone, mechanical reduction, northwest Florida, Eglin Air Force Base

Abstract

We tested whether the intensity of hardwood midstory reduction causes commensurate improvements of herbaceous groundcover in fire-suppressed Pinus palustris (longleaf pine) sandhills. Using a complete randomized block design, we compared the effects of three hardwood reduction techniques (spring burning, application of the ULW® form of the herbicide hexazinone, chainsaw felling/girdling) and a no-treatment control on plant species richness, and on life form and common species densities at Eglin Air Force Base, Florida, U.S.A., from 1995 to 1998. ULW® and felling/girdling plots were burned for fuel reduction two years after initial treatment application. We also sampled the same variables in frequently-burned reference sandhills to establish targets for restoration. Spring burns achieved partial topkill of oaks (17.6–41.1% from 1995 to 1998) compared to reductions of 69.1–94% accomplished by ULW® and of 93.2–67.8% by felling/girdling treatments. We predicted that plant species richness and densities of herbaceous groundcover life forms would increase according to the percent hardwood reductions. Predictions were not supported by treatment effects for species richness because positive responses to fire best explained increases in plant richness, whereas ULW® effects accounted for the largest initial decreases. Legumes, non-legume forbs, and graminoids did not respond to treatments as predicted by the hypothesis. Again, positive responses to fire dominated the results, which was supported by greater herbaceous densities observed in reference plots. Overall, we found that the least effective and least expensive hardwood midstory reduction method, fire, resulted in the greatest groundcover improvements as measured by species richness and herbaceous groundcover plant densities.