PS 37-195 - Controls on ground cover species richness in the longleaf pine-wiregrass ecosystem

Tuesday, August 7, 2012
Exhibit Hall, Oregon Convention Center
Lisa M. Giencke1, L. Katherine Kirkman1, Robert J. Mitchell2, Jason D. McGee1 and R. Scott Taylor1, (1)Joseph W. Jones Ecological Research Center, Newton, GA, (2)Forest Ecology, Joseph W. Jones Ecological Research Center, Newton, GA
Background/Question/Methods
Longleaf pine-wiregrass ecosystems of the southeastern United States are adapted to frequent low-intensity fires, which maintain open, savanna-like landscapes and foster high species richness within the ground cover vascular plant community. The objective of this long-term project is to understand how resource (moisture and nutrients) manipulation and fire exclusion interact to regulate ground cover species diversity. In 2000, we established a 2 x 2 factorial design on 32 plots in which we manipulated moisture and nutrients at both mesic and xeric sites. In an additional 16 plots, we implemented a 2 x 2 factorial design utilizing fire exclusion and nutrient addition. Vascular plant species richness was documented prior to treatment initiation (2000 and 2001) and in 2011using a nested plot design at spatial scales ranging from 0.1 m2 to 400 m2 for the resource manipulation plots and at 0.1 and 1 m2 scales in the burn exclusion sites. Aboveground biomass was measured at the same dates.

Results/Conclusions
Species richness in burned-fertilized plots decreased relative to burned-unfertilized plots at xeric and mesic sites; this effect was significant at spatial scales up to 10 m2 for xeric plots, but only at the 0.1 m2 scale for mesic plots. Species richness in burned-irrigated xeric sites increased relative to burned-unirrigated plots at the 0.1 m2 scale. Species richness in mesic plots was unaffected by increased water availability. Burn exclusion led to a decrease in species richness regardless of spatial scale or site condition (mesic or xeric), and nutrient addition exacerbated these losses in 1 m2 plots at xeric sites. Nutrient addition and irrigation increased aboveground biomass in both burned and unburned sites. These results suggest that the disturbance due to prescribed fire has a greater role in structuring biodiversity than does productivity.