Patterns of Biodiversity

Research Team: Dr. L. Katherine Kirkman (Associate Scientist), Dr. Robert J. Mitchell (Scientist), Kimberly L. Coffey (Research Technician III)

We have examined the distribution of biodiversity in the longleaf pine ecosystem at several levels including floristic inventory, ecological site classification and the relationship between productivity and species richness across a moisture gradient, and characterization of wetland/upland ecotones. We developed a classification of ecosystem types and a GIS layer of potential ecosystem types of Ichauway based on physiography, soils and vegetation. The resulting database and field manual is used to locate potential replicate research sites, and to identify appropriate vegetation types to be restored on disturbed sites. In a productivity/species richness study we found that species richness of the ground flora of Ichauway was similarly high to other longleaf pine ecosystems and that species richness increases with increasing soil moisture and productivity of the site. These results suggest that competitive exclusion is not a significant factor maintaining high species richness in this system, unlike that of other grass-dominated ecosystems such as tallgrass prairies of the Midwest. An ecotone characterization study revealed that hotspots of plant diversity occurred within the upland/wetland ecotone and that discontinuities in vegetation, soil characteristics and hydrologic regime were not necessarily coincident.

Because of the severity of water limitations in the longleaf pine-wiregrass environment, many species in this system appear to be tolerant to drought stress once they are established. Although turnover rates of individuals in these communities are unknown, observations suggest that these species are long-lived perennials. Provided that potential species pools are equivalent, differences in rates of colonization and extinction of species across the resource gradient should directly influence patterns of species richness. Particularly in water-constrained environments, colonization may be a stochastic event coinciding with climatic condition and microsite conditions. Microsites that minimized desiccation are likely important in the early seedling germination and establishment phase of many species. Such microsite may be realized by the presence of neighboring plants that potentially decrease evaporative water loss or decrease extreme temperatures such that a net positive plant-plant interaction occurs (as opposed to competitive effect).

Productivity may be indirectly related to species richness in that the amount of biomass produced may determine the degree of positive plant-plant interactions (particularly of wiregrass, the dominant matrix species) and thus, at the xeric end of the gradient, the inhospitable conditions for germination and establishment are probably exacerbated. Additionally, reproductive output of species may be resource-dependent such that propagule availability varies as a function of the resource gradient.

Additional Information:

Kirkman, L. K., R. J. Mitchell, R. C. Helton and M. B. Drew. 2001. Productivity and species richness across an environmental gradient in a fire-dependent ecosystem. American Journal of Botany 88:2119-2128.

Goebel, P. C., B. J. Palik, L. K. Kirkman, M. B. Drew and L. West. 2001. Forest ecosystems of a lower Gulf Coastal Plain landscape: multifactor classification and analysis. Journal of Torrey Botanical Society 128:47-75.

Kirkman, L. K., P. C. Goebel, L. West, M. B. Drew and B. J. Palik. 2000. Depressional wetland vegetation types: a question of plant community development. Wetlands 20:373-385.

Palik, B. J., P. C. Goebel, L. K. Kirkman, M. B. Drew, L. West, and D. Pederson. 2000. Using landscape hierarchies to guide restoration of disturbed ecosystems. Ecological Applications 10:189-202.

Kirkman, L. K., M. B. Drew, L. West and E. Blood. 1998. Ecotone characterization between upland longleaf pine/wiregrass stands and seasonally-ponded isolated wetlands. Wetlands 18:346-364.

Drew, M. B., L. K. Kirkman and A. K. Gholson. 1998. The vascular flora of Ichauway, Baker County, Georgia: a remnant of longleaf pine/wiregrass ecosystem. Castanea 64:1-24.

Engstrom, T., L. K. Kirkman and R. J. Mitchell. 2001. The natural history of the fire forest. P. 5-18 IN: Georgia Wildlife Federation. The Fire Forest: Longleaf Pine-Wiregrass Ecosystem. Georgia Wildlife 8:5-18.

Funded by: The Joseph W. Jones Ecological Research Center