PATTERNS OF PLANT SPECIES DIVERSITY IN REMNANT AND RESTORED TALLGRASS PRAIRIE

Authors: Polley, Herbert; Derner, Justin; WILSEY, BRIAN - IOWA STATE UNIVERSITY

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/17/2004
Publication Date: 9/1/2005
Citation: Polley, H.W., Derner, J.D., Wilsey, B.J. 2005. Patterns of plant species diversity in remnant and restored tallgrass prairies. Restoration Ecology. 13(3):480-487.

Interpretive Summary: Greater than 90% of the area once occupied by tallgrass prairie in the central U.S. has been modified for agriculture, resulting in a loss of plant and animal diversity. Efforts to restore tallgrass prairies now are widespread, but the goal of re-creating the patterns of plant species richness and abundances (plant diversity) that characterize remnants of the tallgrass prairie has proven difficult to achieve because mechanisms responsible for high diversity in remnant prairies are poorly understood. We measured plant diversity within paired restored and remnant tallgrass prairies at three sites in central Texas. Diversity was studied at different spatial scales (over different aerial extents of prairies) to provide insight into why, as well as how, the number and abundances of plants differed between remnant and restored prairies. Diversity of plant species was greater in remnant than restored prairies at all spatial scales studied. At the scale of prairies, the number of species was greater and species abundances were more equitable or evenly distributed in remnants because of greater spatial variation in species composition. At the scale of small plots, remnant prairies also contained more species. The number of species in plots in remnants apparently was determined more by limitations on the ability of plants to colonize sites and by ecological factors that slow the rate of exclusion of plant species than by the number of species that could reside in plots. Plots in remnant prairies contained more functional groups of species, evidence that partitioning of soil resources like water and nitrogen among species also was greater in remnant prairies. Our results indicate that resource partitioning and colonization limitations contribute to the greater diversity of remnant than restored prairies. Techniques that limit the distribution of dominant plants and increase the proximity of functionally-diverse species thus may be required to re-create patterns of plant diversity found in remnant tallgrass prairies.

Technical Abstract: To restore diversity of native vegetation requires an understanding of the mechanisms responsible for diversity in targeted communities. We measured diversity (Simpson's index) of plant species and functional groups of species (defined based on growth form and phenology) in replicated plots within paired restored and remnant (relic) tallgrass prairies at three locations in central Texas, USA. To aid in identifying mechanisms potentially responsible for diversity differences between prairie types, we decomposed diversity into richness and evenness (relative biomass) and into spatial scales (within-plot, among-plot, total or prairie). Species diversity was greater in remnant than restored prairies at all spatial scales. At the scale of prairies, both species richness and species evenness were greater in remnants because of greater spatial variation in species composition. At the plot scale, remnant prairies were more diverse because of greater richness alone. Plot-scale richness in remnants apparently was determined more by colonization limitations and other ecological factors that slow the rate of competitive exclusion than by size of the species pool. Plots in remnant prairies contained more functional groups and fewer species per group than did plots in restored prairies, evidence that resource partitioning also was greater in relic prairies. Our results indicate that niche partitioning and colonization limitations contribute to the greater diversity of remnant than restored prairies in central Texas. Techniques that limit the distribution of competitive dominants and increase the proximity of plants of different functional groups thus may be required to better simulate the plant diversity of tallgrass prairies.