Fifty-five year changes in species composition on dry prairie remnants in south-central Wisconsin

KRASZEWSKI, S. E. (Land Resources Program, University of Wisconsin-Madison, Madison, WI 53706) AND D. M. WALLER. (Department of Botany, University of Wisconsin-Madison, Madison, WI 53706). Fiftyfive year changes in species composition on dry prairie remnants in south-central Wisconsin. J. Torrey Bot. Soc. 135: 236–244. 2008.—Ten dry prairie remnants in south-central Wisconsin first sampled in 1950 were resampled in 2005 to determine changes in species presence and frequency and to characterize differences between species that increased and decreased in abundance. Combined species richness over all sites has increased (from 147 to 189), but this largely reflects the recruitment of exotic species, woody vegetation, and taller shade-tolerant species. Mean native species richness per site decreased (from 65.2 to 59.7) reflecting the loss of rarer and shorter forbs while mean exotic species richness increased greatly (from 0.3 to 10.1). Although the average number of habitat generalist species per site has remained constant (13.0 vs. 13.6), the number of habitat specialists has declined (from 27.4 to 21.7) contributing to declines in floristic quality. The five native species that decreased in occurrence and 15 that decreased in frequency tended to be short, nonclonal specialist forbs. The seven native increaser species tended to be tall, clonal, and/or woody generalists. Efforts to conserve dry prairies should thus focus on those species most at risk (i.e., rare, short-statured, and non-clonal) and the processes that sustain them. Burning and removing exotic species and woody vegetation appear to enhance our ability to conserve and maintain plant diversity in dry prairie remnants.