EFFECTS OF CRYPTOGAMIC SOIL CRUST ON THE POPULATION-DYNAMICS OF ARABIS-FECUNDA (BRASSICACEAE)

Cryptogamic soil crusts are reported to have both positive and negative effects on recruitment and survival of vascular plants. At four sites in SW Montana, Arabis fecunda (Brassicaceae), a rare regional endemic, occurred more often than expected in cryptogamic soil crust compared to bare soil. At all four sites older larger plants were also more common on soil crust than expected. However, plants in the smallest life-stage class were not more common on soil crust than expected at three of the four sites. Measures of fecundity were independent of substrate at all four sites. These results demonstrate that the presence of soil crust is beneficial to populations of A.fecunda at some sites and suggest that this relationship is likely due to increased survival of older plants rather than enhanced recruitment.