VARIANCE IN SOIL DEPTH AND ITS INFLUENCE ON SPECIES RICHNESS WITHIN AND AMONG CEDAR GLADES IN MIDDLE TENNESSEE

A cedar glade is a karstic ecosystem and endemic plant hotspot in southeastern US, especially middle Tennessee. This ecosystem is characterized primarily by thin soil over limestone bedrock, flat terrain, and low vegetation cover, and it is surrounded mostly by redcedar forest. In cedar glades, soil depth is a major environmental factor since it determines water availability and root volume. Although previous work has stated that soil depth decreases in a linear pattern from forest to the center part of glades, we observed that this was most likely not the case. First, we determined the relationship between mean soil depth and distance to forest edge. Second, since soil depth is supposed to decrease (from forest to glade center), we predicted that bedrock will become more prevalent and the amount of variation in depth will also decrease. Third, we assumed that variation in soil depth and niche availability was positively related, and thus, species richness will increase with increased variation. Five cedar glades were selected in middle Tennessee and random points were generated and mapped on each glade. Soil depth was measured at five points and the number of species was recorded within 1 m² plots at each random point. Mean soil depth decreased as distance from forest edge increased in two of the five glades (R² ≥ 0.12, p ≤ 0.037). Although variation in soil depth was significant for only one glade, it was opposite our prediction (R² = 0.11, p = 0.047). No relationship between soil depth variation and species richness was found in any of the glades. We did not find consistent trends in soil depth mean or variation among the five glades, but did so in species richness. Overall, our study illustrates that soil depth relationships are highly varied among glades and that it is difficult to generalize about soil depth relationships of glades.