| This study examined the soil and vegetation nutrient capital in the landscape mosaic of barrens and hardwood forests on the Pocono Plateau in northeastern Pennsylvania. The Pocono till barrens are assemblages of pitch pine-scrub oak-heath shrublands with an unusual abundance of rare species. They occur primarily on Illinoian-aged glacial till, with some patches growing on Wisconsinan till. Between 1938 and 1992 approximately 65% of these barrens had become forested. As part of a research effort investigating the processes that determine the occurrence and persistence of barrens or forest in this landscape, this study assessed the association of soil and vegetation nutrient capital with plant community type (barrens and forest) and parent material type (Illinoian and Wisconsinan till). I predicted that (1) barrens soils would have lower nutrient content than forest soils, and that (2) under the same vegetation, Illinoian till soils would have lower nutrient content than Wisconsinan till soils. I expected, (3) barrens vegetation to contain a smaller quantity of nutrients than forest vegetation, given the smaller stature and fewer trees in the barrens than in the forest; and (4) if available soil nutrients were exhibiting a strong influence on vegetation nutrient capital, I hypothesized that barrens and forests growing in Illinoian till soils would have smaller quantities of nutrients respectively, than barrens and forests growing in Wisconsinan till soils. I sampled soil in 99 plots and sampled trees and large shrubs, small woody and herbaceous plants, and coarse roots in 63 of these plots. I analyzed the soil samples for total C and N and exchangeable Ca, Mg, K, and Al content, and analyzed the plant tissue samples for C, N, Ca, Mg, K, and P content. I found no indications of parent material controls on soil or vegetation nutrient capital and suggest the mosaic pattern of barrens and forest is probably related instead to plant-driven positive feedbacks involving fire frequency, as demonstrated by others. |
