On variation in forest floor thickness across four red pine plantations inPennsylvania, USA

We studied variation in forest floor thickness in four plantations of red p ine (Pinus resinosa Ait.) which were similar in age, soil type and associat ed vegetation. The plantations were located (west to east) in the Clear Cre ek, Moshannon, Sproul and Tiadaghton State Forests of Pennsylvania, USA. A gradient in forest floor thickness exists across these plantations; the for est floor is thickest in the west and it becomes progressively thinner towa rd the east. Decomposition of imported litter increased from west to east, suggesting that the variation in forest floor thickness is related to varia tion in the rate of decomposition. Decomposition rates were related to sapr otroph abundance. Variation in forest floor N and phenolic concentrations, in overall mycorrhiza density and in the relative proportions of three comm on mycorrhiza morphotypes could not explain the variation in decomposition rate. The P concentrations and pH of the forest floor were significantly lo wer at Clear Creek and Moshannon, where decomposition rates were lowest, co mpared to Sproul and Tiadaghton, where decomposition rates were most rapid. This suggests that P concentration and pH may have exerted some control on decomposition.