The effects of gaps and liming on forest floor decomposition and soil C and N dynamics in a Fagus sylvatica forest

Despite the importance of gaps in the dynamics and management of many forest types, very little is known about the medium- to long-term soil C and N dynamics associated with this disturbance. This study was designed to test the hypothesis that gap creation and lime application, a routine measure in many European forests to ameliorate soil acidity, lead to accelerated litter decomposition and thus a reduction in the forest floor and soil C and N pools. Four gaps were created in 1989 in a mature European beech (Fagus sylvatica L.) forest on acid soil with a moder humus, and lime (3 t dolomite.ha(-1)) was applied to two of these and surrounding areas. Litter and fine-root decomposition was measured in 1992-1993 and 1996-1998 using litterbags. Forest floor (L, F, and H layers) and mineral soil (0-40 cm) C and N pools were determined in 1989 and 1997. Eight years following silvicultural treatments, there was no change in C and N over the entire forest soil profile including forest floor. Reductions in the F and H layers in limed gaps were compensated for by increases in soil C and N in the surface (0-10 cm) mineral soil. Decomposition of F litter was significantly accelerated in limed gaps, leading to the development of a mull-moder, whereas gap creation alone had no effect on mass loss of F material in litterbags. Gap size disturbances in this acid beech forest appear to have minimal influences on soil C and N stocks. However, when combined with liming, changes in the humus form and vertical distribution of soil C and N may occur.