Impact of site-preparation on soil-surface CO₂ fluxes and litter decomposition in a clear-cut in Sweden

Abstract

Boreal forest soil contains significant amounts of organic carbon. Soil disturbance, caused for example by site preparation or stump extraction, may increase decomposition and thus lead to higher CO emissions, contributing to global warming. The aim of this study was to quantify responses of soil-surface CO fluxes (R) and litter (needle and root) decomposition rates following various kinds of soil disturbance commonly caused by mechanical site preparation and stump harvest. For this purpose four treatments were applied in a clear-cut site in central Sweden: i) removal of the humus layer and top 2 cm of mineral soil, ii) placement of a humus layer and 2 cm of mineral soil upside down on top of undisturbed soil, forming a double humus layer buried under mineral soil, iii) heavy mixing of the humus layer and mineral soil, and iv) no disturbance (control). R measurements were acquired with a portable respiration system during two growing seasons. To assess the treatments’ effects on litter decomposition rates, needles or coarse roots (Ø = 6 mm) were incubated in litterbags at positions they would be located after the treatments (buried, or on top of the soil). The results indicate that site preparation-simulating treatments have no effect or may significantly reduce, rather than increase, CO emissions during the following two years. They also show that buried litter decomposes more rapidly than litter on the surface, but in other respects the treatments have little effect on litter decomposition rates.22ss2