Soil contact and prescribed burning accelerate the decomposition of downed woody debris in boreal forests

Abstract

Deadwood enrichment and prescribed burning are closer-to-nature management practices intended to restore biodiversity and ecosystem services in Fennoscandian forests. However, their long-term effects on a key process—deadwood decomposition—remain unquantified. We investigated the decomposition of spruce and birch downed coarse woody debris (logs) 21 years after prescribed burning, tree retention, and deadwood enrichment in upland and paludified biotopes within managed mature Myrtillus-type Norway spruce forests. Cutting trees for deadwood enrichment accelerated decomposition by increasing soil contact. Prescribed burning increased volume loss, particularly in spruce logs, but this effect was weaker in paludified Sphagnum-dominated biotopes. When mass and volume losses of bark and secondary xylem were integrated, the main drivers of decomposition in descending importance were soil contact, Sphagnum cover, tree species, and burning. The total decomposition rate constant was higher for spruce (0.087 yr⁻¹) than for birch (0.066 yr⁻¹). The mean residence time of downed coarse woody debris was 49 years, ranging from 38 years for burned spruce logs to 104 years for spruce logs covered by Sphagnum. Our results demonstrate that restoration practices influence long-term decomposition dynamics. Deadwood enrichment and prescribed burning can hasten carbon and nutrient turnover from coarse woody debris in boreal forests.