Decomposition of stumps 10 years after partial and complete harvesting in a southern boreal forest in Finland

Abstract

We studied the decomposition of cut stumps of Norway spruce ( Picea abies (L.) Karst.), Scots pine ( Pinus sylvestris L.), and birches ( Betula pubescens Ehrh. and Betula pendula Roth.) 10 years after clear felling, low level retention felling, gap felling, and selection felling. Bulk density of wood, mass per surface area of bark, and mass of wood and bark for entire stumps were estimated. Using a single exponential model, annual decomposition rate constants (k) were calculated as 0.071, 0.052, and 0.041 ·year–1 for birch, spruce, and pine, respectively. The k values for wood decreased in the same order. For bark, the order was different: spruce bark decomposed slower than pine bark. Fragmentation accelerated mass loss. Pine and birch bark decomposed faster than pine and birch wood, whereas spruce showed the opposite tendency. The wood density and bark mass did not depend on retention levels. Diameter of stumps did not explain variation in decomposition either. The high importance of stumps for biodiversity, carbon, and nutrient cycling requires refinements to decomposition rate constants. Thus, further research based on new empirical data and meta-analysis of published data is needed to reveal factors influencing the decomposition process in situ.