Dead wood basic density, and the concentration of carbon and nitrogen for main tree species in managed hemiboreal forests

• Deadwood density is given for six main tree species by five decay classes.
• Pine, spruce and grey alder have lower relative loss of density compared to other species.
• No differences in wood density between dry, medium and wet areas was noticed.
• For pine, spruce and birch the C concentrations were affected by the decay class.
• For all the examined tree species the N concentration in dead wood was increasing with increasing decay class.

Forest ecosystems are an important carbon (C) pool, and the decomposition of dead wood plays a key role in its C cycle. Based on the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol, IPCC Guidelines for National Greenhouse Gas Inventories were established. Nations that have signed the agreements are encouraged to quantify C pools and fluxes in their forests, including its proportion occurring as dead wood. There are significant differences in density and C concentration of dead wood among tree species. In managed hemiboreal forests of Estonia the dead wood density, and C and N concentration changes in different decay classes for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), silver and downy birch (Betula pendula Roth. and Betula pubescens Ehrh.), black alder (Alnus glutinosa (L.) Gaertn.), grey alder (Alnus incana (L.) Moench.) and European aspen (Populus tremula L.) have been assessed. All together 548 sample discs taken from logs (measurements were restricted to fallen dead trees only) were collected. The results revealed a decrease in mean dead wood density with progressing decay state for all studied tree species. Pine, spruce and grey alder had the smallest wood density reduction with progressing decay state, retaining 37%, 30%, and 36% of initial density, respectively. Other broadleaved tree species (birch, black alder and aspen) had the greatest density reduction during decomposition, retaining 24%, 23%, and 16% of initial density, respectively. For all studied tree species there were no significant differences of wood density between sites with different moisture conditions (dry, medium or wet areas). In case of pine, spruce and birch the C concentrations were significantly affected by the decay class, while in case of both alders and aspen the C concentrations were not significantly affected by changes in decay classes. For all the assessed tree species the N concentration in dead wood was increasing with increasing decay class.