Dead wood and nutrient storage
Hojka Kraigher
As part of the work in WP7 of Nat-Man we studied the physical and chemical characteristics of beech coarse woody debris (CWD) in selected forest reserves in Denmark, Hungary, The Netherlands and Slovenia. The
aim was to investigate the importance of dead wood for the nutrient cycling and carbon storage.
We examined the time it takes for a beech log to change from freshly fallen wood to complete decomposition by selection of beech logs in different decay phases. The calculated time for decay differed between countries. In
Hungary decay phase 6, which is the phase of strongly decomposed logs, was on average reached 30 years after death. In Slovenia it took over 52 years. In The Netherlands decay phase 5 was reached in 30 years, while
in Denmark the presumed time for total decay was over 50 years.
During the time of decomposition, each beech log goes through considerable structural and chemical changes. This includes processes where certain components decay more rapidly than others, the wood generally becomes
soft and cracked, and the density of the log steadily decreases. In all the studied sites the ratios of C:N and C: S, and pH declined with increasing decay phase, while Dead wood and nutrient storage moisture content, N, S and P concentrations rose with decay phase. The observed increases of concentrations of N, S, P and the decrease in C:N ratio may be used as
indicators for decomposition phases.
Based on the known nutrient concentrations in the dead beech logs, biomass (m3/ha), time of decay, and role in the overall nutrient cycling in the studied sites were extrapolated. The common conclusion was that CWD not
only contributes to biodiversity by its specific dead wood habitat, but also creates micro-sites with relatively high moisture and nutrient content, thus providing specific terrestrial habitats.
Further reading:
Kraigher, H., Jurc, D., Kalan, P., Kutnar, L. Levanic, T., Rupel, M. & Smolej, I. 2003. Beech course woody debris characteristics in two virgin forest reserves in Southern Slovenia. Zbornik gozdarstva in lesarstva 69: 91-134
Odor, P. & Standovar, T., 2003. Nat-Man WP7 Report: Hungary. Changes of physical and chemical properties of dead wood during decay. Nat-Man Working Report 24.
Christensen, M. & Vesterdal, L. 2003. Nat-Man WP7 Report: Denmark. Physical and chemical properties of decaying beech wood in two Danish forest reserves. Nat-Man Working Report 25.
C contents remained at over 45% in DP 1 to 5 in all sites, contributing to long-term C storage in temperate beech forests.
Density decreased with DP, resulting in a decrease in volume and total C and nutrient concentrations per CWD.
N (as well as S and P) concentrations depended in DP1 on site nutrient availability, while an increase with DP (possibly by N- fixation) showed an invasion of diverse microbes and fungi.
Moisture content, increasing with DP, showed that CWD is an important source of water needed for CWD dependent organisms.
Hojka Kraigher