DYNAMICS OF THE DEAD WOOD CARBON POOL IN NORTHWESTERN RUSSIAN BOREAL FORESTS

Our study examines dead wood dynamics in a series of permanent plots e stablished in closed, productive second-growth forest stands of north- west Russia and in temporary plots that represent different succession al stages and types of disturbance. Dead wood stores measured on 63 pl ots 0.2-1.0 ha in size range from 1-8 Mg C ha(-1) in young to mature i ntensively managed stands, 17 Mg C ha(-1) in an old-growth forest, 20 Mg C ha(-1) on a clear-cut, and 21-39 Mg C ha(-1) following a severe w indthrow. A total of 122 logs, snags, and stumps aged by long-term plo t records was sampled for decay rates and to develop a system of decay classes. Annual decomposition rates are: 3.3% for pine, 3.4% for spru ce, and 4.5% for birch. Based on these decay rates the average residen ce time of carbon (C) in the dead wood pool is 22-30 years. The mortal ity input on the permanent plots was 23-60 Mg C ha(-1) over 60 years o f observation or 15-50% of the total biomass increment. This data sugg ests a dead wood mass of 10-22 Mg C ha(-1) would be expected in these mature forests if salvage had not occurred. In old-growth forests, dea d wood comprised about 20% of the total wood mass, a proportion quite similar to the larger, more productive forests of the Pacific Northwes t (USA). If this proportioning is characteristic of cool conifer fores ts it would be useful to estimate potential dead wood mass for old-gro wth forests without dead wood inventories. However, the use of a singl e live/dead wood ratio across the range of successional stages, a comm on practice in C budget calculations, may substantially over- or under -estimate the dead wood C pool depending upon the type of disturbance regime. Intensive forest management including short harvest rotations, thinning and wood salvage reduces dead wood C stores to 5-40% of the potential level found in undisturbed old-growth forest. In contrast, n atural disturbance increases dead wood C pool by a factor of 2-4.