Availability of coarse woody debris in a boreal old-growth Picea abies forest

This study reports temporal (based on cross-dated dead trees) and spatial p atterns of availability of coarse woody debris (CWD) from Picea abies in a Swedish boreal landscape with discrete old-growth forest patches in a wetla nd matrix. Data were collected from 29 patches ranging in size from 0.3 to 28 ha. A total of 897 dead trees with a minimum diameter of > 15 cm occurre d on the 7.2 ha area analysed. The year of death was established for 50 % o f these trees. CWD volume ranged from 17 to 65 m(3)/ha for downed logs and from 0.5 to 13 m(3)/ha for standing snags. CWD of all decay stages and diameter classes oc curred abundantly and the probability of finding logs of all decay stages a nd sizes was very high at the scale of single hectares. Tree mortality diff ered among 5 yr periods. However, during the last 50 yr no 5 yr period prod uced less than 3 logs/ha. Decay rates were highly variable among different logs. Logs with soft wood and some wood pieces lost (decay stage 5) died ca . 34 years ago. This suggests a fairly rapid decay in this northern forest. The data indicate a high and continuous availability of CWD of all types. It is likely, therefore, that selection pressures for efficient dispersal a mong CWD dependent species may not be very high. Consequently, species with narrow habitat demands and/or low dispersal ability may have evolved and t his may contribute to the decrease of certain species in the managed landsc ape.