Coarse woody debris and stand characteristics in mature managed and old-growth boreal mesic forests in southern Finland

Stand structure was studied on thirty 1-ha plots in mature managed and old- growth forest stands dominated by Norway spruce (Picea abies L. Karst.) in southern Finland. The forests were classified into three categories (10 plo ts in each category) according to the age of the dominant spruces and signs of previous cutting: (1) mature managed (95-118 years), (2) overmature man aged (124-145 years) and (3) old-growth (129-198 years). The average volume of the living trees was 299 m(3)/ha in mature, 331 m(3)/ ha in overmature and 396 m(3)/ha in old-growth stands. The dearest differen ce in the Living stand characteristics between the categories was in the nu mbers of large pines (Pinus sylvestris L.) and deciduous trees, which were both ca. 10 times more frequent in old-growth than in mature stands, and in termediate in overmature stands. The average volume of coarse woody debris (CWD) with a minimum diameter of 5 cm was 14 m(3)/ha in mature (range 2-28 m(3)/ha), 22 m(3)/ha in overmature (7-38 m(3)/ha) and 111 m(3)/ha (70-184 m (3)/ha) in old-growth stands. Stand age and basal area of the cut stumps to gether explained over 70% of the variation in the volume of CWD. In old-gro wth forests, ca. 70% of the volume of CWD consisted of logs, 23% of intact dead standing trees and 7% of broken snags. Most of the volume of CWD belon ged to the 20-29 and 30-39 cm diameter classes, but the mean proportion of large trunks greater than or equal to 40 cm was also considerable, 24%. In managed forests man-made CWD, consisting of cut stumps, bolts and logging r esidues, accounted for an average of 25% of the total volume of CWD. In man y cases most of the CWD volume belonged to the small diameter classes, 5-9 and 10-19 cm, and the mean proportion of large trunks was only 8%. We suggest that, considering the low proportion of both old-growth and over mature forests in southern Finland and the long time required for old-growt h characteristics to develop, the most efficient short-term management stra tegy to increase structural diversity and old-growth attributes in managed forests would be to apply harvesting methods retaining the old-growth chara cteristics (i.e, large living trees, snags and logs) that already exist in overmature and mature stands. (C) 2000 Elsevier Science B.V. All rights res erved.