Availability and structure of coarse woody debris in hemiboreal mature to old-growth aspen stands and its implications for forest carbon pool

Abstract

European aspen deadwood is extensively studied as a habitat for saproxylic species, while less is known of its dynamics and role in carbon sequestration. We studied unmanaged mature (41–60 years), moderately overmature (61–80 years), overmature (81–100 years), and old-growth (101–140 years) and managed mature and moderately overmature aspen stands on fertile mineral soils. In unmanaged stands, marginal mean CWD volume was from 67.3 ± 12.1 m3 ha−1 in moderately overmature to 92.4 ± 5.1 m3 ha−1 in old-growth stands, with corresponding marginal mean CWD carbon pool 8.2 ± 1.6 t ha−1 and 12.5 ± 0.7 t ha−1, respectively. Both CWD volume and its carbon pool had substantial yet non-significant differences (all p > 0.05) among the age groups. High CWD volume was present in most stands, by at least two-thirds of plots comprising more than 20 m3 ha−1, and about half of CWD was larger than 30 cm in diameter. Changes in CWD species composition toward a higher proportion of deciduous deadwood in old-growth stands, together with a high volume of recently dead trees, suggest early senescence of the dominant aspen cohort.