Deadwood carbon stock in overmature coniferous forests on different soil types in the hemiboreal region

Abstract

The amount of deadwood is a subject of heated debate regarding biodiversity conservation and carbon (C) storage as an instrument for climate change mitigation in north-eastern Europe. In the region, Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) are among the principal forestry species providing a significant pool of stable deadwood, especially in overmature forests. Deadwood C stocks are highly variable, and regional deadwood estimates can be biased; thus, local data is vital, and accurately quantified deadwood C stocks, particularly in overmature stands on different soil types, are essential.

The study aims to characterise deadwood C stock, modes (standing or lying), and decay classes in hemiboreal overmature coniferous forest stands on dry mineral, drained, and wet organic soils. C stock in deadwood and forest inventory parameters were estimated in 95 overmature (aged 122 to 218 years) coniferous stands using the sample plot method, taking into account the form of deadwood standing, decomposition class and soil type.

Mean deadwood C stock (deadwood with a diameter ≥ 6.1 cm) in coniferous stands ranged from 4.59 C t ha^–1 to 11.25 C t ha^–1 in spruce stands on wet organic soil and pine stands on mineral soil, respectively. However, the amount of deadwood showed large spatial variability; at the same time, a statistically significant relationship between deadwood carbon stock and soil type, basal area, and the mean stand diameter at breast height, explaining a limited effect and maintaining high uncertainties. This suggests that the dynamics of deadwood were complex, driven by ageing, natural disturbances and any past management, perhaps carried out decades ago; for these reasons, the findings should be interpreted with caution due to the potential legacy effect of any disturbances in some stands. Nevertheless, the results highlight the crucial role of large-sized coniferous deadwood as a stable carbon store, contributing to both carbon storage and maintaining biodiversity, in the hemiboreal region.

Keywords: carbon stock; coarse woody debris; decay stage; organic soils; Norway spruce; Scots pine