Effect of stem rot on wood basic density, carbon, and nitrogen content of living deciduous trees in hemiboreal forests

Abstract

While numerous studies have focused on analyzing various aspects of the carbon (C) budget in forests, there appears to be a lack of comprehensive assessments specifically addressing the impact of stem rot on the C budget of broadleaf tree species, especially in old-growth forests where stem rot is prevalent. One of the main challenges in accurately quantifying C losses caused by stem rot is the lack of precise data on the basic density and C content of decayed wood, which are crucial for converting decayed wood volume into biomass and C stocks. Using linear mixed-effects models, we examine the variability of wood basic density, C content, and nitrogen (N) content. Discolored and decomposed wood was collected from the stems of 136 living deciduous trees common in hemiboreal forests in Latvia. Our research indicates a noticeable reduction in the wood basic density, coupled with an increase in the N content within the stem wood throughout the decomposition process in birch (Betula spp.), European aspen (Populus tremula L.), grey alder (Alnus incana (L.) Moench), and common alder (Alnus glutinosa (L.) Gaertn.). While aspen wood showed a decreasing trend in C content as decay progressed, a pairwise comparison test revealed no significant differences in C content between discolored and decomposed wood for the studied species, unlike the findings for basic density and N content. This study emphasizes the need to account for stem rot in old-growth forest carbon budgets, especially in broadleaf species, and calls for more research on stem rot-induced carbon losses.

A Comparative Study of Stem Rot Severity in Mature Deciduous Trees in Latvia

“…Decay development in a living stem can be likened to a disease, and a tree can often respond to the initial infection and defend itself [30]. In our previous fieldwork, we observed a significant decline in basic stem wood density (25-41%) as part of decomposition [17]. This variation depended on the tree species and was associated with biomass loss in tree stems.…”

“…Two discs were obtained from each log, one from each end. Later in the laboratory, the area of stem rot was measured according to previously defined external decay indicators [17]:…”

“…A notable decrease in wood basic density, accompanied by increased wood nitrogen content, occurs within the stem wood during decomposition. Betula exhibited the most substantial reduction in density due to stem rot (mean difference between discolored and decomposed wood = 0.196 g m −3 ), followed by P. tremula (0.152 g m −3 ), A. incana (0.132 g m −3 ), and A. glutinosa (0.102 g m −3 ) [17]. This decrease (25-41%) corresponded to the biomass loss in the decomposed wood volume.…”

“…Most existing data about stem rot spatial distributions in forests originate from research investigations examining its impact on the quantity and value of timber [14][15][16]. However, to track the impact of stem rot on living biomass, more precise and comprehensive data are needed on the extent and proportion of various external indicators of stem rot within tree stems [17]. According to 2022 National Forest Inventory (NFI) data, birch (Betula spp.…”

Sawlog Recovery in Birch, Black Alder, and Aspen Stands of Hemiboreal Forests in Latvia

“…EUR 18.5 million in economic losses annually [18]. However, for broadleaf species, a comprehensive assessment of the impact of internal decay (e.g., stem rot) on merchantable volume and carbon stocks is still lacking [15,19,20]. In addition, disturbances by various pathogens are predicted to intensify with expected warmer and wetter conditions, which are likely to amply disturbances as they interact [21].…”