Impact of the four-eyed fir bark beetle (Polygraphus proximus Blandf.) on coarse woody debris stock and carbon budget of fir forests in Central Siberia

In the boreal forests of Central Siberia, a marked increase in tree mortality caused by the invasive four-eyed fir bark beetle (Polygraphus proximus Blandf.) has raised concerns about its impact on forest carbon dynamics. This study aims to quantify changes in coarse woody debris (CWD) stocks and their associated carbon fluxes under different levels of beetle infestation. Using systematic field surveys across infestation gradients, we measured CWD accumulation and decomposition by component (snags, logs, and stumps). Our results show that CWD stocks varied significantly, ranging from 68.1 to 179.9 Mg ha-1, with the highest amounts observed in the most heavily infested areas. In particular, the proportion of carbon stored in snags increased with infestation severity. Furthermore, our analysis of decomposition rates based on empirical data indicates accelerated carbon dioxide emissions from CWD in severely damaged stands. These findings underline the substantial impact of bark beetle outbreaks on the carbon storage capacity of fir forests and highlight the need for management strategies that account for pest effects on forest carbon budgets. This study contributes to a better understanding of pest-induced changes in forest ecosystems and supports the refinement of carbon dynamics models for boreal forests.