Due to climate change, subtropical forests are increasingly exposed to severe disturbance, which may lead to increased tree mortality. To date, previous research has not sufficiently studied the deadwood biomass within forests over large study plots. To address this research gap, we calculated the deadwood biomass within a 20 hectare (ha) permanent old-growth forest plot in southern China during two censuses and assessed the factors contributing to it. The deadwood biomass was estimated by applying allometric regression equations. There was a total of 11,283 (22.4%) dead individuals in the study plot. Most of these dead trees had very small diameters (1–10 cm). The spatial distribution of the dead individuals differed across subplots and was determined by biotic and abiotic factors. The deadwood biomass storage was 142.5 ton (t) in our study plot. Small (DBH: 0–30 cm) and medium trees (DBH: 30–50 cm) were the largest contributors (54.9% and 30.7%) to deadwood biomass storage. Three dominant tree species contributed 64.8% of the deadwood biomass storage, and the deadwood biomass of 38 tree species was less than 1 t ha⁻¹. Finally, the deadwood biomass was determined by breast diameter and the number of dead individuals, which was influenced by neighboring individuals and environmental factors. This study provides a detailed assessment of the patterns of the deadwood biomass in a subtropical forest and underscores the importance of including community characteristics and abiotic factors (e.g., topography) into research on forest ecosystem carbon. The results of this research provide valuable information that can deepen the understanding of the contribution of subtropical forests to the global carbon cycle and that can be used to improve forest protection and planning strategies.

Associated endogenous hormones were affected by forest fragmentation and significantly correlated with aboveground biomass storage. Forest fragmentation threatens aboveground biomass (AGB) and affects biodiversity and ecosystem functioning in multiple ways. We ask whether and how forest fragmentation influences AGB in forest fragments. We investigated differences in AGB between forest edges and interiors, and how plant community characteristics and endogenous hormones influenced AGB. In six 40 m × 40 m plots spread across three forest fragments, AGB was significantly higher in plots in the forest interior than in those at the edge of forests. The proportion of individuals with a large diameter at breast height (DBH > 40 cm) in the forest edges is higher than that in the forest interiors. Further, trees within a 15–40 cm DBH range had the highest contribution to AGB in all plots. Trees in interior plots had higher abscisic acid (ABA) and lower indole-3-acetic acid (IAA) concentrations than those in edge plots. In addition, AGB was significantly positively and negatively correlated with ABA and IAA concentrations at the community scale. In this study, we provide an account of endogenous hormones’ role as an integrator of environmental signals and, in particular, we highlight the correlation of these endogenous hormone levels with vegetation patterns. Edge effects strongly influenced AGB. In the future, more endogenous hormones and complex interactions should be better explored and understood to support consistent forest conservation and management actions.