Abstract:

Objective: Global climate change has altered precipitation patterns, and tree mortality caused by drought is a magnitude threat to global forest ecosystems. The impact of severe seasonal drought on Cunninghamia lanceolata plantations in southern China has become a hot topic in ecological research. However, the investigation into the damage characteristics and influencing factors of extreme drought on subtropical Chinese fir mixed forests remains limited. This article aims to explore which types of forest stands are more susceptible to the impact of drought, the key influencing factors of tree damage or death caused by drought, in order to provide theoretical support for subtropical forest management in the context of global change. Method: An extreme drought event occurred in southern China in 2022, with the opportunity, this study targeted at mixed plantations of C. lanceolata and Phoebe bournei with similar age. Three plant plots were set up in each of two types of slopes of steep slope and gentle slope, and two types of mixed patterns of mixed plantations with two tree species and mixed plantations with three or more than three tree species. The species composition, diameter at breast height (DBH), tree height, damage rate of individual trees and soil physical properties in the plots were investigated, the characteristics of the extreme drought climate occurred in southern China in 2022, the stand damage rate at various slopes, the composition of damaged trees, and the influencing factors were analyzed. Result: Slope had a greater effect on soil aggregates, while the mixed type of plantations had no effect on soil aggregates. The mixed type had a significant effect on surface (0–20 cm) soil porosity, soil bulk density, maximum water holding capacity, capillary water holding capacity and minimum water holding capacity, and the effect decreased with the increase of soil depth. Different slopes had no significant effect on above these indexes. The drought resulted in varying degrees of damage to trees, with an average damage rate of 29.18%. Among them, mild damage accounted for 15.46%, moderate damage for 2.42%, and severe damage for 11.3%. The severely damaged trees mainly consisted of dominant species in the canopy and understory regeneration layers, with broadleaf trees being more severely impacted than coniferous trees, and planted species more affected than natural regenerating species. Slope gradient and position had the greatest impact on tree damage rates, along with factors such as stand density, soil bulk density, soil aggregate stability index (SASI), elevation, total porosity of the 20 cm soil layer, maximum water holding capacity of soil, and capillary water holding capacity. Conclusion: The extreme drought occurred in southern China in 2022 has demonstrated the characteristics of altered precipitation patterns under global climate change. The mixed plantations with multiple advantageous species are beneficial for improving the drought resistance of forests. Steep slopes and uphill areas are more susceptible to drought, and the impact of drought on forests is the result of multiple factors interacting. In future management of subtropical forests, priority should be given to constructing mixed forests with multiple tree species, determining reasonable stand density, and strengthening surface soil management.

Key words: precipitation pattern, stand structure, soil physical properties, damage to trees, mixed forest