Abstract: The root-to-shoot (R/S) ratio is a critical indicator of the balance between root biomass and shoot biomass, representing the ecological strategies and adaptive responses of plants to environmental conditions. However, the patterns of change in community R/S ratios during forest succession and their response to moisture levels across broad geographic gradients remains unclear. Based on forest biomass data from a national field inventory of 5,825 plots conducted across China between 2011 and 2015, this study looked into allocating biomass shoots and roots at the early, middle, and late stages of growth in plantations and succession in natural forests, and evaluated how moisture availability influences this allocation. The results revealed a significant decline in R/S ratios from early to late stages for both plantations and natural forests. Shoot and root biomass in plantations grew isometrically during the early and middle succession stages but shifted to allometric growth in the late stage, with the slope of the log-transformed shoot–root biomass relationship differing significantly across growth stages. Natural forests, in contrast, maintained isometric growth across successional stages, showing no significant variation in the slope of the log-transformed shoot–root biomass relationship. Environmental factors, particularly moisture levels, strongly influenced R/S ratios. Moisture levels significantly affected size-corrected R/S ratios, particularly in the middle stage of plantations and the early and middle stages of natural forests, supporting the hypothesis of optimal allocation. These findings suggest that in water-limited regions, forest management should prioritize drought-tolerant, deep-rooted native species, encourage mixed-species planting in the early stage, and reduce logging intensity in mature plantations. Conserving natural forests to maintain successional dynamics is essential for long-term ecological resilience. These findings emphasize the importance of balancing productivity with ecological sustainability by adapting practices to specific environments and forest types under climate change.

Key words: Root-to-shoot ratios, Biomass allocation, Forest type, Community stage, Moisture levels, Allometric scaling