Stand Development Stages Reshape Climate-Structure Interactions in Boreal Forest Productivity: A Case Study of China's Cold-Temperate Conifers

The Da Xing'an Mountains region is the only area of cold–temperate coniferous forests in China and functions as an essential ecological barrier. It has a crucial purpose in forest ecosystems and carbon sequestration processes. Stand age is influenced by interactions among population dynamics, mechanisms of disturbance, and forest management approaches, significantly influencing the global carbon cycle. Growth data indicate that forest development is correlated with variations in productivity. Nonetheless, the variability in production throughout several phases of stand development remains largely unexamined, and the influence of contributing elements in this process is still ambiguous. Utilizing the 2005–2010 National Forest Continuous Inventory (NFCI) data from the eastern Da Xing'an Mountains, we examined the influence of stand characteristics, structural diversity, and environmental variables on forest productivity throughout various developmental stages, from young to overaged forests. The findings indicate that (1) forest productivity is collectively limited by stand characteristics, structural diversity, and environmental factors, with stand factors exerting the greatest influence, especially through direct effects. (2) As tree growth stages advance, the impacts of structural variety (ranging from 8.68 to 16.44) and soil (ranging from 8.80 to 10.30) on forest productivity intensify. (3) Altered tree growth stages decrease the influence of climate (from 30.40 to 17.67) and terrain (from 14.55 to 6.28) on forest productivity. By thoroughly integrating the determinants of forest production, our study provides essential system–level insights that establish a theoretical basis for forecasting alterations in forest productivity amid global change. These findings enhance the formulation of more efficacious forest management methods to address the difficulties posed by climate change and biodiversity decline.