Impacts of stand structure characteristics of three forest types on the internal environment and carbon sink functions of forests

This study aims to explore how different forest types (broadleaf forest, mixed coniferous and broadleaf forest, and Chinese fir forest) in natural forests without human interference (mountain closure and forest cultivation) affect their comprehensive environmental functions (including microclimate regulation and air purification) and carbon sink functions. We selected 14 sample plots in western Zhejiang and obtained indicators of forest stand structure, carbon sink functions (including vegetation carbon stock, soil carbon stock, and annual forest vegetation carbon sink), and internal environmental factors (including temperature, humidity, PM_2.5, PM₁₀, and CO₂). The results indicate that different forest types influence the stability of the internal environment (e.g., CO₂ fluctuations within the stand, stability of airborne particulate matter retention) through differences in stand structure. Tree height is a core regulator of temperature and humidity (cooling and humidifying effect) and is also involved in carbon storage accumulation. Canopy closure exerts a bidirectional effect: it optimizes photosynthetic carbon sink capacity through enhanced CO₂ assimilation, but simultaneously exacerbates particulate matter retention by suppressing turbulent exchange. Additionally, the leaf area index (LAI) contributes to driving carbon sinks (positively correlated with the annual carbon sink of plants). The results of this study offer valuable insights into the identification of key forest structural characteristics associated with air pollution mitigation and microclimate regulation. The study confirms that under mountain closure and forest conservation policies, forests can naturally optimize environmental functions and carbon sequestration through structural differentiation, highlighting the synergistic relationship between structure and function for ecological conservation.