An Integrated Naturalness To Diagnose The Forest Restoration in China's Lesser Khingan Mountains

Abstract

The assessment of forest naturalness is emerging as a global issue. However, a simple, precise, and cost-effective approach is lacking, which poses an obstacle to diagnosing degraded forest restoration.We utilized Forest Inventory data (FID) under three disturbance intensities, totalling 32,690 ha and 1282 forest stands in China’s Lesser Khingan Mountains (LKM), combined with 21 sample stands survey data to assess the naturalness. Principal component analysis (PCA) was performed on four variables: stand age, stand hectare storage, stand mean height, and calculated climax adaptation index (CAI). The first principal component (PC1) was selected as naturalness. We tested the difference in naturalness among restoration stages, among disturbance intensities, and among disturbance difficulties. We ran structural equation models to test the changes in CSR strategies and plant species richness during forest restoration. PCA can reduce the four variables to one dimension as an integrated naturalness (PC1 Proportion Var = 0.74). The naturalness increased significantly with forest restoration (p < 0.05). As disturbance intensity decreased and disturbance difficulty increased, the proportion of late-restoration forests increased, and naturalness increased significantly (p < 0.05). Higher naturalness meant higher stress-tolerant (S) and lower ruderal (R) components and was more conducive to increasing plant species richness.Our method for evaluating naturalness is simple and valid. While this method directly applies to the Korean pine forest range in northeast China, it should be easily extendable to the rest of China and other countries where FID is accessible. Increasing the proportion of natural tree species and late-successional species, raising stand age, reducing the disturbance intensity, and strengthening the protection of areas prone to disturbance will benefit the restoration of degraded forests.

Keywords: CSR strategy, degraded forest, forest restoration, naturalness, primary Korean pine forest, richness