Study on the Stability of Forest Communities Based on the Spatial Structure Index

This study was carried out in three forest communities (polar-birch secondary forest, spruce-fir mixed forest and spruce-fir near pristine forest). Based on the Cobb-Douglas production function theory in microeconomics, the production function of the spatial structure of the forests was constructed with three commonly used stand spatial structure indices (mingling degree, neighborhood comparison, and uniform angle index) as inputs and the forest spatial structure as output. The forest spatial structure index (FSSI) was defined and the forest spatial structure distance (FSSD) was calculated. To evaluate the stability of each successional stage, the 5 indices were analyzed and the spatial structure characteristics of the forest communities in different successional stages were compared. Results indicated that the mingling degree of forest communities in different successional stages was diverse. The average mingling degree was highest for the spruce-fir near pristine forest (0.81), followed by that of the spruce-fir mixed forest, and lastly that of the polar-birch secondary forest. Neighborhood comparison had little effect on the spatial structure of the forest communities in different successional stages, and values ranged from 0.49-0.52. Horizontal distribution of the three forest communities indicated random distribution for spruce-fir mixed forest and spruce-fir near pristine forest and aggregated distribution for polar-birch secondary forest. The spatial structure index size and degree of closeness to the ideal structure was in the order spruce-fir near pristine forest >spruce-fir mixed forest >polar-birch secondary forest. Thus, both the spatial structure and stability of the spruce-fir near pristine forest were the best.