[Community stability for spruce-fir forest at different succession stages in Changbai Mountains, Northeast China].

Based on the analysis of three forest communities (polar-birch secondary forest, spruce-fir mixed forest, spruce-fir near pristine forest) in Changbai Mountains, a total of 22 factors of 5 indices, including the population regeneration, soil fertility (soil moisture and soli nutrient), woodland productivity and species diversity that reflected community characteristics were used to evaluate the stability of forest community succession at different stages by calculating subordinate function values of a model based on fuzzy mathematics. The results that the indices of population regeneration, soli nutrient, woodland productivity and species diversity were the highest in the spruce-fir mixed forest, and the indices of soil moisture were the highest in the spruce-fir near-pristine forest. The stability of three forest communities was in order of natural spruce-fir mixed forest > spruce-fir near pristine forest > polar-birch secondary forest.

[Spatial heterogeneity of natural regeneration in a spruce-fir mixed broadleaf-conifer forest in Changbai Mountains].

Based on fieldwork on a plot of 60 m x 60 m in the Changbai Mountain area of Northeast China in August 2012, the spatial distribution pattern and heterogeneity of natural regeneration in the spruce-fir mixed broadleaf-conifer forest were analyzed using semi-variograms, fractal dimensions and Kriging interpolation methods. The results showed that Abies nephrolepis and Acer mono were the most common regeneration species, accounting for 87.4% of the total. The regeneration seedlings and saplings presented an aggregate distribution pattern with the biggest radius of 9.93 m. Distinct spatial autocorrelation existed among regeneration seedlings and saplings, with 88.7% of variation coming from structure factors (biological and ecological properties and environmental heterogeneity) and 11.3% from random factors. The spatial distribution of the regeneration seedlings and saplings presented anisotropy, with the smallest fractal dimension and strongest spatial heterogeneity from north to south, and the highest fractal dimension and weakest spatial heterogeneity from northeast to southwest. The spatial heterogeneity of heights of seedlings and saplings was greater than that of root collar diameters. The distance of spatial autocorrelation for tree root collar diameters was 29.97 m, and that for heights was 31.86 m. Random factors and structure factors were found to contribute equally to the spatial heterogeneity.

[Relationships between coefficient of variation of diameter and height and competition index of main coniferous trees in Changbai Mountains].

A total of 1139 trees from 8 clear-cut stands dominated by fir, spruce, and pine in the Changbai Mountains were selected to study the relationships between the coefficient of variation of diameter and height and the competition index of the three main coniferous tree species in the Mountains. For the test tree species, the variation of height vs. diameter class was relatively small, while the variations of diameter and height vs. age class were larger, with the largest coefficient of variation of diameter vs. age class. The traditional height-diameter models could better reflect the real growth of trees, whereas the diameter-age or height-age models were not good enough. Competition was the main factor inducing the variations of tree diameter and height, suggesting that incorporating the competition index to the traditional models of tree growth and height could improve the model accuracy significantly.