Composition of basal area in natural forests based on the uniform angle index

Abstract This study presents an analysis of the small scale spatial patterns in natural forest plots in different parts of China. The focus of the analysis is to assess the spatial characteristics of different natural forests at a high level of resolution. The results may provide a theoretical basis for nature-approximating forest management practices in plantations established with a regular arrangement of planting points. Method Using a new measure for describing small scale forest structures, known as the Uniform Angle Index, it was possible to identify local structure units as even, random, or clustered. We analysed 11 selected natural forest plots with mapped trees with a wide geographical distribution in different regions of China. In each plot, with a known basal area density, the proportion of the total basal area was assessed that can be assigned to local structure units with specific patterns. Specifically, the basal area of each tree, and the associated local spatial pattern in the vicinity of that tree, provided the information about the distribution of local spatial patterns in the 11 natural forests. Results (1) Most trees were distributed in neighbourhoods with a random structure, regardless of whether the entire forest pattern was classified as even, random, or clustered. Less than half of the tree neighbourhoods were either clustered or evenly structured. (2) More than 50% of the basal area of the reference trees consisted of random units in all 11 natural forests. (3) Similarly, the basal areas of the random structure units occupied more than half of the total basal area. Conclusions Our findings suggest that the major part of the basal area natural forests consists of random structure units. This observation may be helpful in the design of planting patterns or harvesting schedules to improve the stability of planted monocultures.