Spatial structure dynamics of karst evergreen and deciduous broad-leaved forest in Mulun National Nature Reserve

Abstract

The spatial structure evolution of forests in karst areas is a key scientific issue in global forest research. In order to explore the dynamics of spatial structure in karst evergreen and deciduous broad-leaved forests, a study was conducted in Mulun National Nature Reserve, focusing on a fixed monitoring plot of 2 hm2. Based on data from three surveys conducted in 2007, 2012, and 2017, the dynamics of community spatial structure were analyzed using the spatial structure parameters, i. e., angular scale (Wi), mixing degree (Mi), and size ratio (Ui). The results were as follows: (1) The univariate distribution results of spatial structure parameters revealed that the forest structure gradually shifted towards a slightly clumped distribution state as the stand age increased between 2007 and 2017. The mixing degree was at a level of strong mixing and showed a tendency towards extreme mixing. In terms of the size ratio, the stand exhibited a moderate state, shifting towards subdominance as the stand grew. (2) The study of spatial structure for different diameter classes of trees showed that the anglular scale, size ratio, and mixing degree of trees in diameter classes 1-15 cm gradually increased with stand growth. As the diameter class increased, the values of the size ratio showed a decreasing trend while the mixing degree showed an increasing trend. (3) The study of spatial structure for dominant tree species revealed that, during the period from 2007 to 2017, all five dominant tree species groups exhibited a slightly clumped distribution. The size ratio showed a tendency towards subdominance and a moderate distribution state, while the mixing level was at a high degree and gradually shifted towards extreme mixing. In conclusion, the karst evergreen and deciduous broad-leaved forest in Mulun currently exhibits a slightly clumped distribution, a strong degree of mixing, and a tendency towards subdominance. The community is relatively stable, the stand regeneration is in good condition, and the forest is gradually transitioning towards a climax community. The analysis of the dynamic changes in vegetation structure in karst evergreen and deciduous broad-leaved forests is of great significance for predicting the future development and changes of forests.

Keywords

• angular scale (wi)
• mixing degree (mi)
• size ratio (ui)
• structural characteristics
• dynamic change