Regeneration characteristics and influencing factors of woody plant on natural evergreen secondary broad-leaved forests in the subtropical, China

Abstract

Natural regeneration occupies an important position in forest ecosystems and is affected by various factors. Exploring natural regeneration and its influencing factors is helpful to understand the forest community dynamic. Evergreen broad-leaved forest is an essential zonal vegetation type in China. However, the natural regeneration of evergreen broad-leaved forests in the northernmost margin of subtropical zone has not been reported. Here we investigated 22 observed variables, and selected four categories of latent variables stand factor, topographical factor, soil factor and tree diversity as influential factors based on the survey data of 50 (20 m × 20 m) permanent sample plots. The structural equation model was introduced to distinguish the direct, indirect and total effect of influencing factors on understory woody plant regeneration diversity and regeneration density, respectively. We found 51 regeneration species under 31 families and five dominant species Loropetalum chinense, Symplocos sumuntia, Quercus glauca, Ilex chinensis, and Eurya japonica in the study area. Soil factor was the primary control of regeneration, which had the greatest and negative total effect on regeneration diversity (-0.436) and regeneration density (-0.298). The main soil factors that affected regeneration diversity and regeneration density were total phosphorus and soil organic matter, respectively. Soil factor mainly affected indirectly regeneration by mediating through its impacts on tree diversity. Tree diversity and topographical factor all were significantly positively correlated with the regeneration diversity and regeneration density. Stand factor had a significantly negative correlation with regeneration density but a significantly positive with regeneration diversity. Our study provides the basis to introduce appropriate artificial auxiliary measures for improving the natural regeneration of forest stands, so as to promote sustainable forest management.