Changes of vegetation community characteristics of Acacia mangium plantation under natural restoration

【Objective】 To explore the changes in vegetation community characteristics of the Acacia mangium plantation under natural restoration，which could provide theoretical basis for promoting the transformation of A. mangium plantation into the natural forest in Hainan Island Ecological Public Welfare Forest and Hainan Tropical Rainforest National Park. 【Method】 Using the method of space instead of time，A. mangium plantations with different natural restoration times （10，15 and 20 years）were selected as the research objects in the Fengmu Experimental Forest Farm of Hainan，and the natural secondary forest with good natural restoration was used as the control. The vegetation of the tree layer，shrub layer and herb layer was investigated，and the stand structure，growth status，species composition and species diversity characteristics of A. mangium plantations with different natural restoration times and their differences with natural secondary forests were analyzed. 【Result】 In A. mangium plantation，with the increase of natural restoration time，the density of A. mangium decreased gradually，and the canopy density decreased gradually. There was no significant difference in tree regeneration layer density，shrub layer density，average height of shrub layer，and average height of herb layer between A. mangium plantation and natural secondary forest after 20 years of natural restoration（P>0.05，the same below），while the average height of tree regeneration layer and coverage of herb layer were significantly lower than those of natural secondary forest（P<0.05，the same below）. The diameter distribution of the tree regeneration layer of A.mangium plantation with different natural restoration times conformed to the Weibull distribution，and its shape parameter c was less than 1， which was an inverted J-type distribution. The scale parameter b gradually approached the natural secondary forest tree layer with increased natural restoration time. With the increase in natural restoration time，the number of species in A. mangium plantation community increased，and the composition of dominant species in each forest layer changed greatly. Principal coordinate analysis（PCoA）results showed that the species composition of the tree layer and shrub layer gradually evolved into a natural secondary forest. With the increased natural restoration time，the Patrick index and Shannon in‐ dex of the tree layer of the A. mangium plantation increased gradually，while the Simpson index and Pielou index changed slightly. However，the species diversity index of A. mangium plantation tree layer after 20 years of natural restoration was still significantly lower than that of natural secondary forest. With the increase in natural restoration time，the diversity in‐ dex within the shrub layer of A.mangium plantation first increased and then decreased，while that within the herb layer first decreased and then increased. There was no significant difference in the Shannon index，Simpson index and Pielou in‐ dex in shrub layer and herb layer between the A. mangium plantation with natural restoration for 10 years and 20 years and natural secondary forest，but patrick index was significantly lower than natural secondary forest. 【Conclusion】 The stand structure，species composition，and species diversity of A. mangium plantation under natural restoration are gradually ap‐ proaching to those of natural secondary forest，but there is still a certain gap. With the increase in natural restoration time， the stand structure of A. mangium plantation becomes more diverse and complex，and the community has the potential for natural regeneration and positive succession.