干热河谷次生稀树灌木林物种组成变化及群落结构动态 postprint

Abstract: In order to reveal dynamics of community succession of a secondary savanna shrub forest of the arid-hot valley in National Nature Reserve of Cycas panzhihuaensis, this study was based on the first (2020) reexamined data of 1 hm2 permanent fixed plot which was established in 2015. Community dynamics over the past 5 years were analyzed by species composition, community diversity, importance value, mortality rate, recruitment rate and diameter at breast height (DBH). The results were as follows: (1) Woody plants in community changed from 15 families, 17 genera, and 17 species in 2015 to 15 families, 18 genera, and 18 species in 2020. There was no significant change for dominant species composition but a significant change for degree of dominance in the past 5 years. For the 6 common populations with higher important values (>1) in 2020, the importance values of 5 populations increased, and the population of Cycas panzhihuaensis decreased only, when compared with their importance values in 2015. Cycas panzhihuaensis was still the most dominant species and constructive species in the plot, but its importance values declined significantly. However, a significant increase of importance values occurred for some arbor species such as Quercus cocciferoides and Terminalia franchetii. (2) The number of woody plants with DBH≥1 had increased to 1710 by 2020, the average DBH of all woody plant individuals in this community increased from 11.10 cm to 11.17 cm. The average annual mortality was 0.29%, and the average annual recruitment rate was 2.75%, the average DBH of dead and recruited individuals were 11.84 cm and 4.96 cm respectively. Compared with the woody plants living in 2015, individual trees from 7 species had died, and those from 9 species were recruited over the past 5 years. (3) The results also indicated that although Osyris quadripartita declined, the populations of 9 tree species increased, and 4 were stable from 2015 to 2020. The average DBH of Cycas panzhihuaensis and Osyris quadripartita decreased only, but the others increased on different extents. With forest succession, the importance of interspecific competition within community will increase gradually. Dominant position in community will be occupied by arbor tree species such as Quercus cocciferoides and Terminalia franchetii during process of succession in the future, but dominant position of Cycas panzhihuaensis is not threatened in a short term. The main reason of significant decrease of dominance of Cycas panzhihuaensis is plant individuals death of larger diameter class. In the future, a transitional-type secondary community from secondary savanna shrub forest to climax which is occupied by arbor tree species gradually will been consisted of Cycas panzhihuaensis, Quercus cocciferoides, Terminalia franchetii and other arbor trees.