Dynamics Of Community Structure And Regeneration Characteristics Of Major Populations In An Evergreen Broad-leaved Forest In Gutianshan National Natural Reserve,East China

The evergreen broad-leaved forest is one of the typical vegetation types in China. To explore the dynamics of community structure and regeneration characteristics of major populations in an evergreen broad-leaved forest in Gutianshan National Nature Reserve, a5-ha dynamic plot was established in2002. All woody plants with DBH (diameter at breast height)≥1cm were tagged, mapped, measured and identified to species. Based on data from one census each in2002and2007, we analyzed species composition, DBH size distribution, the characteristics of dead and recruited individuals to estimate mortality and recruitment rates, and population size changes for43tree species. The results showed the following:(1) The species richness of all woody plants in the plot increased from136to143, and the number of individuals also increased from13,338to16,812, with a26.05%growth rate. A total of4,758stems were recruited and1,384died during the five years. The number of recruits within three growth forms (tree, subtree or shrub, and subshrub) all declined as DBH size class increased; a pattern different from that observed in dead individuals. Castanopsis eyrei, Schima superba, Pinus massoniana and Camellia fraterna are the dominant species, among which Castanopsis eyrei and Camellia fraterna regenerated well.(2) The annual mortality and recruitment rate of all woody plants was2.02%and6.65%, respectively. The average annual mortality and recruitment rate of43tree species was2.26%and5.90%, respectively. Comparing mortality and recruitment rates in each DBH class, we found that19subtree or shrub species consistently had higher recruitment than mortality rates in small DBH classes (1cm≤DBH<2.5cm), and almost no difference in both middle (2.5cm≤BH<5cm) and large (DBH≥5cm) DBH classes.31out of43species showed population growth, while12species’ populations declined slightly. Populations of10species increased or decreased at an annual rate of>5%, indicating that they were experiencing fast turnover. Among these, Chimonanthus salicifolius (45.13%) and Itea oblonga (16.35%) had the highest rate of growth in population size, whereas Loropetalum chinense (-3.10%) and Quercus serrata var. brevipetiolata (-1.86%) had the highest rate of decline.(3)The Shannon-Wiener index decreased from3.722to3.712, and the Pielou index declined from0.758to0.748, while the Simpson index rose from0.039to0.041, showing that both community evenness and species diversity had a slight decline, and dominant species reached a slightly higher dominant level. The slight fluctuation of these indexes suggested that there was no severe change in species diversity and species composition. The similarity index of community in2002and2007was0.869, indicating a high similarity during5years.(4) The DBH size distributions of all woody plants in2002and2007both showed a reversed J type; most stems are of small DBH size (1cm≤BH<10cm), indicating that the community was growing. Wilcoxon signed-rank test showed that there was no significant difference in DBH size distribution of community between2002and2007.(5)The mortality rate of Castanopsis fargesii was the highest and that of Pinus massoniana was the lowest among the43tree species. The recruitment rate of Chimonanthus salicifolius was the highest and that of Quercus serrata var. brevipetiolata was the lowest among the43tree species. Sciophytes had the highest recruitment rate, while heliophytes had the lowest rate, which suggests that there were few forest gaps in the plot. In conclusion, both recruitment and mortality rates varied among species and among DBH size classes, pointing to the unique regeneration dynamics of the43tree species. These differences might be associated with patterns of density dependence in addition to habitat fluctuations.(6) The analysis of the DBH size distribution of8dominant species showed that, the population structures of Schima superba. Pinus massoniana. Daphniphyllum oldhamii, Loropetalum chinensis. Rhododendron ovatum showed almost no change during5years, while that of Camellia fraterna, Eurya muricata, Castanopsis eyrei changed significantly due to a large number of recruits in the small DBH size class. Population structures of Castanopsis eyrei. Daphniphyllum oldhamii, Rhododendron ovatum, Loropetalum chinensis were stationary, while those of Camellia fraterna and Eurya muricata were growing, that of Schima superba was mature but tended to be in a temporary decline, and that of Pinus massoniana was in decline overall.(7) The Kruskal-Wallis rank sum test and Wilcoxon signed-rank test indicated that both recruitment rate and number of recruits significantly differed among species of different lifeforms. Other traits, however,(life cycle, leaf size, light tolerance, fruit size, fruit type) had no significant effect on the difference of mortality rate, recruitment rate, number of dead individuals and recruits.