关键词: 乔木层, 群落结构, 天目山, 常绿落叶阔叶混交林, 动态变化

Abstract: [Objective] Using long-term exploration of community dynamics (ranging from 1996 to 2012), this study was aimed to provide scientific support for forest protection, management and operation in Tianmu Mountain. [Method] In 1996, a field site with the size of 1hm² locating in evergreen and deciduous broad-leaved mixed forest of Tianmu Mountain, a national nature reserve in Zhejiang province was built, and then each tree in the site was numbered, labeled and recorded it's species name, height, diameter at breast height (DBH), location and other information. In 2012, the above data was determined again to compare the community dynamics of the trees with the DBH more than 10 cm during the past 16 years. [Result] The results showed that in 1996, the evergreen broad-leaved trees and deciduous broad-leaved trees accounted for 54.97% and 45.03% of the total number of trees, respectively, while in 2012, the ratios changed to 62.81% and 37.19% respectively. The community structure changed from 40 species, 34 genera and 24 families in 1996 to 48 species, 40 genera and 29 families in 2012. During the 16 years, there were 14 species emerged which are belonging to 11 genera and 8 families and 6 species disappeared which are belonging to 5 genera and 3 families. Among them, 66.67% of the disappeared species were accidental species (defined as the total number of individuals varying from 1 to 3),while in new emergent species, 92.86% of which were accidental species.. The total number of trees increased from 553 in 1996 to 597 in 2012, of which the dead was 191 and the regeneration was 235. The richness index, Simpson diversity index, Shannon-Wiener index and Pielou evenness index were changed from 40, 0.72, 3.98, and 1.03 in 1996, respectively to 48, 0.88, 3.88, and 1.05 in 2012, respectively. The small DBH class (DBH<20 cm) trees were accounted for 49.55% and 55.11% in 1996 and 2012, respectively and the mortality ratio was 25.73%; the medium DBH class (20 cm≤DBH < 60 cm) trees were 47.92% and 42.88%, respectively and the mortality ratio was 22.89%; while the large DBH class(>60 cm) trees were 2.53% and 2.01%, respectively and the mortality ratio was 7.69%; In general, the DBH class varied little and all are with the reverse "J"-shaped structure. The mean tree height decreased from 11.47 m in 1996 to 9.47 m in 2012, and the percentage of higher trees (>10 m) was decreased from 50.27% to 36.01% with the normal distribution.[Conclusion] The community remains its appearance of evergreen and deciduous broad-leaved mixed forest during the 16 years, but the number of evergreen trees tended to increase significantly, and that of deciduous trees tended to decrease remarkably. Except of the significant increase in the number and importance values of Daphniphyllum macropodum there were no obvious changes in other trees. However, the number of accidental species changed a lot, accounting for 50% of the changes. Accidental species were the main causes of the community dynamics, and contributed to the increase of richness index and Simpson diversity index. Further, there were high competition and mortality rates in medium and small DBH class trees.

Key words: arborous layer, community structure, Tianmu Mountain, mixed evergreen and deciduous broad-leaved forest, community dynamics