Habitat fragmentation is widely recognized as a leading threat to biodiversity. Understanding the long-term habitat fragmentation influences species composition and plant mortality is necessary for biodiversity conservation. We established forest dynamics plots (FDPs) on 29 land-bridge islands in the Thousand Island Lake formed in 1959 due to dam construction in East China. These islands are covered with secondary Masson pine (Pinus massoniana) forests regenerated after the dam construction. We conducted two community censuses in these FDPs in 2009-2010 and 2014-2015. In each census, all woody plants with diameter at breast height (DBH) ≥ 1 cm were tagged, measured, identified and georeferenced. In this study, we divided the 29 islands into small island (<1 ha; 20 islands), mediate island (1-10 ha; 6 islands) and large island (>10 ha; 3 islands) to estimate area effects on the dynamics of community composition and mortality. We also set 20 m × 20 m independent plots on the edge and interior of the islands, to estimate the edge effects on mortality rate on the islands.
We recorded 186,781 stems belonging to 76 woody plant species in the 2009-2010 census. During the following five years, 33,125 stems (17.73%) and two species were lost. We found the annual tree mortality rate was positively correlated with stem density (P<0.01), and they were both positively correlated with island size on small and mediate islands. The turnover rate of community composition (i.e., the change in species composition with abundance weighted) also increased with island area. Specifically, we also found that although the annual morality of shade-tolerant and shade-intolerant species both increased with island area, shade-tolerant species showed lower annual morality than shade-intolerant species. Further, the tree annual mortality in interior habitat was higher than in edge habitat. Overall, we conclude that patch area and edge effect influence woody plant species composition and mortality in the study fragmented landscape.