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The influence of changes in water availability on seedling mortality of a subtropical evergreen broadleaf forest on Ailao Mountain
Author(s): 
Pages: 2521-2528
Year: Issue:  8
Journal: Acta Ecologica Sinica

Keyword:  droughtseedling dynamicssoil mass water contentrainfallwood density;
Abstract: In order to understand the influence of changes in water availability on the seedling dynamics of subtropical forests and the relationship between wood density and seedling mortality during a prolonged drought period,we studied seedling mortality patterns across all species and of 5 common tree species from an evergreen broadleaf forest on Ailao Mountain,southwest( SW) China from 2005 to 2011. The five tree species studied were Machilus bombycina,Neolitsea polycarpa,Symplocos ramosissima,Neolitsea chuii,and Illicium macranthum. The relationships between seedling mortality and rainy days,rainfall,soil water mass content(0—20 cm) during the dry season,and wood density were also analyzed.Our results showed that 1) Seedling mortality was negatively correlated with number of rainy days in the dry season and dryseason soil water mass content,but not with total dry season rainfall; 2) The seedling mortalities of all species as a whole and of each of the 5 species studied reached a historical maximum in the 2010 SW China extreme drought,which were 2 to10 times more intense than for 2009( Machilus bombycina and Symplocos ramosissima had the highest seedling mortalities while Illicium macranthum had the lowest in 2010); 3) Across species,the seedling mortality in the 2010 drought was positively correlated with species-specific wood densities; species with higher wood densities had higher seedling mortalities. Previous studies have shown that trees in this forest did not experience severe drought stress during the 2010 SW China drought. However,the present study suggests that the seedlings were severely influenced by the rainfall anomaly during the 2010 dry season,probably owing to their shallow rooting depths and consequently high sensitivities to changes in rainfall. Additionally,because of the lower seedling mortalities in lower wood density species,the potential increase in drought frequency and severity in the future may increase the relative abundance of low wood density species,which may potentially lead to changes in forest species composition.
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