Habitat heterogeneity and biotic interactions mediate climate influences on seedling survival in a temperate forest

Abstract

Seedling stage has long been recognized as the bottleneck of forest regeneration, and the biotic and abiotic processes that dominate at seedling stage largely affect the dynamics of forest. Seedlings might be particularly vulnerable to climate stress, so elucidating the role of interannual climate variation in fostering community dynamics is crucial to understanding the response of forest to climate change. Using seedling survival data of 69 woody species collected for five consecutive years from a 25-ha permanent plot in a temperate deciduous forest, we identified the effects of biotic interactions and habitat factors on seedling survival, and examined how those effects changed over time. We found that interannual climate variations, followed by biotic interactions and habitat conditions, were the most significant predictors of seedling survival. Understory light showed a positive impact on seedling mortality, and seedling survival responded differently to soil and air temperature. Effects of conspecific neighbor density were significantly strengthened with the increase of maximum air temperature and vapor pressure deficits in the growing season, but were weakened by increased maximum soil temperature and precipitation in the non-growing season. Surprisingly, seedling survival was strongly correlated with interannual climate variability at all life stages, and the strength of the correlation increased with seedling age. In addition, the importance of biotic and abiotic factors on seedling survival differed significantly among species-trait groups. Thus, the neighborhood-mediated effects on mortality might be significantly contributing or even inverting the direct effects of varying abiotic conditions on seedling survival, and density-dependent effects could not be the only important factor influencing seedling survival at an early stage.