Seasonal differentiation in density‐dependent seedling survival in a tropical rain forest

Abstract

ummary 1. Density-dependent survival is prevalent in tropical forests and is recognized as a potentially important mechanism for maintaining tree species diversity. However, there is little knowledge of how density dependence changes in fluctuating environments. 2. Across the 20-ha Xishuangbanna tropical seasonal rain forest dynamics plot in southwest China, which has distinct dry and wet seasons, we monitored seedling survival in 453 1-m 2 quadrats over 2 years. Density dependence was assessed using generalized linear mixed models with crossed random effects.3. When pooling all species at the community level, there were strong negative effects of conspecific tree neighbours on seedling survival over the dry-season, wet-season and 2-year intervals. The proportion of conspecific seedling neighbours had a significant negative effect in the dry season, but not in the wet season. 4. At the species level, the effects of conspecific tree and seedling neighbours varied widely among species in the community and were significantly positively related to population basal area in the community over the dry-season interval. In contrast, over the wet-season interval, the effects of conspecific tree and seedling neighbours did not significantly vary among species in the community.Overall community-and species-level results suggest that local-scale negative density dependence (NDD) tends to be stronger in the dry than wet season in the Xishuangbanna tropical forest. 5. At the scale of the 20-ha plot, we found a community compensatory trend (CCT), in which rare species had relatively higher seedling survival than common species in both the wet and dry seasons. A positive association between potential NDD and population basal area suggests that the CCT results from local-scale NDD, specifically because of negative effects of conspecific tree neighbours. 6. Synthesis. Our results demonstrate that the strength of density-dependent seedling survival can vary between seasons and among species in tropical forests. Future research is needed to assess the underlying mechanisms of this temporal and interspecific variation in NDD and its consequences for species coexistence and community composition.

Measuring the demographic impact of conspecific negative density dependence

“…Kobe and Vriesendorp (2011) and Lin et al (2012) quantify 'potential NDD' for each species by multiplying CNDD strength by the maximum conspecific density at which seedlings of a species were observed in the field. This index is proportional to the maximum potential demographic impact of CNDD on a population, but may not be a strong measure of the actual demographic impact if a species exhibits variation in local conspecific density.…”

Variant responses of tree seedling to seasonal drought stress along an elevational transect in tropical montane forests

“…Prior to the end of rainy season, in a number of tree species’ seeds were found to be dispersed, germinated and established, probably in order to achieve maximum seedling survival in rainy season, and avoid potentially high mortality caused by drought stress in the dry season4344. This may lead to a rapid increase in both seedling species richness and abundance in rainy season and a decrease in dry season4546. However, species richness at high elevations did not show significant difference between the two seasons, suggesting that the seasonality does not notably affect the species composition of seedlings (Fig.…”

How does habitat filtering affect the detection of conspecific and phylogenetic density dependence?

“…Previous studies suggest that this should be sufficient to account for autocorrelation 272 , Chen et al 2010). Furthermore, we included species identity as a random 273 effect, because seedlings of different species were expected to respond differently to local 274 neighborhood variables (Lin et al 2012). 275…”

“…However, tropical forest investigations 54 that have partitioned their analyses into conspecific and heterospecific effects have often found 55 significant differences in intra-and inter-specific effects (e.g., Peters Lin et al 2012). This has supported the widespread view that seedling 57 performance is limited more by interactions with conspecific individuals than heterospecific 58 individuals.…”