Biotic vs abiotic drivers of seedling persistence in a tropical karst forest

QuestionQuantifying the duration and drivers of seedling persistence is critical for understanding seedling dynamics and species co-existence in plant communities. In this study, we incorporated data from multiple seedling censuses to characterize patterns of seedling persistence in a tropical karst forest. Specifically, we evaluated the effects of density dependence, habitat heterogeneity and recruitment timing on seedling persistence. LocationA tropical karst forest in Taiwan. MethodsUsing data from 144 seedling plots censused every 3mo from 2007 to 2012, we examined persistence times of 6399 seedlings of 36 species. Seedling survival was estimated by the Kaplan-Meier method. Mixed effects Cox models were used to identify significant biotic (i.e. initial height, conspecific and heterospecific seedling and adult densities) and abiotic (i.e. mean elevation, convexity, slope, effective soil depth and recruitment time) drivers of seedling persistence at the community, guild and species levels. ResultsAt the community level, newly recruited seedlings had a median survival time of 6mo. Median survival time was higher for seedlings in the shade-tolerant guild compared to seedlings in the shade-intolerant guild (9 vs 3mo). When all species were analysed together, seedling persistence significantly increased with increasing initial size and soil depth and significantly decreased with increasing density of conspecific and heterospecific seedling neighbours. Drivers of seedling persistence tended to be guild and species specific, however negative effects of conspecific seedling neighbours were consistently detected in all models, indicating strong and pervasive conspecific negative density dependence. Significant effects of recruitment time, soil depth and convexity were revealed by guild- and species-specific models, suggesting abiotic niche differences. ConclusionsThis study highlights the importance of multiple ecological processes for seedling persistence. Both abiotic and biotic factors may play an important role in species co-existence in this forest via niche partitioning and negative density dependence. Among these factors, negative conspecific density dependence had the strongest and most consistent effect. In addition, soil depth played a key role in shaping seedling regeneration, likely through effects of soil moisture. Overall, this study contributes to a better understanding of the ecology of karst forests. Analysing seedling persistence in karst forest expands our general understanding of forest dynamics and species co-existence in tropical forests as a whole, especially at sites with high spatial heterogeneity.