Contribution of conspecific negative density dependence to species diversity is increasing towards low environmental limitation in Japanese forests

Abstract

Species coexistence is a result of biotic interactions, environmental and historical conditions. The Janzen-Connell hypothesis assumes that conspecific negative density dependence (CNDD) is one of the local processes maintaining high species diversity by decreasing population growth rates at high densities. However, the contribution of CNDD to species richness variation across environmental gradients remains unclear. In 32 large forest plots all over the Japanese archipelago covering > 40,000 individual trees of > 300 species and based on size distributions, we analysed the strength of CNDD of individual species and its contribution to species number and diversity across altitude, mean annual temperature, mean annual precipitation and maximum snow depth gradients. The strength of CNDD was increasing towards low altitudes and high tree species number and diversity. The effect of CNDD on species number was changing across altitude, temperature and snow depth gradients and their combined effects contributed 11–18% of the overall explained variance. Our results suggest that CNDD can work as a mechanism structuring forest communities in the Japanese archipelago. Strong CNDD was observed to be connected with high species diversity under low environmental limitations where local biotic interactions are expected to be stronger than in niche-based community assemblies under high environmental filtering.

Community vertical stratification drives temporal taxonomic and phylogenetic beta diversity in a mixed broadleaf-conifer forest

“…On the other hand, the phylogenetic turnover of the lower canopy changed from being driven by randomized individuals to closely related individuals. This may be due to different responses from different vertical stratification to biotic/abiotic factors such as extreme drought and negative density dependence (Fibich et al, 2021;Yan et al, 2022). The relative contribution of different vertical stratification to temporal taxonomic and phylogenetic beta diversity in the Dongbaishan forest.…”

Forest monitoring data of 45 plots across the Japanese archipelago during 1980–2021

“…The project's website (http://www.biodic.go.jp/moni1000/findings/index.html) presents the data collected in most of these plots. This dataset was used to reveal recent forest dynamics and compositional shifts (Mori, 2018; Suzuki et al, 2015) and ecosystem processes (Fibich et al, 2021). However, the project only covers the periods after 2004 and a limited range of regions.…”