Phylogenetic structure and β-diversity reveal assembly mechanisms of sub-alpine Abies forests in South Korea

Sub-alpine coniferous forest ecosystems are sensitive to climate change.
However, the community formation mechanisms of sub-alpine coniferous
forests in northeastern Asia remain poorly understood. In this study, we
assessed the factors controlling the phylogenetic community structure in
different strata (whole strata, upperstory, and understory) of Abies
nephrolepis and Abies koreana forests in the sub-alpine zone in South
Korea. Piecewise structural equation modeling (pSEM) was performed based
on terrain, climate, taxonomic diversity, stand structure characteristics,
and disturbance factors. The controlling factors presented different
responses for each species depending on the stratum and phylogenetic
community structure indices (net relatedness index and nearest taxon
index). A. nephrolepis showed a unique community formation mechanism and
formed climate refugia through high rock exposure, whereas A. koreana
showed niche conservation at high elevations and a community
overdispersion trend when forest gaps appeared due to overstory vegetation
loss. The Mantel test and partial Mantel test were performed to examine
the impact of turnover and nestedness on phylogenetic β-diversity, as well
as to establish their correlations with climatic, geographic, and
environmental distance. Turnover was a major contributing factor to
β–diversity and strongly correlated with environmental distance. Further,
geographical and climatic distance presented differential contributions to
each species depending on the community characteristics. Integrated
analyses of phylogenetic community structure and β-diversity provided
detailed insights into the mechanisms underlying community formation and
biodiversity patterns. This reveals that biodiversity patterns are driven
by interactions between community structure and inter-community
characteristics, with internal structure as a key mechanism influencing
β-diversity.