Topography and forest diversity facets regulate overstory and understory aboveground biomass in a temperate forest of South Korea

Abstract

Diversity-biomass studies across (sub-)tropical forest strata have been explored, but our understanding on how multiple facets of forest diversity and abiotic factors regulate aboveground biomass across forest strata in temperate forests remains somehow unclear. Here, we conducted a comprehensive analysis of the effects and relative importance of taxonomic, phylogenetic and functional diversity, community-weighted mean (CWM) of trait values, coefficient of variation in individual tree diameter at breast height (CV DBH), and soil and topographic factors on aboveground biomass to select the diversity facets that could have the strongest response to abiotic factors across over- and understory and whole community in a temperate forest of South Korea. We used forest inventory, functional traits and environmental factors data from 259 plots to select the most important diversity facets with abiotic factors through multi-model inference tests, and we then used structural equation models. In the overstory, the most important regulators of aboveground biomass were topographic factor, species evenness, functional richness, and CV DBH. In the understory, the significant drivers of aboveground biomass were topographic factor, species evenness, phylogenetic species richness and CWM of height. In addition, diversity facets of overstory such as functional richness and CV DBH also had significant direct and/or indirect effects on understory aboveground biomass. Moreover, the diversity facets influencing aboveground biomass at the whole community were the combination of the multiple facets of forest diversity influencing aboveground biomass at each forest stratum. The role of functional dominance (CWM of height) seems to be negligible in the overstory but significant in the understory, indicating different diversity drivers as shown previously for a subtropical forest. Hence, our study suggests the urgent need of exploring diversity-biomass studies across forest strata in different forest ecosystems and types in order to provide more specific guidelines for the management of a specific natural forest.

Keywords: Mass ratio; Niche complementarity; Overstory; Stand structural diversity; Topographic factor; Understory; Whole-community.