Changes in functional structure characteristics mediate ecosystem functions during human-induced land-cover alteration: A case study in southwest China

Abstract

Past studies have provided extensive documentation of changes in species diversity in response to land-cover alteration; however, little is known about the effects of land-cover alteration on the patterns of functional structures and ecosystem functions. In this study, we introduce a functional trait-based methodology for incorporating multiple levels of functional structures into models to assess the impacts of human-induced land-cover changes on functional structures and to evaluate how these functional attributes affect ecosystem functions. To this purpose, different functional structure indices (species diversity, functional diversity, and community-weighted mean trait values) in three widespread communities (a man-made Pinus yunnanensis forest, a man-made Eucalyptus smithii forest, and a natural secondary forest) were determined, with a focus on our study sites in southwest China. Meanwhile, ecosystem functions (soil nutrients, water and soil conservation, and multifunctionality) were quantified. Our results showed that most community diversity indices were affected by human-dominated land-cover changes, except species richness and functional evenness. Changes in the relationship between species diversity and functional diversity displayed two patterns. The first pattern reflected reduced species diversity with an increase in functional diversity, whereas the second pattern was associated with a correlated loss of species and functional diversity, indicating the removal of environmental filters in response to changes from natural secondary forest to man-made forests. Community-weighted mean trait values (related to leaf nitrogen [N] concentration, leaf phosphorus [P] concentration, and seed mass) were negatively correlated with water and soil conservation and multifunctionality, which accounted for 65.9% and 48.5% of the variance, respectively. Functional diversity (based on functional richness, quadratic entropy, and functional dispersion) was positively associated with soil nutrients and explained 33.6% of the variance. These results suggest that the community functional structure was affected by land-cover alteration through changes in environmental filters and replacement by functionally different species. Moreover, changes in functional structure characteristics mediate different ecosystem functions by niche complementarity or the mass ratio effect under land-cover alteration.