Plant coverage is more sensitive than species diversity in indicating the dynamics of the above-ground biomass along a precipitation gradient on the Tibetan Plateau

Abstract

Species diversity (SD) and total plant coverage (PC) are commonly used predictors of primary productivity (i.e., above ground biomass (ABG)). PC is a characteristic frequently used in remote sensing to assess land cover, land use, and vegetative condition, while species diversity serves as a measure of the existence and utilization of ecological niches. Both SD and PC are thought to be positively related to primary productivity, with SD further contributing to community stability. We investigate the effects of SD and PC on ABG under different mean annual precipitation (MAP) levels. The influences of SD and PC on community stability and biomass allocation were analyzed using redundancy analysis (RDA), correlation analysis (CA), and generalized linear models (GLM). Significantly positive relationships between precipitation and above-ground biomass, species diversity, and plant coverage occurred in the low rainfall gradient (100–400mm/y) in the alpine steppes, while these relationships appeared in the high rainfall gradient (500–700mm/y) in alpine meadow ecosystems. Second, we determined that plant coverage (r2=0.88, P<0.001) provided a better explanation for above-ground biomass than species diversity (r2=0.67, P<0.001). Moreover, we found that the relationships between SD and AGB and PC and AGB (r2=0.52, P<0.001, and r2=0.85, P<0.001, respectively) were more positive in the alpine steppes than in the alpine meadows (r2=0.41, P<0.001, and r2=0.77, P<0.001, respectively). Third, at the different precipitation gradients, especially at the 400–500mm/y and >600mm/y ranges, the PC continued to increase, while SD decreased with increasing AGB. Moreover, SD was more sensitive to community stability and reproduction allocation than PC. Overall, plant coverage is better than species diversity in indicating the dynamics of above-ground biomass along a precipitation gradient.