Drivers of aboveground biomass of high mountain vegetation in the Andes

Abstract The biomass of plant communities in the high mountains of the Andes (paramo) is a key factor controlling the carbon retention and freshwater supply, which are important environmental services for the human population. Using d-sep tests, we examined four causal path models that show how the aboveground biomass of a series of small plots in undisturbed paramo vegetation in southern Colombia was explained by the abiotic environment (elevation, and five soil variables: pH, exchangeable Al, available P, carbon, and bulk density), vascular species composition (as extracted four axes of a Non-Metric Multidimensional Scaling ordination) and trait information related to plant productivity (community weighted means of specific leaf area (SLA) and maximum plant height). Causality could not be rejected for most path models. Nearly 50% of the aboveground plant biomass was explained by path models in which trait information together with soil variables and species composition had a direct influence on aboveground plant biomass. Community weighted means of SLA were negatively related with aboveground biomass and those of maximum plant height positively. Soil acidity and to a lesser degree soil bulk density acted as key soil variables driving the aboveground biomass. Species composition most strongly affected the variation in the aboveground biomass.