Evaluating the effect of plant diversity on above-ground biomass dynamics along an elevation gradient in Andean Forests

Abstract

The Andean montane forests (AFs) represent a natural laboratory to evaluate the ecological mechanisms driving ecosystem functioning, such as the above-ground carbon (AGC) dynamics across steep environmental gradients. Understanding these mechanisms is critical for anticipating their responses to ongoing climate change or human disturbances on the environmental services they provide. This study examines biotic and abiotic drivers of AGC stocks (AGCfinal), net change (AGCnc), productivity (AGCp), and mortality (AGCk) along an elevational gradient of ~3,000 m in secondary forests in the Ecuadorian Andes, integrating data from 16 plots across three censuses conducted in a period of four years. Patterns of taxonomic, functional, and phylogenetic diversity, and their alpha and beta components, were described where temperature constituted the primary environmental filter for most of the diversity metrics, while degradation history, soil properties and geographic distances were secondary drivers of diversity. Phylogenetic structure revealed clustering at both extremes of the gradient, driven by contrasting mechanisms: past disturbances filtering pioneer species with key functional traits, wider and taller trunks, to store and gain more AGC at the lowlands, and abiotic stress filtering at high elevations. Leaf functional traits, particularly specific leaf area and leaf blade thickness, captured the shift from acquisitive to conservative plant strategies with increasing elevation and provided additional explanatory power beyond climate variables alone. Deep phylogenetic turnover (β-MPD) between neighboring plots was positively associated with AGCp, whereas shallow phylogenetic turnover (β-MNTD) predicted elevated AGCk, suggesting that gains and losses of C operate differently depending on the evolutionary depth at which communities diverge. General additive and causality models confirmed that the environment shapes all three diversity dimensions simultaneously. Phylogenetic and functional diversity determine the variation in AGC stocks and productivity along the elevation gradient, while temperature indirectly influences AGC dynamics through species richness and community-level trait filtering. Collectively, these findings recommend using additional diversity metrics (dimensions) to generate more accurate models for estimating carbon dynamics. A multidimensional view of biodiversity is essential for understanding forest functioning and for guiding conservation strategies in Andean forests facing continued climate and land-use pressures.