Environmental heterogeneity and spatial variation mediates plant diversity and ecosystem stability in mountain ecosystems of the Mediterranean Andes

Globally, mountains are highly diverse ecosystems that serve as natural laboratories for testing ecological theories, while providing vital ecosystem services. Their biodiversity arises from the interaction between elevational gradients and topographic complexity, which generate strong variation in environmental conditions across short spatial scales. These gradients, in turn, influence the maintenance of ecosystem functions, such as vegetation productivity, over time. However, how topography influences ecosystem stability and its relation with different facets of biodiversity in naturally‐assembled communities remains relatively unexplored. Here, we evaluated how environmental heterogeneity and spatial variation influence taxonomic and phylogenetic plant diversity, and how these components together affect ecosystem stability. Using a highly replicated fractal sampling design, we estimated plant taxonomic and phylogenetic diversity locally and across space. We estimated the temporal stability of vegetation productivity with a high‐resolution, remotely sensed time series in the Mediterranean Andes of central Chile. We assessed how environmental heterogeneity and spatial variation (i.e. spatial autocorrelation, spatial structure, and distance) mediate relationships between topography, plant diversity, and ecosystem stability using generalized linear and structural equation models. As expected, taxonomic and phylogenetic diversity declined with elevation, and both diversity and ecosystem stability varied along gradients in environmental heterogeneity. Our structural equation models revealed that spatial variation was the main factor directly stabilizing vegetation productivity, while species turnover had only minor effects. When spatial variation was excluded, diversity components influenced stability but explained less variation, emphasizing the key role of spatial processes captured by spatial variation in maintaining ecosystem stability. Our findings indicate that diversity–stability relationships in naturally assembled plant communities emerge from spatial processes governing patterns of plant diversity and ecosystem stability. We provide empirical evidence that spatially structured ecosystems should be prioritized for biodiversity conservation and the maintenance of key ecosystem functions in mountain ecosystems.