Elevational filtering reshapes mountain understory communities through diversity decline, functional shifts, and species replacement

Mountain understory communities are structured along elevational gradients, as environmental constraints filter which species and ecological strategies can persist and where. Yet, how community differentiation, local diversity, functional strategies, and species replacement are shaped by elevational gradients remains poorly resolved. Here, we examine 107 herbaceous species across 27 sites spanning 2,202-3,696 m a.s.l. and three elevational zones. We determine how elevation reorganizes multiple dimensions of community assembly. We hypothesize that increasing elevation differentiates community composition, reduces -diversity, favors persistence-oriented strategies, and drives {beta}-diversity primarily through species turnover, rather than nestedness. We test our hypotheses by integrating taxonomic, functional, and {beta}-diversity patterns across the elevational gradient. A coherent pattern of community reassembly emerges as elevation increases: communities become increasingly distinct with elevational separation and locally less diverse toward higher elevations. Functional composition changes concurrently, with perennial and chamaephytic groups increasing as annual and therophytic groups decline. We find that increasing community differentiation primarily reflects species replacement rather than progressive species loss. Species turnover accounts for 97.95% of total Sorensen {beta}-diversity and increases with elevational separation, whereas nestedness declines. Our findings therefore show that elevation reorganizes herbaceous understory communities through linked changes in diversity, functional strategies, and species identity. Indeed, environmental filtering favors persistence-oriented strategies while progressively replacing species across elevations, linking taxonomic and functional differentiation within a common process of mountain understory community assembly.