Native and non-native plant richness and diversity along an elevational gradient in the Ecuadorian Andes

Ecuador, recognized as a megadiverse country, faces growing threats from biological invasions, particularly in the mountainous ecosystems of the Andes. We described patterns of native and non-native plant richness and diversity along an elevational gradient (2,000–4,400 m a.s.l.) on the Tungurahua volcano, testing whether patterns of non-native plant diversity are consistent with directional environmental filtering along the gradient or explained by the effects of residence time, climate-matching, and disturbance intensity. Twenty-five 10 × 2 m transects were established at 100-m elevational intervals following a MIREN-T-adapted protocol. Vegetation cover, abundance, and disturbance were recorded in each plot. A total of 247 taxa were identified, distributed across 75 families and 171 genera. Of these, 180 were native (including 11 endemic), 38 non-native, and the remainder of undetermined origin. Non-native taxa were predominantly herbaceous and originated from Africa, Europe, and Asia. Along the gradient, non-native taxa were concentrated at lower elevations, with narrower elevational ranges and lower maximum elevations than native taxa. Native richness exhibited a mid-elevation peak (~ 3,400 m), whereas non-native richness declined steadily with elevation. Alpha diversity decreased with elevation in both groups, but sharply in non-natives. Beta diversity analyses showed higher turnover among native assemblages, while non-native communities were more homogeneous along the gradient. Overall, these patterns support the directional environmental filtering hypothesis, with climatic constraints limiting the upslope expansion of non-native taxa and weaker evidence for effects of residence time, climate-matching, or disturbance intensity. These findings provide key insights for the management and conservation of tropical mountain ecosystems.