Phylogeny reveals competition within communities and cryptic filtering by soil moisture and pH in semiarid montane plant communities, undetected by abundance-based approaches

Understanding plant community assembly in montane ecosystems is vital, yet mechanisms in semiarid regions remain poorly resolved, particularly regarding cryptic environmental filters. We aimed to (1) determine whether lack of environment – abundance correlation reflects stochasticity or competition, and (2) evaluate whether phylogenetic structure is a more sensitive indicator of cryptic filters in semiarid mountains. In 25 plots, we recorded species abundance and calculated phylogenetic metrics (NRI, NTI) from regional phylogeny. Mantel tests compared abundance – phylogeny correlations. Canonical Correspondence Analysis (CCA), PERMANOVA, and NMDS linked environmental variables (soil moisture, pH, EC; elevation, slope) to abundance. PERMANOVA and Principal Coordinates of Phylogenetic Structure (PCPS) assessed environment – phylogeny relationships. Abundance showed no significant correlation with environmental variables (CCA/PERMANOVA/NMDS). Mantel tests confirmed no abundance – phylogeny correlation. Phylogenetic overdispersion (negative NRI/NTI) indicated competitive exclusion. Phylogeny revealed significant filtering by soil moisture and pH (PERMANOVA) and moisture/pH/EC (PCPS) – undetected by abundance methods. Topography showed no effect. Phylogeny revealed dual assembly dynamics: competitive overdispersion and cryptic filtering by soil moisture/pH. This shows the greater sensitivity of phylogeny, detecting deterministic filters where abundance data showed only weak trends. In semiarid mountains, local edaphic gradients override topography impact, underscoring essential role of phylogeny in revealing assembly mechanisms. Prioritise soil conservation in semiarid mountains Conservation policies must clearly protect soil water and chemistry as primary cryptic environmental filters shaping communities in semiarid mountains.Adopt phylogenetic monitoring Integrate phylogeny into biodiversity monitoring programmes to identify vulnerable communities earlier since phylogeny detects critical environmental stressors undetectable by traditional abundance-based surveys.Rethink climate adaptation strategies Topography (elevation/aspect) showed no significant filtering effect in a semiarid mountainous region - contrary to assumptions on which conservation planning is based on in mesic mountains.Mandate multi-metric assessments Policy frameworks should require complementary phylogenetic and abundance-based analyses to reveal hidden assembly mechanisms and avoid mis-diagnosing drivers of biodiversity change. Prioritise soil conservation in semiarid mountains Conservation policies must clearly protect soil water and chemistry as primary cryptic environmental filters shaping communities in semiarid mountains. Adopt phylogenetic monitoring Integrate phylogeny into biodiversity monitoring programmes to identify vulnerable communities earlier since phylogeny detects critical environmental stressors undetectable by traditional abundance-based surveys. Rethink climate adaptation strategies Topography (elevation/aspect) showed no significant filtering effect in a semiarid mountainous region - contrary to assumptions on which conservation planning is based on in mesic mountains. Mandate multi-metric assessments Policy frameworks should require complementary phylogenetic and abundance-based analyses to reveal hidden assembly mechanisms and avoid mis-diagnosing drivers of biodiversity change.