Phylogenetic Diversity and Community Assembly of Vascular Plants Along Environmental Gradients in the Western Pamir–Alay: A Case Study From Surkhandarya Province, Southern Uzbekistan

Biodiversity plays a fundamental role in ecosystem structure, function, and stability, but its response to environmental gradients is poorly understood in Central Asia. We studied plant species richness, phylogenetic diversity, and community phylogenetic structure along elevational, temperature, and precipitation gradients in Surkhandarya province of southern Uzbekistan. Data were compiled from a 5-year field survey (2020-2024), herbarium records (TASH, ASH, BM, E, H, LE, M, MW, TAD, MOSM), and digital records from the Plantarium database (plantarium.ru), totalling over 64,500 occurrence records. The flora comprises 2202 species across 615 genera and 96 families, including 62 endemics. Species richness and PD exhibited a left-skewed, hump-shaped pattern with a peak at 1000-1100 m, while high-elevation communities were phylogenetically clustered due to environmental filtering. Mid-elevations showed phylogenetic overdispersion, reflecting the coexistence of distantly related species. Along climatic gradients, species richness peaked at intermediate temperatures (8°C-12°C) and precipitation (400-500 mm), with phylogenetic structure similarly reflecting clustering at extremes and overdispersion at intermediate conditions. Low-elevation communities were dominated by drought- and salt-tolerant families (Poaceae, Asteraceae, Amaranthaceae), whereas mid-elevations supported the highest family diversity. Using endemic and Red Book species records (1504 occurrences of 140 species), a proximity-weighted conservation prioritization identified a minimal set of areas covering 7.43% of the region, with 4.56% requiring expansion beyond existing protected areas to achieve complete species representation.