Complementary hotspots of vegetation diversity in Andean Patagonian forests

Biodiversity hotspot delineation is critical for conservation prioritization, yet traditional species richness approaches fail to capture the full spectrum of conservation value, frequently overlooking sites harboring rare species or unique assemblages important for ecosystem functions and evolutionary processes. We examined spatial relationships among three diversity metrics—species richness (S), rarity-weighted richness (RWR), and local contribution to beta diversity (LCBD)—using vascular plant data from Andean Patagonian forests. These temperate forests provide an ideal system as steep environmental gradients and fire disturbances create habitat mosaics ranging from species-rich generalist communities to unique assemblages dominated by rare specialists. We hypothesized that high species richness and high ecological uniqueness areas would be spatially segregated, mediated by rare species distribution. Random forest models explained 27% of variance in richness, 17% in rarity, and 46% in uniqueness, with mean annual temperature the dominant predictor. Richness peaked in warmer, moderately productive shrublands and wetlands, while uniqueness concentrated in cooler, low-productivity subalpine forests. Hotspots (top 5% of values) showed complete spatial segregation between richness and uniqueness. Null models confirmed negative spatial association between metrics. Unexpectedly, rarity showed minimal overlap with uniqueness (1%) despite positive correlation, indicating spatially offset hotspots. This segregation reflects distinct assembly processes: competitive exclusion drives richness in productive environments, while environmental filtering generates uniqueness at climatic extremes. Disturbance amplifies decoupling by favoring widespread generalists in species-rich sites. These findings highlight that no single metric captures full conservation value. Patagonian forests exhibit complementary hotspots structured by interacting gradients of energy, stress, and disturbance. Conservation planning should adopt a portfolio approach jointly protecting species-rich reservoirs, rare-species habitats, and compositionally unique assemblages to maintain biodiversity resilience under increasing fire disturbance and climate change.