Complementary Hotspots of Vegetation Diversity in Andean Patagonian Forests

Abstract

Aim

Examining spatial relationships among three vegetation diversity metrics—species richness (S), rarity-weighted richness (RWR) and local contribution to beta diversity (LCBD) as a measure of compositional uniqueness and quantifying the spatial congruence of their hotspots to assess conservation value.

Location

Andean Patagonian temperate forests of the eastern Rio Puelo watershed (Argentina).

Methods

We used floristic surveys of vascular plants combined with random forest models to predict spatial patterns of vegetation richness, rarity and uniqueness. We identified hotspots (top 5% of values) for each metric and quantified their congruence employing Jaccard indices. Using null models, we tested whether richness and uniqueness hotspots are more spatially segregated than expected by chance (repulsion hypothesis) and whether rarity and uniqueness hotspots show greater overlap than expected by chance (attraction hypothesis).

Results

Models explained 36%, 27% and 49% of variance in richness, rarity and uniqueness respectively (cross-validated R²), with climatic variables as the dominant predictors. Hotspots showed near-complete spatial segregation between richness and uniqueness (J = 0.1%; ρ = 0.004, n.s.), while rarity and uniqueness showed significant spatial attraction (J = 3.6%; ρ = 0.611, p = 0.001), though the low rarity model accuracy limits confidence in the spatial precision of this association. Richness hotspots in shrublands and wetlands were dominated by widespread warm-environment taxa, while uniqueness hotspots in subalpine forests harboured cold-adapted specialists.

Main Conclusions

No single diversity metric captures full vegetation conservation value. Patagonian forests exhibit complementary hotspots structured by climatic gradients. Coarse-resolution predictors adequately capture richness and uniqueness patterns but are insufficient to map fine-scale rarity. Conservation should adopt a portfolio approach protecting species-rich montane forests and shrublands, compositionally unique subalpine forests, and rare-species habitats across ecotonal forests.