Patterns and Drivers of Tree Species Accumulation in Three Biodiversity Hotspots of Northwestern South America

ABSTRACT Aim This study aims to understand the relative importance of climatic anomalies since the Last Glacial Maximum (LGM) and regional biogeographic (evolutionary) features as drivers of local and regional tree species accumulation across three neotropical biodiversity hotspots in northwestern South America (Northwestern Amazon, Northern Andes and Chocó). We assess the relative influence of phylogenetic structure and dispersal on shaping tree assemblages and the role of climatic and biogeographical features as drivers of species accumulation. Location Northwestern Amazon, Northern Andes and Chocó, northwestern South America. Taxon Angiosperm trees. Methods We analysed data from 49 permanent 1‐ha plots across the three regions. Taxonomic and Phylogenetic structure were quantified using Mean Pairwise Distance (MPD) and Mean Nearest Taxon Distance (MNTD), along with their standardised effect sizes (ses.MPD and ses.MNTD, respectively). We applied generalised linear models (GLMs) to evaluate the effect of climatic anomalies since the LGM and biogeographic region on both ses.MPD and ses.MNTD. Results There were significant differences in species richness, diversity, and ses.MNTD between Northwestern Amazon and both Northern Andes and Chocó, but not between the latter two. In contrast, we did not find significant differences in ses.MPD among regions. Regional diversity was highest in the Northwestern Amazon, followed by Chocó and the Northern Andes. Precipitation seasonality anomaly (PSa) emerged as a significant predictor of ses.MPD, whereas mean annual temperature anomaly (MATa) and biogeographic region were identified as the primary driver of ses.MNTD. Main Conclusions Our findings show the Northwestern Amazon as the region with the highest tree diversity, largely due to higher species accumulation of some dominant clades that have had long time to evolve in a geographic area large enough to promote species coexistence and persistence through time. In contrast, the high diversity in Chocó and Northern Andes was mainly shaped by historical dispersal from tropical and extra‐tropical regions. Ses.MPD was significantly correlated with PSa and temperature seasonality anomaly (TSa), while ses.MNTD showed significant correlations with MATa, TSa and PSa. Geological and evolutionary processes associated with biogeographic regions played a key role determining species accumulation at both local and regional scales.