Climatic niche dynamics of Himalayan conifers across the Outer and Inner Himalaya

The Indian Himalayan region harbours a diverse assemblage of conifer species distributed across contrasting Inner (monsoon rain-shadow) and Outer (monsoon-exposed) zones. Understanding their climatic niches is essential for explaining distribution patterns, adaptive capacity, and vulnerability to climate change. We quantified niche dynamics of 11 Himalayan conifers by assessing climatic niche overlap (Schoener’s D), hypervolume-based niche breadth, and environmental variable contributions across the two zones. Niche overlap between Inner and Outer Himalayan populations was generally low (D = 0.01–0.21), with Cedrus deodara showing the highest overlap and Cupressus torulosa exhibiting near-complete divergence. Hypervolume analysis revealed broader niches in the Outer Himalaya, suggesting greater environmental heterogeneity and wider climatic tolerance, whereas species in the Inner Himalaya occupied narrower and more specialized climatic spaces. Principal Component Analysis identified temperature variables (bio1, bio3, bio5, bio7, bio10) and precipitation variables (bio12, bio16, bio17, bio18) as the main drivers of niche differentiation. However, niche equivalency and similarity tests indicated that observed differences were not greater than expected by chance, suggesting overall climatic niche conservatism. These results indicate that Himalayan conifer distributions are shaped by the interaction of temperature and monsoon-driven precipitation, with regional climatic variability influencing niche breadth.