Diversity, distribution and drivers of alien flora in the Indian Himalayan region

The Himalaya – a global biodiversity hotspot – harbors diverse flora and fauna, but increasingly beset with multiple threats, including biological invasion by alien species. Here, we aimed to investigate the diversity, distribution, and drivers of alien flora in the Indian Himalayan Region (IHR), a region spread across 12 states/union territories in India. We developed a comprehensive checklist on alien flora of IHR based on review of 141 studies published during the years 1934 to 2022, and further disentangled the key environmental (average annual rainfall, total area, protected area, forest area, total plant richness) and socioeconomic (total population, traffic length) drivers that better explain regional alien and naturalized plant richness. We recorded 771 alien plant species, including 375 cultivated and 396 naturalized species. We found that the species native to Southern America and those with perennial life span and herbaceous growth form were most represented in the IHR. Similarly, the annual herbs native to Southern America had a higher probability to become naturalized in the IHR. Based on the species composition of the total alien and naturalized flora distributed across different parts of the IHR, we found evidence of distance decay of floristic similarity. The total alien plant richness was best explained by the average annual rainfall, while the naturalized plant richness was best predicted by total traffic length. Our results identify the key environmental (i.e., average annual rainfall) and socioeconomic (i.e., total traffic length) drivers that determine the diversity and distribution patterns of alien and naturalized plants in the IHR. Our findings have practical applications in developing a scientifically-informed management and policy framework to mitigate the impacts of plant invasions and to predict the potential future plant invaders in the Himalaya. Overall, the checklist of alien flora of the IHR represents a step forward in filling the knowledge gaps on biological invasions from the Himalaya – a globally data-deficient region.