Alien flora causes biotic homogenization in the biodiversity hotspot regions of India.

Biotic homogenization by invasive alien species is one of the dominant drivers of global environmental change. However, little is known about the patterns of biotic homogenization in global biodiversity hotspots. Here, we fill this knowledge gap by studying the patterns of biotic homogenization and associated geographic and climatic correlates in Indian Himalayan Region (IHR). For this, we use a novel biodiversity database comprising 10,685 native and 771 alien plant species across 12 provinces of the IHR. The database was assembled by screening 295 and 141 studies published from 1934 to 2022 for natives and aliens, respectively. Our results revealed that each native species on average was distributed among 2.8 provinces, whereas the alien species in 3.6 provinces, thereby indicating wider distribution range of alien species in the IHR. The Jaccard's similarity index between the provinces was higher for alien species (mean = 0.29) as compared to natives (mean = 0.16). Addition of alien species pool has homogenized most of the provincial pairwise floras (89.4 %) across the IHR, with greater dissimilarity in their native floras. Our results revealed that the alien species have strong homogenization effect on the provincial floras, regardless of their differences in geographic and climatic distances. The biogeographic patterns of alien and native species richness in the IHR were better explained by a different set of climatic variables, the former by precipitation of driest month and the latter by annual mean temperature. Our study contributes to better understanding of the patterns of biotic homogenization in the IHR and its geographic and climatic correlates. Looking ahead, in an era of Anthropocene, we discuss the wide implications of our findings in guiding biodiversity conservation and ecosystem restoration in global hotspot regions.