Rapid decline in a regionally important plant species across an aridity gradient is associated with increasing temperature and decreasing precipitation

<title>Abstract</title> <p> <italic>Lagochilus inebrians</italic> is a significant medicinal semi-shrub native to Central Asia and is one of many species that have recently been added to the endangered species list in Uzbekistan. Grazing and human harvesting negatively affect this species, but the role of climate remains less clear. We hypothesized that populations of <italic>L. inebrians</italic> are under more stress due to drought. To assess climate effects on <italic>Lagochilus inebrians</italic> , we analyzed: (1) population structure at three sites across a climatic aridity gradient over five years; (2) stable carbon isotope ratios (δ ¹³ C) of leaf tissues from historical and current herbarium samples as an indicator of drought stress over time and space, and (3) the Standardised Precipitation Evapotranspiration Index (SPEI) to assess aridity over the past 120 years across the study sites. Within our five years of observation, <italic>L. inebrians</italic> populations rapidly shifted to an older structure with few young individuals. δ ¹³ C values increased with temperature and decreased with precipitation indicating greater drought stress. Our results suggest that warming and drying conditions in Uzbekistan are contributing to <italic>L. inebrians</italic> stress and decline. Given the expected drier and hotter climate in Central Asia in the upcoming decades, prioritizing the conservation of <italic>L. inebrians</italic> populations should be crucial. While assisted migration of arid-adapted populations may help preserve this species, it is important to note that population declines were observed across sites. </p>