Invasion of old world Tamarix chinensis and T. ramosissima in the new world: ecological niche shifts during the invasion process.

Biological invasions under global climate change can profoundly affect ecosystem functions and biodiversity. Understanding how invasive species adjust their ecological niches in novel environments is essential for predicting invasion risks and informing management strategies. This study focuses on two rapidly expanding Tamarix species in North America, T. chinensis and T. ramosissima, aiming to determine whether niche shifts occurred during invasion and to identify their potential drivers. We initially considered 19 bioclimatic variables for analysis, but retained eight after correlation filtering. These variables were then used to compare populations between the native range (Eurasia) and the invaded range (North America) to identify the key climatic determinants of distribution patterns. Niche overlap analyses revealed low niche similarity between Eurasian and North American populations, while niche centroid shifts indicated a tendency of the invaded populations toward drier and warmer environments, accompanied by a slight contraction trend. Using the MaxEnt model with current climate data (1970–2000) and future projections for 2070 under SSP1-2.6 and SSP5-8.5, we found that suitable habitats for both species are expected to expand further across the Northern Hemisphere and shift markedly toward higher latitudes. These findings provide a novel empirical perspective for exploring the ecological niche adaptation of invasive species and their responses to environmental changes.