Native Community Resistance Mediates Plant Invasion Responses to Global Change Along Mediterranean Mountain Roads

Aim: Climate warming, human modification and global connectivity are eroding the abiotic barriers (i.e., climatic filtering and low propagule pressure) that have traditionally limited the spread of non-native species in mountain ecosystems. Meanwhile, these global changes are also reshaping native plant communities, potentially weakening their biotic resistance to invasion. Yet, the role of native community resistance in mediating the upslope spread of non-native species remains largely overlooked, limiting our understanding of the indirect effects of global change on mountain plant invasions. Location: Central Apennines Mountain range, Italy. Methods: Following the Mountain Invasion Research Network (MIREN) protocol, we surveyed native and non-native vegetation close and far from roads at 60 sites along three mountain roads. Using current and historical climatic data and aerial images from the 1950s, we quantified climate and land-use changes. Dominant plant traits and functional diversity were used to capture the biotic resistance of native communities. We then applied structural equation modelling to investigate how native biotic resistance mediates the effect of global change drivers, that is, road disturbance and changes in land-use and climate, on the occurrence and cover of non-native species. Results: We found that, beside climatic filtering, the biotic resistance of native communities is among the strongest drivers of non-native species occurrence and abundance. The changes in land-use occurred over the past 70 years indirectly influenced invasions by altering native community resistance. Agricultural abandonment at low- to middle elevations favoured short-statured native communities, offering low resistance. In contrast, forest expansion strengthened resistance through dominance of conservative native species. Main Conclusion: Native community resistance, alongside climate and disturbance, is a key determinant of invasion patterns along elevational gradients in Mediterranean mountains. Despite global changes facilitating non-native plant upward shifts, native communities can mediate this spread and may still maintain a certain resistance to invasion.