Assessing ecophysiological patterns of Ailanthus altissima and differences with native vegetation classes using Copernicus satellite mission in a Mediterranean island

Invasive alien plants negatively affect biodiversity and ecosystem services. The EU Copernicus Mission delivers free remote sensing data, facilitating cost-effective and timely monitoring of invaded areas. This study deploys multispectral (Sentinel-2) and thermal (Sentinel-3) satellites to characterize ecophysiological traits of vegetation patches invaded by Ailanthus altissima in Sardinia, and analyzes seasonal ecophysiological changes between highly invaded and native vegetation classes. A total of 176 invaded patches and their non-invaded buffer areas were identified on aerial orthophotos, digitized and rasterized at the resolution of 20 m2. These cells were classified to the second level of the regional vegetation map (Carta della Natura) in A. altissima and native vegetation classes. A. altissima dominance was found in six vegetation classes: Mediterranean maquis, Mediterranean sub-nitrophilous grassland, deciduous woody vegetation, evergreen woody vegetation, agricultural herbaceous areas, and agricultural woody areas. After, we calculated a set of spectral indices as proxies of leaf chlorophyll and carotenoid content (CVI, SIPI3), productivity and canopy biomass (EVI, LAI), leaf water content (NMDI, MSI), soil features (CI), and daily evapotranspiration. We analyzed the monthly trends of these indices in invaded patches and buffer areas and their seasonal differences between invaded and not invaded cells, using linear mixed models (LMMs), two-way ANOVA, and Estimated Marginal Means. Our results highlighted the potential of Copernicus mission in capturing the temporal trends of ecophysiological spectral traits in invaded areas, as the high conditional R2 values of LMMs ranged from 0.522 of CVI to 0.776 of LAI. The greatest significant differences between invaded and not invaded cells were observed during summer, i.e. higher productivity and canopy biomass, greater leaf water content, lower leaf carotenoid content, and lower bare soil presence. These results confirmed that A. altissima might have a competitive advantage over native vegetation, especially during the summer drought period of the Mediterranean basin.