Monitoring Pontederia crassipes Mart. and Hydrocotyle ranunculoides L.f. invasion on a Mediterranean island using multi-temporal satellite images

Abstract The present study aimed to investigate the role of multispectral images from Sentinel-2 satellites to map and monitor in the Mediterranean island of Sardinia (Italy), from 2018 to 2021, Pontederia crassipes and Hydrocotyle ranunculoides, two aquatic macrophytes included in the list of invasive alien species of European Union concern. The vegetation index NDVI was used to assess the level of vigor of these species and the area of invasion on waterways to understand their expansion over time. At the same time, the correlation between recorded monthly mean air temperatures and NDVI values was calculated. The coverage, during this 4-yearstudy, affected almost entirely the study area, with high coverage values in the summer and autumn periods. This study demonstrates the usefulness of Sentinel-2 satellite imagery in mapping and monitoring invasive alien macrophytes. In fact, large areas can be monitored and mapped quickly in a short time and have measurements every five days due to the images released by European Space Agency (ESA), unless there is excessive cloud covering. In combination with GIS and modelling tools, the tested multitemporal methodology could represent a suitable tool for prevention, drafting of dedicated action plans, priority setting for intervention both for P. crassipes and H. ranunculoides to meet the requirements of the Regulation (EU) No. 1143/2014 on Invasive Alien Species (the IAS Regulation).