Invasive alien species (IAS) are na important driver of degradation in Mediterranean riparian ecosystems, threatening biodiversity, ecosystem functioning and the conservation of priority habitats. Within the LIFE ALNUS TAEJO project, "Conservation and restoration of Mediterranean alder forests priority habitat in the Western International Tagus River Basin", that aims to restore habitat 91E0* under the EU Habitats Directive along 513 km of rivers in the International Tagus Basin promoting natural regeneration to enhance ecological connectivity.

An ecological characterization was conducted, including assessments of the river habitat index, riparian woodland connectivity, environmental pressures, phytosociological relevés, and the design of conservation measures. Vegetation mapping was carried out, with special attention to distribution áreas of IAS. Fieldwork includes more than 250 relevés and identified IAS as the primary ecological pressure and threat on the surveyed riparian stretches, providing essential knowledge on their distribution and impact along the International Tagus River Basin (Spain and Portugal).

We present the results of the mapping of the IAS, as well the control measures already implemented under the LIFE ALNUS TAEJO project, with a particular focus on the transboundary areas of the Sever and Erges rivers. Results show a high reduction of IAS cover within the first two years monitoring period, accompanied by a progressive increase in native species cover. Early trajectories indicate partial convergence towards reference communities in locations where native target species were planted.

This study highlights the critical role of monitoring and transboundary cooperation to control biological invasions and enhance the resilience of Mediterranean riparian ecosystems.