Identifying alien plants linkages between irrigated orchards and adjacent riparian habitats from a trait-based approach

• We study linkages between orchards and floodplains regarding alien and native plants.
• Native plants thriving in floodplains were different from those of orchards.
• Alien plant composition is similar in flood irrigated orchards and the muddy line.
• Adaptations to disturbance and flooding are related to distribution of alien plants.
• Weed control and natural water flow may limit alien weeds in agricultural floodplains.

Floodplains and crops are particularly susceptible to alien plant invasion, often leading to negative ecologic and economic impacts. As irrigated crops and riparian habitats are interconnected at the landscape scale, plant species of each habitat may be susceptible to colonizing the other. In order to avoid alien plant invasions of natural habitats and surrounding crops and to develop management practices to face this problem, it is not only essential to understand which traits favour the success of alien plants in irrigated crops and floodplains, but also whether a flow of species between these two habitats actually exists. With this aim, floristic surveys were carried out on riparian habitats (riparian forest, reedbed and muddy line) and on irrigated orchards at a gradient of distance from the river. Differences in weed management techniques applied in orchards were taken into account during the surveys. Plant diversity, composition and invasion levels were evaluated for each habitat and differences in floristic composition were interpreted in terms of functional traits. Natural habitats were well differentiated from crops in terms of native plants, but when considering alien plants, muddy line and flood irrigated orchards showed similar floristic composition. Alien plant community in the muddy line was a subset of that of flooded orchards and it was composed by C4 species, with clonal growth, perennial graminoids and water seed dispersal. This work proves that, unlike native species, alien species are shared between irrigated orchards and adjacent floodplains, which is favoured by a set of traits that allows them to colonize and establish new populations there. These results can help to develop strategies for preventing the establishment of alien plants in these habitats and to manage already present populations.