Management as a driver of functional patterns and alien species prominence in weed communities of irrigated orchards in Mediterranean areas

Abstract

Abstract Weed communities in irrigated orchards form spontaneous vegetative cover containing a remarkable presence of alien species. This plant cover can negatively affect the growth and productivity of orchards by reducing yield, but can also play a positive role by preventing soil erosion, increasing biodiversity and providing pollination services. Compositional and functional attributes of these weed communities are configured by management practices. Therefore, it is crucial to disentangle which differences in weed communities are mediated by management practices in order to establish management that promotes weed covers that enhance benefits while reducing negative effects on the orchards. In irrigated orchards of the Mediterranean area, management is dominated by irrigation (flood/drip) and weed control (mechanical/chemical). To identify how differences in irrigation and weed control modify weed communities in orchards, floristic surveys were carried out in mowed and herbicide-treated plots on drip and flood irrigated orchards. Weed community structure was evaluated in terms of species cover, diversity and the prominence of alien species for each management regime from a floristic and a functional approach. Results showed that irrigation system is the main factor influencing weed community structure. Compared to drip, flood irrigation is associated with a denser weed community with higher presence of alien weeds. Similarly, environmental conditions created by irrigation determine taxonomical and functional composition of weed communities and modulate the effect of weed control methods Flooding favours alien species, C4, perennial grasses, clonal species, zoochorous and hydrochorous and wind-pollinated species, whereas drip irrigation selects mostly native C3 forbs, non-clonal, wind-dispersed and insect pollinated species. Therefore, this study provides insights into how modernizing irrigation method from a flood to a drip system can promote vegetative cover that maximizes benefits to the orchards and the environment while minimizing negative effects of the weeds and prominence of alien species within the weed community.