How weed management influence plant community composition, taxonomic diversity and crop yield: A long-term study in a Mediterranean vineyard

Agricultural expansion and intensification is a major driver of biodiversity loss. Conventional weed management (e.g. tillage, herbicide) has encouraged the promotion of a few more competitive species over a wide range of arable plants that are now in decline. A reduction in plant diversity would negatively affect the provision of key ecosystem services in agroecosystems. In vineyards, the use of plant covers has emerged as the principal alternative to conventional weed management, providing multiple ecosystem services such as enhance biodiversity, but usually with a decrease in yields in Mediterranean vineyards. This long-term study assessed how weed management (herbicide, mowing, tillage) influenced plant community composition, taxonomic diversity and vineyard yield. Plant surveys and grape yield measurements were carried out from 2015 to 2018 in an experiment established in 2008. Effects on plant community composition were analysed, focusing on two groups: noxious grapevine weeds and terophytic grassland species. In addition, three fundamental components of taxonomic diversity were measured: β-diversity, evenness and species richness. Linear mixed models and generalised linear mixed model were used to examine the response of different variables to weed management. Position (row, inter-row) as well as the indirect effect of adjacent management on the subplots were also included as fixed factors. Furthermore, the percentage of bare soil, related to disturbance degree associated with management, was explored as a potential predictor of taxonomic diversity and vineyard yield. Results indicated that plant community composition was affected by weed management and to a lesser extent by position. Noxious grapevine weeds were more abundant in herbicide-sprayed rows, while terophytic grasslands species showed a higher presence in mown subplots. Weed management had a strong effect on bare soil, which proved to be a good predictor of the variables studied. Indeed, the highest species richness were associated with the lowest percentages of bare soil (mown subplots), while the lowest values were found at high percentages of bare soil (tilled subplots). Herbicide showed intermediate values, with a response dependent on adjacent management. On the other hand, vineyard yields were higher with increased bare soil, although with the consequent loss of species richness. Conversely, mowing in spontaneous plant covers caused a decrease in yield, but still production was within the maximum limit established by the Regulatory Council, while increasing the species richness and a significant presence of therophytic grasslands species. These findings could foster the development of more sustainable management in Mediterranean vineyards.