Landscape complexity affects cover and species richness of weeds in Brazilian agricultural environments

Abstract

The influence of the landscape context on weed communities in farmland has been investigated mostly in temperate regions, while there is a paucity of information for the Neotropics. The aim of this study was to estimate the effects of landscape complexity on local weed communities in Paraná State, southern Brazil. We addressed three questions: (i) Do species richness and percent cover of weeds increase with increasing landscape complexity? (ii) Does landscape complexity similarly affect native and exotic species? and (iii) Do the effects of landscape attributes on local weed communities differ between spatial scales? To answer these questions, we assessed species richness and cover of weeds along the edges of 18 wheat fields. Altitude, field size and three landscape complexity metrics (percent cover of non-crop habitats; edge density and habitat diversity) were used as explanatory variables. Landscape metrics were calculated at four spatial scales: 0.5, 1, 1.5 and 2 km. We recorded 52 weed species (24 exotic, 25 native and 3 morphospecies) belonging to 45 genera and 18 families. Total richness and native richness increased with increasing SDI and ED at 0.5, 1.5 and 2.0 km radii, while exotic richness was related only to SDI at 0.5 km. Percent cover of weeds was positively correlated with ED at 0.5, 1.5 and 2.0 km radii; native cover and exotic cover did not respond to landscape complexity nor local factors. Our findings suggest that the increment of landscape complexity benefited particularly native species which seem to be less adapted to constant disturbances in the crop matrix than exotic species and probably depend on the presence of more stable habitats in the surrounding landscape. Therefore, agri-environment schemes designed to preserve biodiversity in farmland must promote landscape complexity through the diversification of crops and conservation of non-crop habitats at multiple spatial scales.