The effect of agronomic filters on arable plant communities: What weeds are we selecting for?

Abstract

Functional diversity in arable plant communities affects their detriment, as different arable plants occupy different niche spaces which dictate their competitiveness to the crop. This functional diversity can be examined using Grime’s CSR triangle; most common arable plants are thought to occupy a region of this triangle indicating low levels of stress tolerance, and preference for disturbance and abundant nutrition. Prior research has, however, only examined this with regard to specific management practices or cropping systems, rather than the ecological conditions they generate, the ‘agronomic filters’ applied. Using a dataset of all arable plant species in Sweden, we used multivariate statistics to determine the functional characteristics of problematic weeds, and how they differed from other plant species present in these communities. This was examined with regard to Grime’s life strategy, perceived detriment, conservation status, and preference for agronomic filters relating to nutrition, disturbance, moisture, and light. Our results show that intense agronomic management constrains the niche and limits the function of the non-crop community, with stress-tolerators (S) being absent and, as theorised, competitive and pure ruderals (CR and R respectively) overrepresented. CR strategists favoured nutrition, light and disturbance, and were often considered problematic according to agronomic experts. R strategists generally showed less preference for nutrition, and were more often considered rare and non-weedy, probably due to their lesser competitiveness. These findings can be applied by modifying the agronomic filters favoured by problematic weeds. Specifically, more effective nutrient management would break the ‘agronomic trap’ of fertilisation benefitting dominant, competitive weeds. Increased grazing or mowing is also suggested to limit plant height in favour of less competitive species, and increased cropping diversity will also alter selection for agronomic filters depending on crop niche. Using these agronomic filters, we provide a theoretical guide to achieving ecological weed management in practice.