In arable fields, plant species richness consistently increases at field edges. This potentially makes the field edge an important habitat for the conservation of the ruderal arable flora (or ‘weeds’) and the invertebrates and birds it supports. Increased diversity and abundance of weeds in crop edges could be owing to either a reduction in agricultural inputs towards the field edge and/or spatial mass effects associated with dispersal from the surrounding landscape.
We contend that the diversity of weed species in an arable field is a combination of
resident
species, that can persist under the intense selection pressure of regular cultivation and agrochemical inputs (typically more ruderal species), and
transient
species that rely on regular dispersal from neighbouring habitats (characterised by a more ‘competitive’ ecological strategy).
We analysed a large dataset of conventionally managed arable fields in the UK to study the effect of the immediate landscape on in‐field plant diversity and abundance and to quantify the contribution of spatial mass effects to plant diversity in arable fields in the context of the ecological strategy of the resulting community.
We demonstrated that the decline in diversity with distance into an arable field is highly dependent on the immediate landscape, indicating the important role of spatial mass effects in explaining the increased species richness at field edges in conventionally managed fields.
We observed an increase in the proportion of typical arable weeds away from the field edge towards the centre. This increase was dependent on the immediate landscape and was associated with a higher proportion of more competitive species, with a lower fidelity to arable habitats, at the field edge.
Synthesis and applications
. Conserving the ruderal arable plant community, and the invertebrates and birds that use it as a resource, in conventionally managed arable fields typically relies on the targeted reduction of fertilisers and herbicides in so‐called ‘conservation headlands’. The success of these options will depend on the neighbouring habitat and boundary. They should be placed along margins where the potential for ingress of competitive species, that may become dominant in the absence of herbicides, is limited. This will enhance ecosystem services delivered by the ruderal flora and reduce the risk of competitive species occurring in the crop.
Through a meta-analysis, Mupepele et al. (BMC Ecol Evol 21:1–193, 2021) assessed the effects of European agroforestry systems on biodiversity, estimated by species richness or species diversity. They showed that the effects of silvoarable and silvopastoral systems depend on the systems they are compared to and the taxa studied. Further, they found that only silvoarable systems increased species richness or diversity, compared to cropland. The authors conclude that agroforestry systems have weak effects on biodiversity and that landscape context or land-use history are probably more important than the practice of agroforestry in itself. However, we draw attention to important shortcomings in this meta-analysis, which downplay the potential of agroforestry for biodiversity conservation in agricultural landscapes. We hope that the meta-analysis by Mupepele et al. (BMC Ecol Evol 21:1–193, 2021), and our comments, will contribute to improving the quality of research on agroforestry systems and biodiversity conservation.
Developing agroecological practices that enhance biological control of crop pests is a major issue for the transition of agriculture towards sustainable and biodiversityfriendly systems. Agroecological infrastructures (AEI) are devoted to the support of ecosystem service providers, although they have mixed effects on natural enemies of crop pests. In temperate regions, alley cropping agroforestry involves within-field AEI, in the form of tree rows and associated understory vegetation strips. The objective of this study was to assess the potential of generalist predators (carabid beetles and cursorial spiders) to control weed seeds and invertebrate pests in alley cropping vs pure crop systems, under two contrasting farming systems (conventional vs organic). Predator surveys were carried out in May and June 2017 in SouthWestern France over 12 winter cereal fields. Our study revealed that the effect of alley cropping was modulated by the farming system. Under conventional farming, alley cropping had a negative effect on the activity-density and species richness of generalist predators, especially regarding carnivorous carabids whose activity-density was reduced by nearly 50%. Under organic farming, alley cropping enhanced both the activity-density and complementarity of generalist predators, with a twofold increase in the activity-density of seed-feeding carabids (predominantly granivorous and omnivorous), potentially promoting weed seed and invertebrate pest control. Our results suggest that the effectiveness of AEI in promoting natural enemies depends on the farming system at the field scale, which affects resource availability and determines spillover intensity between habitats. AEI are often perceived as sources of natural enemies. However, sink and retention effects (i.e. reduced or delayed spillover into crop fields due to higher 3 attractiveness of AEI) are overlooked and very likely to explain the mixed impacts of AEI on natural enemy communities.
Field margins are major habitats for biodiversity conservation and ecosystem functioning in agricultural landscapes, but biotic homogenization of plant communities threatens their ecological and agronomic functions. Our objective is to determine the drivers of plant diversity in field margins for conservation and restoration purposes. To do so, we assessed the effects of field margin structure and long-term management over 20 years (1995–2015) on the taxonomic and functional α- and β-diversity, and the functional composition of herbaceous plant communities. In 2015, we surveyed 302 field margins in bocage landscapes of Brittany, northwestern France. Results were very similar between taxonomic and functional diversity but revealed important discrepancies between the drivers of α- and β-diversity. Deep ditches, mowing and grazing increased α-diversity but did not affect β-diversity. Denser hedgerows had lower α-diversity than other field margins but strongly contributed to β-diversity by harbouring more unique sets of species or life strategies. Long-term herbicide spraying in field margins and cropping intensity in adjacent habitats did not affect α-diversity, but had more complex effects on β-diversity and selected for common weeds. All in all, preservation of dense hedgerows, abandonment of herbicide spraying, and protection against agrochemical drifts are key measures to prevent the establishment of common weeds and biotic homogenization of herbaceous plant communities in field margins. Above all, our study shows how important it is to go beyond α-diversity to make robust conservation and restoration decisions.
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