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The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies.

Reconciling biodiversity and sustainable agriculture is a major challenge. In Brazil, environmental protection laws, including a ban on the use of fire, have been introduced to reduce deforestation in the Amazon region. These laws are very constraining for smallholder farmers for whom slash-and-burn is the most viable cropping system. These farmers are now responsible for most of the deforestation occurring in the Amazon region. The environmental regulation and the increasing land pressure result in a reduction of the fallow period in smallholder production systems, leading to a decrease in yields of cassava and other crops. While the soil can recover during the fallow period, loss of soil fertility and the associated decrease in crop productivity is common after several cycles of slash-and-burn. Besides the dynamics in soil fertility, recent studies also put forward that reduced fallow periods may result in increased weed pressure. Since most of the farmers' labour time is dedicated to weeding, an increased weed pressure has important implications for the operation of the farms. We conducted an agronomic diagnosis to better understand which factors are responsible for the decrease of cassava productivity when reducing the fallow period. The underlying objective was to explore options for alternative practices to slash-and-burn. Our study was conducted in Paragominas, in the Brazilian eastern Amazon region. We selected 37 slash-and-burn cassava fields representing a gradient in swidden-fallow cycle length. For each field, management data were collected during the cropping cycle and the labour time dedicated to weeding during the season was assessed. In addition, soil samples were taken in five subplots (5x5 m²) in all the fields, and bulk density, total nitrogen, organic carbon, texture, available phosphorus and pH were assessed. Cassava yields in the subplots were assessed by destructive harvesting. Cassava fresh matter yields were on average of 8.32 T/ha, and ranged from 1.54 to 23.6 T/ha. We found no relationships between yield and land-use history, labour for weeding or soil organic carbon. However, there was a clear effect of land-use history on soil fertility and weed pressure. The total amount of labour dedicated to weeding increased by 12 man days/ha per year for each additional cultivation-fallow cycle in a ten years' time window. Time spent on weeding the field during the cropping season decreased with the period of the fallow before burning. Our results emphasise the importance of the weed pressure in the slash-and-burn systems. Reducing the cultivation-fallow cycle length will increase the build-up of weed populations and put pressure on the farmer's workload, which is important to take into consideration when considering for alternatives to slash-and-burn. Future work will focus on identification of factors explaining yield variability.

Different semi-natural habitats occur on farmland, and it is the vegetation's traits and structure that subsequently determine their ability to support natural enemies and their associated contribution to conservation biocontrol. New habitats can be created and existing ones improved with agri-environment scheme funding in all EU member states. Understanding the contribution of each habitat type can aid the development of conservation control strategies. Here we review the extent to which the predominant habitat types in Europe support natural enemies, whether this results in enhanced natural enemy densities in the adjacent crop and whether this leads to reduced pest densities. Considerable variation exists in the available information for the different habitat types and trophic levels. Natural enemies within each habitat were the most studied, with less information on whether they were enhanced in adjacent fields, while their impact on pests was rarely investigated. Most information was available for woody and herbaceous linear habitats, yet not for woodland which can be the most common semi-natural habitat in many regions. While the management and design of habitats offer potential to stimulate conservation biocontrol, we also identified knowledge gaps. A better understanding of the relationship between resource availability and arthropod communities across habitat types, the spatiotemporal distribution of resources in the landscape and interactions with other factors that play a role in pest regulation could contribute to an informed management of semi-natural habitats for biocontrol.

Linking experimentation, field data collection and modelling is essential in the design of alternative agricultural systems. Most alternative agricultural systems, such as conservation agriculture (CA), organic farming or ecologically intensive low-input systems, rely largely on biologically mediated processes and ecological-based support and regulation services. Since deterministic modelling of such systems typically fails to reproduce their intrinsic behaviour and complexity, experimentation remains indispensable in many cases. We show through examples that field measurements, experiments and modelling can support each other when one is diagnosing a specific problem or exploring viable alternatives as part of the design of, for example, disease-tolerant cropping systems, pest-suppressive landscapes or closely integrated crop-livestock farming systems. Expert knowledge and farmer perceptions may provide essential clues for validating models at scales transcending the field-plot scale. Instead of segregating modelling from field observations, experiments or practitioner knowledge, we propose a framework for their integration in the design of alternative agricultural systems.

Biodiversity-ecosystem functioning (BEF) research grew rapidly following concerns that biodiversity loss would negatively affect ecosystem functions and the ecosystem services they underpin. However, despite evidence that biodiversity strongly affects ecosystem functioning, the influence of BEF research upon policy and the management of ‘real-world’ ecosystems, i.e., semi-natural habitats and agroecosystems, has been limited. Here, we address this issue by classifying BEF research into three clusters based on the degree of human control over species composition and the spatial scale, in terms of grain, of the study, and discussing how the research of each cluster is best suited to inform particular fields of ecosystem management. Research in the first cluster, small-grain highly controlled studies, is best able to provide general insights into mechanisms and to inform the management of species-poor and highly managed systems such as croplands, plantations, and the restoration of heavily degraded ecosystems. Research from the second cluster, small-grain observational studies, and species removal and addition studies, may allow for direct predictions of the impacts of species loss in specific semi-natural ecosystems. Research in the third cluster, large-grain uncontrolled studies, may best inform landscape-scale management and national-scale policy. We discuss barriers to transfer within each cluster and suggest how new research and knowledge exchange mechanisms may overcome these challenges. To meet the potential for BEF research to address global challenges, we recommend transdisciplinary research that goes beyond these current clusters and considers the social-ecological context of the ecosystems in which BEF knowledge is generated. This requires recognizing the social and economic value of biodiversity for ecosystem services at scales, and in units, that matter to land managers and policy makers.