The provisioning of pest control services in crop fields adjacent to flower strips was enhanced by 16% on average compared to fields without flower strips. On average, pest control services were also increased in crops adjacent to hedgerows, but effects were more variable and overall not statistically significant . Pest control services declined exponentially with distance from the field edge, but the slopes of the distance functions between fields with and without adjacent floral plantings did not differ . Crop pollination effects were more variable across studies and overall not significantly different between crops with or without adjacent floral planting across all studies and within- field distances . However, effects of distance to field edge differed for fields with floral plantings compared with control fields . Pollination services were increased near floral plantings and decreased exponentially with increasing distance from plantings, while no such effect of distance to field edge was detected for control fields . The fitted distance curves for fields with or without floral plantings intersected at 43 m .Crop pollination services, 25 liter pot but not pest control services, tended to increase with flowering plant species richness of the adjacent flower strip .
Crop pollination services also tended to increase with time since establishment of the adjacent flower strip, but showed a positive saturating relationship .Pollination services increased by 27% in 2 year old strips compared with the youngest plantings , while the additional predicted increase from 2 to 4 years or older strips was approximately 5% on average . Pest control services in crops adjacent to flower strips did not increase with flower strip age .Our quantitative synthesis demonstrates a generally positive effect of flower strips on pest control services but these effects did not consistently translate into higher yields. Although in most cases beneficial effects of plantings were also found for crop pollination services, effects on crop pollination and final crop yield were variable and overall not significant. The effect of wildflower strips on pollination services increased with age and species-richness suggesting that the quality of such plantings plays a pivotal role in effective service provision. Moreover, crop pollination declined with increasing distance to floral plantings . These results indicate that floral plantings have great potential to benefit ecosystem service provision, but to do so will need to be carefully tailored for functioning at specific spatial scales. Flower diversity and strip age are important drivers through which this can be achieved and they should be considered integrally before floral plantings can make a significant contribution to the ecological intensification of agricultural production.
We found positive effects of flower strips on ecosystem service provisioning in support of the ‘exporter’ hypothesis , although effects were generally variable and only significant for flower strips enhancing pest control services by 16% on average. This is an important finding as it provides general empirical evidence that flower strips can reduce crop pest pressures across various crops, landscape contexts and geographical regions. One explanation for the more consistent positive effects on pest control services of flower strips compared to hedgerows may be that in many of the studied flower strips the selection of flowering plants was tailored to the requirements of the target natural enemy taxa while this was generally less the case in the studied hedgerow plantings. Wildflower plantings have been heralded as one of the most effective measures to enhance the provision of ecosystem service to crops with many studies showing positive effects on service provisioning . Our synthesis shows, however, that although general significant effects of flower strips were found for pest control service provisioning, effects of plantings on crop pollination services were highly variable. This highlights the need to better understand these conditions and drivers of success or failure of floral plantings to promote pollination services. Our synthesis identifies several drivers explaining this variability in delivered services and therefore offers pathways to enhance the effectiveness of these measures in the future. First, the success of flower strips to promote crop pollination services increased with their age. The strongest increase was detected up to roughly three years since the planting date.
Pollination services also appeared to continue to increase with establishment time beyond three years. This trend needs to be interpreted with caution as only three studies assessed four years old or older flower strips highlighting that scarcity of long-term data on the effects of floral plantings on services provisioning and yield, which represents an important knowledge gap. We found no evidence that this increase in effectiveness with age is driven by floral abundance, as flower abundance did not increase with flower strip age. Case studies from Central and Northwestern Europe suggest that abundance and species richness of flowering herbaceous plants in sown flower strips on the highly fertilised soils in these agricultural regions often even decline with age after the second or third year as grasses take over . The observed positive effect of flower strip age is, however, in agreement with the expectation that the build-up and restoration of local crop pollinator populations need time . It may also be explained by greater provision of nesting and overwintering opportunities in older floral plantings which are likely scarce in short-lived annual flower strips that could even be ecological traps for overwintering arthropods . In fact, Kremen and M’Gonigle found higher incidence of above-ground cavity nesting bees compared to ground-nesting bees with hedgerow maturation; Ganser et al. reported increased overwintering of arthropod predators and pollinators of perennial compared to annual flower strips. Second, our findings reveal that higher species richness of flowering plants tends to enhance pollination service delivery in adjacent crops. This is an important finding as it indicates that restoring plant diversity can not only promote rare pollinator species and pollinator diversity , but also crop pollination services. Flowering plant diversity likely promotes complementary floral resources for numerous pollinator taxa with different resource needs and continuity of floral resource availability throughout the season . The identification of species or traits contributing particularly strongly to such effects is a promising area of research . Moreover, appropriate management, such as reducing the frequency of hedgerow cutting, is important to ensuring high availability and diversity of floral resources . Our synthesis reveals that floral plantings enhance pollination services, but only in the part of adjacent crops near to plantings, declining exponentially with distance to plantings . The exponential decline function predicts pollination service provisioning of less than 50% at 10 m and slightly more than 20% at 20 m compared to the level of service provisioning directly adjacent to plantings, partially explaining the overall non-significant benefits when considering all measured distances across the entire field . This may also explain part of the high variability observed across studies and reconcile some of the contrasting findings with respect to pollination service provisioning in studies measuring services relatively near plantings , or up to larger distances, e.g. up to 200 m; Morandin and Kremen ; Sardinas ~ et al.. We found no indication that the degree of the dependency of a crop on insect pollination significantly contributed the observed variability in effects of plantings on crop pollination services or yield . Consistent with previous studies , landscape simplification was associated with decreased pollination services, irrespective of the presence of floral plantings. In contrast, no such effects were detected for pest control services, raspberry cultivation pot in agreement with recent studies . The effect of adding a flower strip or hedgerow was, however, independent of landscape context. Although individual case studies found support for the intermediate landscape hypothesis, enhanced ecosystem services associated with floral plantings were not generally limited to moderately complex landscape contexts, which should encourage farmers to adopt these measures irrespective of the type of landscape in which they are farming. Crop yield is affected by a complex interplay of a multitude of agricultural management practices such as fertilisation, level of pesticide use, pest pressures, soil cultivation and other factors such as local soil and climatic conditions , which can potentially mask benefits from improved natural pest regulation or pollination services .
Positive effects of floral plantings have been shown by some case studies included in this synthesis , although sometimes only several years after the establishment of plantings , but we did not detect consistent effects on crop yield associated with adjacent floral plantings. The identified drivers of the effectiveness of floral plantings to enhance crop pollination services, such as age and flowering plant diversity, could provide promising pathways towards optimising plantings as measures contributing to ecological intensification. Future optimisations should also consider the potential for synergistic interactions of enhanced pollination and pest control services by ‘multi-service’ designs of plantings , temporal dynamics , optimised ratios of floral planting to crop area , and the distance-dependency of services quantified by this synthesis. However, floral plantings are also established for other goals than yield increase. From an environmental and health perspective, maintaining crop yields through a replacement of insecticides by enhanced natural pest control services, should be considered as a great achievement . Moreover, floral plantings, of sufficient ecological quality, for example in terms of native plant species diversity, contribute also to further ecosystem services, especially biodiversity conservation ; but farmers are often reluctant to adopt such measures due to concerns of negative effects on crop yield, for example due to spillover of pests. Our synthesis demonstrates enhanced natural pest control services to crops adjacent flower strips plantings, across a broad suite of regions, cropping systems and types of flower strips studied. However, it also reveals inconsistent and highly variable effects of flower strips and hedgerows on crop pollination services and yield. This highlights a strong need to identify the key factors driving this variability and the effectiveness of different types of floral plantings in contributing to ecosystem service delivery. Informed by such improved understanding, the design, implementation and management of floral plantings can increase their effectiveness as measures for ecological intensification. This synthesis identifies several promising pathways towards more effective floral plantings for the provision of ecosystem services and ecological intensification: the modelled exponential distance-decay function of pollination service provisioning by floral plantings into crop field helps to predict service provision in crop fields; together with the lack of a strong planting area effect, our findings suggest that a dense spatial network of relatively small plantings will be more effective than a few large ones to optimise pollination service provisioning. Moreover, it identifies important drivers of the effectiveness of floral plantings for delivery of crop pollination services: flowering plant diversity and age. Based on these findings we strongly encourage the establishment, adequate management and restoration of existing perennial floral plantings that ensure the availability of high floral diversity across several years as promising pathways towards optimised measures for ecological intensification.Plants are some of the greatest chemists on our planet. They offer a vast, barely tapped repository of potentially bioactive compounds, with current estimates predicting over 200,000 unique specialized metabolites across the plant kingdom . Many of these metabolites act as therapeutic phytochemicals and essential nutrients in humans, making plants an invaluable source of bioactive compounds. However, barriers, such as the lack of access to healthy foods, limit the availability of these essential nutrients for human consumption . Plants also produce a wealth of therapeutic phytochemicals, both pharmaceuticals and nutraceuticals , that are difficult to chemically synthesize, leaving consumption of medicinal plants or plant extracts as the sole source of these important chemicals . Additionally, many important phytochemicals are expressed in plants that are difficult to cultivate or produce insignificant amounts of the desired phytochemical . With an increasing global population, new tools are needed to provide highly nutritive foods and low-cost therapeutics to a larger populace. Synthetic biology is a proven approach to reconstitute metabolic pathways for the production of valuable chemicals; so far, microbes have been the production platform of choice. While an extremely robust synthetic biology platform, microbes are unicellular organisms, hindering the reconstitution of certain complex plant metabolic pathways that normally take place in multiple cellular compartments and tissue types . Additionally, many plant enzymesdo not function properly in microbial systems . Microbial production also requires the use of expensive, large-scale fermenters and the extraction of metabolites produced, incurring significant costs.