Discrepancies between the drivers of alpha and beta plant diversity in arable field margins.

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 ß-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 ß-diversity. Deep ditches, mowing and grazing increased α-diversity but did not affect ß-diversity. Denser hedgerows had lower α-diversity than other field margins but strongly contributed to ß-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 ß-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.

Increasing crop heterogeneity enhances multitrophic diversity across agricultural regions.

Agricultural landscape homogenization has detrimental effects on biodiversity and key ecosystem services. Increasing agricultural landscape heterogeneity by increasing seminatural cover can help to mitigate biodiversity loss. However, the amount of seminatural cover is generally low and difficult to increase in many intensively managed agricultural landscapes. We hypothesized that increasing the heterogeneity of the crop mosaic itself (hereafter "crop heterogeneity") can also have positive effects on biodiversity. In 8 contrasting regions of Europe and North America, we selected 435 landscapes along independent gradients of crop diversity and mean field size. Within each landscape, we selected 3 sampling sites in 1, 2, or 3 crop types. We sampled 7 taxa (plants, bees, butterflies, hoverflies, carabids, spiders, and birds) and calculated a synthetic index of multitrophic diversity at the landscape level. Increasing crop heterogeneity was more beneficial for multitrophic diversity than increasing seminatural cover. For instance, the effect of decreasing mean field size from 5 to 2.8 ha was as strong as the effect of increasing seminatural cover from 0.5 to 11%. Decreasing mean field size benefited multitrophic diversity even in the absence of seminatural vegetation between fields. Increasing the number of crop types sampled had a positive effect on landscape-level multitrophic diversity. However, the effect of increasing crop diversity in the landscape surrounding fields sampled depended on the amount of seminatural cover. Our study provides large-scale, multitrophic, cross-regional evidence that increasing crop heterogeneity can be an effective way to increase biodiversity in agricultural landscapes without taking land out of agricultural production.

On the restoration of hedgerow ground vegetation: Local and landscape drivers of plant diversity and weed colonization.

Hedgerows are among the most stable refugia for biodiversity in agricultural landscapes, providing food and shelter to many living organisms. However, the destruction and alteration of hedgerow ground vegetation compromise their potential for biodiversity conservation. The purpose of this study was to find local and landscape-scale drivers that promote plant diversity in hedgerows and prevent their colonization by troublesome weeds. Using a functional approach, we assessed the effects of hedgerow features, adjacent farming systems (conventional vs organic) and landscape context (bocage, semi-natural habitat cover, organic farming cover) on the diversity and composition of plant communities in 40 hedgerows, in Brittany (France). Hedgerow features had no effect on species diversity, but influenced functional diversity measured as a standardized effect size (SES), i.e. independent of species diversity. Organic farming at local scale was the main driver increasing both species and functional diversity (SES), doubling the cover of insect-pollinated forbs. High organic farming cover in the landscape increased species diversity, but not functional diversity (SES), of hedgerows adjoining conventional farming systems. Besides, high cover of semi-natural habitats and organic farming in the landscape prevented colonization of hedgerows by troublesome weeds. Promoting extensive management at both local and landscape scale is thus necessary for successful restoration of hedgerow ground vegetation, which should favour biodiversity conservation and ecosystem service provision.

Crop pests and predators exhibit inconsistent responses to surrounding landscape composition.

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.

Time-lagged response of carabid species richness and composition to past management practices and landscape context of semi-natural field margins.

Field margins are key features for the maintenance of biodiversity and associated ecosystem services in agricultural landscapes. Little is known about the effects of management practices of old semi-natural field margins, and their historical dimension regarding past management practices and landscape context is rarely considered. In this paper, the relative influence of recent and past management practices and landscape context (during the last five years) were assessed on the local biodiversity (species richness and composition) of carabid assemblages of field margins in agricultural landscapes of northwestern France. The results showed that recent patterns of carabid species richness and composition were best explained by management practices and landscape context measured four or five years ago. It suggests the existence of a time lag in the response of carabid assemblages to past environmental conditions of field margins. The relative contribution of past management practices and past landscape context varied depending on the spatial scale at which landscape context was taken into account. Carabid species richness was higher in grazed or sprayed field margins probably due to increased heterogeneity in habitat conditions. Field margins surrounded by grasslands and crops harbored species associated with open habitats whilst forest species dominated field margins surrounded by woodland. Landscape effect was higher at fine spatial scale, within 50 m around field margins. The present study highlights the importance of considering time-lagged responses of biodiversity when managing environment. It also suggests that old semi-natural field margins should not be considered as undisturbed habitats but more as management units being part of farming activities in agricultural landscapes, as for arable fields.

How ecological research on human-dominated ecosystems incorporates agricultural and forestry practices: A literature analysis.

Understanding the nexus between practices and ecosystems is a critical challenge for sustainability, but it is unclear how ecological sciences have explored the question. To bring clarification, we conducted an analysis of ecology literature dealing with agricultural and forestry practices (AF practices), scanning a total of 27 556 references. Scientometric analyses showed that AF practices were addressed by 5.5% of ecology literature, and that this proportion increased from 2.5 to 8.1% between 1956 and 2017. Content analyses showed that research has mainly focused on monospecific systems in the Global North, predominantly using plot-level experimental approaches. Temporal monitoring, real-world practices and their social context were poorly investigated. This analysis stresses the need to reinforce research in complex agroecosystems, in particular in non-Western countries. Multilevel and spatio-temporal approaches, as well as participatory research, should also be encouraged to build a social-ecological understanding and formulate more grounded, relevant policy recommendations for sustainability.

Research on agroforestry systems and biodiversity conservation: what can we conclude so far and what should we improve?

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.

Meta-analysis of multidecadal biodiversity trends in Europe.

Local biodiversity trends over time are likely to be decoupled from global trends, as local processes may compensate or counteract global change. We analyze 161 long-term biological time series (15-91 years) collected across Europe, using a comprehensive dataset comprising ~6,200 marine, freshwater and terrestrial taxa. We test whether (i) local long-term biodiversity trends are consistent among biogeoregions, realms and taxonomic groups, and (ii) changes in biodiversity correlate with regional climate and local conditions. Our results reveal that local trends of abundance, richness and diversity differ among biogeoregions, realms and taxonomic groups, demonstrating that biodiversity changes at local scale are often complex and cannot be easily generalized. However, we find increases in richness and abundance with increasing temperature and naturalness as well as a clear spatial pattern in changes in community composition (i.e. temporal taxonomic turnover) in most biogeoregions of Northern and Eastern Europe.

The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project.

The PREDICTS project-Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)-has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity.

Landscape effects on the abundance and larval diet of the polyphagous pest Helicoverpa armigera in cotton fields in North Benin.

BACKGROUND: The noctuid Helicoverpa armigera is one of the key cotton pests in the Old World. One possible pest regulation method may be the management of host crop in the landscapes. For polyphagous pests such as H. armigera, crop diversity and rotations can offer sequential and alternate resources that may enhance abundance. We explore the impact of landscape composition and host crop diversity on the abundance and natal host plant use of H. armigera in northern Benin. RESULTS: Host plant diversity at the largest scale examined (500 m diameter) was positively correlated with H. armigera abundance. Host plant diversity and the cover of tomato crops were the most important variables in relation to high abundance of H. armigera. Host plant (cotton, maize, tomato, sorghum) proportions and C3 versus C4 plants did not consistently correlate positively with H. armigera abundance. Moth proportion derived from cotton-fed larvae was low, 15% in 2011 and 11% in 2012, and not significantly related to H. armigera abundance. CONCLUSION: Cotton crop cover was not significantly related to H. armigera abundance and may be considered as a sink crop. Landscape composition and sequential availability of host plants should be considered as keys factors for further studies on H. armigera regulation. © 2015 Society of Chemical Industry.