Deux communications orales au colloque Landscape 2021

Dynafor a participé au colloque Landscape 2021 https://landscape2021.org/ avec 2 communications orales :

1°) Rivers-Moore J., Andrieu E., Vialatte A., Carrié R., Ladet S., Ouin A. (2021) Positive effects of different semi-natural habitats in agricultural landscapes to support wild bee diversity and mitigate negative effects of pesticide use

Abstract : Wild bees are the most important pollinators and their decline in diversity and abundance is reported worldwide. The use of pesticides and the lack of resources caused by the simplification of landscapes are often cited as the main drivers of this dramatic loss of essential auxiliary species. Few studies have yet simultaneously investigated local and landscape effects on wild bees and pollination in agricultural landscapes. In this study, we test the following hypotheses: (i) the complexity of the landscape and the presence of wooded semi-natural habitats like hedgerows or woods around the crop counterbalance

the negative effect of pesticide use on the diversity of wild bees, (ii) landscape composition and farming practices also influence functional diversity and composition of bee communities, and (iii) bee taxonomic and functional diversity have a positive impact on pollination potential in agricultural landscapes.

Our study took place in south-western France, in the LTSER « Vallées et Côteaux de Gascogne », a region characterized by a mosaic of small woodlands, permanent grasslands and crop fields. To test the hypotheses, we investigated a data set of 104 cultivated plots (cereals and sunflower) on the edge of which wild bees were captured once in Spring, using pan traps, between 2013 and 2019. Botanical surveys were carried out in each plot (weeds), and phytosanitary treatments on the crop were listed over the year. At the landscape level, the proportions of different types of land use were calculated in two radii of 500m and 1374m, including different types of crops and semi-natural elements such as hedgerows, woods and permanent grasslands. Finally, the pollination potential at the field level was measured at the edge of the crop using phytometers. We built generalized linear mixed-effect models (GLMM) to test the impacts of landscape and local variables and their interactions on wild bee diversity at specific and functional levels. We also used RLQ analysis to assess the link between the environmental descriptors (landscape composition and farming practices in the crop) and wild bee traits. We caught 1508 wild-bees of 86 different species during six years of sampling. We found that the presence of woods in a 500m-radius had a positive impact on wild bee abundance and species richness. Moreover, permanent grassland proportion compensated for the negative effect of the number of phytosanitary treatments in the crop on taxonomic and functional diversity of bees. Oligolectic and small bee species were favoured in heterogeneous landscapes with more semi-natural habitats, and were absent or underrepresented in landscapes dominated by crops and when local farming practices were more intensive. None of our studied ariables had any effect on pollination potential. This study may help to better understand how diverse habitats in agricultural landscapes complement each other to increase wild bee diversity and mitigate the detrimental consequences of agricultural activities.

Keywords: Landscape composition, Wooded habitats, Wild bees, Functional diversity, Pesticides.

2°) Petit S., Alignier A., Allart R., Aviron S., Boussard H., Esquerre D., Franck P., Gibert C., Ladet S., Lavigne C., Lecuyer L., Moncamp M., Muneret L., Plantegenest M., Poggi S., Ricci B., Rusch A., Tolle P., Vialatte A., Young J. (2021) Exploring the potential of co-designed landscapes to promote biological pest control

Abstract : Farming management options reinforcing the control of pests and weeds by their natural enemies can contribute to the overarching goal of reducing pesticide use in modern agriculture. Practices implemented at a field-scale are key drivers of the local intensity of natural pest control but their effect is highly variable and context-dependent. In part, this variability results from a modulation of the impact of local practices on pest control through landscape-scale management. This situation calls for exploring with farmers how their own management decisions and the management decisions of their neighbours can affect natural pest control in individual fields across landscapes. Here, we report on the implementation of this approach in five French regions that are part of the two long-term monitoring networks SEBIOPAG (sebiopag.inrae.fr) and BACCHUS (siteatelier-bacchus.com).

Data collected in the networks demonstrate that crop diversity, proportional cover of semi-natural habitats and the level of pesticide use within a 1km2 area significantly affected natural pest control, often in interaction with the level of pesticide use in the focal fields (Muneret et al., 2018; Ricci et al, 2019). This knowledge led us to conduct an exploration of potential ways to enhance pest control in scenario-based co-designed landscapes. A workshop was organised in each region with local farmers to present our findings. Formalised exchanges were then mobilised to assess which practices and landscape-scale factors farmers would be willing to modify and to what extent as well as to explore with farmers their perception and willingness to engage into concerted management. Outcomes of the workshops were mobilised to develop spatially explicit scenarios of landscape changes for a 3 x 3 km landscape in each region. The procedure for land use allocation in the scenario-based maps takes account of the nature and spatial distribution of farm types and constraints that prevail at the farm level (Martel et al., 2019). The statistical models developed for predicting levels of natural pest control in response to local and landscape scale were then coupled with the land map scenarios. The resulting simulation tool enables us to predict the level of natural pest control for each field of the map. Outcomes of the simulations conducted in each region are due to be discussed with local farmers in a second workshop. In this presentation, we will detail the generic approach and illustrate the different steps with examples derived from the five regions.

Keywords: Landscape scenarios, pesticide use, crop diversity.