Flying pollinators data in invaded and restored riparian ecosystems

[Lien vers la fiche source] Asian knotweeds (Reynoutria spp.) are one of the world's most invasive species, according to the International Union for Conservation of Nature. In particular, they colonize riverbanks, where they spread during floods and rapidly form dense monocultures. In addition to impacting spontaneous plant biodiversity through competitive exclusion, they are also known to modify the biochemical functioning of the soil. They also affect the composition and structure of terrestrial invertebrate communities. However, they are nectariferous and their interest for insect pollinators has recently been demonstrated (Davis et al. 2018). The effects of Asian knotweeds are therefore not exclusively negative, and no multitrophic study integrating several essential components of ecosystem functioning (soil, plants, pollinator communities) yet exists. The omnipresence of Asian knotweeds in our riparian environments is prompting managers to take action, in order to slow its development and mitigate its impact. Ecological engineering, which consists in introducing competitive plants into areas invaded by Asian knotweeds, has several advantages: in addition to reducing the development of Asian knotweeds, it also enables the restoration of a competitive plant community closer to those that spontaneously establish themselves in these environments, while relying on the self-organizing capacities of living systems. However, to date, there is no information on the effect of these practices on ecosystem functioning, whether in terms of the return of spontaneous flora, soil biochemical components or the insect communities they support. Similarly, there is very little feedback on the medium-term results of these projects, despite the fact that they are being launched in ever-increasing numbers by managers. Using a comparative approach between three types of plots (plots invaded by Asian knotweeds, “reference” plots and “restored” plots), the study of flying insect communities and soil chemistry will make it possible to explore other ecosystem compartments. A study of the composition of flying insects, in particular pollinators, should make it possible to account for any effects of knotweeds invasion and ecological engineering management interventions. This dataset contains the species of flying pollinators caught on the various plots sampled from April to September 2021, as well as their abundance (number of individuals caught). METHODOLOGY The colored cup capture method was chosen (Westphal et al. 2008, Davis et al. 2018). Indeed, this method has the advantage of targeting pollinating insects (attracted by color) compared to more exhaustive but less selective methods such as Malaise tents. Moreover, it is less sensitive to observer bias and is particularly effective for inventories of bees, the taxa initially targeted by the BEECOVER study (Westphal et al. 2008). What's more, the cups can be placed at different heights, enabling flying insects to be collected both on the ground and at heights of several meters. This method is therefore particularly well-suited to the multi-stratum environments involved in this study. Last but not least, it enables flying insects to be collected over a continuous 72-hour period, thus avoiding the vagaries of sunlight on which direct observation methods depend. Three sets of three cups were placed each month between April and September on each of the 21 study plots. The 21 study plots were situated along two watersheds in the Rhône and Isère Departments and are divided into 7 triptychs of invaded/invaded-then-restored/reference plots. Each set of cups consisted of a white, a blue and a yellow cup. From April to June, the cups used were neutral-colored plant fiber cups (Beige bagasse bowl, 750ml, Ø 170mm, www.pro-jet.fr) spray-painted (blue, white and yellow ROCOL® 650ml plotter, www.mabeo-direct.com). From July onwards, in view of recurring sealing problems, the bagasse cups were replaced by transparent food-grade plastic cups (PET plastic bowl, 750ml, Ø165mm, SABERT®, www.monouso.fr), also spray-painted using the same painting material. The diameter of the cardboard cups was 170mm, and that of the plastic cups 165mm. The cups were placed on metal supports attached to wooden stakes at different heights (0.50, 1.50, 3.50 m) to capture the vertical structure of the plant community. Each month, the height of the cups was redistributed and randomly assigned to each stake to avoid any bias. Stakes were positioned at 5, 10 and 15m along the transect of each plot. Only the height of the cups varied for each capture session. Each month between April and September, the cups were set up at the end of the day or early in the morning, filled with water and a drop of lemon dishwashing detergent to reduce surface tension and facilitate capture. The traps were retrieved 72 hours later, filtered and transferred to a pillbox filled with 70° ethanol for preservation prior to identification. Identification was carried out by entomology specialist David GENOUD. Davis, E. S., R. Kelly, C. A. Maggs, and J. C. Stout. 2018. Contrasting impacts of highly invasive plant species on flower-visiting insect communities. Biodiversity and Conservation 27:2069-2085. Westphal, C., R. Bommarco, G. Carre, E. Lamborn, N. Morison, T. Petanidou, S. G. Potts, S. P. M. Roberts, H. Szentgyorgyi, T. Tscheulin, B. E. Vaissiere, M. Woyciechowski, J. C. Biesmeijer, W. E. Kunin, J. Settele, and I. Steffan-Dewenter. 2008. Measuring bee diversity in different European habitats and biogeographical regions. Ecological Monographs 78:653-671.