Wildflower strips and areas linked in a network of biodiversity corridors are just what agricultural landscapes may need to bring rich insect and wild plant diversity back to intensively farmed land. In collaboration with the Bee Care Center, ecologists are assessing the impact of ecological enhancement measures in Germany’s Upper Rhine area. The results look promising.
// The Upper Rhine Valley research project is investigating how wildflower strips and areas can enrich the number of species and diversity, as well as individual numbers (abundance) of bees and butterflies in intensively-farmed areas.
// Various mixtures of annual, winter-hardy and perennial wildflowers were sown.
// Results, after eight years, show that creating wildflower areas on ten percent of arable farmland substantially increases the diversity and abundance of wild bees and butterflies.
Agricultural areas worldwide have grown continuously over the past 50 years, as farmers work to feed our planet’s ever-growing population. This increased food supply benefits consumers; but the land use changes it brings, significantly reduces natural and semi-natural habitats for many insect species and limit their ability to survive in some locations.
In an effort to develop tools to reverse this trend – and help farmers bring back wild plant and insect biodiversity to areas of intensified food production – the Bayer Bee Care Center has commissioned two ecology and nature conservation institutes to test approaches to provide vegetation that offers pollinator habitats. A long-term project in Germany’s Upper Rhine Valley is working to increase the understanding of how ecological enhancement measures can help attract wild bees, butterflies and other pollinators. New habitats with wild flowers and other plants have been created on the agricultural land at the project sites.
The project is in its 9th year of study in the relatively-intensely farmed Upper Rhine region. It’s a partnership with landscape ecologists from the Institute for Agro-Ecology and Biodiversity (IFAB) in Mannheim, and the Institute for Landscape Ecology and Nature Conservation (ILN) in Bühl, both located in Germany.
Modern agriculture has been very efficient at producing high-quality food but these practices do not always provide habitats for pollinators to nest and thrive. In many ways, pollinators make the world go round. Some 90 percent of flowering plants on the planet rely at least partly, on the transfer of pollen by insects and other animals, to flourish. So, farmers and managers of agricultural landscapes can make a big contribution to sustainable agriculture if they use ecological enhancement practices to create pollinator-friendly areas at and near their farmlands.
“Bayer’s scientific initiatives explore ways to help farmers support pollinators in a pragmatic farming approach,” explains Dr. Christian Maus, Global Lead Scientist at the Bayer Bee Care Center.
Wild bees and butterflies being surveyed in a wildflower area.
The project focuses on two sites of farmed arable land that have very little grassland nearby, at Dettenheim and at Rheinmünster in southwest Germany. The main crops here are maize and cereals, along with linseed and alfalfa on a smaller scale.
The first biodiversity strips for the project were sown in 2011. This followed the completion of a baseline survey in 2010 which recorded the initial situation, regarding landscape and populations of wild bees and butterflies on the sites. These wildflower fields are designed as nature-rich ‘biodiversity corridors’ that weave a mix of flowers and other plants around farmlands, to encourage more wild pollinators to live there.
Wildflower strips are used as a biodiversityenhancing measure in many countries. However, this study is among the first to do a rigorous scientific assessment of the effectiveness of the approach, according to Dr. Rainer Oppermann, IFAB’s head: “We compare results from two 50-hectare wildflower research sites with two parallel 50-hectare control sites. The long-term character of the study is also unique. Only few collaborators would fund this type of long-term data collection, so this project is bringing rich new insights that we can share with others,” he explains.
Creating wildflower strips in agricultural landscapes can improve living conditions of insects incl. wild bees and butterflies.
Red Mason Bee (Osmia bicornis)
Large Copper Butterfly (Lycaena dispar)
// Sowing of wildflower strips and areas on ten percent of farmers’ arable land. Strips blend different flower types – annual, winter-hardy and perennial. The strips are partly interconnected by corridors to create a network of natural and semi-natural areas around the farmland.
// Creating ‘bee banks’. These soil mounds (10-20 meters long) are specially created to attract ground-nesting wild bees to make their nests there.
Location of the two farms in southwest Germany.
Upper Rhine winter-hardy flower mix in June 2015
Bee bank in Dettenheim after clearing with a brushcutter in July 2015
// Food sources: Many wild bee species are fussy eaters, preferring specific foraging plants.
// ‘Stepping stones’ are needed to connect natural or semi-natural areas across landscapes fragmented by farming. Steps can be flowering strips, hedgerows, small forest patches with surrounding vegetation or other landscape structures.
// Nesting sites: Different wild bee species prefer different environments and materials for nesting. Many nest in the ground, so creating soil mounds in a landscape invites them to nest there.
The Upper Rhein Valley project gained insight into insects’ needs, to give farmers useful tips to welcome more pollinators to live near their fields.
The researchers report encouraging overall results. The project shows how this kind of targeted ecological enhancement in intensively farmed landscapes greatly increases the number of pollinator insects (their ‘abundance’) and species diversity. And that perseverance pays off, with implementation of the measures only showing a clear, positive impact from the third year onwards.
Over five years, both study areas with ecological enhancement measures registered significant increases in wild bee species diversity and abundance. Increases were also registered for butterflies, though to a lesser extent. The researchers note that the number of butterfly species and the number of individual insects show considerable fluctuations from year-to-year. These variations are caused by factors such as changing weather conditions.
For wild bees, results reveal a steady increase in the number of species recorded, from eight in each of the trial sites in 2010 (baseline) to 30 and 49 species in 2017 at Rheinmünster and Dettenheim, respectively (see figures 1 and 2). Both study sites also logged increases in the number of individuals per wild bee species and in the number of different species registered on the German endangered species Red List.
For butterflies, the number of species ranged from ten in 2010 to 17 in 2017 at the Rheinmünster site, with a peak of 23 species in 2015. At the Dettenheim site, numbers ranged from seven in 2010 to 19 species in 2017, more than twice as many species as in the control sites (see figures 3 and 4).
Farmers and other stakeholders involved in agriculture can be encouraged to help boost the diversity of wild bees and butterflies in their agricultural landscape by creating wildflower strips around fields.
Here’s how it could be done:
// Choose wildflower mixes to suit conditions of the site.
// Mix plant species to bring season-round flowering for insect forage.
// Sow in spring and fall.
// Leave growth over the winter; don’t mulch until end of winter (late February), and only in half the area.
// Combine annual and perennial seed mixes – 50 % new sowings / 50 % leftover, for overwintering and egg-laying insects.
// Managing weeds in wildflower areas reduces undergrowth; creates attractive bee nesting habitats.
In 2011, different wildflower mixtures were tested. As the resulting flowering patches could not be fully surveyed, consistent figures are only available from 2012 (which are depicted in the graph).
Average number of wild bee species per sampling area – Rheinmünster
Average number of wild bee species per sampling area – Dettenheim
Average number of butterflies per sampling area – Rheinmünster
Average number of butterflies per sampling area – Dettenheim
preserves and creates spaces for natural and semi-natural habitats by making land use more efficient, helping to preserve the biodiversity of plants and animals, including pollinators.
Violet-winged Mining Bee (Andrena agilissima)
Common carder bee (Bombus pascuorum)
Mining bee (Andrena limata)
Large Bear-clawed Nomad Bee (Nomada alboguttata)
A number of nationally-endangered species of bee were also identified in the study sites in each year of the project. Rheinmünster registered two extremely rare bee species – the Wild Carder (Anthidium septemspinosum) and Squat Furrow Bees (Lasioglossum pauperatum). In Dettenheim, an endangered Mining bee species and the Squat Furrow bee (Andrena limata, Lasioglossum pauperatum) were observed in 2013. Some endangered butterfly species were also documented.
In contrast, the bee banks were less successful. Bees only nested here when vegetation was cleared regularly. This points out the need to have land management strategies when measures like bee banks are implemented, with staff tasked to regularly clear the bank to make it attractive for
Other key learning points from the project:
// Flower diversity is key. Patches of perennial and winter-hardy flowers are an important early-foraging source for insects. Also, sowing a diverse mix of flower types and speciallyadapted mixtures was more effective at attracting bees and butterflies, than standard flower mixtures used in earlier trials.
// Smart management ensures diversity. Active management of wildflower areas prevents dominant plant species, which will have a negative effect on biodiversity, from emerging.
The next step is to move the project’s learning into policy action. Yet, currently, putting policy ideas into action seems to be unnecessarily complicated in Germany. Although the benefits of ecological enhancement measures in the agricultural landscape are recognized and supported by public funding under certain circumstances, the implementation is hampered by the substantial bureaucratic effort required. Therefore, many potentially-interested farmers may not make use of the supported measures. Moreover, ecological expertise is not always sufficiently available to advise the farmers on how to go about implementing meaningful measures.
Dr. Christian Maus concludes: “We, in any case, hope that the publications on the lessons we have learned from our project will further inform farmers, policy makers and agricultural planners alike on the flower strip concept as a part of sustainable farming efforts. It can make a real contribution to improving conditions for wild pollinators to thrive in agricultural areas. And that is exactly the reason why we commissioned this research – to contribute to the protection of pollinators.”
The Upper Rhine Valley project is building on its nine years of research, to see how ecological know-how from the project can be transferred to wider groups of farmers and other stakeholders involved in agriculture.
This research will continue for the next two years with assessments of how the diversity and abundance of bees and butterflies respond to different sizes of flowering strips. Here, researchers are assessing if similar results can be achieved with smaller-scale wildflower strips – reduced from ten percent to five percent of farmland. This insight is key to offering useful options to agricultural planners and farmers that strike a balance between the concerns of both crop production and ecology.