Scotland’s pollinators are a vital part of the country’s biodiversity and crucial for agricultural productivity. Globally, 75% the world’s crops rely on animal pollinators and these crops account for 35% of global food production. In light of the global climate change conference (COP26) and the UN Biodiversity Conference (COP 15) held this year, we should also look at the importance of pollinators for agriculture, and how correctly managed agricultural systems can benefit the environment, rural farmers, and the world’s food supply.
In this blog, we highlight SEFARI research on the positive benefits that pollinators and legume crops have on each other, and how diversifying the agricultural landscape may be the key to pollinator survival and agricultural sustainability.
Status of Pollinators
There are at least 1500 known species of insect pollinators (species of bees, hoverflies, moths, wasps, butterflies etc.) in the UK. Within the National Pollinator Strategy, we know that of the 26 bumble bee species recorded in the UK 80 years ago, 2 are no longer present and 6 have seen considerable reductions in their range (i.e. the area in which they are found). Other pollinators have been found to be decreasing, increasing, or staying the same - with generalist species (can survive in a wide variety of habitats) typically faring better than specialist species (requiring certain types of plants or habitats).
Despite the Common Agricultural Policy’s increased focus on environmental protection, insect pollinators still face many dangers in the UK. They are susceptible to habitat loss, pests and diseases, extreme weather events, competition from invasive species, climate change, and the use of some pesticides. Often habitat loss is due to agricultural intensification and a decrease in wildflowers, forests and habitat corridors. How can we reverse habitat loss and make our productive agricultural land a habitable place for pollinators?
Beans Protecting Pollinators, Protecting Beans
Legumes are essential agricultural crops given their excellent nutritional value - often acting as a cheaper alternative protein source to meat. Given their high protein content and climate resilience - legumes may be an important crop to improve sustainability within the Scottish food production landscape.
“Legumes and vegetables play a critical role in sustainable agricultural systems and their prevalence in our countryside is predicted to increase.” - Cole et al., 2021.
Legumes also support tiny root nodules (small growths) which house nitrogen-fixing bacteria that can take nitrogen from the atmosphere and convert it into ammonia, which can in turn be used by the plant to grow. By increasing the amount of nitrogen present in the soil, less inorganic fertilizer is required and this not only promotes soil health but can also reduce a farm’s environmental footprint (both in terms of carbon dioxide and nitrous oxide emissions).
Many legumes require insect pollination to reproduce. In return, the legumes provide sugar-rich nectar and protein-rich pollen to the pollinators. The ability of pollinators to access floral rewards depends on both the shape of the flower and the mouthparts of the pollinator. Including a diversity of nitrogen-fixing plants can ensure that floral rewards are accessible to a wide range of pollinators, such as the marmalade hoverfly with its short mouthparts and garden bumblebees with their long-tongues. It is a win for the crops and a win for the pollinators.
Pollinator Preferences - Diversity is Key!
In a new research paper by SEFARI researchers, pollinator behaviour, diversity and abundance were studied at different Scottish agricultural legume plots. To find the most suitable landscape for pollinators, the researchers grew a variety of experimental legume crops ranging from monocultures to mixtures and explored how pollinators reacted to each crop type. These plots were planted with different combinations of species - including grain legumes (e.g., field beans) and forage legumes (e.g., white clover).
The study showed that different types of pollinators prefer different plants at different times of year. Preference for plants depends on quite a few factors (as outlined here and seen in the figure below):
- Physiology. The ability of a pollinator’s tongue, or proboscis, to fit where the flower produces pollen and nectar.
- Timing or duration of flowering. Field beans flower early while red clover flowers later in the season.
- Quality of nectar and pollen. Pollinators preferred crimson clover over field beans indicating it provided high quality floral rewards.
Plots with a mix of both legumes and other wildflowers are preferable for pollinators.
Figure: Pollinators and their preferences during the summer-fall months.
Managing forage legumes for pollinators
There are concerns that frequent grazing and mowing in forage legumes (e.g., lucerne, clover) limits their value to insect pollinators - out of sight, out of mind. With most pollinators being mobile and able to track floral resources at the farm level, staggering cutting or grazing (e.g., through multi paddock grazing) could help ensure some fields/areas of fields are in flower throughout the season.
To Mix or Not to Mix - A Patchwork Landscape Is Needed to Protect Pollinators
Finding the optimal agricultural landscape is difficult, as certain legumes and wildflowers can promote or compete with one another. For example, vetch and beans can outcompete low-lying clover plants, preventing them from flowering. The research shows careful consideration must be taken when deciding what plants to include in mixtures. This decision should not just consider the shape of the flower and the timing and duration of flowering, but also how competitive the flower species are. Afterall, there is no point in including species in a mixture if they are simply going to be swamped by more competitive species.
In addition, legumes cannot provide all the resources pollinators require to survive and their use ought to be combined with other agri-environmental options such as hedgerows, woodlands, ponds and ditches. As highlighted earlier, creating a diverse patchwork of habitats in the agriculture-ecosystem can help pollinators to move around from suitable habitat to suitable habitat, finding the nutrients and forage they require to thrive.
Future of Farming and Agriculture - Policies, COP26 and Going Forward
Legumes reduce the need for external inputs (e.g., inorganic fertilisers) and can benefit both agricultural yield, farm sustainability and pollinator survival. They are consequently key to mitigating the impacts of climate change, food insecurities, and biodiversity loss. It is of utmost importance that within the scope of the COP26 deliberations, before, during and after, we reflect on the role that pollinators and biodiversity plays within our food production systems and our wider rural agricultural landscapes. The future of farming and agricultural policy needs to include diverse habitats and planting techniques within plots that compliment pollinator survival and diversity - making the future of our food systems good for beans, good for bees, and good for people.
Cole, L. J., Baddeley, J. A., Robertson, D., Topp, C. F. E., Walker, R. L. and Watson, C. A. (2021) ‘Supporting wild pollinators in agricultural landscapes through targeted legume mixtures’. Agriculture, Ecosystems & Environment, 323, https://doi.org/10.1016/j.agee.2021.107648.
Legume cropping systems & pollinators - Ensuring legume cropping systems help mitigate pollinator declines. 1st September 2021. Available here.
Lili Paradi has helped with the writing of this blog. She is currently on work placement with SEFARI Gateway and is pursuing her MSc in Science Communication and Public Engagement at University of Edinburgh.