Pastures new for pollinators?

In this post Associate Editor Peter Manning discusses the paper he recently handled from Katherine Orford and colleagues ‘Modest enhancements to conventional grassland diversity improve the provision of pollination services‘

You can also read a blog post from Katherine here: Managing ecosystem services: a grassland experiment

Pollinator insects have undergone a global decline, and there is evidence that this may be placing both crop production and the maintenance of wild plant diversity at risk. This problem is now widely acknowledged by both the general public and scientific community and in response a global research effort has taken place to assess the cause of this decline and investigate how it can be reversed.

One result of this effort is a new paper in Journal of Applied Ecology by Orford et al. entitled ‘Modest enhancements to conventional grassland diversity improves the provision of pollination services’. This paper provides evidence that boosting the plant diversity of pastures, can in turn boost the pollinator communities of pastures and correspondingly provide benefits to wild plants and neighboring croplands.

These conclusions are drawn from data acquired from a nice combination of experimental and observational approaches. For example, plant phytometers (plants placed into the landscape and monitored) of two species (strawberry and red campion, but not broad bean) showed higher rates of pollination when close to species rich grasslands. Pollinator communities also showed higher functional diversity, species richness and greater abundance in these situations.

The results of the study show the plant species most favoured by pollinators are large asters, probably because of their large composite flowers. Some of these, e.g. creeping thistle (Cirsium arvense) are unwanted by farmers as they are injurious to livestock but other species identified as beneficial in the study are unlikely to be a problem and might even boost forage quality and other ecosystem services, e.g. chicory (Cichorium intybus).

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These results suggest that pollinators can be given a much needed boost by encouraging certain pasture flower species. Such findings are encouraging but I suspect that emerging questions need to be addressed by the next generation of pollinator research if farming practices are to be modified in the most effective way possible. For example, maintaining floral resources in pastures could be difficult. Many farmers fertilize pastures in order to boost forage yield and this fertilization is widely known to greatly reduce the diversity of herbs.

Additionally, there is also a cost to planting flowers (e.g. through adding cuttings from diverse pastures or sowing in herb species) and agricultural yield could be lost if fertilizer applications are reduced and land is set aside for flowers. Are the benefits of increased pollination enough to offset these costs, and are there other benefits provided by flowers (e.g. aesthetic) that might help subsidise these? Environmental context could further influence this balance too, e.g. perhaps the balance of benefit to cost is greatest close to crops that require insect pollinators? In such cases benefits could be sufficiently great that financial incentives (e.g. via agri-environment schemes), are not required.

While such questions should not discourage initiatives that aim to maintain and boost the plant diversity of pastures, their answers could enhance the effectiveness of such schemes.