Harvesting the Research: Common, Easily Enhanced Species Are Most Important to Crop Pollinatio

Surprising findings indicate that some wild pollinators might be much more important to farmers than others

Food Tank interviewed David Kleijn, lead author of a paper on crop pollination services by wild species. Enhancing the ecosystem service of pollination will be key to the ecological intensification of agriculture.

The overall message: The authors found that the economic benefit of crop pollination services is provided mostly by common species. They therefore conclude that a focus on the economic value of pollinator services is an insufficient argument for preserving rare and threatened species of pollinators.

The research: Using data from 90 studies that spanned 1,394 crop fields, the authors tested three hypotheses:

1. The majority of pollination services are provided by a small number of wild species.
2. These species are relatively common, while rare and threatened species do not contribute much to the ecosystem service of pollination.
3. These common species can be easily enhanced by simple farm management practices.

The findings of the paper confirmed all three hypotheses. Only 2 percent of the 735 wild bee species observed in the datasets provided over 80 percent of pollination services.

Food Tank (FT): What are two key points of your paper, in laymens’ terms?

David Kleijn (DK): The first key point is that wild pollinators are just as important as honeybees for crop pollination. We can use the importance of wild pollinators to interest farmers in implementing new conservation measures. We are already seeing examples of this in the United States and in the Netherlands, where fruit farmers are establishing wild pollinator habitat next to fruit crops, often without government subsidies.

The second key point of the paper is that only a small number of common wild bee species visit crop flowers. These species can be enhanced relatively easily to contribute to crop pollination. Most other bee species do not occur on cropland and/or do not forage on crop flowers; the preservation of these species, many of which are threatened in their existence, requires traditional conservation practices such as protected areas and reserves. We therefore concluded that a sole focus on ecosystem services might occur at the expense of these threatened species that don’t contribute much to crop pollination. We need both.

FT: Why is your review relevant to the transition to sustainable agriculture?

DK: Our review shows which species contribute to crop pollination and which species do not. This has two advantageous. First, it will help better target measures that intend to preserve pollination services. We can make recommendations on which plant species will enhance floral resources for wild pollinators outside of the crop flowering period, and we can tell farmers where to plant them. This will make preservation efforts much more effective.

Second, it will show which wild bee species might benefit from the planting of insect-pollinated crops; farmers can have positive side effects on pollinators through their crop choices. Indeed, other studies have already found that bee species using floral resources from crops have more positive population trends than bee species that use wild plant species.

FT: In the paper, you contend rare and threatened species contribute very little to plant pollination. Could this be because their populations are already quite diminished? Might they not contribute in valuable (and perhaps unforeseen) ways if their populations were to be replenished?

DK: The rarity of threatened bee species is part of the reason why they contribute little, but certainly not the whole story. Some species that fly on crops used to be quite common and used to contribute substantially to crop pollination. Their decline is mostly related to land use change and a shift in the types of crops that are grown. 

The decline of semi-natural habitat, in both quantity and quality, has resulted in the unintended consequence of loss of pollinator habitat, which has lessened the contribution of these species to crop pollination. Another reason for the limited contribution of threatened species to crop pollination is that they specialize on certain non-crop flowers or habitats that have declined over the years. It is unlikely that these species will become important for crop pollination even if they become more abundant once again.

FT: Despite the lower economic payoff of conservation of rare and threatened species, you do contend that their preservation is still of vital importance. How might this importance be valued if no economic benefit can be quantified? Could rare pollinator species conservation be incorporated into payment for ecosystem services schemes such that this importance is conveyed through public policy?

DK: Yes, I think it is of vital importance that we conserve also the species for which we have no evidence that we benefit economically from their existence. Quantifying the value of nature is quite useful to demonstrate to the general public that we benefit from biodiversity, something most people do not realize. However, it is useless to try to place a price on everything or argue that we should only conserve things if we benefit economically from it. That is not how people think. We conserve many things, like art and old buildings, because it makes us feel good, because we think it is the right thing to do, or just for the fun of it. I think policymakers, conservationists, and scientists should use both arguments for conservation.

The need to conserve biodiversity for the ecosystem services it provides has become the dominant conservation paradigm, especially amongst policymakers. Our paper warns that too much focus on ecosystem services might go at the expense of all the other species that do not contribute much to service provisioning. We need both.

FT: Do your results also have implications for farm management practices? How would you explain the results of your paper to a farmer looking to participate in a transition to sustainable intensification?

DK: Our study shows that it is easy to enhance the common species that provide most of the pollination services to farmers. Other papers have shown that an increase in wild pollinators results in higher yields or higher quality products, and/or can partly replace nutrient inputs. If a farmer wanted to become more sustainable, the first action to take would be to enhance flower abundance in pre-existing semi-natural landscape elements on the farm.

These areas could include roadside ditches, hedges, or leftover areas around barns and sheds. These habitats are usually of limited value to pollinators currently, because they contain few flowers and represent poor nesting habitat. Since these areas are not suitable for crops and require minimal changes in management, this is pretty much a win-win method to farm in a more sustainable way.