Wild flower patches in agriculture: positive for insects, neutral for crops?
In debates about ecology and conservation, the term ‘ecosystem services’ usually pops up pretty quickly. What this means is essentially the bang for your buck that any conservation attempts bring, and in the case of arthropods, the services with the biggest dollar signs attached are crop pollination and pest control.
The addition of more wild flowers in agricultural settings is often suggested as a smart move towards bringing in the bugs to deliver such benefits. Restoring field margins and introducing wild flower strips have proved popular choices from among the options available in the UK’s Countryside Stewardship subsidy scheme.
So, everyone’s benefitting from an increased buzz about the fields, right? The truth may not be quite so simple.
Pollinators sticking to the fringes — and risking sickness?
A new review from Chilean and Spanish researchers suggests that while there are indeed increased pollinator numbers and diversity around the edges of fields with enhanced floral features, this is not translating into a major migration into the middle, where their pollination would be most desired. Where crop yield is measured (and it’s surprisingly not that often), the results don’t scream ‘ecosystem service in action’ either.
Another study looking only at bumblebees found that flower strips boost bee reproduction, but have a drawback in the form of increased exposure to pathogens, risking infection. The effects of this possibility on crop pollination are currently unknown, but it’s unlikely to be a winner. It must be stressed, however, that this is just one study, and one type of pollinator, not to be taken as insight into the broader realm of beneficial insects.
It takes time to see restored ecosystem benefits
Despite how they look, these examples are far from signs that bringing more flowers into agricultural environments is a bad idea. As far as the apparent lack of pollinator action in the centre of fields goes, this might just be because we’re expecting too much, too soon.
The study’s authors concede that the comparatively short duration of the research available to date may well be a contributing factor to its seeming lack of conclusive evidence that flowers do power profitable pollination. For the full impact of increased invertebrate populations to be felt in any field context, it can often take a number of a years.
There’s no single solution
Most likely, the truth is that setting aside areas for wild flowers alone, while guaranteed to be popular with flower-visiting insects, will not bring all possible benefits for all who might require them. Broader agricultural diversity is likely to be the answer. Two other recent studies use different methods to reach similar conclusions on this matter.
A large piece of analysis based on two long-term experiments in Europe and America has found that species diversity can have a massive impact on just how much plants get nibbled by pests. Plants in monocultures got more than double the attention from hungry herbivores than those in diverse mixtures. The authors suggest that this was likely due to the twofold effect of plant diversity favouring predators and dilution of those plant resources considered the most nutritious to herbivore species.
Pests do like an easy life, and tend to favour huge blocks of just the thing they love to scoff — consider how much of a target bright yellow fields of oil seed rape are likely to be to a pest such as a flea beetle. Creating greater habitat complexity can throw pests off-course in their mission for quality food, while also favouring their natural enemies in their own quest to evade predators such as birds and small mammals.
A review looking across the whole scope of potential agricultural diversification, from flower strips to crop rotation and agroforestry, found that in the main, ecosystem services are in fact going hand in hand with yield improvements. Effects are to be found above and below ground on diversified agricultural ecosystems, and looking at the two above-ground services touched on in this article, pollination and pest control, there appears to be compelling evidence to support the idea that they are affected positively.
By improving prospects for beneficial species, a virtuous cycle can be created which helps farmers too — though it remains a truism that those who put the most in tend to get the most out. With the UK Government’s new Environmental Land Management (ELM) subsidy scheme, which offers payments for measures that purport to improve biodiversity, replacing EU funding in the New Year, it is an apt time for those working in agriculture to consider bold moves on their land.
