Pollinators have a critical, but largely unappreciated, role to play when it comes to climate change, says ecologist Jeff Ollerton
17 March 2021
YOU would be forgiven for not knowing that there are two large United Nations environmental events happening this year. The UN Climate Change Conference (COP 26) in Glasgow, UK, is receiving a huge amount of media attention; the UN Biodiversity Conference (COP 15) in Kunming, China, much less so. At least, outside New Scientist.
This is a source of frustration to us ecologists, but it is fairly typical: the climate emergency often overshadows the ecological emergency, even though the two overlap both in their causes and their solutions.
Although ceasing the extraction of fossil fuels is a priority, if we are going to reverse the effects of climate change we need nature-based solutions, built on conservation of biodiversity, to capture the carbon dioxide from the atmosphere. Pollinators are crucial to this, but their numbers are declining, some species have gone extinct and others are critically endangered.
Around 75 per cent of the world’s main types of crops rely on pollinators. Without them, our diets and farmers would be poorer. But their value in combating climate change is often overlooked. Almost 90 per cent of the 352,000 species of flowering plants are pollinated by insects and vertebrates such as birds and bats. As such, pollinators ensure the continuation of plant populations that lock up carbon in their woody stems, roots, bulbs and tubers. The best way to restore natural habitats to help fight global warming is through natural regeneration from seeds, and for that we need pollinators.
But this may not be the most important role of pollinators in relation to climate change; how they affect soils may be more critical. When a pollinator visits a flower it sets in motion a chain of events that leads not just to seeds, but also to a series of structures that support plant reproduction. These include woody fruit casings that protect the developing embryo, as well as dispersal structures such as the wings of sycamore seeds. All of these contain a very high proportion of carbon. Once they have fulfilled their function, they fall to the ground where they enter the soil as a source of locked-in carbon.
Soils are the world’s second-most important carbon store, and much more important than the vegetation that they support. In fact, three-quarters of terrestrial carbon accumulates in soils. Only the oceans contain more carbon by mass.
How much carbon enters the soil thanks to the activities of pollinators? We have no idea as it hasn’t been measured. Ecologists studying forest carbon dynamics use fine nets strung between stakes to measure the “litter” that falls from trees each year. The contribution of reproductive litter, as opposed to leaves or twigs, isn’t always calculated, but when it is values of 10 to 20 per cent of the total litter are typical, depending on the type of plant.
We have limited understanding of what happens when this material enters the soil. A large number of seeds are stored in the soil and they can be persistent, and reproductive litter can be very woody compared with leaves, and thus their carbon storage capacity may be greater.
For these reasons, it is vital that we pay more attention to international agreements, such as the Convention on Biological Diversity, and enact policies that safeguard pollinators, for example by banning harmful pesticides and creating larger protected areas. This requires action now at all levels, from governments to conservation groups, to create and restore habitats in which pollinators can thrive.
Drawing down carbon from the atmosphere and sequestering it requires multiple approaches; there is no single solution. Without pollinators as allies, reversing the effects of climate change will be much harder.
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