I wanted to share a new study that came out this week in the journal Science. We generally agree how important bees, butterflies, and other pollinators are, not only for our crops but for the health of ecosystems as a whole. Yet, despite decades of awareness, pollinator numbers continue to decline worldwide. Dr. Gabriella Bishop used a meta-data approach in this study to examine why pollinators are struggling. The study concluded that current conservation targets for habitat area are simply not large enough.
The project combined datasets from 59 studies across 19 countries to measure how populations of wild bees, bumble bees, hoverflies, and butterflies respond to natural habitat around farms. I was fortunate to contribute some of my previously collected data on pollinator communities in the California Central Valley and be included as an author. Overall, by combining datasets, Dr. Bishop had information on 178,000 insects collected from 1,200 field sites, which allowed for the calculation of the minimum amount of habitat each group needs.
Many global and regional policies, like the EU Biodiversity Strategy, suggest setting aside about 10 percent of farmland as habitat for pollinators. But Dr. Bishop found that pollinators need far more space to thrive. The minimums vary group, with solitary bees needing ~16% in temperate areas and ~38% in the tropics. Butterflies needed ~37%. Hoverflies were more flexible, with the lowest threshold for habitat requirements at ~6%). Overall, this means hedgerows, woodlots, meadows, and wildflower-rich grasslands must make up a much larger share of the landscape if we want to halt pollinator declines. And critically, these areas need to be managed for the long haul. Short-term fixes such as seasonal wildflower strips can provide temporary boosts, but they do not sustain pollinator populations in the long run.
For gardeners and land stewards, the message is clear. Every patch of habitat counts, but scale does in fact matter. Planting flowers that bloom across the seasons is important, but so is maintaining semi-natural spaces for decades, not just years. If we want future generations to enjoy these insects, we must think BIGGER.
OH! Without native to ecoregion where grown woody plants, trees and shrubs,grown by seed in their native ecoregion, there will be no pollinators. If the goal is truly to help restore ecosystems and habitat the need is far more than “flowers that bloom” and “semi natural spaces”. It is truly curious to read that insects are something for people to enjoy. ? “E.O.Wilson’s biggest (and most unappreciated) contribution was to recognize that life as we know it depends on insects.”https://pacifichorticulture.org/articles/remembering-e-o-wilson-foreward-by-doug-tallamy/
This perception is incorrect; there is a robust body of literature that shows woody plant nativity is one of the least important factors for wildlife biodiversity. Please refer to this peer-reviewed factsheet which is based on a comprehensive review of the peer-reviewed literature: https://www.researchgate.net/publication/336056922_ARE_NATIVE_TREES_AND_SHRUBS_BETTER_CHOICES_FOR_WILDLIFE_IN_HOME_LANDSCAPES
This makes sense and aligns with one of the entomologists up at Western. I would love more spaces set aside. Telling people their yard attempts aren’t enough may be truthful, but I worry that would have unintended consequences where they just give up. One solution offered by folks is using medians and shoulders of interstates…but a problem with that is road kill slaughter of animals and insects that would live in those areas. I wonder how farmers, for example, could afford to set aside 16% to 37% of their land. My grandfather’s farm was 160 acres, but 5 of that was homestead (house, sheds, barns, cribs, silos, etc). 10 acres were depression slough like area. Leaving 145 acres of cropland. Now, 1/4 of that was set aside annually or planted in the equivalent of cover crops, then in rotation turned over. Leaving about 108 acres of cropland. People don’t understand that all that “farm” isn’t producing crops at the same time! They couldn’t earn a living off that, and sadly had to sell it off in the 90’s to a larger farm group. For farmers taking out another 33%….I am not sure that planting hedgerows and fence lines would make enough difference to fill the estimated needs. If cropland is reduced, so is supply and prices skyrocket, or then we have to get more imported foods, which means lands/forests in those regions are cut down to plant crops….shifting the problem elsewhere (and potentially with more disastrous consequences). I don’t know what the solution is, but the loss is troubling.
I agree with your comment. I don’t know many of farmers who would be ABLE to give up farmland to habitat, even if they were willing. I like the idea of finding creative spaces for habitat conservation, like adding floral diversity to medians and parking lots. It would serve to beautify our urban spaces, something we sorely need in California cities. Thank you for your thoughts on the issue.
Compounding the difficulty is the factor of habitat specialization. Many pollinators can get pollen from plants of multiple taxa but the majority of North America’s native bees need particular genera or even species for their life history to unfold every year. My personal favorite is the Spring Beauty Miner Bee, which only gathers the pink pollen from Spring Beauty (Claytonia virginica), a spring ephemeral in the eastern forests.
Your comment is fine, but your perception of how many native bees are specialists is incorrect: the majority are generalists, not specialists. https://www.usgs.gov/faqs/what-role-native-bees-united-states
If only we could talk about the needs of more than bees and plants. Lepidopteran larvae, leaf miners, gall insects, and many, many species, or example, are easily dismissed when we cannot measure what we don’t know, or cannot pony up research funds to look more deeply. Truth is a moving evolving target, and I am comfortable in knowing that many questions are still unanswered. I measure the species in my own yard over time and several other properties.
Thank you for your comment. I hadn’t heard of the Spring Beauty Miner Bee. What a lovely name for a bee!