The Cows and the Bees
Featured Image: Cattle grazing on rangeland east of Steens Mountain. By Greg Shine, BLM.
Featured article: Shapira, T., Henkin, Z., Dag, A., and Mandelik, Y. 2020. Rangeland sharing by cattle and bees: moderate grazing does not impair bee communities and resource availability. Ecological Applications 00( 00):e02066. doi:10.1002/eap.2066
In January, the Chattahoochee Nature Center unveiled Georgia’s first highway pollinator garden, in the hope that sharing the land between commuters and pollinators can remedy a problem that’s been worrying conservationists and farmers alike: the decline of bees.
While the decline has been a known issue for some time, unfortunately, the honeybee population drop hasn’t leveled out– increased insecticide use from agriculture has further depleted their numbers, with some estimates saying that the populations declined by nearly 40% in the winter of 2018. This is a critical problem; up to ⅓ of the food we eat comes from bee-pollinated crops.
To combat the bee decline, perhaps we need to go beyond the pollinator garden. What if there was a way to keep up agricultural production without endangering honeybees and wild bees?
This Land is Bee’s Land
All land, even land with an agricultural land use, is part of a larger ecosystem– and the way that land is used can have cascading effects. A ranger might use their land for cattle grazing, but bees and other wildlife don’t live by the land uses that we’ve set. This means that the cattle grazing– the plants that it chooses to eat and chooses to leave behind– affects more than just the plants; it can also affect the wildlife that depend on those plants for survival.
While the goals of agriculture can potentially be in contest with the goals of conservation, perhaps they don’t have to be. The concept of “land sharing” has arisen as a way to use the land to benefit both agriculture and species of concern. But before it can be used to save bees, we need to know: can rangelands be shared to serve multiple needs?
Can rangelands be shared to serve multiple needs?
This is how a team of researchers led by Tal Shapira found themselves in the rangelands of Israel. There, grazing is a historical part of the landscape, meaning that the plants and pollinators have likely evolved with moderate grazing throughout history. This makes their study site it a unique place to test how cattle grazing affects the plant community– and also how a change in the plant community could affect pollinators.
The team went to work: building fenced plots to keep enough cattle in for moderate grazing, and other fenced plots built to keep cattle out. They studied the areas with and without cattle for two years, paying attention to the plants as well as honeybees and native bees. The researchers spent days surveying which species of plants were in each area and how abundant each species was, and they sat for hours to monitor bee diversity and foraging behavior.
What they found wasn’t a simple story. The grazing, as expected, changed the menu of plants that were available to the bees for foraging and nesting. But this change in plant composition did not negatively affect the bees; the abundance, number of species and types of bees were all unaffected by grazing. While there were some differences in bee communities between different sets of plots, the researchers attribute that to factors other than cattle, such as variation in climate between years and locations.
The researchers think that this indifference to grazing is because many of the bees studied were not habitat specialists; not many were so picky as to only frequent the grazed plot, for example.
This is not the first time grazing impacts have been studied: ecologists have long turned to the “intermediate disturbance hypothesis”, which states that an ecosystem with a moderate amount of disturbance can host the most diversity of plants and animals. The cattle, then, make room for an array of plants to grow. This is good news for bees and rangeland sharing.
When we think about how we use land, it’s important to think on multiple levels; to see how our actions can have unusual linkages to other parts of the ecosystem. Land use sharing is one way to bring this kind of thinking to the fore– from sharing rangelands, to sharing highways.