As the insects that pollinate our crops disappear, a team of scientists has learned that they thrive on land grazed by cattle
The research was led by Berkeley environmental sciences professor Dr. Claire Kremen, among the world's foremost pollinator authorities. The team evaluated the role of wild pollinators, concluding that they are essential to our food system and that livestock grazing areas are vital for protecting them. "Preserving rangelands has significant economic value, not only to the ranchers who graze their cattle there, but also to farmers who need the pollinators," Kremen concluded from her study.
Globally, about three-quarters of crop species depend on animal pollinators to produce fruits or seeds, and over 90 percent of vitamins A and C in foods are derived from pollinator-dependent crops. More than a third of total crop biomass depends on animal pollinators, especially bees.
Yet domesticated bees are struggling on multiple fronts, and their populations have plummeted. These problems have been particularly acute since 2005, "probably due to synergistic effects of viral and parasitic diseases, malnutrition, loss of genetic diversity, and pesticide exposure," the Berkeley researchers note. This makes wild pollinators more important than ever—and that need stimulated the Berkeley team to undertake its study. They focused on California, which has the largest U.S. farm economy.
Rangelands, including those grazed by cattle, provide an important "ecosystem service" in farming by offering foraging and nesting habitat that supports populations of wild bees and other naturally occurring crop pollinators, the Berkeley paper notes. These habitats include "undisturbed ground, cavities in the ground and trees, and hollow-stemmed grasses and reeds that are suitable for species of ground-nesting, wood- and cavity-nesting, and stem-nesting bees, respectively." The report further notes that "rangeland habitats often provide a diverse array of flowering forbs [herbaceous plants], shrubs, and trees that furnish successive blooms, supporting the needs of multiple bee species."
About one-third of the value of California's agricultural production—$11.7 billion annually—requires pollination. Of that, the new study estimates, wild pollinators residing in California's natural habitats, chiefly rangelands, provide between 35 and 39 percent of all pollination services to the state's crops—the first calculation of the percentage of crop pollinators that are wild and free-living, and of the economic value of their pollination services. Thus, the report concludes, California's wild pollinators add somewhere between $937 million to $2.4 billion every year to the state's agricultural economy.
I first heard Dr. Kremen present this groundbreaking research at Stanford University, a few weeks before the study was officially released. The event was a "dialogue" hosted by several entities at Stanford—the biology department, the Woods Institute for the Environment, and The Bill Lane Center for the American West. Kremen was among a series of scientists presenting research about the ecological, cultural, and economic importance of protecting rangelands used by cattle and other grazing animals.
Dr. Lynn Huntsinger, a UC Berkeley professor of rangeland ecology, who was also at the Stanford dialogue, later stated she welcomed the study, which she identified as the first to establish that conserving rangelands enhances crop production. Huntsinger noted that precisely because rangelands have been used for ranching—livestock grazing—ranchers have kept the land conserved and stewarded it in ways that result in habitat that sustains wild bee species and other wildlife. "Studies in some ecosystems," she added, "have shown that well-managed grazing can keep invasive grasses from shading out the flowering herbs that native pollinators rely on."
Dr. Harold Mooney, a Stanford biology professor who has extensively researched agriculture's environmental impacts, co-hosted the dialogue. After Dr. Kremen's presentation, he told me he was "blown away" by what he'd just heard. I felt the same way.
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