This California native bee pollinates manzanitas — and blueberries

Wild bees do far more for California agriculture than expected, fertilizing up to 40% of pollinator-dependent crops and thus providing up to $2.4 billion in ecosystem services. “We were surprised by how much native bees can provide”, says lead author Rebecca Chaplin-Kramer of the University of California, Berkeley. “It’s much higher than other estimates.” Earlier work had put US crop pollination services from wild bees at only 15%.

Why the difference? The previous estimate assumed a fixed ratio of wild bees to European honeybees (Apis mellifera), rather than accounting for the fact that wild bee numbers vary greatly among habitat types. “There was a huge piece missing”, Chaplin-Kramer points out. “Where were pollinators coming from and were we really getting services?” In contrast, she and her colleagues mapped the types of wildland habitats near farmlands. The researchers identified wild-bee-rich habitats based partly on their flowering plants, which supply nectar for bees. They had previously shown that the proportion of natural habitat around farms determines the pollination services from wild bees, and used this relationship to calculate these services statewide in their study, which appeared in the June issue of Rangelands
(doi:10.2111/1551-501X-33.3.33).

“Mapping can identify hotspots of natural habitat that will benefit farmers the most”, Chaplin-Kramer continues. Worldwide, about 75% of crop types depend on pollinators to some degree; melons and squash, for example, require pollinators, while crop yields of almonds, stone fruits, and most berries are enhanced by pollinators.

The researchers’ close look at the wildlands around farms also revealed that most wild bee pollination services in California come from rangelands. “This was the other big surprise”, Chaplin-Kramer says. “Farmers are benefitting from rangelands and not just pristine ecosystems.” Rangelands include grasslands, meadows, savannas, and shrublands, and this diversity of habitats fosters a diversity of wild bees.Rangelands provide bees with nectar sources that bloom successively from spring through fall, as well as nest sites, including holes in the ground, hollow-stemmed grasses, and tree cavities.

These findings suggest that boosting rangeland conservation – and thus wild bee populations – could help counteract the decline of the European honeybee, which many California farmers currently depend on for pollination. “It’s good insurance to have wild bees in case the honeybees crash”, remarks Chaplin-Kramer.

Frontiers in Ecology and the Environment, 2011