California agriculture reaps $937 million to $2.4 billion per year in economic value from wild, free-living bee species that serve the critical function of pollinating crops, according to a new study by scientists at the University of California, Berkeley, published this week in the June issue of the journal Rangelands.

About one-third of the value of California agriculture comes from pollinator-dependent crops, representing a net value of $11.7 billion per year, according to the study. Currently, many farmers rent European honeybees to ensure crop pollination, and it has been widely assumed that wild pollinators were not a significant source of crop pollination. However, the new study estimated that wild pollinators residing in California’s natural habitats, chiefly rangelands, provide 35-39 percent, or more than one-third, of all pollination “services” to the state’s crops.

“This means that preserving rangelands has significant economic value, not only to the ranchers who graze their cattle there, but also to farmers who need the pollinators,” said Claire Kremen, UC Berkeley associate professor of environmental science, policy and management, and senior author of the study.

The study is the first to calculate the percentage of crop pollinators that are wild, free-living species based on their proximity to natural habitats, and thus to identify the economic value of the pollination service due to wild pollinators.

Researchers said both rented European honeybees and wild pollinator bee species are currently experiencing supply problems. More than 1 million honeybee colonies are imported to California each year, chiefly for almond pollination. Recently, beekeepers have suffered high rates of colony losses due to diseases, pesticides and management factors, increasing the uncertainty of both supply and rental prices.

Wild pollinator species also show declines in abundance and diversity on farmlands, most likely due to habitat loss from the intensive monoculture, or single crop, production system that typifies much of California’s agricultural lands.

“Currently, wild pollinators are least abundant in intensive monoculture production areas such as sunflowers, almonds and melons, where demand for pollination services is largest,” said Kremen, who was named a 2007 MacArthur Fellow for her work in ecology, biodiversity and agriculture.