The researchers measured the abundance and diversity of wild bees on all three types of farms during the 2001 growing season. They also measured how rapidly pollen accumulated on flowers living on each farm type. Domesticated bees weren't used during the experiments.
Kremen and her teammates found more than twice as many beesfrom more than twice as many different specieson organic farms near wild habitats than they did on either organic farms farther from natural habitats or conventional farms close to nature.
The researchers also found that native bees delivered an average of nearly 1,800 pollen grains per day to each flower on organic farms near natural lands, but only about 600 and 300 grains per flower per day, respectively, to the second and third farm types. About 1,000 pollen grains per flower per day are required for successful fertilization, they estimated.
"On organic farms near natural habitat, we found that native bee communities could provide full pollination services," the researchers concluded in a paper that will appear in an upcoming issue of the journal Proceeds of the National Academy of Sciences.
"All other farms, however, experienced greatly reduced diversity and abundance of native bees, resulting in insufficient pollination services from native bees alone," the trio wrote.
A Beeline for the Bottom Line
Kremen said that farming techniques that appear friendly to native bees include avoiding herbicide and pesticide use; growing a diversity of crops on each plot of land, rather than a single crop; and cultivating some plants that don't have economic value on their own but that help provide a continual supply of food for native bees. In some cases, she said, it may even be advantageous to allow weeds to grown along the borders of fields.
"We couldn't do away with honeybees all together," said Kremen. But, she said, farmers could "reduce the [number of] honeybees that they rent and plow that money into these small restoration efforts," which could help native bee populations grow and might ultimately pay dividends.
The resulting diversity of bee species would also offer an insurance policy against, for example, attacks by parasites that pray mainly on honeybees.
"If honeybees continue to decline, [these farmers] will be better off, because they'll have these natural pollinators," said Kremen.
"As we destroy natural habitats, we are reducing our options," she said. "We are destroying an insurance policy."
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