"Like any animal, native bees need a place to live," he said. "They need nest sites and floral resources, and if they don't have them, they won't be there."
According to Black, people can take small steps to augment wild bee populations, such as making nesting areas available. Given that about 70 percent of wild bees nest directly in the ground, not in hives, this is simpler than it seems, he added.
Wild bees also need natural habitat to forage, which can include small woodlots, areas along a stream, or even a hedgerow between fields of crops. As an added bonus, Kremen said, wild bees help keep wild areas healthy.
"They help us maintain the natural landscape, which provides spiritual beauty, recreational quality, and other ecosystem services we depend on," she said.
Kremen has been documenting the extent wild bees play in crop pollination in California and has found that on farms in narrow valleys surrounded by wild vegetation the native bees can do most of the work.
But this is the exception, not the rule. The bulk of California farms are sprawling monoculture fields in the central valley that are completely devoid of natural bee habitat, meaning that wild bees will never be able to provide all of a farmer's pollination needs.
"In most of the central valleyno way. The bee populations are not healthy enough," she said. "There's a dramatic decline in bee diversity and bee abundance when you go from the narrow valleys to the wide central valley."
Robust wild bee populations do not thrive in the central valley's monoculture fields. But Kremen said small improvements could allow some native bees to flourish, as long as larger source areas are also restored and protected. These small steps could include reintroduced native vegetation to areas around tractor sheds and irrigation ditches.
"If you can get 10, 20, 30 percent of your needs met by wild bees, that would help a lot," she said.
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