Buzzkill: Can native bees do the job?
On the right kind of farm — one with nearby natural habitat and organic management — the answer is yes, according to UC Berkeley professor Clare Kremen, an expert on native bees. Kremen shared this finding and other interesting facts about bees in a talk at the Commonwealth Club in San Francisco a few weeks ago. (A recording of her talk appeared on the Commonwealth Club's podcast feed but isn't yet on their website.)
Bee prepared for disaster
If all of the world's pollinators were to suddenly disappear, there would be a massive disruption of plant communities, as most of them require active pollination to reproduce. Our food supply would see significant changes. Even though two-thirds of world crop production is not dependent on active pollination — grains like wheat, rice, millet and sorghum are pollinated by the wind — some of the most interesting and nutritious foods, such as almonds, cacao, coffee, avocados, and carrots, do depend on outside pollinators.
In today's industrial agriculture system in the United States, the pollinators are primarily managed hives of honey bees (Apis mellifera). For example, according to a report from Cornell University (PDF), the U.S. almond crop is completely dependent on pollination by the honey bee; for avocados and carrots, honey bees provide about 90% of the pollination. Honey bees therefore provide tremendous economic value. The report from Cornell estimates that the marginal value of honey bees (the value of increased yield and quality caused by honey bee pollination) is over $14 billion annually. For a frame of reference, California's output of fruit, nuts, vegetables and melons in 2006 was about $17 billion (according to the California Department of Agriculture, PDF).
Kremen said that there are several thousand bee species native to the United States (maybe tens of thousands) and we don't know how many actually pollinate crops. Bees are exceptional pollinators for several reasons. First, they collect pollen, not only nectar like ants and other flower visitors. Second, bees are biologically adapted to carry pollen and therefore are effective collectors. Third, they exhibit "floral constancy," which means that they visit many individuals from the same species of flower on their foraging trips, making it more likely that pollen will be transferred.
For most of our agricultural history, humans have relied on native bees and unmanaged honey bees to pollinate our crops and ornamental plants. Trucking scores of bee hives across hundreds or thousands of miles as an on-demand pollination service is a recent development brought about by the ascendancy of industrial agriculture. Although this is the type of agriculture that most needs pollinators, it offers the worst habitat for them. Take almonds, an extreme example: they have a very short blossom period, and because of the similarity of the climate in almond-producing areas, most of the trees bloom at the same time. Thus, thousands of colonies converge on the central valley of California during the spring: in 2004, 60% of the 2.5 million "for-hire" honey bee colonies in the U.S. were involved in pollination of California almond orchards, according to the Agricultural and Resource Economics Update.
Honey bees have been struggling in recent decades because of the varroa mite, diseases, and most recently the mysterious Colony Collapse Disorder. (A Congressional Research Service report and an episode of PBS's Nature provides a good background of CCD.) Between 1945 and 2005, there was a a major decrease in the number of managed colonies, according to USDA data summarized in a report from the National Academies (on page 40). There is much effort underway to find the cause of CCD, and at the same time, some experts like Kremen are looking at ways to find local help for honey bees by improving the conditions for native bees.
For 10 years, Kremen has studied wild bees. Some of her research has been in Yolo County, a rural county to the northeast of the S.F. Bay Area and home to some amazing farms that supply Bay Area markets and restaurants. Kremen and her collaborators are investigating the behavior of native bees along "gradients of agricultural intensification": one gradient starts with farms near natural habitat and ends in wall-to-wall agriculture. Another starts at organic and ends at industrial. Along this gradient, you have smaller farms with a polyculture, low use of pesticides, a tolerance of weeds (which often have flowers that provide food for pollinators) on one end, and monoculture, regular pesticide use, and a barren landscape on the other.
At each study site, Kremen's team documented bee diversity by collecting specimens, counting visitors, and measuring pollen efficiency. They did some clever and painstaking experiments to determine how much pollination comes from native bees, such as watching an individual watermelon flower, or carrying around a watermelon flower as 'bait' and then counting what landed.
On farms near natural areas, they found 30 species of native bees active in the fields and orchards; in wall-to-wall agricultural areas, just a few. They also discovered that the most efficient native pollinators live closest to the natural areas. In sum:
- 80% of organic farms near natural habitat received enough pollination from wild bees
- 50% of conventional farms near natural habitat received enough pollination from wild bees
- 0% of conventional farms in exclusively agricultural areas received pollination from wild bees
- Little pollination (she didn't give a number) was provided by native bees on organic farms located in exclusively agricultural areas
The team also looked at farms in New Jersey and Pennsylvania, two states with smaller-scale and more diverse agricultural systems. In both places, the in-place bee communities (native bees, non-mobile honey bees, and feral honey bees) handle the pollination.
Bumbling attempts to help
Near the end of her talk Kremen asked, "Can wild bees pollinate modern agriculture?" Her answer was no. Modern agriculture provides too few nesting sites, too little floral resources, and too many flowers to pollinate at once.
But that doesn't mean that farmers should give up on native bees. They can create suitable habitat and nesting sites by allowing weeds and cover crops to flower, by growing a variety of crops, planting strips of flowering vegetation between fields, restoring patches of native habitat around the farm, and through creating nest sites (leaving soil undisturbed, keeping dead trees in place, and installing nest blocks). Unfortunately, these very practices have come under attack by industrial food-safety advocates who think that farms should be sterile sites devoid of anything natural except for the crops, as an op ed from 2007 by Full Belly Farms co-owner Judith Redmond points out (PDF).
Kremen has been working with the Xerxes Society and several other organizations to test some of these ideas on real farms in Yolo County. The group started a project in a wall-to-wall agricultural area that involves planting hedgerows of native flowering plants and installing nesting boxes for bees. An interesting feature of the project is that they are enlisting "citizen scientists" to monitor parts of the project and have been very happy with the quality of their work. (Part of a segment of the television program Quest is about the project.)
She concluded the talk by saying that it will take many actions to help native bees provide more pollination services to our crops. We will need improved conservation programs in agricultural areas, restoration of degraded lands, and changes in farm management practices (like more polycultures and reduced pesticide use).
- An article about Kremen's work in the San Francisco Chronicle
- The Pollinator Partnership website contains a wealth of information
- Scribbly Gum has a piece about Australia's native bees
- The Times Online (London) has a story about the native bees of the British Isles
- "Taking 'Eating Local' a Bit Too Far, my blog post about honey bees trying to build a nest outside of my kitchen
Photo of bumble bee on a lavender flower from velodenz's flickr collection, subject to a Creative Commons License; photo of a bumble bee on a pink flower from Strange One's flickr collection, subject to a Creative Commons License;photo of bees on an onion flower by the author.
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