Managing Woodlots for Pollinators
For many, the subject of pollination paints a pretty picture of insects navigating through flowers and gardens, but what many people might not realize is that trees can also play an important role in the process.
Rhode Island’s NRCS State Biologist Gary Casabona says interest in pollinators picked up roughly a decade ago when researchers discovered colony collapse disorder of the European honeybee. The disorder drew the interest of USDA because pollinators ensure crop production.
Not all crops need pollinators. For example, sun gold cherry tomatoes grown in California can survive on wind pollination, but research has shown the crop yield to be two-and-a-half times greater when bumblebees are present, says Casabona. Bumblebees are the most important pollinators to protect, he says, because they do buzz pollination. “They grab the flower and vibrate at an incredible rate to shake loose the maximum amount of pollen. The bee is dusted with it before moving on to the next flower.”
For private landowners, the key to effective pollinator planning is to accommodate insect needs. “The rule of thumb is to have a minimum of three species blooming during each of the three blooming seasons: early, middle and late,” Casabona says.
This plan can include several tree species--such as willow, maple and red bud trees—all of which produce copious amounts of pollen; but more importantly, all of which produce it early in the year. “Bumble bee colonies die off each fall, with the new bumble bee queens going to ground in the soil and leaf litter. They remain dormant throughout the winter, and when the queens emerge, the pollen supplied by maples and willows is available to sustain them as they establish new colonies for the growing season,” he says.
Positioning is also critical to successful pollinator planning. Native bees will not travel deep into shaded forested areas- they prefer more open areas with at least some dappled sunlight—so Casabona suggests planting pollinator-friendly trees and shrubs at the edge of your forest. Elderberry, blackberry and raspberry serve a dual role. Their fruit is preferred by migratory birds, and bees tunnel into their canes for resting habitat.
Trees are at their best when complementing other pollinator-friendly plant types, such as milkweed, bee balm, lupine, aster, and wild mint. “If we’re recommending woody seeds we’re doing it in conjunction with heavy herbaceous seeding,” Casabona says. “The combination gives us heavy coverage on the ground.”
Forest landowners are also encouraged to leave dead and dying trees standing, unless they pose a safety hazard. Dead and dying trees provide habitat for many prey insects, such as beetles and ants, which are an important food source for birds, like woodpeckers. Tree cavities also provide nesting sites for native bees.
Research conducted by the Xerces Society for Invertebrate Conservation and the NRCS Plant Material Center has shown certain species to be highly attractive to insects. Xerces has released a number of publications on the topic, including some as focused as “How to Create Habitat for Pollinator Insects on Golf Courses,” and is working on pollinator plant guidelines for every region. The research has given land managers and biologists like Casabona insight into how to maximize pollination efforts. “Natives plants are more likely to have success,” Casabona says, “although there are non-native plants that act as good resources for pollinators, such as buckwheat and alfalfa, both of which are also good cover crops.”
Agroforestry is also an asset to pollination strategies. The National Agroforestry Center (NAC) has produced several agroforestry-related publications that conservation districts can share with landowners. The following resources can be downloaded from the NAC website at no cost:
Agroforestry: Sustaining Native Bee Habitat For Crop Pollination
Improving Forage For Native Bee Crop Pollinators
Enhancing Nest Sites For Native Bee Crop Pollinators
Pesticide Considerations For Native Bees In Agroforestry
A few years ago, NAC Research Landscape Planner Gary Bentrup prepared illustrated planning and design guidelines for buffers, including recommendations for crop-pollinator habitat. According to the document: “Buffers can provide valuable resources for crop pollinators including shade, nesting sites, water, nectar and pollen, and protection from pesticides. Buffers can reduce wind and aid in foraging and pollination efficiency. Ideally, buffers should be less than 1000 feet from the crop.”
To learn more about how woodlands can assist with pollination, visit the Xerces Society for Invertebrate Conservation website at www.xerces.org, or visit the NAC website at http://nac.unl.edu. The book “Managing Native Pollinators” can be downloaded free of charge from the Sustainable Agriculture Research and Education site.