[Pollinator] The Overstory #211--Improving forage for native bee crop pollinators
Jennifer Tsang
jt at pollinator.org
Tue Oct 14 12:28:01 PDT 2008
Thanks to Patricia S. De Angelis, Ph.D. for forwarding the below.
Publication date: October 13, 2008
The Overstory #211--Improving forage for native bee crop pollinators
by Mace Vaughan and Scott Hoffman Black
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The Overstory #211--Improving forage for native bee crop pollinators
by Mace Vaughan and Scott Hoffman Black
Contents:
: INTRODUCTION
: --> Step 1: Identify and protect bee forage already in place
: --> Step 2: Ensure that flowers are present throughout the growing
season
: --> Step 3: Identify the best sites to enhance forage
: --> Step 4: Identify the best plants
: --> Step 5: Plan ahead to ensure successful installation and maintenance
: CONCLUSION
: TABLE 1
: ADDITIONAL INFORMATON
: ORIGINAL SOURCE
: ABOUT THE AUTHORS
: WEB LINKS
: RELATED EDITIONS OF THE OVERSTORY
: PUBLISHER NOTES
: SUBSCRIPTIONS
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INTRODUCTION
Agroforestry practices can provide essential habitat for bees, our most
important crop pollinators. The European honey bee receives most of the
credit for crop pollination, but the number of managed honey bee hives
is half of what it was in the 1950s; and this number continues to
decline because of disease and the immigration of aggressive races of
honey bees. Native bees, however, significantly contribute to crop
pollination - and, in some cases, provide all of the pollination.
In order to support the native bee community, a wealth of flowers is
necessary. Unfortunately, heavily managed farm landscapes often lack the
diversity and abundance of flowers that native bees require. By
providing abundant and diverse pollen and nectar sources, a diverse
community of native bee species will increase, adjacent crops may yield
more, growers could rely less on imported European honey bees, and farm
biodiversity and other wildlife species will benefit.
This article discusses how to maximize the ability of an agroforestry
practice to support crop-pollinating bees, including a step-by-step
method for planning forage enhancements. Other floral visitors, like
butterflies, do not pollinate crops, but will also benefit from the
techniques below.
--> Step 1: Identify and protect bee forage already in place
Existing pollen and nectar sources can often be found near fencerows or
hedgerows, riparian buffers, other natural areas, or any place on or
around the site where a variety of plants (weeds or otherwise) grow. To
identify good forage plants, observe flowers early in the morning and in
the middle of the day to note how intensively each species is visited by
bees and other insects. Honeybees and bumblebees are both good,
recognizable indicators of flowering plants that other native bees will
use. Try to protect these sites and their flowering plants within the
constraints of the landowner's goals.
--> Step 2: Ensure that flowers are present throughout the growing
season
Bees are most active from February to November, longer in mild climates.
The social bumble bee is often seen in any of these months, whereas the
emergence and short (two to four weeks) active adult life of many
solitary-nesting bees depends upon the species, and can occur from early
spring to late summer. Therefore, a sequence of plants that provide a
diversity of flowers throughout the growing season is necessary to
support a diverse community of native bee species.
Bumble bees are some of our most efficient crop pollinators. When forage
is available early in the growing season (like willow, red bud, maple,
or manzanita), freshly emerged, overwintering bumble bee queens are more
successful in establishing their colonies. Also, some solitary bees
produce multiple generations each year, so reproductive success in the
spring and early summer can lead to larger populations in the mid- to
late-summer, when many fruits and vegetables are in bloom.
Remember to include plants that bloom in the fall. When plants such as
goldenrod and asters are in bloom, some native bee species, as well as
honey bees, will benefit from the abundant late-season forage. For
example, the next year's bumble bee queens will be able to go into
hibernation with more energy reserves than they would otherwise.
--> Step 3: Identify the best sites to enhance forage
Agroforestry provides a unique opportunity to enhance nectar and pollen
sources and nesting sites for crop-pollinating bees. Weed control should
be concentrated to a narrow strip nearest the trees to leave as much
undisturbed area as possible for flowering plants and nesting sites.
Riparian forest buffers are excellent locations to incorporate early
flowering willows, as well as shrubs and forbs that require more water
than is naturally available elsewhere. Riparian buffers are especially
important for bees during hot summer months in areas where plants in
upland areas dry out.
Windbreaks and hedgerows, by design, reduce wind velocity in adjacent
fields. Windbreaks provide places to plant flowering trees and shrubs
and other blooming perennials close to fields. Make a special effort to
include flowering forbs on the margins of the windbreak or hedgerow. The
area between the trees could also be used for beneficial forbs during
the establishment period of the windbreak.
Silvopasture provides an open understory where a variety of flowering
forbs, like alfalfa or clover, can be over seeded. When combined with
rotational grazing practices, these legumes will have an opportunity to
flower before being eaten. Clusters of flowering shrubs could provide
benefits for pollinators and other wildlife. Depending on the location,
harvestable flowering trees, such as black cherry, black locust, or
maple, can be included into a silvopasture system.
Alley cropping presents an opportunity to grow plants in close proximity
that have complementary flowering periods. By paying careful attention
to bloom periods and using multiple species, an alley cropping system
can provide nearly continuous pollen and nectar forage within a single
farmscape. Consider flowering trees like black cherry or basswood along
with the more typical alley cropping trees of walnut, pecan, or oak. A
legume forage crop between rows will not only fix nitrogen but also
provide nectar and pollen for bees. Diverse native forbs and shrubs, may
be planted in rows for cut flowers, berry production, or the nursery
market, as well as for pollinators.
Forest farming simultaneously manages both forest overstory and
understory plants. Include insect-pollinated valuable crop trees, like
yellow (tulip) poplar, maple, basswood, and black cherry, in the
overstory to benefit pollinators. Some cultivated understory plants,
such as ginseng, goldenseal, or black cohosh, may also benefit from
pollinators. For example, black cohosh generally relies on bumble bees
for pollination, but it does not produce nectar to attract the bees. It
must rely on nearby prolific nectar producers, such as pale touch-me-not
or whiteflower leafcup, to attract the bees. The pollination of these
different forest understory plants is not well understood, but
pollinators should be encouraged.
Other sites, such as existing natural habitat, field and road edges,
drainage ditches, land around buildings, and fields that are too wet or
too dry for crop production, also provide convenient, underutilized
places to cultivate bee forage.
--> Step 4: Identify the best plants
Wherever possible, consider how to include trees that provide pollen and
nectar for bees (see Table 1). Around and under each tree provide a
diversity of plants that, together, produce continuous, abundant
flowers.
For the maximum benefit to pollinators, as well as ease of
implementation, consider the following criteria:
Locally native plants are generally well-adapted to an area's growing
conditions; can thrive with minimum attention; are good sources of
nectar and pollen for native bees; and are usually not "weeds."
Flowers with a diversity of shapes, sizes, and colors will support the
greatest variety of crop pollinators.
Alternative, specialty crops provide a product for landowners and are
also great for pollinators. For example, berry-producing shrubs such as
blueberries and raspberries, ornamental plants such as curly willow and
red twig dogwood, medicinal plants such as goldenseal, and hardwoods
such as black cherry and maple all provide a harvestable crop as well as
pollen and nectar for bees.
Highly invasive plant species are aggressive and can spread to dominate
other species; will reduce the diversity and value of the habitat; and
will increase maintenance. Check with your county for code restrictions
on noxious weed species.
--> Step 5: Plan ahead to ensure successful installation and maintenance
Post signs and educate others. It is important to make sure that farm
staff, neighbors, and county road and electric crews know about the
habitat. Signs help educate others about what is happening on the farm
and, potentially, encourage them to do similar work.
Eventually replace mulch. Weed control and irrigation (in drier
climates) is often needed to establish new agroforestry plantings. While
mulch helps conserve water and control weeds, it may also prevent
ground-nesting bees from accessing the soil surface. After trees are
established, consider replacing mulch with an understory of bunch
grasses or flowering forbs, which will help control weeds and, at the
same time, provide opportunities for solitary bees to construct ground
nests.
Minimize herbicide use. If herbicides are necessary to control noxious
weeds, only spot treat weeds and completely avoid important flowering
plants.
CONCLUSION
The best way to attract and support a healthy pollinator population is
to ensure a rich, diverse plant community. Agroforestry practices can
help provide this rich source of pollen and nectar. In return, an
abundance and variety of insect pollinators will yield a fertile and
productive landscape.
=== BEGIN TABLE 1 ===
North American trees and shrubs that provide significant forage for
native bees
Native Trees* /Approximate flowering period in native range**/
Willow (Salix) /Early spring/
Sassafras (Sassafras) /March to May/
Redbud (Cercis) /March to May/
Horse chestnut (Aesculus) /March to June/
Maples (Acer) /March to June/
Madrone (Arbutus) /Mid-March to June/
Cherry (Prunus) /Late March to June/
Sumac (Rhus)*** /Spring to summer/
Black locust (Robinia) /May to June/
Palo Verde (Parkinsonia) /May to June/
Honey locust (Gleditsia) /Mid-May to June/
Serviceberry (Amelanchier) /Early summer/
Basswood (Tilia) /Late May to July/
Sourwood (Oxydendrum) /Mid-summer/
California-laurel (Umbellularia) /November to May/
Native Shrubs* /Approximate flowering period in native range**/
Barberry, Mahonia (Berberis, Mahonia) /March to May/
Serviceberry (Amelanchier) /April to June/
Golden currant (Ribes aureum) /April to June/
Buckbrush (Ceanothus) /April to June/
Blueberries (Vaccinium) /May to June/
Raspberry, Blackberry (Rubus)*** /May to August/
Elderberry (Sambucus)*** /May to August/
Wild rose (Rosa) /June to August/
Oceanspray, Cliff spirea (Holodiscus) /June to August/
Spirea (Spirea) /July to August/
Fruit Trees* /Approximate flowering period in native range**/
Almond, Apple, Cherry, Plum, Persimmon /Spring/
* Check sources for species and varieties that are adapted to your area.
** The actual flowering period depends upon species, latitude,
elevation, and year-to-year variation, and may only last for a short
time (a couple of weeks) within these ranges. It is important to consult
with local native plant experts to develop a list of plants with
overlapping bloom times
*** When twigs are clipped on these plants, the soft pith provides
nesting opportunities for small, tunnel-nesting bees.
=== END TABLE 1 ===
::::::::::::::
ADDITIONAL INFORMATON
AF Note - 32: "Agroforestry: Sustaining Native Bee Habitat For Crop
Pollination," Vaughan, Mace and Black, Scott Hoffman, 2006. USDA
National Agroforestry Center.
AF Note - 34: "Enhancing Nest Sites For Native Bee Crop Pollinators,"
Vaughan, Mace and Black, Scott Hoffman, 2006. USDA National Agroforestry
Center.
AF Note - 35: "Pesticide Considerations For Native Bees In
Agroforestry," Vaughan, Mace and Black, Scott Hoffman, 2006. USDA
National Agroforestry Center.
Conservation Security Program Job Sheet: "Nectar Corridors," Plant
Management EPL 41. USDA NRCS,
<http://www.wv.nrcs.usda.gov/programs/csp/06csp/JobSheets/nectarCorridorsEL4
1.pdf>
::::::::::::::
ORIGINAL SOURCE
This article was excerpted with the kind permission of the publisher from:
Vaughan, M. and S. Hoffman Black. 2006. Improving Forage For Native Bee
Crop Pollinators. Agroforestry Note 33. USDA National Agroforestry
Center (NAC), Lincoln, Nebraska. <http://www.unl.edu/nac>.
The authors wish to acknowledge the helpful comments provided by
native bee scientists from across the country: James Cane, USDA ARS;
T'ai Roulston, University of Virginia; and Blair Sampson, USDA ARS.
::::::::::::::
ABOUT THE AUTHORS
Mace Vaughan is Conservation Director of the Xerces Society for
Invertebrate Conservation. Mr. Vaughan has led the Xerces Society's
Agricultural Pollinator Conservation program for the last three years.
He has written articles on the conservation of bees, butterflies,
aquatic invertebrates, and insects, and is co-author of the Pollinator
Conservation Handbook and Farming for Bees: Guidelines for Providing
Native Bee Habitat on Farms. He has spoken on numerous occasions about
pollinator conservation and invertebrate conservation and he was a
lecturer on honey bee biology and beekeeping at Cornell University. His
background includes Masters Degrees in Entomology and Teaching from
Cornell University, research into the behavior and community ecology of
insects, and stints as an insect wrangler for PBS Nature.
Scott Hoffman Black is Executive Director of the Xerces Society for
Invertebrate Conservation, an international organization dedicated to
protecting biological diversity through invertebrate conservation. He
has degrees in ecology, plant science and entomology from Colorado State
University. As a researcher, conservationist and teacher he has worked
to advocate science based conservation and has extensive experience in
endangered species conservation. Scott has authored many scientific and
popular publications and his work has been featured in newspaper,
magazines and books and on radio and TV. Scott is co-author of such
pollinator related publications as: The Red List of Pollinator Insects
of North America and the Pollinator Conservation Handbook.
The authors can be contacted at Xerces Society For Invertebrate
Conservation, 4828 SE Hawthorne Boulevard, Portland, Oregon 97215.
Phone: 503-232-6639; fax: 503-233-6794; e-mail: info at xerces.org.
::::::::::::::
WEB LINKS
AF Note - 32: "Sustaining native bee habitat for crop pollination,"
Mace Vaughan and Scott Hoffman Black, 2006. USDA National Agroforestry
Center. <http://www.unl.edu/nac>.
AF Note - 33: "Improving Forage For Native Bee Crop Pollinators,"
Mace Vaughan and Scott Hoffman Black, 2006. USDA National Agroforestry
Center. <http://www.unl.edu/nac>.
AF Note - 35: "Pesticide Considerations For Native Bees In
Agroforestry," Mace Vaughan and Scott Hoffman Black, 2006. USDA National
Agroforestry
Center. <http://www.unl.edu/nac>.
"Farming for Bees: Guidelines for Providing Native Bee Habitat on
Farms," Vaughan, M., M. Shepherd, C. Kremen, and S. Black. 2004. Xerces
Society. 34 pp. <http://www.xerces.org/Pollinator_Insect_Conservation/>
NRCS Pollinator Technical Note.
<http://plants.usda.gov/pollinators/NRCSdocuments.html>
Xerces Society Pollinator Program.
<http://www.xerces.org/Pollinator_Insect_Conservation/>
::::::::::::::
RELATED EDITIONS OF THE OVERSTORY
The Overstory #187--Enhancing nest sites for native bee crop pollinators
The Overstory #178--Sustaining native bee habitat for crop pollination
The Overstory #149--Live Fences, Isolated Trees, and Windbreaks: Tools
for Conserving Biodiversity
The Overstory #98--Integrating Forestry into Farms
<http://www.agroforestry.net/overstory/overstory98.html>
The Overstory #73--Buffers, Common-Sense Conservation
<http://www.agroforestry.net/overstory/overstory73.html>
The Overstory #56--Integrating Understory and Tree Crops
<http://www.agroforestry.net/overstory/overstory56.html>
The Overstory #55--Nontimber Forest Products Part II: NTFP Enterprises
<http://www.agroforestry.net/overstory/overstory55.html>
The Overstory #53 Nontimber Forest Products--An Introduction
<http://www.agroforestry.net/overstory/overstory53.html>
The Overstory #40--Bees and Agroforestry
<http://www.agroforestry.net/overstory/overstory40.html>
::::::::::::::
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