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R. P. Udawatta, S. Jose (eds.), Agroforestry and Ecosystem Services,
https://doi.org/10.1007/978-3-030-80060-4_11
The Role ofTemperate Agroforestry
Practices inSupporting Pollinators
GaryBentrup, JenniferHopwood, NancyLeeAdamson, RaePowers,
andMaceVaughan
Introduction
Agroforestry is the intentional integration of trees and/or shrubs with herbaceous
crops and/or livestock in an agricultural production system. In temperate regions,
agroforestry systems include many different practices such as windbreaks, riparian
buffers, alley cropping, hedgerows, shelterbelts, silvopasture, and forest farming.
Agroforestry practices can deliver a suite of ecosystem services from provisioning,
regulating, cultural, and supporting services (Smith etal. 2013). With some excep-
tions (e.g., pollinator hedgerows), ecosystem services provided by insect pollinators
are often not specically considered in the design and management of agroforestry
practices (Udawatta etal. 2019). However, whether using alley cropping or a wind-
break, managing a riparian buffer, or forest farming, agroforestry practices can
G. Bentrup ()
U.S.Department of Agriculture, U.S.Forest Service, National Agroforestry Center,
Lincoln, NE, USA
e-mail: gary.bentrup@usda.gov
J. Hopwood
Xerces Society for Invertebrate Conservation, Omaha, NE, USA
e-mail: jennifer.hopwood@xerces.org
N. L. Adamson
International Center for Agricultural Research in the Dry Areas, Rabat, Morocco
e-mail: nancy.adamson@xerces.org
R. Powers
Xerces Society for Invertebrate Conservation, Lincoln, NE, USA
e-mail: raeann.powers@xerces.org
M. Vaughan
Xerces Society for Invertebrate Conservation, Portland, OR, USA
e-mail: mace.vaughan@xerces.org
276
increase the overall diversity of plants and physical structure in landscapes and, as
a result, provide habitat for pollinators and other insects benecial for agriculture
such as predators and parasitoids of crop pests and decomposers. Agroforestry
plantings can also have indirect benets for pollinators including habitat connectiv-
ity and protection from pesticide exposure. This chapter provides an overview of the
current scientic knowledge regarding how agroforestry practices can support pol-
linators and pollination services.
Importance ofPollinators
Plant pollination by animals is one of the most well-known and important ecosys-
tem services and is essential in both natural and agricultural landscapes (IPBES
2016). An estimated 85% of the world’s owering plants depend on animals—
mostly insects—for pollination (Ollerton etal. 2011). Pollination is a mutually ben-
ecial interaction between plants and pollinators. Animals, particularly insects, visit
owers seeking sustenance, and in the process transfer pollen grains from one
ower or plant to another, allowing owering plants to reproduce. Sugary nectar
and/or protein-packed pollen grains are food resources for pollinators.
Insect pollination is critical to agricultural production. Eighty-seven of the
world’s 124 most commonly cultivated crops (70%) are reliant on or benet from
animal pollination, including crops that produce fruits, vegetables, spices, nuts, and
seeds (Klein etal. 2007). Additionally, insect-pollinated plants such as alfalfa and
clover provide feed for livestock. Roughly 35% of global crop production is depen-
dent on pollination by animals (Klein etal. 2007). The majority of minerals, vita-
mins, and nutrients needed to maintain human health (such as vitamin C, calcium,
and folic acid) come from crop plants that depend partially or fully on animal pol-
linators (Eilers etal. 2011). The value of crops directly dependent on pollination by
insects (e.g., apples, squash) was estimated in 2009 at $15.1 billion in the United
States, and the value of crops indirectly dependent on pollinators (e.g., alfalfa hay,
onions) was estimated in 2004 at $12 billion (Calderone 2012).
Pollinators are a keystone group in most terrestrial ecosystems, necessary for
plant reproduction and important for wildlife food webs (Kearns etal. 1998). They
sustain wildland plant communities that provide food and shelter for myriad wild-
life. Fruits, seeds, and nuts, that result from animal pollination, are food for many
insects, birds, and mammals. Pollinators can also be direct prey for wildlife. For
example, pollinator larvae are an important part of the diet of many young birds
(Buehler etal. 2002). Healthy habitat that supports pollinators often confers other
ecosystem services such as reduced soil erosion, enhanced rainwater inltration,
improved water quality, reduced wind velocity, carbon sequestration, recreation
spaces for humans, and habitat for a variety of wildlife, including arthropod preda-
tors and parasitoids that reduce crop pests.
G. Bentrup et al.
277
Important Groups ofPollinators
The great majority of pollinators are insects, including bees, wasps, ies, beetles,
butteries, and moths (Table 1; Allen-Wardell et al. 1998; Kevan 1999; Kearns
2001), but some bird and bat species pollinate as well (Grant 1994; Valiente-Banuet
etal. 2004). Bees are considered the most important group of pollinators for agri-
cultural crops (McGregor 1976; Morse and Calderone 2000; Garibaldi etal. 2013)
as well as for wild plants in temperate climates (Michener 2007). Bees are such
efcient pollinators of many plants because 1) they actively collect both pollen and
nectar; 2) they make many trips to owers as they are foraging to collect nest provi-
sions for their offspring; and 3) they have more ower constancy, i.e., once they nd
a good forage source they visit that type of ower over and over.
The domesticated European honey bee (Apis mellifera) is the most widely recog-
nized bee worldwide and is an important managed crop pollinator. Studies indicate
that honey bee pollination accounts for more than $15 billion in crop production
annually in the United States (Morse and Calderone 2000; Calderone 2012).
Based on Ascher and Pickering (2020), there are over 5200 species of native bees
in North America, many of which are important crop pollinators. Native bees are
important in the production of crops worth an estimated $3 billion annually to the
US economy (Losey and Vaughan 2006), though this may be an underestimate of
their contribution. A recent analysis of 41 crop systems worldwide found that man-
aged honey bees do not replace the pollination services provided by a diverse com-
munity of native bees (Garibaldi et al. 2013). Native bees provide pollination
services in colder, windier weather (Brittain etal. 2013) and are more efcient than
honey bees on an individual bee basis at pollinating particular crops, such as squash,
berries, and tree fruits (e.g., Tepedino 1981; Bosch and Kemp 2001; Javorek etal.
2002; Garibaldi etal. 2013).
Most native bees live solitary lives, with each female working alone to build her
nests and collect and provide food for her offspring. Some solitary bees visit a diver-
sity of owers to collect pollen, and others collect from owers of a particular plant
species or group of species. Bumble bees and some sweat bees are the only native
bees that form social colonies. Their colonies usually have fewer than 200 bees, and
are much smaller than a honey bee hive which may house up to 30,000 individuals.
Bumble bees are particularly important pollinators. They are able to y in cooler
temperatures and lower light levels than many other bees, which extends their work-
day and improves the pollination of crops during inclement weather (Corbet etal.
1993). In addition to commercially important crops, bumble bees also play a vital
role as generalist pollinators of native owering plants (Memmott etal. 2004). They
and many native bees also possess the ability to “buzz pollinate,” dislodging pollen
with a vibration that forces release from poricidal anthers found in owers such as
blueberries, cranberries, tomatoes, and peppers (Buchmann 1983).
Of the other orders of pollinating insects, ies (Diptera) also provide substantial
pollination services (Kearns 2001; Larson etal. 2001; Inouye etal. 2015), espe-
cially in alpine areas and tundra. Other insects such as beetles (Coleoptera) and
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
278
Table 1 Common insect pollinator groups
Honey bee Bumble bees Ground-nesting bees
Order: Hymenoptera
Family: Apidae
Genus and species: Apis
mellifera
Order: Hymenoptera
Family: Apidae
Genus: Bombus
Order: Hymenoptera
Families: Andrenidae, Apidae,
Colletidae, Halictidae
The European honey bee
(native to Europe, Africa,
and Asia) is a domesticated
species that lives in large
perennial social colonies
(hives), with division of
labor within the colony. Only
the queen reproduces, while
others gather nectar and
pollen to feed brood (larvae)
and store food (honey) for
the winter. Feral colonies in
the United States are
somewhat rare; most hives
are managed by beekeepers
Bumble bees form annual
social colonies. Queen bumble
bees that mated the previous
fall start nests in spring and by
mid-summer colonies can have
dozens or hundreds of workers.
They nest in insulated cavities
such as under clumps of bunch
grass or in old rodent nests.
There are 46 recognized
bumble bee species in North
America
Most native bees live solitary
lives, with each female working
alone to build her nests and
collect and provide food for her
offspring. About 70% of our
solitary bee species nest
underground, digging slender
tunnels in which they build
individual cells for each egg and
its provisions
Tunnel-nesting bees Flower-visiting ies Flower-visiting beetles
Order: Hymenoptera
Families: Apidae, Colletidae,
Halictidae, Megachilidae
Order: Diptera
Families: Anthomyiidae,
Bombyliidae, Syrphidae,
Tachinidae, others
Order: Coleoptera
Families: Cantharidae,
Coccinellidae, Scarabaeidae,
others
Approximately 30% of
solitary bee species nest in
tunnels, inside already
hollow stems or by chewing
into the pithy center of
stems, or in existing holes in
wood, sometimes man-made.
Most tunnel-nesting bees are
solitary species
Flower-visiting ies consume
nectar and sometimes pollen.
Many hover ies (family
Syrphidae) resemble bees or
wasps in coloration. Larvae of
some species are voracious
predators of small insects, like
aphids
Flower-visiting beetles consume
nectar and pollen, and may also
chew on ower parts. Larvae of
some species are predatory,
hunting other insects (including
crop pests) as food, while others
are herbivorous or are
decomposers
(continued)
G. Bentrup et al.
279
wasps (Hymenoptera) provide pollination services, though to a lesser extent (e.g.,
Frankie etal. 1990; Kevan 1999). The contribution of most buttery and moth spe-
cies (Lepidoptera) to pollination services is not well known (e.g., Frankie etal.
1990; Allen-Wardell et al. 1998; Westerkamp and Gottsberger 2000; MacGregor
etal. 2015), but there are instances where butteries have been documented polli-
nating wild plant species, including some owering plants specially adapted for
buttery pollination (e.g., Russelia, Phlox, and Lantana) (Fallon et al. 2014).
Ollerton (2017) estimate that more than 140,000 species of moths and butteries
visit owers. Many buttery species y great distances between owers and may
carry pollen for a long time, and thus they may be effective as dispersers of pollen.
In addition to insect pollinators, there are two groups of nectar-feeding verte-
brates that play an important role in pollination: hummingbirds (Trochilidae) and
bats (Phyllostomidae). There are 12 species of nectar-feeding bats that are known
pollinators in North America (National Research Council 2007). The known ranges
for these bats correspond closely with the distribution of columnar cacti (e.g.,
saguaro [Carnegiea gigantea], Pachycereus spp., Stenocereus spp., Lophocereus
spp.) and agaves (Agave spp.), the main species they are known to pollinate
(Valiente-Banuet et al. 2004), primarily in the deserts of Arizona, California,
Nevada, New Mexico, and Texas. Hummingbirds, which pollinate about 130 native
Table 1 (continued)
Flower-visiting wasps Flower-visiting moths Butteries
Order: Hymenoptera
Families: Sphecidae,
Vespidae, Tiphiidae,
Scoliidae, others
Order: Lepidoptera
Families: Sphingidae,
Noctuidae, Arctiidae
Order: Lepidoptera
Families: Papilionidae,
Hesperiidae, Pieridae,
Lycaenidae, Nymphalidae
Predatory wasps, most of
which are solitary, hunt for
prey to bring back to their
nest as food for their young.
They build nests in cavities
or in the ground, and may
utilize pieces of grass, mud,
or resin in construction of
their nest. Adults maintain
their energy by consuming
nectar and/or pollen, and in
the process may also transfer
pollen between owers
Moths, which are often
subdued in color and tend to
y at dusk or night, are less
visible than other groups, but
many are important specialist
pollinators of wild plants,
while some also pollinate
crops. Moths as a group form a
critical food source for other
wildlife
With their striking
transformation from a chubby
plant-chewing caterpillar to a
delicate pupa to a graceful
nectar-drinking adult, butteries
are some of the most beloved
insects. Some species have
narrow host plant needs for their
caterpillars while others feed on
a wide variety of plants
Source: Flower-visiting beetle image by Jennifer Hopwood and remaining images by Nancy
Lee Adamson
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
280
plant species with owers adapted for hummingbird pollination, make long migra-
tory journeys in North America and depend on nectar corridors to sustain their long-
distance movements (Nabhan etal. 2004).
Pollinator Status andThreats
Globally, pollinators are in decline (Biesmeijer et al. 2006; National Research
Council 2007; Potts et al. 2010; Sánchez-Bayo and Wyckhuys 2019), with some
estimates that 40% of invertebrate pollinator species may be at risk of extinction
worldwide (IPBES 2016). Threats such as the loss, degradation, and fragmentation
of habitat (e.g., Kremen etal. 2002; Williams and Kremen 2007; Potts etal. 2010);
introduced species (e.g., Tallamy and Shropshire 2009; Fiedler etal. 2012); use of
pesticides (e.g., Dover etal. 1990; Kearns and Inouye 1997; Kevan 1999; Whitehorn
etal. 2012); and diseases and parasites (e.g., Altizer and Oberhauser 1999; Colla
etal. 2006; Cameron etal. 2011) all contribute to pollinator decline.
In the United States, the number of honey bee colonies has been in decline over
the past half-century due to diseases, parasites, lack of oral resources, insecticides,
and other factors (National Research Council 2007). Since 2012, beekeepers have
experienced record high annual hive losses of 33% or more; an average of 40% of
managed colonies were lost in the 2018–2019 season (Bee Informed
Partnership 2019).
Much less is known about the status of most of North America’s native pollina-
tors, though what data does exist suggests that numerous species are experiencing
declines similar to or more severe than the declines seen in honey bees. One-quarter
of North America’s bumble bees have experienced signicant declines (Hateld
etal. 2014), including declines in species that were formerly some of the most com-
mon species (Cameron etal. 2011). In 2017, the once common rusty patched bum-
ble bee (Bombus afnis) was added to the US Fish and Wildlife list of endangered
species (US Fish and Wildlife Service 2019).
In the United States, some butteries are also in decline. NatureServe assessed
all of the country’s roughly 800 buttery species and found that 19% are at risk of
extinction (NatureServe 2018). A number of generalist buttery species have seen
signicant declines in recent years (Forister etal. 2011). In particular, monarch but-
teries (Danaus plexippus) in North America are now vulnerable to extinction,
according to a recently completed assessment (Semmens etal. 2016). The popula-
tion of monarchs has dropped by over 80% east of the Rocky Mountains (Rendón-
Salinas and Tavera-Alonso 2014) and by over 90% to the west (Schultz etal. 2017).
The loss of milkweeds (Asclepias spp.), the monarch’s larval host plants, has been
signicant, particularly within agricultural elds (Pleasants and Oberhauser 2012).
The populations of both hummingbirds and nectar-feeding bats throughout the
southwestern United States have also experienced declines (National Research
Council 2007). Hummingbirds face disruption of migratory routes and loss of
G. Bentrup et al.
281
habitat (Calder 2004), while nectar-feeding bats face disturbance of their roost sites
and removal of foraging habitat and nectar sources (US Fish and Wildlife
Service 2006).
The loss of pollinators negatively affects plant reproduction and plant commu-
nity diversity (Bawa 1990; Fontaine etal. 2005; Brosi and Briggs 2013). Threats to
pollinators may have profound consequences for ecosystem health as well as our
food systems (Kearns et al. 1998; Spira 2001; Steffan-Dewenter and Westphal
2008). Concerns about pollinator decline and its repercussions have led to increased
efforts to reduce threats to pollinators. Managing existing habitat for insect pollina-
tors and restoring additional habitat have been demonstrated to increase pollinator
abundance and diversity (e.g., Fiedler etal. 2012; Klein etal. 2012; Morandin and
Kremen 2013). By adding structural and functional diversity in landscapes, agrofor-
estry may provide habitat and other benets for insect and other pollinators and
pollination services.
Agroforestry’s Role
Based on a review of available scientic literature, agroforestry practices can confer
three key benets for insect pollinators and pollination services: 1) providing habi-
tat including foraging resources and nesting or egg-laying sites, 2) enhancing site
and landscape connectivity, and 3) reducing pesticide exposure (Bentrup et al.
2019). Current research on supporting pollinators in agricultural landscapes has
focused primarily on honey bees and native bees but general concepts may apply
across other pollinator groups.
Providing Habitat
Foraging Resources
Pollinators require a diversity of owers to provide nectar and pollen resources to
meet their nutritional needs. Nectar is an aqueous solution of sugars, amino acids,
and other secondary metabolites that provides a rich source of energy for bees, but-
teries, hummingbirds, bats, and some moths, wasps, beetles, and ies. Pollen is a
protein-rich resource that is used by native bees, honey bees, and some wasps to
feed their brood or to provision their eggs or by some adult ies and beetles as a
food source. Agroforestry practices can be important sources of nectar and pollen
for pollinators when appropriate plants are used (Table2). If the agroforestry prac-
tice lacks pollinator-suitable oral resources, pollinator use can be limited. For
instance, Macdonald et al. (2018) found limited pollinator use of shelterbelts in
New Zealand that were predominantly comprised of Monterey pine (Pinus radiata
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
282
Table 2 North American trees and shrubs that provide abundant nectar and/or pollena
Scientic name Common name Bloom timebHeightcRegiond
Acer spp.eMaple Spring to early
summer
T WCE
Amelanchier spp.fServiceberry Early spring to
summer
SM WCE
Amorpha spp. Leadplant, false indigo Spring to summer S WCE
Arbutus spp.a,g Madrone Early spring to
summer
MT WC
Aronia spp.fChokeberry Spring to summer S ChE
Atriplex canescens Four-wing saltbush Spring to fall SM W
Baccharis spp.aBaccharis Summer to fall S WCE
Callicarpa americana Beautyberry Early summer S CEh
Ceanothus spp. Native lilac, NJ tea Early spring to
summer
SM WCE
Cephalanthus
occidentalis
Buttonbush Summer SM WCE
Cercis spp. Redbud Spring M WCE
Chrysothamnus spp. Rabbitbrush Summer-fall SM W
Clethra alnifolia Sweet pepperbush Summer S E
Crataegus spp. Hawthorn Spring M WCE
Dasiphora spp. Cinquefoil Spring S WCE
Diospyros spp.e,f Persimmon Spring T WCE
Ericameria spp. Rabbitbrush Summer-fall SM WC
Eriogonum spp.Buckwheat Summer S WC
Gaylussacia spp.fHuckleberry Early spring S CE
Gleditsia spp.fHoney locust Spring T WCE
Halesia spp. Silverbell Early spring MT Eh
Holodiscus spp. Cliff spirea Summer S WC
Hypericum spp. Shrubby St.-John’s-wort Late spring S WCE
Ilex spp.a,g Holly, inkberry Spring SMT WCE
Itea virginica Virginia sweetspire Spring S CE
Krascheninnikovia
lanata
Winterfat Summer S W
Liriodendron tulipiferaeTulip tree Spring T CE
Mahonia spp.aOregon grape Spring to early
summer
S WCE
Nyssa spp.fBlack gum Spring MT CE
Oxydendrum arboreum Sourwood Summer T E
Parkinsonia spp. Palo Verde Spring M WCEh
Philadelphus spp. Mock orange Spring S WCE
Physocarpus spp. Ninebark Spring to summer S WCE
Prunus spp.e,f Cherry, plum, peach,
apricot
Spring M WCE
Purshia tridentata Antelope bitterbrush Spring S W
(continued)
G. Bentrup et al.
283
D. Don) and Monterey cypress (Hesperocyparis macrocarpa (Hartw.) Bartel)
(wind-pollinated exotic species).
Many woody species offer abundant nectar with relatively high sugar contents
such as maple (Acer spp.), horse chestnut (Aesculus spp.), basswood (Tilia spp.), wil-
low (Salix spp.), brambles (Rubus spp.), cherry and plum (Prunus spp.), and service-
berry (Amelanchier spp.) (Batra 1985; Stubbs etal. 1992; Loose etal. 2005; Ostaff
etal. 2015; Baude etal. 2016; Somme etal. 2016; Donkersley 2019). For example,
sugar content in horse chestnut (Aesculus hippocastanum L.) ranges from 0.58 to
3.57mg/ower/24h, while black locust (Robinia pseudoacacia L.) ranges from 0.76
to 4.0 mg/ower/24 h (Crane and Walker 1985). For comparison, white clover
(Trifolium repens L.) ranges from 0.01 to 0.20mg/ower/24h and alfalfa (Medicago
sativa L.) ranges from 0.07 to 0.25mg/ower/24h (Crane and Walker 1985).
Willow, maple, cherry and plum, brambles, chestnut (Castanea spp.), and ash
(Fraxinus spp.) are woody species that can provide pollen with high concentrations
of amino acids, sterols, trace minerals, and other nutritionally important compounds
for bees and other pollinators (Batra 1985; Tasei and Aupinel 2008; Di Pasquale
etal. 2013; Ostaff etal. 2015; Russo and Danforth 2017; Filipiak 2019). Some bees
are pollen specialists (oligolectic), wholly dependent on specic shrubs and trees in
certain families, such as willows, dogwoods (Cornaceae), heaths like blueberry and
huckleberry (Ericaceae), buckthorns such as New Jersey tea (Rhamnaceae), and
Table 2 (continued)
Scientic name Common name Bloom timebHeightcRegiond
Rhododendron spp.aRhododendron, azalea Early spring SM WCE
Rhus spp.fSumac Spring to summer M WCE
Robinia pseudoacacia e,fBlack locust Spring T Ei
Rosa spp.fRose Summer S WCE
Rubus spp.fBlackberry, raspberry Spring to fall S WCE
Salix spp.fWillow Early spring MT WCE
Sambucus spp.fElderberry Spring to summer S WCE
Sassafras albidum Sassafras Spring MT CE
Shepherdia spp. Buffaloberry Spring SM WC
Spiraea spp. Spirea Summer S WCE
Tilia spp.eBasswood Spring to summer T CE
Umbellularia californica California laurel Fall to spring T W
Vaccinium spp.f,g Blueberry, huckleberry Early spring S WCE
aIncludes some or all evergreen species
bFlowering times depend on species, location, and environmental conditions, varying from year to
year. Consult with local native plant experts to plan for overlapping bloom times
cShort (S), medium (M), tall (T)
dWest (W), Central (C), East (E)
eAdded value as timber
fAdded value of fruit or other culinary crops
gAdded value of decorative cut twigs for the oral industry
hSouthern distribution only
iThis species is invasive in some parts of the country and should not be planted in those regions
Source: Modied from Adamson etal. (2011)
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
284
roses (Rosaceae) (Dötterl and Vereecken 2010; Fowler 2016). These nutritionally
rich pollen sources are often sought out by native bees (Stubbs etal. 1992; Ostaff
etal. 2015) and have been shown to result in higher reproductive success and better
immunity in bumble bees (e.g., Tasei and Aupinel 2008; Di Pasquale etal. 2013).
Tree and shrub plantings with overlapping bloom times provide nectar and pollen
resources throughout the growing season and are key for sustaining diverse pollinator
populations (Loose et al. 2005; Hannon and Sisk 2009; Miñarro and Prida 2013).
Many temperate-zone trees and shrubs ower early in spring and can deliver some of
the rst pollen and nectar resources of the season, boosting early-season pollinator
populations (Table2) (Dirr 1990; Batra 1985; Ostaff etal. 2015; Somme etal. 2016).
In Michigan, United States, Wood etal. (2018) determined that willows, maples, and
Prunus spp. provided over 90% of the pollen collected in April by social and solitary
bees. When forage is available early in the growing season, freshly emerged bumble
bee queens are more successful in establishing their colonies (Carvell etal. 2017).
Plantings that include a diversity of owers of various sizes, shapes, and colors
can support a rich and abundant community of bees and other pollinators (Potts
etal. 2003; Roulston and Goodell 2011; Nicholls and Altieri 2013). Flower density
and subsequent nectar availability can be higher in some tree and shrub species
compared to herbaceous species (Crane and Walker 1985; Loose etal. 2005). For
example during peak owering season, gray willow (Salix cinerea L.) can produce
334,178 owers/m2 and oneseed hawthorn (Crataegus monogyna Jacq.) 19,003
owers/m2 compared to sea aster (Aster tripolium L.) 9565 owers/m2 and butter-
cup (Ranunculus acris L.) 688 owers/m2 (Baude etal. 2016). Respectively, nectar
productivity for these species is 3612, 584, 169, and 50kg/ha cover/year. Spatially,
agroforestry practices that incorporate a diversity of owering woody and herba-
ceous species can deliver a high density of oral resources relative to the land area
occupied due to vertical layering (Miñarro and Prida 2013; Morandin and Kremen
2013; Ponisio etal. 2016; Somme etal. 2016; Donkersley 2019). Timberlake etal.
(2019) documented approximately two and four times greater nectar per unit area in
hedgerows compared to woodlands and pasture, respectively.
Bees also collect resins and oils from trees and other plants (Wcislo and Cane
1996; Cane etal. 2007; Policarová etal. 2019). Some tunnel-nesting native bees use
tree resins to seal off their nests while honey bees use plant resins mixed with saliva
and beeswax to make propolis to seal unwanted holes in their hives. Propolis has
antibacterial properties that help prevent disease transmission or pest/parasite inva-
sion (Simone-Finstrom et al. 2017). Poplar trees (Populus spp.) are a common
source for these resins (Greenaway etal. 1990; Bankova etal. 2000; König 1985;
Drescher etal. 2019). Other tree species including pine (Pinus spp.), birch (Betula
spp.), elm (Ulmus spp.), alder (Alnus spp.), beech (Fagus spp.), and horse chestnut
can provide resin sources when poplar species are not present (Ghisalberti 1979;
König 1985; Drescher etal. 2019).
Pollinator behavior, foraging, and resulting pollination services are strongly
inuenced by weather conditions (e.g., ambient temperature, wind speed, precipita-
tion) (Corbet 1990; Vicens and Bosch 2000). Temperature and wind speed are two
primary weather variables that agroforestry practices can inuence.
G. Bentrup et al.
285
Windbreaks, alley cropping, and other agroforestry practices can reduce air
movement and modify temperatures in the cropped area. Daytime air temperatures
are several degrees warmer within a certain distance downwind of windbreaks
(8–10 times the windbreak height) (McNaughton 1988). These elevated tempera-
tures can increase pollinator activity and pollination, particularly in vegetable- and
fruit-growing regions where air temperatures at pollination time can often be below
optimum (Norton 1988). The vertical structure and shaded conditions provided by
agroforestry practices can offer niches that allow pollinators to nd suitable sites for
thermal regulation, which is becoming increasingly important under climate change
(Kjøhl etal. 2011). Papanikolaou etal. (2017) found that agricultural landscapes
that had a higher proportion of hedgerows and seminatural habitats (i.e., 17% com-
pared to 2%) decreased the detrimental effects of warmer temperatures on native
bee species richness and abundance.
Agroforestry plantings can address additional thermoregulation considerations
for managed honey bees. Honey bees expend energy to cool themselves and their
hives during hot weather. If the hives are shaded, that energy can be diverted to
honey production and hive maintenance activities (Nye 1962). Trees and shrubs are
useful for shading beehives, especially if the hives are placed on the north or north-
east sides of the woody plantings to receive maximum shading during the summer
heat (Hill and Webster 1995). Windbreaks and other woody buffers can also provide
protection from winter temperatures and winds if the hives are located on the lee-
ward side, helping reduce winter mortality (Haydak 1958). In Kansas, Merrill
(1923) documented that populations in overwintered hives can be up to 52% higher
when protected by windbreaks.
Foraging in moderate to high winds increases energetic costs for pollinators and
reduces pollination efciency (Vicens and Bosch 2000; Brittain et al. 2013).
Agroforestry practices designed to reduce wind speeds can increase pollinator ef-
ciency and allow pollinators to forage during wind events that would normally
reduce or prohibit foraging. The protective effect on insect ight extends up to a
distance equal to about nine times the height of the windbreak (Pinzauti 1986) and
the sheltered zone can contain higher numbers of pollinating insects (Pasek 1988),
increasing pollination and fruit set (Norton 1988). Agroforestry practices that
reduce winds, such as windbreaks and hedgerows, can enhance pollination by
reducing ower shedding and increasing overall owering (Peri and Bloomberg 2002).
Nesting andEgg-Laying Sites
The availability of nesting and egg-laying sites is also key for successful pollinator
conservation (Potts etal. 2005; Steffan-Dewenter and Schiele 2008; Sardiñas etal.
2016b). The short foraging and dispersal distances of many pollinator species
require that, along with food resources, nesting resources should be available within
a localized area (Gathmann and Tscharntke 2002).
Solitary tunnel-nesting bees build their nests aboveground in hollow tunnels in
the soft pithy centers of twigs of some plants, in abandoned wood-boring beetle
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
286
tunnels, or in tunnels they excavate themselves into wood, especially rotting logs
and snags (e.g., Potts etal. 2005; Cane etal. 2007). Hedgerows and other agrofor-
estry practices that incorporate woody species with soft pithy centers can increase
the availability of nesting sites (Table2) (Morandin and Kremen 2013; Kremen and
M’Gonigle 2015). A modeling study calculated a higher nesting potential for cavity-
nesting species in landscapes with agroforestry compared to landscapes without
agroforestry (Kay etal. 2019). Dead trees and branches left within an agroforestry
practice can also provide nesting sites (Brown 2002).
Solitary ground nesters excavate underground tunnels for nesting that can be nega-
tively impacted by tillage in agricultural elds (Shuler etal. 2005; Kim etal. 2006). The
presence of trees and shrubs provides protected nesting areas that have limited soil dis-
turbance. Hedgerows have been documented to provide suitable ground-nesting habitat
and increase diversity of ground-nesting bees (Morandin and Kremen 2013; Kremen
and M’Gonigle 2015; Ponisio etal. 2016); however, another study did not nd enhanced
nesting rates for ground-nesting bees in hedgerows (Sardiñas etal. 2016a).
Bumble bee queens often hibernate under trees in leaf litter. Upon emerging in
early spring, bumble bee queens seek rodent burrows and other insulated cavities in
which to start their colonies and rear their brood or offspring. Bumble bees often
select nest sites at the interface between elds and linear woody habitat such as
hedgerows and windbreaks (Svensson etal. 2000; Kells and Goulson 2003). One
study documented bumble bee nest densities twice as great in these linear woody
habitats when compared with grassland and other woodland habitats (Osborne etal.
2008b) while another study found hedgerows to be less preferred when compared to
herbaceous eld margins and grasslands for nest-searching bumble bee queen (Lye
etal. 2009). Non-cropped habitat suitable for nesting may also facilitate movement
of queens into the wider landscape (Carvell etal. 2017).
Agroforestry practices can provide egg-laying sites, larval host plants, and over-
wintering sites for lepidopteran (buttery and moth) species (Dover and Sparks
2000; Maudsley 2000; Merckx etal. 2012). Woody species were found to support
ten times more lepidopteran species than herbaceous plants in the US mid-Atlantic
region (Tallamy and Shropshire 2009). This work also documented that lepidopteran
species used native woody plant species as larval hosts 14 times more than nonna-
tive ornamental woody species. Some of the most highly used plant genera by lepi-
dopteran species include poplar, willows, cherry, plum, birch, and oaks (Quercus
spp.) (Tallamy and Shropshire 2009; Dumroese and Luna 2016). Lepidopteran spe-
cies and other pollinators including beetles overwinter under bark and leaf litter
found in hedgerows (Dover and Sparks 2000; Maudsley 2000; Pywell etal. 2005).
Enhancing Connectivity
Habitat is becoming increasingly fragmented due to agricultural intensication,
urban expansion, and other human activities (Saunders etal. 1991). Pollination ser-
vices at the farm and landscape scale are impacted by this fragmentation (e.g., Aizen
G. Bentrup et al.
287
and Feinsinger 1994; Sipes and Tepedino 1995). For example, Garibaldi et al.
(2011) estimated fruit set of pollinator-dependent crops decreased by 16% at 1km
distance from the nearest pollinator habitat.
Based on eld-level studies and modeling efforts, agroforestry practices can pro-
vide pollinator habitat close to crops and at a scale that benets foraging and crop
pollination (e.g., Morandin and Kremen 2013; Kremen and M’Gonigle 2015;
Morandin etal. 2016; Sutter etal. 2018; Graham and Nassauer 2019). For example,
the spatial distribution of windbreak and alley cropping plantings across elds to
achieve other nonpollinator-related services places habitat within the foraging range
of many pollinators, including short-distance foragers (Fig. 1) (Gathmann and
Tscharntke 2002; Benjamin etal. 2014; Moisan-DeSerres etal. 2015). The benets
of agroforestry practices for pollination services are often higher when this semi-
natural habitat is added to structurally simple elds and landscapes (e.g., Carvell
etal. 2011; Klein etal. 2012; Ponisio etal. 2016; Ponisio etal. 2019). This distribu-
tion of habitat also supports other insect-based services in agricultural elds such as
pest management by natural predatory insects. For instance, Morandin etal. (2014)
documented pest control by benecial insects extending 100m into crop elds from
hedgerows while Tscharntke etal. (2002) demonstrated that maintaining diverse
habitat on more than 20% of a farm helps ensure effective pest control by predatory
and parasitoid insects.
At the landscape scale, habitat connectivity is important for sustaining pollinator
diversity, reproduction, and dispersal. Different groups of pollinators respond to
habitat fragmentation in different ways (Cane etal. 2006; Brosi etal. 2008; Boscolo
etal. 2017). Although some pollinators can complete their entire life cycle within
hedgerows or riparian buffers, other pollinators may use agroforestry plantings for
Fig. 1 Windbreaks are typically planted at intervals of 10–15 times windbreak height (H) for
reducing erosion and enhancing crop yields through microclimate modication. Using an H of
18m as an example, the windbreaks would be spaced at 180–270 m across a eld. This would
place pollinator habitat within 90–135m from the center of the cropped area, well within the forag-
ing range of most pollinators as well as within the range of predatory and parasitoid insects to prey
on crop pests. Within a 1km2 eld, a 20m wide and 18m tall windbreak could provide 10% non-
cropped habitat area to support pollinators
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
288
only a portion of their life cycle. Some pollinators can nest or overwinter in one
habitat and forage in another if the distances between the patches are within their
ight capabilities. Pollinators with limited dispersal capability, such as tiny sweat
bees that have foraging ranges of less than 250m (Greenleaf etal. 2007; Gathmann
and Tscharntke 2002) or butteries that are poor iers, may need plantings directly
connected to habitat to aid their dispersal. In contrast, bumble bees can forage up to
2km or more (Osborne etal. 2008a). Habitats with greater connectivity allow pol-
linators to travel more safely between patches to nd resources, disperse to new
habitat, and encounter potential mates.
Agroforestry practices can serve as habitat corridors connecting larger patches of
habitat that facilitate movement of organisms between habitat fragments, aid in
establishing or maintaining populations, promote greater genetic ow among popu-
lations, and increase species diversity within isolated areas (Tewksbury etal. 2002).
Experimental corridors have been found to increase the movement of pollinators
(Haddad 1999) as well as facilitate pollination (Tewksbury etal. 2002; Townsend
and Levey 2005). Evidence documenting pollinator use of agroforestry habitat as
corridors includes hedgerow-promoted movement of butteries (Ouin and Burel
2002), moths (Couthard etal. 2016), and bees (Cranmer etal. 2012; Klaus etal.
2015) and buttery travel along windbreaks (Dover and Fry 2001) and riparian buf-
fers (Meier etal. 2005). Corridors may not always need to directly connect habitat
areas to help organisms to disperse (Fried etal. 2005) as patches of habitat can serve
as stepping stones between isolated fragments in otherwise inhospitable landscapes
(Ottewell etal. 2009).
Agroforestry plantings extending across rural and urban landscapes often con-
tain greater plant diversity than adjacent lands, are longer term in nature, and are
generally protected from further development and major disturbances. In developed
landscapes, like intensively managed agricultural lands or cities, agroforestry plant-
ings are particularly valuable (Senapathi etal. 2017). Additionally, agroforestry cor-
ridors are likely to be particularly benecial in agricultural landscapes where natural
or seminatural habitat benets pollinator populations (e.g., Klein et al. 2012;
McKechnie etal. 2017) as well as crop pollination (Morandin and Winston 2006;
Blaauw and Isaacs 2014; Klatt etal. 2014). Hedgerows in intensively managed agri-
cultural landscapes, for example, increase bee, syrphid y, and other benecial
insect abundance and diversity in adjacent crop elds (Morandin and Kremen 2013;
Morandin etal. 2014).
However, agroforestry plantings may act as barriers to some pollinators, inhibit-
ing movement between habitats. Pollen ow can also potentially be reduced across
hedgerows (Klaus et al. 2015) and possibly other tree-row plantings. Krewenka
et al. (2011) found that bee foraging was not impacted by hedgerows; however,
another study found that bombyliid ies had reduced pollen transfer (Campagne
etal. 2009). Windbreaks and hedgerows can act as barriers for buttery movement
(Dover and Fry 2001). Hedgerows may channel pollinator movement, which could
enhance connectivity but restrict movement across hedgerows, isolating some plant
populations (Klaus etal. 2015). The orientation of plant rows may inuence hedge-
rows’ abilities to promote movement or act as barriers (Ouin and Burel 2002).
G. Bentrup et al.
289
Climate change impacts pollinators and their relationships with plants by driving
shifts in the ranges of pollinators or their host plants (Forister etal. 2010; Chen etal.
2011; Kerr etal. 2015), altering plant and pollinator phenology (Parmesan 2007;
Bartomeus et al. 2011), decreasing protein concentration in oral pollen (Ziska
etal. 2016), and increasing the impacts of other drivers of pollinator decline (Settele
etal. 2016). Increasing landscape connectivity is one proposed strategy to reduce
negative impacts of climate change on pollinators by enhancing the ability of spe-
cies to move into new regions as climate shifts (Krosby etal. 2010; Gilchrist etal.
2016). Agroforestry may help enhance connectivity across rural and urban land-
scapes, thereby helping species extend their ranges and have some resiliency in the
face of a changing climate.
Reducing Pesticide Exposure
Pesticides can have acute toxicity leading to pollinator mortality and sublethal
effects on growth and development, behavior, and other activities (Stanley and
Preetha 2016). Sublethal effects of pesticide exposure at very low concentrations
are reported on homing and foraging, larval development and adult emergence, and
visual and olfactory learning (Desneux etal. 2007; Sánchez-Bayo and Goka 2014).
Among social insects like honey bees and bumble bees, pesticides carried back to
the nest may also impact larvae, nestmates, and the queen, and delay emergence of
new adults (Wu etal. 2011). Pesticides can also suppress the immune system, mak-
ing bees (and likely other organisms) more susceptible to disease and parasites (e.g.,
Sánchez-Bayo etal. 2016; Czerwinski and Sadd 2017; Evans etal. 2018).
On farms and in other landscapes, pollinators may come into contact with pesti-
cides through several exposure pathways (Fig.2) (e.g., Krupke etal. 2012; Botías
etal. 2015; Chagnon etal. 2015; Johnson 2015; Hladik etal. 2016; Long and Krupke
2016; Stanley and Preetha 2016). Pollinators may also be exposed to multiple pes-
ticides over time (with higher cumulative levels of toxicity than an individual pesti-
cide or synergistic effects) (Sánchez-Bayo and Goka 2014). USDA (2014) provides
additional information on pesticide exposure pathways and methods for preventing
and mitigating potential negative impacts of pesticides on pollinators.
Agroforestry practices can help reduce pollinator exposure to pesticides that are
used for managing crop pests and diseases or reducing weed competition (Vaughan
etal. 2017). By understanding potential pesticide exposure pathways, farmers and
land managers can better design plantings such as windbreaks, hedgerows, and
riparian buffers that help reduce or mitigate potential negative impacts of pesticides
(Fig.3). The same agroforestry practices aimed at protecting pollinators can also
help reduce pesticide use and associated costs by supporting natural enemies of
crop pests, such as predatory and parasitic insects and other arthropods that reduce
pest populations (Morandin etal. 2016; Staton etal. 2019).
Windbreaks, hedgerows, and other linear plantings can reduce spray drift by up
to 80–90% by reducing wind speeds and trapping particles (Ucar and Hall 2001;
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
290
Otto etal. 2015). Buffers slow wind speeds, and the porosity of plant buffers lets
wind move through the vegetation (vs. pushing up and over a solid barrier). At
slower wind speeds, particles are more likely to fall out and become trapped in foli-
age. Agroforestry buffers that are 2.5–3m tall, with 40–50% porosity and ne, ever-
green foliage (large surface area), are generally the most effective for drift prevention
(Ucar and Hall 2001; Wenneker and Van de Zande 2008; Mercer 2009; Otto et al.
2015; Chen etal. 2017). Yet, even hedgerows with porosity of nearly 75% have been
found to be effective in reducing drift by more than 80% (Lazzaro etal. 2008).
In orchards or other crop systems being sprayed early in the growing season,
buffers comprised of evergreen species can substantially reduce potential pollinator
exposure risk from spray drift (Wenneker and Van de Zande 2008; Felsot et al.
2010). Fine, evergreen, coniferous foliage can capture 2–4 times that of broadleaf
species, with the additional benet of trapping air pollutants in winter (Chen etal.
2017). Leaf roughness, hairiness, waxiness, and other factors can affect foliage cap-
ture of particulate matter and some research indicates that the arrangement of a lter
strip (with trees, shrubs, and grasses, and of an adequate length) is more important
than species composition (Terzaghi etal. 2013; Chen etal. 2016).
Agroforestry buffers can also help capture pesticide runoff, prevent or slow pesti-
cide movement through soil, and help to break down some pesticides (Chaudhry etal.
Fig. 2 Potential pesticide exposure pathways encountered by pollinators in an agricultural
landscape
Fig. 3 Using agroforestry practices to mitigate potential negative impacts of pesticides on
pollinators
G. Bentrup et al.
291
2005; Jose 2009; Pavlidis and Tsihrintzis 2017). A meta-analysis by Zhang et al.
(2010) highlights how sediment captured by vegetative buffers helps improve pesti-
cide removal, particularly those pesticides that are strongly hydrophobic such as pyre-
throids and many organophosphates. Based on a review of available studies, Pavlidis
and Tsihrintzis (2017) documented a 40–100% reduction of pesticides (including her-
bicides) in runoff using agroforestry systems. Plants and rhizosphere microorganisms
vary in their ability to degrade or immobilize pesticides. Poplar, willow, birch, alder,
black locust, and sycamore (Platanus spp.) are North American native trees with doc-
umented effectiveness in capturing pesticide runoff or immobilizing pesticides within
their woody tissue (Pavlidis and Tsihrintzis 2017; Pavlidis and Tsihrintzis 2018).
However, the same factors making agroforestry practices effective buffers can also
lead to pesticide accumulation and pose danger for pollinators, particularly from sys-
temic pesticides and those with long residual activity such as neonicotinoids (Krupke
etal. 2012; Hopwood etal. 2016). Nectar and pollen of early- owering tree and shrub
species may become contaminated by systemic action of neonicotinoids or through
nontarget drift of treated seed-coating dust during crop planting (Long and Krupke
2016). Pesticide droplets and particles or pesticides adhering to dust can also accumu-
late in the foliage or at the base of agroforestry buffers (Zaady etal. 2018). Pollinators
may ingest or carry back to the nest particles contaminated with pesticides (Krupke
etal. 2012). If the pesticides or their metabolites have long residual activity and/or are
systemically taken up into the plants, the accumulated levels could mean chronic and
increased exposure over time. Pesticides accumulating in soil pose higher risks for the
approximately 70% of native bees that nest in the ground.
Increasing the proportion of non-cropped habitat in agricultural landscapes has
been shown to buffer the effects of pesticide on native bees (Park et al. 2015).
Agroforestry practices can provide this habitat, especially when the plantings are pro-
tected from pesticide exposure. No-spray buffer zones can be used to protect agrofor-
estry plantings that provide pollinator refuge (Davis and Williams 1990; Ucar and
Hall 2001). Spray drift deposition in hedgerows was reduced by 72% when a 12m
no-spray buffer zone was used next to the hedgerows (Kjær etal. 2014). Depending
on the cropping systems (and their potential spray regimes), it may be important to use
plants that do not provide pollinator forage in the rst rows adjacent to a eld (Fig.3).
Crop Pollination Services
Available scientic evidence demonstrates the conservation benets that agroforestry
practices can provide to insect pollinators, including greater pollinator abundance and
richness. Although these benets should translate into enhanced pollination services
leading to increased crop yields and quality, few studies have been conducted to docu-
ment this direct agronomic benet (Klein etal. 2012; Staton etal. 2019). Studies have
shown positive effects on canola (Brassica napus L.) yields due to hedgerows
(Morandin etal. 2016; Dainese etal. 2017) while another study showed no effects on
crop pollination in sunower (Helianthus annuus L.) (Sardiñas and Kremen 2015). In
apple orchards, researchers found increased pollinator abundance adjacent to an arti-
cial windbreak, which led to a 20–30% increase in fruit set with no reduction in fruit
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
292
size (Smith and Lewis 1972). While the articial windbreak was created out of coir
netting, this study may suggest potential yield increases due to pollinator activity in
apple orchards with planted windbreaks.
Many factors are likely to inuence the ability of agroforestry practices to pro-
mote crop pollination services, including specic pollinator attributes, eld size,
crop type, plant composition of the agroforestry practice, and landscape context
(IPBES 2016). The diversity of interacting variables makes it challenging to con-
duct studies and develop guidelines for producers. For instance, the ratio of agrofor-
estry practice to crop area in order to supply sufcient pollination service is largely
unexplored (Venturini et al. 2017). One study demonstrated that native bees can
provide full pollination services for watermelon (Citrullus lanatus Thunb.) when
around 30% of the land within 1.2km of a eld is in natural habitat (Kremen etal.
2004), which could be an approximate analog to an agroforestry practice. Regarding
landscape context, one study found an increase in quality and quantity of strawber-
ries grown adjacent to forest-connected hedgerows, as compared to isolated hedge-
rows or grass margins (Castle et al. 2019). Plants placed at forest-connected
hedgerows produced more high-quality strawberries with 90% classied as “mar-
ketable.” In comparison, only 75% of strawberries from plants at isolated hedge-
rows, 48% of strawberries from plants on grassy margins, and 41% of strawberries
from self-pollinated control plants were classied as marketable. Based on market
prices of 2016, the increase in economic value between strawberries produced at
grassy margins and forest-connected hedgerows amounted to 61% (Castle etal.
2019). Cost-benet studies that assess the benets of an agroforestry practice for
pollination services compared to the costs of installation and maintenance, opportu-
nity costs, and costs of potential unintended negative effects are also very limited.
Morandin et al. (2016) estimated that 7 years would be required for farmers to
recover hedgerow implementation costs based on the estimated yield benets from
both pollination and pest control to the crop (Morandin etal. 2016). Future cost-
benet analyses should consider the range of agronomic effects in order to provide
comprehensive economic assessment of ecosystem services.
Summary
Agroforestry is a multifunctional land-use approach that provides a range of ecosystem
services in support of production and environmental stewardship goals (Nair 2007).
Capitalizing on insect-based ecosystem services, agroforestry offers opportunities to
benet pollinators and other benecial insects and their services including crop pollina-
tion and biological pest management. Based on the available scientic literature, agro-
forestry practices in temperate regions can aid pollinators and pollination services by
providing habitat, including foraging resources and nesting or egg-laying sites, enhanc-
ing site and landscape connectivity, and mitigating pesticide exposure.
A primary advantage for using agroforestry to support pollinators is that these prac-
tices inherently provide some pollinator benets and with additional considerations dur-
ing design and management, the effectiveness of agroforestry practices for pollinators
G. Bentrup et al.
293
can be enhanced. Due to common landscape settings and spatial congurations, each
agroforestry practice provides different options and advantages for providing pollinator
habitat, enhancing connectivity, and protecting against pesticides (Table3).
Table 3 General considerations for promoting pollinators and pollination services for each
agroforestry practice
Practice Considerations for pollinators
Alley cropping
(also called
tree-based
intercropping)
Alley cropping presents an opportunity to grow plants in close proximity that
have complementary owering 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 owering trees like black cherry, black locust, or basswood along
with the more typical alley cropping trees of walnut, pecan, or oak. Diverse
forbs and shrubs may be planted in rows for cut owers, berry production, or
the nursery market, as well as for pollinators. A legume forage crop between
rows will not only x nitrogen and help manage weeds, but also provide
nectar and pollen if allowed to ower
Windbreaks
(also includes
shelterbelts,
hedgerows)
These practices help reduce wind speed, making it easier for pollinators to y
and visit owers. When planted with diverse owering shrubs and trees,
windbreaks can provide shelter, pollen, and nectar for pollinators.
Windbreaks and other linear plantings can serve as buffers against drifting
pesticides. Do not use plants that will attract pollinators in windbreaks
designed to intercept pesticide drift. Planting wildowers during
establishment can enhance pollinator resources and reduce weed pressure
Riparian forest
buffers
Riparian forest buffers are especially important for pollinators during hot
summer months when upland plants may not produce nectar or pollen.
Early-owering willows, as well as fruit and nut-bearing shrubs, can provide
additional farm income as cut owers or produce, while also providing
reliable food resources for pollinators. Honey bees may also visit muddy
shorelines to gather water for cooling their hives. Riparian buffers are
important corridors for landscape connectivity from rural to urban areas,
facilitating pollinator dispersal
Silvopasture Silvopastures provide an open understory where a variety of owering forbs
(forage legumes, such as alfalfa or clover, or native wildowers) can grow.
Rotational grazing practices can give these forbs an opportunity to recover
from grazing or ower before being eaten. Harvestable owering trees, such
as basswood, black locust, maple, persimmon, or tulip tree, can enhance a
silvopasture system. Using thinning and prescribed re to daylight existing
seedbanks can restore natural diversity and promote owering plants that
benet pollinators
Forest farming
(also called
multistory
cropping)
Many valuable overstory crop trees, like tulip tree, maple, basswood, and
black cherry, provide excellent pollinator habitat. Cultivated understory
plants, such as ginseng, goldenseal, and black cohosh, may benet from
pollinator visits. For example, diverse bees pollinate black cohosh. Black
cohosh does not produce nectar to attract bees, but relies on nearby prolic
nectar producers, such as pale touch-me-not or whiteower leafcup. The
pollination needs of many forest-farmed crops are not well understood, but
providing diverse habitat niches is the best way to support diverse pollinators.
Flies are likely important pollinators since some ies are active in cooler
temperatures, when many of the forest crops ower
Source: Modied from Vaughan and Black 2006
The Role ofTemperate Agroforestry Practices inSupporting Pollinators
294
Typically, agroforestry practices are planned for sites on individual farms and
ranches. Pollinator-friendly agroforestry plantings on a single farm can have
important benets for pollinators. Even greater impact can be achieved through
these plantings when planning and design are combined with other nearby farms
and ranches which are using pollinator-friendly practices. While it may be uncom-
mon for pollinators and other benecial insects to be considered in landscape
planning efforts (Steingröver etal. 2010), there are many potential benets from
broadening existing large-scale planning efforts to include pollinator issues.
Working across site and landscape scales, agroforestry practices can support pol-
linator abundance and richness, protect biodiversity, enhance pollination, and
increase food security.
Acknowledgements We would like to thank Justin Runyon, Judy Wu-Smart, Michele
Schoeneberger, Aimee Code, and two anonymous reviewers whose comments and feedback helped
to improve the chapter. This work was supported by funding provided by a contribution agreement
with the United States Department of Agriculture (USDA)-Natural Resources Conservation
Service (NRCS) to the Xerces Society.
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