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New Research and BMPs in Natural Areas: A Synthesis of the Pollinator
Management Symposium from the 44th Natural Areas Conference, October 2017
Author(s): Victoria Wojcik, Lisa Smith, William Carromero, Laurie Davies Adams, Seth Davis, Sandra
J. DeBano, Candace Fallon, Rich Hatfield, Scott Hoffman Black, Thomas Kaye, Sarina Jepsen, Stephanie
McKnight, Lora Morandin, Emma Pelton, Paul Rhoades, Kelly Rourke, Mary Rowland and Wade
Tinkham
Source: Natural Areas Journal, 38(5):334-346.
Published By: Natural Areas Association
https://doi.org/10.3375/043.038.0503
URL: http://www.bioone.org/doi/full/10.3375/043.038.0503
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334 Natural Areas Journal Volume 38 (5), 2018
INTRODUCTION
Land managers face constant challenges when balancing mul-
tiple land use goals that include ensuring that keystone species
are protected. As mindful stewards of our natural areas we aim
to promote, secure, and enhance our natural landscapes and the
species that make them their home. When we focus our efforts
on protecting and promoting pollinators as well as the ecosystem
services they provide we are met with an additional challenge.
Limited resources and guidance are available, the data is patchy,
and there is an enormous diversity of species. More than 30,000
bees (Michener 2000), 150,000 butterflies and moths (Grimal-
di and Engel 2005), 150,000 flies (Thompson 2006), 12 bats
(Medellin et al. 1997), 63 birds (Arizmendi and Ornelas 1990),
and over 350,000 other arthropods, primarily beetles (Grimaldi
and Engel 2005), visit flowers, transferring pollen and aiding in
reproduction. This is compounded by the diversity of ecosystems
globally and the sheer number of plant–pollinator interactions
that can be expected. Pollinators are directly responsible for the
reproduction of 67–96% of flowering plants globally (Ollerton
et al. 2011); these flowering plants define our natural landscapes
and ecosystems.
When pollinators are considered in management decisions, eco-
system benefits can include increased pollination services and
overall support of other key ecosystem services. Evidence of the
impact that proactive pollinator management has is most clear
and abundant in agricultural systems, where hedgerow and habitat
planting translates to increased pollinator occurrence (Shepherd
et al. 2003; Kremen et al. 2004; Ricketts et al. 2008) and often
benefits crop yields (Klein et al. 2003; Greenleaf and Kremen
2006; Garibaldi et al. 2014). Increasing floral diversity in urban
and suburban areas through habitat planting and gardening shows
the same positive trend of attracting diverse communities of pol-
linators (Hernandez et al. 2009; Wojcik and McBride 2012). Less
evidence exists for the restoration of natural landscapes; neverthe-
less, case studies indicate that planting for pollinators (Cane and
Love 2016; Tonietto and Larkin 2018) or modifying management
practices and seed mixes (Galea et al. 2016; Harmon-Threatt and
Chin 2016) indeed results in corresponding positive changes in
the pollinator community: more pollinators using the landscape
and more plant reproduction as a result.
To address the growing interest and expressed need for pollinator
management strategies a special pollinator symposium was held at
the 2017 annual meeting of the Natural Areas Association, curated
by William Carromero of the US Forest Service and Lisa Smith
of the Natural Areas Association. The overarching goal of this
symposium was to present new research and the current body of
knowledge surrounding pollinator system management to practi-
tioners, giving them the tools to better manage this essential natural
resource. Although such an extensive topic can hardly be examined
fully in a half-day symposium, the topics presented showed that
research is progressing in an effort to fine-tune best management
practices across ecosystems. Active research into pollinator
management and conservation on natural areas addressed large
ungulate grazing and forest management, with a focus on alpine
systems. Reviews of research, practices, and programs intended to
provide management guidance focused on honeybee pasturing on
natural lands, prairie restoration seeding, and managing pollinators
in western regions. This synthesis, written by the presenters and
participants, recapitulates the symposium with a presentation of
research and review findings, and an assessment of key gaps and
next steps in topic area. Pollinator management in natural areas
is a broad topic. The symposium allowed us a detailed look at a
subset of topics, starting the discussion on how we aim to consider
pollinators in our land management decisions.
•
New Research and BMPs in Natural Areas:
A Synthesis of the Pollinator Management Symposium from the
44th Natural Areas Conference, October 2017
Victoria Wojcik1, Lisa Smith, William Carromero, Laurie Davies Adams, Seth Davis, Sandra J. DeBano, Candace Fallon,
Rich Hatfield, Scott Hoffman Black, Thomas Kaye, Sarina Jepsen, Stephanie McKnight, Lora Morandin, Emma Pelton,
Paul Rhoades, Kelly Rourke, Mary Rowland, and Wade Tinkham
•
FEATURED PAPER
Natural Areas Journal 38:334–346
1 Corresponding author: vw@pollinator.org;
(647) 546-3890
Index terms: bee competition, Best Management Practices, forest management, grazing, restoration seeding
Volume 38 (5), 2018 Natural Areas Journal 335
NATIVE BEES AND LARGE MAMMALS: VERTEBRATE–
INVERTEBRATE INTERACTIONS IN RIPARIAN NATURAL
AREAS
Presented by Mary Rowland
Grazing is perhaps one of the most common managed land uses
in natural landscapes. Its management focuses on both native
ungulate species, which provide recreational, socioeconomic,
and cultural benefits, and nonnative livestock species, such as
cattle (Bos taurus) and sheep (Ovis aries). Livestock grazing
has occurred for well over a century in North America. While it
can be well-managed, many gaps remain in our understanding of
its impact on the full scope of ecosystem services provided by
natural lands and its interaction with native ungulate herbivory.
Investigations of how grazing impacts pollinators are beginning
to illuminate how grazing-induced changes in floral abundance,
plant community composition, plant architecture, and soil char-
acteristics, such as compaction (a key factor for ground-nesting
bees), influence pollinator communities (e.g., Carvell 2002;
Kruess and Tscharntke 2002b; Vulliamy et al. 2006; Hatfield and
LeBuhn 2007; Sjödin 2007; Kearns and Oliveras 2009; Kimoto
et al. 2012). There remains, however, very little known about the
effects of native ungulate herbivory on pollinators, especially in
the United States.
The degree to which strategies for managing ungulates and pol-
linators in natural areas may conflict with each other is not well
understood, especially in sensitive areas such as riparian zones
(DeBano et al. 2016). Riparian systems provide key resources
to native grazers and are often preferred by livestock, especially
during summer when green forage has senesced in upland areas.
Significant impacts of livestock grazing in riparian areas have been
documented, particularly for cattle in arid ecosystems (Kauffman
and Krueger 1984; Belsky et al. 1999). However, herbivory by
wild ungulates such as deer (Odocoileus spp.) and elk (Cervus
canadensis) can also affect vegetation in riparian areas (Averett
et al. 2017). Riparian systems are often a focus of restoration and
management, in recognition of the relatively high biodiversity and
ecosystem services these lands provide compared to other systems
(Kauffman and Krueger 1984). Riparian areas also often contain
species assemblages that differ from upland ecosystems (DeBano
et al. 2004). These wetland systems have a history of frequent
disturbance and subsequent restoration, and thus often represent
a very actively managed landscape type within natural areas.
What is our current state of knowledge of impacts of ungulate
grazing on pollinators? Herbivory can impact plant architecture,
abundance, growth, diversity, and species composition (Black et
al. 2011). Depending on the preferences of the grazing ungulate
involved, herbivory can alter potential food resources for pollina-
tors, both by decreasing and, in some cases, increasing biomass
and abundance of certain species (Vázquez and Simberloff 2004;
Vulliamy et al. 2006).These changes can, in turn, influence the
abundance of pollen and nectar available to pollinators, as well
as the availability of nesting material and habitat. The physical
presence of large mammals in the landscape can also impact
soils, including compaction and stability, which can affect habitat
quality for ground-nesting bees (Kimoto et al. 2012; Schmalz et
al. 2013). A more nuanced impact of grazing is the alteration of
microhabitat conditions, including changes in temperature and
humidity (DeBano 2006). Both temperature and humidity can
impact pollen and nectar availability in plants, as well as the
development of bees in some cases.
Given the variety of factors that may be influenced by ungulate
grazing, a first step in developing best management practices in
riparian areas that consider ungulates and pollinators is to identify
areas of shared niche space between these groups. Diet overlap
between large herbivores and pollen- and nectar-seeking species,
combined with common feeding habitats, create the potential for
competition of food resources. At the most fundamental level,
grazing removes plant resources that pollinators use (i.e., flow-
ers). However, direct competition may be reduced depending on
the timing of herbivory (e.g., pollinators may feed on the plant
prior to the grazing event or regrowth may occur after blooming,
including additional blooming). Nevertheless, ungulate herbivo-
ry can alter the availability of pollen or nectar in a system and
understanding the basics of diet overlap among these groups can
help managers predict where and when such interactions might
occur and their outcomes.
As part of a larger, collaborative project evaluating interactions
of ungulate grazing and riparian restoration for salmonids at the
Starkey Experimental Forest and Range (Starkey) in northeastern
Oregon, a US Forest Service (USFS) and Oregon State University
(OSU) research team is exploring how herbivory by large mammals
may influence native bees. First, the team conducted a literature
review aimed at understanding the potential of dietary overlap
among native bees, deer, elk, and cattle, focusing on riparian spe-
cies recorded along Meadow Creek within Starkey (DeBano et al.
2016). The review revealed that bees may use approximately 30%
of plant species present in this riparian area; elk were reported
as feeding on 43% of Meadow Creek species, deer were reported
feeding on 19%, and cattle on 16%. The relative percentage of
species documented in diets of ungulates that were also identified
as important to bees was approximately 55% (DeBano et al. 2016).
In summary, the literature review showed that ungulate grazers
and bees have high potential for dietary overlap, with over half
the species found within this riparian area that are believed to be
important to bees also known to be consumed by ungulate grazers.
Current research is underway to examine the realized resource
overlap among these species in the Meadow Creek riparian area by
documenting which plants are actually used by bees for nectar and
pollen, and by comparing cattle vs. deer and elk impacts on floral
resources. Bees make use of a variety of woody and herbaceous
plants such as willows and yarrow.
Research Methods and Initial Results
A major goal of the USFS pollinator research at the Meadow
Creek site within Starkey is to examine wild ungulate and live-
336 Natural Areas Journal Volume 38 (5), 2018
stock impacts on floral resources for native bees, partitioning
out effects by ungulate type. A series of exclusion experiments
within a newly restored riparian area has been in place since
2014 (Averett et al. 2017). Native bees and floral resources were
sampled from spring to fall in 2014–2016 along a 14 km reach of
Meadow Creek to document flowering species most commonly
visited by native bees and the seasonal and spatial dynamics of
the bee community, and to quantify how herbivory by deer and
elk influences flowering plant communities. (Cattle were not
introduced into the system until 2017.) Half of the 12 sampling
sites were excluded from native ungulate grazing to provide a
comparative baseline to grazed sites. More than 150 species of
flowering forbs and shrubs were recorded along Meadow Creek
during this time, and plant visitation records of more than 900
bees representing more than 80 species has been documented
(Roof et al. 2018).
Initial analyses suggest that floral abundance, quantified by bloom-
ing stems, was generally higher in ungrazed sites than in grazed
sites, although patterns were highly variable in time and space
and across plant species. Because the flowering plant community
at Meadow Creek is particularly diverse and site-to-site variability
is high, responses to herbivory are complex. However, several
individual species focused on thus far suggest that some plant
species may be of greater concern relative to ungulate management
and native bees. For example, one common dominant flowering
species commonly visited by bees, slender cinquefoil (Potentilla
gracilis), became significantly less dominant in ungulate-grazed
sites over time. Some plant species, however, displayed no response
to grazing, such as common yarrow (Achillea millefolium), while
other species showed tendencies to decrease in abundance over
time when excluded from grazing.
Management Considerations for Grazing and Pollinators
Both livestock and native ungulates are known to be common
ecosystem engineers (Jones et al. 1997). While spatiotemporal
patterns of herbivory have varied effects, herbivory’s impact
on floral communities may have consequences for ecologically
significant invertebrates such as native bees. Although Starkey
research is ongoing, some guiding principles and concepts are
emerging. First, there are key areas of spatial and temporal
overlap between ungulate grazing and pollinator usage, and our
knowledge of the extent of this overlap is becoming more refined
as research progresses. Native ungulates and livestock graze on
many of the same species that native bees rely on for pollen and
nectar, but the potential for dietary overlap does not necessarily
mean competition to the detriment of pollinators, especially if
resource use by ungulates and pollinators is spatially and/or tem-
porally separated, if plants are able to compensate for grazing, or
if plants respond to grazing with more growth. Research suggests
that managers should pay particular attention to flowering species
highly preferred as forage by native ungulates and livestock and
determine whether those plant species are also preferred floral
resources for native pollinators. This may be particularly import-
ant for pollinator species of concern that appear to rely heavily
on ungulate-preferred plant species, and if temporal and spatial
overlap with grazing ungulates is likely. When riparian restoration
involves planting of mass-blooming shrubs or forbs that may
provide pollen or nectar—or both—for pollinators, short-term
exclusion of plantings from herbivory may be beneficial. Future
lines of research addressing this topic would benefit restoration
ecology in natural areas where pollinator conservation is of interest.
BIOLOGICAL DIVERSITY OF POLLINATORS IN A HIGH-
ELEVATION SPRUCE FOREST
Presented by Seth Davis
Forests make up a substantial portion of natural lands in North
America and are managed for a variety of objectives including
recreation, restoration of natural processes, and timber harvest.
Although management activities may alter the structure, function,
and composition of forest ecosystems, there is little known about
how these shifts may impact native pollinator communities, espe-
cially high-elevation forests. There is a general lack of foundational
knowledge on the basic biodiversity and abundance of pollinators
in alpine systems, which detracts from the ability of practitioners
to design forest management applications that meet objectives
while simultaneously promoting conservation of pollinator hab-
itat. However, high-elevation forest landscapes in western North
America are vast and may serve as valuable refugia for endemic
pollinators, especially under continued land use intensification
and an expanding wildland–urban interface (Platt 2010). Climate
change is also predicted to have a more major impact on high-el-
evation forest. Accordingly, there is a pressing need to develop an
understanding of pollinator communities in alpine forests, and to
quantify the factors that may relate to pollinator site occupancy.
Various natural disturbance processes of forest ecosystems have
dramatic impacts on the structure of western coniferous forests,
particularly fire and bark beetles (Tinkham et al. 2016). These
disturbances can significantly alter floral resource availability,
which has a corresponding impact on bee pollinators. For ex-
ample, in fire-adapted forest ecosystems bee richness increases
rapidly following fire disturbances but then gradually declines
as successional patterns alter floral reward structure (Potts et al.
2003). Similarly, bark beetle outbreaks in European spruce forests
are positively correlated with site occupancy of both common and
red-listed bees and wasps (Beudert et al. 2015), probably due to
the effects of newly created canopy gaps resulting from bark beetle
kill. However, anthropogenic disturbances that fragment forest
landscapes can have deleterious effects on pollinator communi-
ties. In particular, reduced landscape connectivity that decreases
habitat patch size can have strong effects on the composition, but
not abundance, of bee species assemblages in forest ecosystems
(Brosi et al. 2008). Consequently, the mechanisms by which both
natural and anthropogenic disturbance may influence pollinator
richness and abundance in forests are complex, but critical for
developing adaptive conservation strategies.
Volume 38 (5), 2018 Natural Areas Journal 337
Our goal was to provide a first report of the bee fauna in a high-el-
evation spruce forest in the southern Rocky Mountains, with the
goal of quantifying links between forest structure, understory plant
species richness, and foraging bee pollinators. These links must
be considered in the context of seasonal variability, as pollinator
communities may shift dramatically in abundance or composition
as degree days accrue—not accounting for this variability could
provide reduced estimates of biodiversity or site occupancy.
Research Methods and Initial Results
Bee sampling was conducted passively using a randomized array of
blue vane traps (common passive sampling traps that were co-opt-
ed from early pest management assessments when it was found
that bees favored them). Overall γ-diversity (species composition
among sites) in the first season of sampling was characterized by
19 genera of bees representing five families (Andrenidae, Apidae,
Colletidae, Halictidae, and Megachilidae) and 39 unique species,
categorized from 932 specimens (Rhoades et al. 2018). Seasonal
variation in abundance and community composition was substantial
and early-season (Apr) communities were dominated by Osmia
spp. and midsummer (Jun–Jul) communities were dominated by
Bombus spp., but bee abundance and γ-diversity were on average
88% and 74% higher midsummer than early- and late-season. It
is not surprising that bumblebees were prominent in the sample;
bumblebees are known to be prevalent at higher latitudes and at
higher elevations, with a corresponding community shift often
predicted or expected along an altitudinal gradient. Seasonal
sampling further indicated a shift toward increased bumblebee
dominance toward the late summer. This may be due in part to
the greater thermal mass of larger bees, which may allow them
to remain active even when temperatures are cool for extended
periods. However, this hypothesis has not yet been tested.
Forest basal area was negatively correlated with bee γ-diversity
and abundance, as well as understory plant species richness—
indicating that densely vegetated forest may be inferior habitat
to low-density forests. Trapping locations where basal area
ranged from 7.5 m2 ha−1 to 20.0 m2 ha−1 exhibited ~55% higher
bee abundances and ~45% higher γ-diversity than locations that
exceeded 20.0 m2 ha−1 basal area. Bee diversity and abundance
increased with understory species richness, and species richness
increased as stand basal area decreased, suggesting that forested
sites with low basal area corresponded to overstory canopy gaps
and increased site occupancy by flowering plants.
Management Considerations for Pollinators in Alpine
Forests
With this first investigation into the bee community of forested
systems, the question arises as to how alpine systems compare to
other ecosystems in terms of pollinator community structure and
richness. This study indicated that bee richness and diversity in
nearby urban and rural areas may be higher in studies conducted
by Kearns and Oliveras (2009). Community structure varied, with
bumblebees being the dominant species group in alpine systems
while smaller sweat bees such as members of the genera Lasi-
oglossum and Augochlorella were dominant in urban and rural
areas. The highest-richness bee communities have been noted
from the arid Southwest. Bee richness within these regions often
corresponded to increased spatiotemporal habitat opportunities.
Forest management practices that alter forest density are likely to
impact floral resources, and hence forest structural elements may
be important for predicting biodiversity of wild bee assemblages.
This study of pollinator diversity in alpine forests provides basal
area thresholds that may be useful for resource management prac-
titioners concerned with creating or conserving pollinator habitats.
The study also provided new information on sampling efforts in
high-elevation forest habitats and suggests that spatial independence
of passive sampling methods may be achieved at distances of ~450
m, which may inform future studies. Additionally, this inventory
provides a baseline for comparing “non-affected” spruce forests
to those impacted by natural or anthropogenic disturbances in the
southern Rocky Mountain region.
Although it is often assumed that pollinator density in temperate
coniferous forests is low, the present study provides evidence to
the contrary and indicates that alpine landscapes should not be
discounted for their value to native bee conservation. With climate
change, alpine systems are expected to undergo significant change
(Potts et al. 2010). Beginning to assess and qualify them now pro-
vides an increased opportunity for proactive conservation efforts.
COMPETITION AND INTERACTIONS BETWEEN
MANAGED HONEYBEES AND NATIVE BEES IN NORTH
AMERICA
Presented by Victoria Wojcik
Can we predict the interaction between honeybees and native
bees on natural lands, and how do we, as land managers, account
for balancing multiple land uses? A key question has arisen in
the case of support of honeybee health for agriculture, and the
conservation of native bees: are honeybees outcompeting native
bees for food resources in shared landscapes? Managed honeybees
(Apis mellifera) and native bees both require nectar and pollen
from flowers, and therefore, there is potential for resource-based
competition between domesticated and wild bees. While concerns
that introduced honeybees may limit resources for native bees are
not new (Schaffer et al. 1983), recent evidence showing declines
in native bee populations (e.g., Potts et al. 2010; Bartomeus et
al. 2013) have intensified worries of potential impacts of com-
petition. With the significant role that managed honeybees play
in crop pollination, their health and well-being are a key concern
for sustainable food production (Aizen and Harder 2009), and
this has driven policy and practice aiming for access to forage.
The question that is arising now is if there is cause of concern
with respect to native bee populations, and if there is sufficient
evidence to guide management.
338 Natural Areas Journal Volume 38 (5), 2018
In order to provide a more definitive assessment on competition
between managed honeybees and native bees, researchers at Polli-
nator Partnership conducted a literature review focusing on studies
that conducted direct tests of competition using methodologies
that examined reproductive and/or population outcomes. Goals
of this review were to provide evidence-based recommendations
for management, pending sufficient data; determine gaps in
knowledge; and outline what studies are needed to address gaps.
Evidence for Competition
With the small body of literature there was a near even split with
support for the negative impacts of honeybees on wild bees seen in
ten studies (Sugden and Pyke 1991; Gross 2001; Thomson 2004;
Paini and Roberts 2006; Goulson and Sparrow 2009; Rogers et al.
2013; Elbgami et al. 2014; Hudewenz and Klein 2015; Herbertsson
et al. 2016; Lindstrom et al. 2016) and no conclusive evidence
for competition in nine (Schaffer et al. 1983; Steffan-Dewenter
and Tscharntke 2000; Goulson et al. 2002; Forup and Memmott
2005; Thomson 2006; Walther-Hellwig et al. 2006; Hudenwenz
and Klein 2013; Shavit et al. 2013; Torne-Noguera et al. 2016).
A key point to note, and a finding outlined by some of the pub-
lications reviewed (Thomson 2006; Goulson and Sparrow 2009)
is that foraging patterns do not necessarily correlate with fitness
outcomes. In some cases, increased forager recruitment as a re-
sponse to competition was at the expense of colony reproduction.
Focusing exclusively on foraging patterns would appear as a null
response to the presence of a competitor when in fact there is a
negative impact.
Without actually monitoring fitness or reproduction, there is
little that can be said about competition. Experiments examining
reproductive consequences of competition are unfortunately the
minority. Yet, six of the seven studies that examined reproductive
consequence found evidence of exploitative competition with
negative developmental or reproductive consequences in native
bees in the presence of honeybees (Gross 2001; Thomson 2004;
Paini and Roberts 2005; Goulson and Sparrow 2009; Elbgami et al.
2014; Hudewenz and Klein 2015). These included two studies of
native solitary bees, and one of a native semi-social species. Osmia
bicornis exhibited lower foraging rates and lower reproductive
output in the presence of honeybees when their shared resource
was limited (Hudenwenz and Klein 2015). Reduced fecundity was
recorded in a tube-nesting native bee, Hylaeus alcyones, in the
presence of managed honeybees in a natural field setting. They
found that even when resources are not limited, other factors
such as preemption and local exploitation can impact native bees
with short foraging ranges (Paini and Roberts 2005). Colonies
of Exoneura asimillima, a semi-social bee, were found to have
significantly reduced larval number, size, and reduced pollen loads
at sites where honeybees were present Sugden and Pyke (1991).
These three studies of bumblebees showed consistent trends in
reduced colony growth and reproduction of native bees (lower
number of queens and/or drones) in the presence of honeybees.
Across these three studies, only five species of the 265 species of
bumblebees have been examined; nevertheless, consistent trends in
reduced growth and reproductive output were seen. The workers
of B. pascuorum, B. lucorum, B. lapidaries, and B. terrestris were
noted to be smaller in size in areas that had honeybee colonies
present and foraging in the landscape (Goulson and Sparrow 2009);
B. occidentalis shifted energy resource allocation to foraging in
the presence of honeybees, and as a consequence produced less
brood and fewer males and queens than bumblebees considered
to be foraging in the absence of honeybees (Thomson 2004);
another test on Bombus terrestris showed that colonies near
honeybee apiaries gained less weight and produced fewer and
smaller queens compared to those located away from honeybees
(Elbgami et al. 2014).
Noncompetitive Interactions
There are other interactions that can occur between honeybees and
wild bees, and with the floral community that could have impacts
on community structure and composition. The foraging activities
of honeybees in a landscape could alter the floral community and
possibly initiate a shift in plant species dominance. This could
result in a net benefit for wild bees by increasing preferred food
resources, or there could be an augmentation of plant species not
preferred by the native bee community. A change to local polli-
nation networks could be expected, but the direction and impact
of this change is difficult to predict and will be context specific.
Pathogen spillover from one bee species to another is also a concern
(Otterstatter and Thomson 2008). Common foraging resources are
potential transmission vectors for pathogens, viruses, and para-
sites (Morkeski and Averill 2010; Blitzer et al. 2012). Pathogens
can move both to wild populations from managed ones, and to
managed populations from wild ones. Pathogen spillover from
managed bee species is however, more commonly documented
into wild populations (Graystock et al. 2013).
Managing Honeybee Pasture on Natural Lands
While research on native bee and honeybee competition was
found to be very limited, there is evidence of negative interaction
between honeybees and some native bees in some environments.
The clearest evidence comes from negative fitness impacts seen
in bumblebees, which are general feeders that have substantial
potential niche overlap with honeybees. More specialized native
bees, such as tube-nesting species that have much narrower niches
and less direct overlap with honeybees, also showed signs of fitness
decline in the presence of honeybees, suggesting in this case that
they have been excluded from a portion of their narrow niche space.
The issue of maintaining honeybee colony health for pollination
services while causing minimal impact to already threatened
communities of native bees should be considered when putting
honeybees in natural areas. There is evidence that the addition
of honeybee colonies can negatively impact some native bees,
particularly bumblebees and other bees that overlap in honeybee
resource use. Caution therefore should be used when honeybees are
put into landscapes where interactions with bumblebees are likely,
Volume 38 (5), 2018 Natural Areas Journal 339
especially during times of colony growth, queen development,
and if local populations of bumblebees are known to be under
threats or other stresses.
RESTORATION AND MANAGEMENT OF PRAIRIE
HABITATS TO SUPPORT POLLINATING INSECTS
Presented by Thomas Kaye
Prairie landscapes once accounted for a significant portion of
North America, but have dwindled to a small percentage of their
former extent, and those that are left are highly fragmented and
often relegated to tiny remnants (Noss et al. 1995). Restoring and
managing prairies has therefore been a priority and our under-
standing of these practices has improved greatly (e.g., Krueger
et al. 2014). Specific use of restoration techniques that are com-
patible with and support enhancement of pollinator populations
is a logical next step. A restoration ecologist’s tool kit includes
a series of standard practices, and the impacts of each on insect
pollinators varies. Mindful implementation of restoration and
management practices to optimize benefits for pollinators, or
minimize short term negative impacts, aids in decision making
to ultimately benefit a healthy insect community.
Insect pollinators may form an ecological guild (Cane et al. 2005),
but as a group they are exceptionally diverse in their taxonomy
and habitat requirements. The wide variety of bees, flies, lepi-
dopterans, beetles, and wasps that make up most floral visitors
in prairies means that restored habitat must accommodate the
needs of many different insects. Habitat restoration in general
and prairie restoration in particular can best improve habitat for
pollinating insects by increasing plant diversity for floral resources
(Scherber et al. 2010), providing nesting substrates such as bare
soil, cavities, and plants with pithy stems (Potts et al. 2005), and
placing restoration in the setting of adjacent habitats and parcels
(Artz and Waddington 2006; Cusser and Goodell 2013). For the
most part, plant diversity and nesting habitat are components of the
individual site, while the surrounding vegetation, its heterogeneity,
and land use make up the landscape context, which may or may
not be under the control of land managers at any given location.
Restoration seeding provides the fundamental groundwork for
ecosystem structure and function. As such we might consider
restoration and reseeding actions in the context of priming an
ecosystem for pollinator function. Yet, much restoration work
continues to focus heavily on quick solutions to soil stabilization
and ground cover. The essential tool of restoration, the restoration
seed mix, has often been designed without pollinators in mind,
and often, but not always, lacks key plant species that attract
key pollinators. With a focus on western prairie restoration,
The Institute for Applied Ecology has produced and presented
an overview of best restoration management strategies that aim
to provide referenced context for technical advice. Within each
common restoration strategy, there is the opportunity to adjust
practices to enhance benefits to pollinators.
Prairie Restoration Treatments
Many restoration treatments may be strongly beneficial for prai-
rie community diversity, but have short-term negative effects on
pollinator populations depending on their frequency and intensity.
Burning, for example, can be strongly beneficial for many prairie
and grassland plant species, and the improvement in the floral
community through burns aids in pollinator recolonization (Potts
et al. 2005). But the intensity of a burn and depth of heat pene-
tration can have a significant impact on some ground-nesting bee
species, especially shallow nesters that are found in the top 5 cm
of soil (Cane and Neff 2011). Even so, most pollinators are either
unaffected by fire or recolonize burned sites after 1–3 y (Panzer
2002). Mechanical disturbance, such as mowing or haying, can have
similar effects as burns and often promote bee diversity in prairie
restoration (Weiner et al. 2011; Hudewenz et al. 2012). And like
fire, the effects of mowing can vary with timing and frequency,
location, ecosystem, and pollinator in question (Campbell et al.
2007; Smart et al. 2013; Prevéy et al. 2014). Grazing with livestock
can have mixed impacts on pollinators (Kruess and Tscharntke
2002a; Kearns and Oliveras 2009; Kimoto et al. 2012). Land
clearing, as defined by herbicide use, tillage, or solarization, and
when followed with seeding of native plants, can have immediate,
short-term negative impacts, but the benefits for pollinators can be
seen in a few years after implementation, making even extreme
treatments effective methods for pollinator conservation (Shuler
et al. 2005; Balbuena et al. 2015).
Soil Nutrient Manipulation
Addition of nutrients to the soil can be used to boost plant growth.
Most commonly this involves the addition of N and other nutrients,
but generally results in increased competition for resources and
a decline in plant diversity (Wedin and Tilman 1996; Suding et
al. 2005), an increase in exotic invasive species that impede the
success of natives (Huenneke et al. 1990; Bobbink et al. 1998),
grass domination and a loss of insect-pollinated plants (Wesche et
al. 2012), and reduction in pollinator resources (Burkle and Irwin
2010; Biederman et al. 2017). Therefore, fertilization to promote
plant growth is not recommended for restoration of prairies or to
improve conditions for pollinating insects. On the other hand, ad-
dition of C can result in nutrient depletion, and in some cases can
lead to a reduction in invasive plants but also can lead to lowered
diversity and productivity, and effects on different functional groups
that vary by study (Blumenthal et al. 2003; Averett et al. 2004;
Perry et al. 2010). The use of C addition to improve conditions
for pollinators is largely untested but could have benefits in some
cases, especially where soils have been enriched with N artificially.
Seed Mixes That Benefit Pollinator Diversity
Ensuring that plant species that support specialist insects are present
can enhance pollinator diversity and ecosystem function. Adding
species through seeding or planting plugs is necessary for increas-
340 Natural Areas Journal Volume 38 (5), 2018
ing species richness in seed-limited prairies (Stanley et al. 2011),
and therefore improving the ability of prairies to support diverse
insect assemblages. Well-planned seed mixes provide sustained
long-term benefits whereby plant communities are structured to
include early seral species, those that protect and promote the
germination of latent perennials, and overall results in a more
resilient system (Williams et al. 2015; Havens and Vitt 2016).
Some insect groups specialize in visiting the flowers of specif-
ic plant taxa. The incorporation of plant species that support
specialist pollinators can add diversity that might otherwise be
missed with standard mixes. For example, some insects that
have few body hairs are capable of handling the stringy pollen
from flowers of plants in the Onagraceae, such as Lasioglossum
oenotherae, a specialist on the pollen of evening primrose (Zayed
and Packer 2007). Insects in the genus Diadasia (sunflower bees)
often specialize on the flowers of plants in the Malvaceae, and
although they may switch among specific hosts, their evolution
may be driven in part by chemical or morphological traits of
the plants they visit (Sipes and Tepedino 2005). Some Andrena
(mining bees) specialize on Nemophila spp. (e.g., Cruden 1972).
Deliberately including seeds or plugs of plants that can support
local specialist insects can lead to enhanced pollinator diversity
in restored prairies.
That the availability of nesting habitat for pollinators can limit
their abundance in prairies and provide for enhanced nesting
opportunities for multiple insect groups should be considered
when planning prairie restorations. Leaving dead plant material
with hollow or pithy stems during the restoration process can
support nesting by leafcutter bees (Megachile spp.), promoting
the establishment and growth of clumping grasses can provide
nesting opportunities for smaller bees (e.g., Lassioglossum), and
creating or maintaining open soil can benefit ground-nesting
species (Potts et al. 2005). Many native social bees (bumblebees
in particular) make use of cavities and these should be protected
during restorations whenever possible.
In summary, the following are best management practices for
supporting pollinators in restored prairies: (1) increase the di-
versity of flowering plants, (2) ensure the availability of nesting
substrates, and (3) promote connectivity to adjacent habitats.
BEST MANAGEMENT PRACTICES FOR POLLINATORS:
CREATING PRACTICES THAT ARE MEANINGFUL AND
IMPLEMENTABLE FOR RANGELANDS ACROSS THE WEST
Presented by Scott H. Black
Rangelands comprise the majority of public lands in the western
United States, spanning a huge diversity of ecological regions,
habitat types, and elevations—from grasslands to sagebrush steppe
to pinyon-juniper woodlands to mountain meadows. Native pol-
linators are an important but often overlooked group of animals
that both rely upon and help maintain rangeland ecosystems. It
is estimated that 40% of invertebrate pollinator species may be at
risk of extinction worldwide due to stressors including habitat loss,
pesticides, disease, and effects of climate change (IPBES 2016).
A lack of pollinators can have major ecological and economic
impacts on rangelands. Pollinators provide pollination services for
flowering plants, which are fundamental components of rangeland
ecosystems; approximately 85% of flowering plant species are
pollinated by animals (Ollerton et al. 2011) including threatened
and endangered species.
To help guide land managers on how to consider pollinators in
management decisions, the Xerces Society for Invertebrate Con-
servation has developed two publications:
• Best Management Practices for Pollinators on Western
Rangelands
• Managing for Monarchs in the West: Best Management Prac-
tices for Conserving the Butterfly and its Habitat on Public Lands
These BMPs were informed by literature reviews as well as sur-
veys and interviews with pollinator experts and land managers.
Together, they provided the state-of-the-knowledge on managing
for pollinators in western rangelands. Below is an introduction to
the concepts addressed in these BMPs.
What is Good Pollinator Habitat?
Food: Nectar, Pollen, and Host Plants
Providing a diverse, abundant, and season-long supply of food
sources is an important component of good pollinator habitat.
Provide for a wide range of flower structure, shape, color, and size
as certain flowers are more attractive to some pollinator species
than others (e.g., long, tubular flowers are often more attractive to
butterflies and hummingbirds than to bees). Early- and late-season
flowering resources can be especially important for bumblebees,
which are often active in the “shoulder seasons,” as well as migrat-
ing monarch butterflies. Immature butterflies feed on plant tissue
and require specific host plants; some butterflies can utilize only
one to a few different species of plants as caterpillars whereas
other butterflies can reproduce on a wide variety of plant genera.
Milkweed is vital for monarch reproduction but in the western
United States it is unknown if milkweed has declined throughout
the monarch’s breeding range—the decline observed in the western
population may be attributable to other causes.
Shelter and Nest Sites
Pollinators also need places to live and find shelter. To provide for
a wide suite of pollinators leave some woody, hollow, or pithy-
stemmed vegetation and ground litter intact and in place permanent-
ly. Many native bees nest below ground and require bare ground
or existing cavities in which to nest. Leave some bare ground and
abandoned rodent nests and preserve microtopography such as is
formed by grass tussocks. Avoid mowing, burning, or grazing an
entire area down to the ground. Overwintering pollinators, even
Volume 38 (5), 2018 Natural Areas Journal 341
adults, are generally immobile at low temperatures and unable
to escape blades, flames, or livestock.
Protection from Pathogens and Competition
Managed pollinators are critical for the pollination of many
agricultural crops and honey is an important industry. However,
as more areas of natural habitat are converted to agricultural
and suburban uses, the pressures to use public lands and other
natural areas for placing honeybee hives and as a source for col-
lecting native bees (e.g., mason bees) for commercial purposes
are increasing. Managed pollinators can compete with native
pollinators for resources directly or indirectly by affecting the
plant community and transmitting diseases. A recent review of
the literature by Mallinger et al. (2017) reported that a majority
of studies identified potential negative effects of managed bees
on native bees via pathogen transmission and competition. This is
of particular concern for areas with declining pollinator species,
including many native bumblebees.
Protection from Pesticides
In the West, management practices include the use of pesticides—
which includes herbicides, insecticides, and fungicides—to remove
unwanted vegetation from roadsides, control invasive weeds, and
reduce outbreaks of insects that compromise rangeland produc-
tivity for livestock. Herbicides are by far the most often applied
pesticide on US Forest Service lands (Cota 2004). However,
insecticides such as carbaryl are sometimes used on rangelands
to control grasshoppers and Mormon crickets. Pesticides can
have both direct (lethal and sublethal) and indirect (harm via
the effect on plants that pollinators use) effects on pollinators
(Thompson 2003; Decourtye et al. 2004; Desneux et al. 2007;
Kopit and Pitts-Singer 2018). It is vital to minimize the exposure
of pollinators to pesticides—especially insecticides.
General Considerations in Pollinator Management and
Restoration
There are thousands of native pollinator species in the West, each
with unique phenologies, ranges, life history strategies, and floral
and nest habitat requirements. Many species, including some
bumblebees, have broad geographic ranges with varying phenolo-
gies—emerging as early as January and as late as December—and
they visit a variety of flowering plants (Hatfield et al. 2012). For
example, beyond milkweed as a host plant, monarch butterflies
visit a variety of plants to drink nectar. For a full list of plants
that monarchs use visit the Xerces Society website (https://xerces.
org/monarch-nectar-plants/).
A few species of bees are extreme specialists with narrow geo-
graphic ranges, diet breadth, or phenologies that are timed with
the emergence of a single plant species they visit exclusively
(Minckley et al. 2013; Wilson and Messinger Carril 2015). In
addition, native bee and buttery communities and their phenology
can vary widely across the landscape, such that sites even within
a few miles of one another can be quite distinct (Fleishman et al.
1999; Kimoto et al. 2012; McIver and Macke 2014; DeBano t al.
2016). This dizzying diversity, and limited information in many
areas, makes it impossible to prescribe a single management
plan that is ideal for all pollinators in all places. However, there
are general considerations that will benet pollinators. Habitat
management tools—grazing, re, mowing, and herbicide appli-
cations—can be used to benet pollinators and their habitat, but
can also cause damage, especially in the short term. To minimize
harm to pollinators, the following guidance applies to most man-
agement activities.
Create Heterogeneity in the Plant Community and Provide
Refuge for Pollinators
In general, diversity in vegetation, structure, and management
practices can maximize biodiversity including the diversity of
pollinators (Gilgert and Vaughan 2011). To conserve the diversity
of native bees that once inhabited the landscape, use and encourage
plant species that benefit generalist bees, as well as species that
are relied upon by specialist bees and butterflies in your region.
Historically, rangeland landscapes contained sufficient areas where
vegetation was in various stages of succession to support a wide
range of pollinators with differing habitat needs. Today, some
rangeland habitat is reduced to fragments in intensively managed
or disturbed landscapes, and managers have to consider the distance
and connection potential between pollinator populations (USDA
USFS 2012). Mowing, burning, or intensively grazing an entire
habitat area at once or in the same year, for example, can severely
impact local pollinator populations and slow recolonization. It is
better to treat separate areas of a site in a multi-year cycle, re-
taining undisturbed refuges from which pollinators can disperse.
A general consideration is to treat no more than one-third of an
area of continuous habitat or site (e.g., a meadow, riparian area)
with a single management action (such as prescribed burning) in
a single year. Even within treatment areas, leaving small untreated
patches (e.g., areas skipped by mowing, fire, or grazing) provides
micro-refuges and greater heterogeneity in the landscape, which
can support a wider range of pollinators. With season-long grazing,
try to keep at least some areas (especially sensitive areas such as
springs) free from disturbance.
Consider How Management Interacts with Natural Stressors
to Affect Pollinators
For example, if a drought severely suppresses wildflower blooms
one season, grazing it heavily may further stress pollinators’
ability to find sufficient nectar and pollen. To help minimize the
effects of interacting stressors, you may need to adjust grazing
pressure in years of drought. Focus efforts on conserving existing
habitat that is of high value to pollinators and strive to establish
plant communities that are both resilient and resistant to grazing
disturbance.
342 Natural Areas Journal Volume 38 (5), 2018
Use an Adaptive Management Framework
The response of pollinators to livestock grazing and many other
management practices in the West has been largely unstudied,
and more research is needed to further refine rangeland manage-
ment for pollinators. Given imperfect and incomplete knowledge,
adaptive management using the best currently available science
is necessary. Experiment on small areas, keep records, and share
what works and what fails with others. Monitor vegetation and,
when possible, the pollinators themselves to see how they respond
to management.
Time Management to Minimize Negative Impacts on
Pollinators
Timing management actions so that they occur at times when
pollinators are less susceptible to harm (e.g., mobile and able to
move out of the way, at a less critical developmental stage, after
reproduction) significantly minimizes the likelihood of negative
interactions. Seasonal patterns of pollinator occurrence and the
best time to manage for bees, butterflies, and specifically mon-
archs, has been outlined for western regions. The BMP guide
offers broad guidance on when native bees are less likely to be
affected by management such as burning, grazing, or mowing.
However, note that above-ground nesting bees (including some
bumblebees) may be sensitive to management year-round. Man-
agement windows for monarch butterfly breeding habitat are
recommended by ecoregion. Good pollinator habitat—whether it
is for bees, monarchs or other butterflies—provides food, shelter,
and nest sites, is connected to other habitat patches, is safe from
pesticides and high levels of pathogens, and limits competition
from managed pollinators. Overall, management and restoration
that aims to incorporate pollinators should focus on incorporating
heterogeneity into the landscape, considering interactions among
management and environmental fluctuations, and using an adaptive
management framework.
Management practices addressed in the Xerces BMPs include
grazing, mowing, prescribed fire, and pesticide use. Incorporating
pollinators into restoration projects including seeding post-wild-
fire and sourcing and establishing native plants are addressed, as
are invasive nonnative and noxious plant management, managed
pollinators, recreation, and climate change impacts.
For a complete set of Best Management Practices for both polli-
nators on rangelands in the West and monarch butterflies in the
West, visit www.xerces.org.
NEXT STEPS: BEYOND THE SYMPOSIUM
Although such an extensive topic can hardly be examined fully in
a half-day symposium, the topics presented showed that research
is progressing in an effort to fine-tune best management practices
across ecosystems, but also that we are not working in a void.
There is a body of critical knowledge on pollinator management
and conservation that can be put into action for the immediate
betterment of natural landscapes and pollinators. Best practice
in many cases is a precautionary best practice based on limited
information, exemplified by questions of competition between
managed honeybees and wild bees. The presence of honeybees
appears to consistently correlate with reduced fitness in bumble-
bees, as well as other wild solitary bees. In cases of niche overlap
and partitioned niche space honeybees are exerting an impact, and
caution is warranted when making land use decisions that allow
honeybee pasture on natural lands. For monarch butterflies the
picture is clearer. We know where critical habitats remain, and we
have identified not only the pressures that impact these areas, but
clear targets for restoration. Still, monarch populations in the West
have declined even more rapidly than in the rest of North America,
again warranting quick action. For other pollinators occurring in
the West, the data is patchy, and our management predictions may
be imperfect, but we can lean on a wealth of information relating
to pollinator occurrence, plant phenology, and other interactions
to create solid management plans that allow for the necessary
actions while minimizing negative impacts. We can reliably make
evidence-based management decisions that address issues of fire,
restoration, roadside management, and invasive species, all while
protecting and promoting pollinators.
New research presented aiming to develop more BMPs has fo-
cused on the impact of grazing on pollinators in riparian areas
and pollinator management in alpine forest communities, often
considered too sparse in pollinators, yet the opposite has been
shown. These are just two of many unique ecosystems that we
are beginning to outline in more detail, but many more remain.
How does one go forward from this point? The gaps that remain
need to be filled, and it will likely be a slow process limited by
access to available trained personnel and funding, certainly not by
a lack of interest or urgency. This situation is nothing new to land
managers and conservation biologists, and unlikely to change. The
more we learn about our ecosystems the more we realize that there
is much more to learn. With pollinators we are in a good place;
for all that is lacking, interest and enthusiasm is not. Continued
monitoring of land management actions on pollinator populations
is needed. The implementation and test of current BMPs across
various ecosystems is an essential strategy that will allow us to
refine techniques and the guidance that we can offer. We look
forward to continuing the discourse on pollinator conservation
and management. Looking ahead we anticipate NAA members
to present work on new ecosystems and management strategies
where pollinators are the focus.
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