Evaluating Native Perennial Flower Strips for Enhancing Native Bees and Pollination Services on Farmlands

Evaluating Native Perennial Flower Strips for Enhancing Native Bees and Pollination Services on Farmlands

Summary

During the first year of this project (spring 2013), we established flower strips comprised of nine native perennial species onto four participating farms. Throughout the summer, we sampled the bee community using three different methods and also assessed floral densities to determine the background abundance and diversity of bees and floral resources at each farm. This past summer (2014) all the plants in the flower strips bloomed and, in addition to repeating the same sampling of bees and background floral resources as the previous year, we measured floral abundance of each wildflower species in each flower strip throughout the summer and also sampled bees visiting the flower strips at each farm. We will compare the abundance and diversity of native bees collected this year to the background abundance and diversity of bees collected in 2013, prior to establishment and blooming of the flower strips. We will examine bee floral preferences and identify native plant species that are important food resources throughout the growing season for bees on farmlands.

To determine the effects of flower strips on pollination and whether crops are pollen-limited on farms, we 1) observed bees visiting experimental squash and sunflower plants, 2) performed hand pollinations, and 3) measured crop yields in 2013 and 2014. We conducted preliminary analyses of 2013 squash data and are analyzing 2014 squash data, as well as 2013 and 2014 sunflower data.

Flower strips produced enough blooms this summer that we were able to collect wildflower seeds to determine whether flower strips could serve an additional function as a source for local, adapted, organic wildflower seed for sale through various outlets. We are in the process of conducting preliminary economic analyses using data we collected on costs and benefits associated with flower strip establishment, maintenance, seed harvesting and processing, and potential profits.

To communicate our projects’ progress and findings, we 1) participated in one field day (2013), 2) presented several talks and workshops to the general public (2014), 3) hosted two WWOOF (World Wide Opportunities on Organic Farms) volunteers for a day (2014), and 4) spoke to students in the Sustainable Food and Bioenergy Systems practicum at Montana State University (2014), many of whom aspire to become farmers or play some other role in sustainable food systems. We are creating a website to share further details of our project, as well as pictures and videos of research and outreach activities.

Objectives/Performance Targets

This research project has four main objectives: 1) determine the effects of native perennial flower strips on the abundance, diversity, and foraging behavior of native bees in agricultural crop fields, 2) determine the value of flower strips in improving crop pollination and yields through increases in the abundance, diversity, or behavior of native bees, 3) evaluate the potential of flower strips for native seed production and sales, and 4) execute a research-based outreach program to communicate our findings to producers, land managers, agricultural professionals (e.g., NRCS personnel and Extension agents), scientists, and the general public.

Accomplishments/Milestones

Objective 1. Determine the effects of native perennial flower strips on the abundance, diversity, and foraging behavior of native bees in agricultural crop fields.

The USDA Natural Resources Conservation Service (NRCS) offers cost-share programs, such as the Wildlife Habitat Incentives Program (WHIP) and the Environmental Quality Incentives Program (EQIP), to encourage producers to provide pollinator habitat on agricultural lands using native plants. However, the effects of these plantings on native bees and pollination in agroecosystems have not been rigorously assessed in most cases. Using a variety of resources as a guide, including the USDA-NRCS publication “Montana Native Plants for Pollinator-Friendly Plantings” and results from research being conducted at Montana State University on wildflower drought tolerance and pollinator attraction, we selected a set of nine native perennial wildflowers to incorporate into flower strips being planted at four participating farms in the Gallatin Valley. We chose plants with different blooms times, colors, and floral morphologies that would span the entire growing season (Table 1). In the greenhouse in the spring of 2013, we propagated >600 wildflower plant plugs in cone-tainers (SC10U-98 cells per tray) to use in flower strips. We used plugs rather than seeding flower strips in order to hasten flower strip establishment. Wildflower plugs (153 per farm) were transplanted in early June into plots (approximately 4ft x 108ft=432ft²) that were prepared that spring and consisted of bare soil, IRT (InfraRed Transmitting) plastic, or black landscape fabric, depending on the particular site’s farming methods (Figure 1). The plots were further broken up into 27 smaller plots to accommodate three replicates of each of the nine plant species. We planted either five, six, or nine plugs into each of the 27 smaller plots, depending on the plant species and its growth habits, to maximize floral display. In 2013, we focused on establishing flower strips and keeping them watered and weeded throughout the summer. We were surprised to see some flowering for seven of the nine plant species in the first year, though this varied greatly by farm. In the spring of 2014, we recorded winter mortality/survival of individual plants and replanted anything that did not survive using additional plugs we grew. In general plants had low winter mortality. Compared to 2013, we saw a marked increase in vegetative growth and flowering of all nine species at all four farms (Figure 2).

To determine whether the addition of flower strips leads to changes in the community composition, relative species abundance, or plant visitation rates of native bees, we measured components of the flower strips, surrounding vegetation, and bee community. We also measured floral density of naturally-occurring plant species found at each farm at two different times during the summer in 2013 and 2014 to better understand background floral densities before and after flower strip establishment. From the onset of flowering in 2014, we conducted weekly measures of floral abundance of the nine species in the flower strips to gain a better understanding of the amount of newly added food resources available to foraging bees. Because we did see some blooming of the flower strips in late summer of 2013, we sampled bees visiting flower strips as another measure of the bee community. We sampled bees weekly from May-September in 2013 and 2014 at all farms using three methods; including insect nets, yellow pan traps, and trap nests.

Insect nets. Using insect nets, we captured bees visiting flowers on the surrounding floral vegetation (2013 and 2014) and the flower strips (primarily 2014) during timed observations. Bees were placed in vials, labeled, and stored in a freezer for later processing (i.e., pinning, labeling) and identification to the lowest taxonomic level. All of the 2013 samples have been processed and identified (at least to genus and to species when possible). The 2014 samples have also been processed and we will begin identifications during spring 2015. Because of the difficulties associated with identifying bees to species, and because Montana has been little studied with respect to its bee diversity, we are traveling to Logan, Utah the week of March 9-13 for assistance from bee specialists at the USDA Bee Biology and Systematics Laboratory.

In 2013, we collected 108 honey bees (Apis mellifera) and 210 native bees comprising 24 taxa and 18 genera visiting flower strips on five sampling dates across farms. Preliminary analyses indicate no differences in total bee abundance among farms, but there were differences between sampling weeks. Among farms, the three most abundant bee taxa captured on flower strips included two bumble bee species (Bombus huntii and B. rufocinctus) and undetermined species of sweat bees (Lasioglossum (Dialictus) spp.). We collected 207 honey bees and 161 native bees comprising 22 taxa and 13 genera visiting the surrounding floral vegetation on three sampling dates across farms. Preliminary analyses indicate differences among farms in total bee abundance, but no differences between sampling weeks. Among farms, the three most abundant bee taxa captured on surrounding flowers included one bumble bee species (B. rufocinctus) and two different types of sweat bees (Halictus ligatus and undetermined species of Lasioglossum (Dialictus) spp.). The surrounding vegetation consisted mainly of agricultural “weeds” (e.g., Lotus corncualatus, Melilotus officinalis, Trifolium repens, Cirsium arvense, Tanacetum vulgare, etc.), and although we have not yet analyzed the data for surrounding flower abundances, there are obvious visual differences in the amounts of surrounding vegetation at each farm.   

Yellow pan traps. We used yellow pan traps filled with soapy water that attract bees to passively sample the bee community at each farm. We placed pan traps out along four linear transects (i.e. along the flower strip and at three distances (20 m, 60 m, and 180 m) from the flower strip). Bees were placed into Whirl-paks® with alcohol, labeled, and placed in cold storage until they could be processed and identified. All of the 2013 samples have been processed and identified and we are in the process of pinning all of the 2014 samples.

We collected 31 honey bees and 1,870 native bees comprising 44 taxa and 33 genera among farms using pan traps in 2013. Preliminary analyses indicate differences in total bee abundance among farms, sampling weeks, sampling weeks by farm, and distances (position relative to flower strips). However, we need to re-examine these data with total surrounding flower abundance added as a covariate. The number of taxa (from 24 to 34) and genera (from 19 to 25) also varied by farm. Bees from the family Halictidae (sweat bees) were the most abundant across all farms (Figure 3). The five most abundant bee taxa across farms included three types of sweat bees (Lasioglossum (Dialictus) spp., Halictus tripartitus, and Halictus ligatus), yellow-faced bees (Hylaeus spp.), and mining bees (Panurginus spp.) (Figure 4).

Trap nests. We prepared and placed two sets of trap nests at each farm in late May to provide nest sites for cavity-nesting bees. We monitored trap nests weekly (i.e., remove completed nests and replaced with empty nest tubes) from May-September. We retrieved trap nests from each farm in October, removed and labeled all filled nesting tubes, and then placed them in cold storage for overwintering of bee offspring. In the spring of 2014, we removed the nesting tubes from cold storage to initiate development and emergence of adult bees. Bees that emerged were labeled and freeze-killed for later identification. We have pinned all the bees that emerged from trap nests collected in 2013 and will identify them in spring 2015. The trap nests collected in 2014 are currently in cold storage for overwintering until spring 2015.    

Objective 2. Determine the value of flower strips in improving crop pollination and yields through increases in the abundance, diversity, or behavior of native bees.

To measure pollination services and determine whether crops are pollen-limited on farmlands due to a lack of pollinators (either diversity or abundance), we established three experimental crops strips comprised of squash and sunflower plants at each farm site at varying distances from the flower strips (20 m, 60 m, 180 m). In the greenhouse in the spring of 2013 and 2014, we propagated 100 acorn squash and 100 confection-type sunflower plants and, in mid-June, planted eight squash and eight sunflower plants at each of the three distances at each farm (i.e. 24 plants of each species at each farm). We chose these crop plants because they have different bloom times and flower morphologies, and so likely attract different suites of bee pollinators. As the plants began to bloom (late July) we hand-pollinated half of the squash and sunflower plants weekly in each crop strip, while leaving the other half to be open-pollinated in order to determine whether plants are pollen-limited. (Hand pollination provides supplemental pollen to flowers to determine the maximum yield possible). We also conducted bi-weekly timed observations in 2013 and weekly observation in 2014 at each of the crop strips during flowering (July-September) and captured bees visiting flowers. Bees were placed in vials, labeled, and stored in a freezer for later processing and identification. All of the 2013 samples have been processed and identified. All of the 2014 samples have also been processed and we will begin identifications in spring 2015.

We collected 1,012 honey bees and 104 native bees across farms during squash observations in 2013. Preliminary analyses indicate no differences among farms in total abundance of honey bees or native bees visiting squash; however, we need to reexamine these data with total squash flower abundance as a covariate. Bees visiting squash comprised only two families (Halictidae and Apidae). The most dominant native bee taxa included one bumble bee species (B. huntii) and several types of sweat bees (Lasioglossum (Dialictus) spp., Augochlorella spp., and Halictus rubicundus) (Figure 5). We collected eight honey bees and 50 native bees comprising nine taxa during sunflower observations in 2013. The most abundant taxa were sunflower bees (Melissodes spp.) and one species of bumble bee (B. huntii) (Figure 6).

To determine crop yields for both hand- and open-pollinated plants, we harvested and processed all of the squash fruits and sunflower seed heads at the end of the summer/early fall in 2013 and 2014. For sunflowers, we also measured the height and stem width of plants before harvesting them as an estimate of biomass. Seeds were removed from flower heads, cleaned, categorizing (mature vs. non-mature), counted, and weighed. For squash, whole plants were harvested, and the vegetation was dried and weighted. The fruits were counted and weighed, and then the seeds were removed, cleaned, dried, categorizing (mature vs. non-mature), counted, and weighed.

Preliminary analyses indicate squash plant biomass was highly variable among farms, distances, and distance by farm in both years. This was likely due to differences in locality, irrigation, and growing conditions among farms, but even within a single farm there were differences among the three locations where the crops were planted. For 2013 squash data, we also found differences for total fruit weight among farms and at different distances within farms; however, there were no treatment effects (hand-pollinated versus open-pollinated). From a farmer’s perspective this is good news because pollination did not affect the size of the fruits (i.e., the saleable product). However, from a plant reproduction point of view, there were treatment effects for several measures of pollination success, including total number of seeds and total seed weight, which were higher for hand-pollinated plants. This indicates that squash flowers were pollen-limited on farms in 2013. We are currently analyzing the 2014 squash data as well as the 2013 and 2014 sunflower data.

Objective 3. Evaluate the potential of flower strips for native seed production and sales.

In addition to providing habitat for supporting native bees, another possible benefit of establishing flower strips are the sale of locally produced, regionally adapted, organic, wildflower seed for CSA shares, farmer’s markets, retail stores, or habitat restoration projects. Consequently, we set out to conduct an economic analysis to determine the feasibility of harvesting and selling wildflower seeds.

Flower strips were established on farms in the spring of 2013 and we saw some flowering that summer, but not in any great amounts for seed collecting. This past summer (2014), however, the blooms were abundant and overall it appeared to be worth collecting seed. We hand-harvested seed weekly from all flower strips as it matured. The ease of harvesting seed was species specific. For example, some species, like yellow penstemon (P. confertus), had seed that matured essentially all at once and resulted in fewer visits to gather the majority of the seed. Whereas other species, like blanket flower (G. aristata), false hairy golden-aster (H. villosa), silverleaf phacelia (P. hastata), and bluebells (C. rotundifolia) continued to flower as they also set mature seed, requiring many weeks of repeated collecting. Because we needed to keep the seed separated by collection date, repetition, and farm for data analyses, we were not able to combine the seed into large enough quantities for mechanized cleaning and, therefore, had to clean all of the seed by hand. It took approximately 125 man-hours to process, clean, and weigh all of the seed collected from each farm. At minimum wage this equates to just over $1,000. As with seed harvesting, some species were much more labor intensive to process and clean, like sticky geranium (G. viscosissimum; 28 hours) and Maximilian sunflower (H. maximiliani; 42 hours mainly because of the sheer quantity of plant material). By weight, we collected a total of 5,050.56 g (over 11 lbs. of wildflower seed) across farms for all species (Figure 7). This amount varied greatly by farm, likely due to factors, including planting (i.e. IRT plastic, bare ground, black fabric) and irrigation methods (i.e. drip tape, overhead sprinklers), as well as differences in climate/location that contributed to differences in the overall size of plants and hence the number of blooms, which are undoubtedly correlated with seed production. However, there could also be differences in the quality of the seed produced (i.e. size, viability), so our next goal is to determine the average mass per seed and germination rate for each species to see if there are any differences in these measures among farms.

We are currently conducting a preliminary cost-benefit analysis to determine the potential for seed sales this coming spring. We have kept records of costs associated with installing and maintaining flower strips (i.e., cost of plant materials, labor involved with growing plants, preparing the planting site, planting the strips, weeding, and watering) and harvesting seed (i.e., collecting, processing, and cleaning). We will calculate the potential income to growers from seed sales using wildflower seed yields and current market values for native seed. For example, a local vendor here in Montana sells sticky geranium seed for $1.95 for 500 mg of seed. Across the four farms we collected 103,220 mg of seed, which equates to a value of c. $400. If our overall results are favorable, we will initiate seed sales beginning with a trial seed sale at a farm field day event or the farmer’s market.

Objective 4. Execute a research-based outreach program to communicate our findings to producers, land managers, agricultural professionals (e.g., NRCS personnel and Extension agents), scientists, and the general public.

To improve producers and the public’s awareness of using native perennial wildflowers as a management strategy to improve bee habitat on farmlands and other types of managed lands, we have taken part in several outreach efforts. We participated in the Horticulture Farm and Towne’s Harvest Garden Field Day sponsored by Montana State University College of Agriculture and Montana Organic Association in 2013. In 2014, we presented a talk for the Montana Native Plant Society (MNPS) Valley of the Flowers chapter titled “Attracting and conserving native bees using native plants in Montana,” which was open to the public and had an attendance of approximately 50-60 people. We also presented a talk on native bees and native plants for the MNPS Calypso chapter at the 7^th Annual Gardening with Natives Workshop (general public; more than 80 people). We presented a talk on native bees and native plants at a local garden center (general public; 15-20 people). At the MNPS Annual Meeting we presented a workshop titled “Introduction to Montana native bees” (general public; 15 people). We also presented a “Pollinator Identification Workshop” at the 8^th Annual Montana Plant Conservation Conference, sponsored by the MNPS, Montana Natural Heritage Program, U.S. Forest Service, and NRCS (about 100 people from diverse background including scientists, NRCS personnel, Extension agents, and the general public). We hosted two WWOOF (World Wide Opportunities on Organic Farms) volunteers for a day at one of our participating organic farms. This is an organization that links organic farms in need of help with volunteers who would like to gain experience in organic farming. Using our approved pre- and post-outreach surveys, we surveyed the volunteers at the start of the day to determine their level of knowledge on several topics related to our project and again at the end of the day (after conducting sampling and talking with the volunteers about the project and its goals) to measure changes in their understanding and opinions of these same topics. We also spoke to 20 students (many of which are hopeful future farmers) in the Sustainable Food and Bioenergy Systems Practicum at Montana State University about our research being conducted at Towne’s Harvest Garden, which is also the site of the hands-on learning aspect of the course. As we did with the WWOOF volunteers, we used pre- and post-outreach surveys to survey the students before and after speaking with them about our project. We are currently designing a website, which we hope to publish sometime in February, as another means of sharing information about our project, its progress, and our findings, as well as pictures and videos of research and outreach activities during the summers of 2013 and 2014.

• Table 1. Observed bloom periods for nine native perennial wildflower species planted in flower strips at four participating farms.
• Figure 5. Pictures of bees visiting squash flowers.
• Figure 6. Pictures of bees visiting sunflowers.
• Figure 3. Total number of bees collected in yellow pan traps at four farms.
• Figure 1. Example of a flower strip being planted at one participating farm.
• Figure 2. Example of flower strip establishment and blooming in 2014 at one participating farm.
• Figure 4. Total number of five most abundant bee taxa collected in yellow pan traps at four farms.
• Figure 7. Total weight (g) of native perennial wildflower seed collected at four farms.

Impacts and Contributions/Outcomes

Because we did not expect the plants in our flower strips to bloom during the establishment phase, the first year of field sampling for our multi-year project provided primarily baseline data and information on typical bee assemblages prior to flower strip establishment and blooming. We did successfully establish flower strips at all farms, and, after completing a second year of field sampling, we have obtained the necessary data for comparisons of bee assemblages before and after the flower strip additions. And, once we complete bee sample processing and identifications in the next few months, we will conduct these analyses. We do not yet know if flower strips have increased pollination of focal crops, but we do know that squash was pollen-limited in the first year of this study and are analyzing 2014 data, as well as two years of sunflower data. We have collected and processed over 11 lbs. of wildflower seed from our flower strips, and if our economic analyses prove positive, we will initiate trial seed sales this spring.

We have shared information about our project and its objectives with growers, students (potential future farmers), and the public through a field day, presentations, workshops, and volunteering opportunities and we hope to conduct more outreach this winter by attending several winter famers markets and distributing surveys and informational handouts, which we are creating. We have also begun designing a website to share the progress and findings of our project and to serve as a location for pictures, videos, surveys, and future outreach materials. This coming field season we expect to see even more blooming in the flower strips and to obtain another year of post-flower strip establishment bee and crop pollination data for further comparisons.

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