Tag Archives: ecology research

An Update on Native Plant Studies from The Garden Ecology Lab at Oregon State University

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A version of this article was originally written for the ‘Growing Knowledge‘ section of Digger Magazine, published by the Oregon Association of Nurseries.

The Garden Ecology Lab was founded in 2017 to advance an understanding of how to plan, plant, and manage garden systems to promote environmental and human health. It is one of two labs in the United States, and the only one in the Western US, to specifically focus on studies of garden ecology.

In this article, I provide an update on our native plant studies, with a focus on results that may be of particular interest to nursery owners. Brief summaries of many of our lab’s studies can be found on the ‘For Gardeners’ page of our lab website. Some nurseries have printed out copies of these lab briefs, so that their customers can see the ecological benefits of various plants. More briefs are planned for this year. Periodically visit our website for updates.

Native Plants in Garden Retail Centers

Interest in native plant gardening has drastically grown in recent years, but many native plants remain difficult to find for purchase. In the April 2019 issue of The Digger, Dr. Aaron Anderson highlighted three barriers that gardeners face, when trying to purchase native plants: 1) lack of advertising by native plant nurseries or gardeners’ lack of familiarity with these nurseries, 2) variation in nursery stock among native plant growers, and 3) geographic distance that gardeners might have to travel to find the plants they are looking for. These specific barriers were ones that Aaron faced when he was setting up his field study of insect communities associated with 23 species of Pacific Northwest Native plants.

Aaron used the Oregon Flora’s gardening resource page to locate where he could buy his study plants. He ultimately ended up purchasing plants from two retail nurseries (one in Corvallis and the other in Forest Grove) and two pop up native plant sales (one in Corvallis and one in Portland). He also worked with two wholesale nurseries that were generous enough to sell or donate study plants or seed in the small quantities he was seeking (one in Salem and one in Silverton). Because he has been asked this question, often, Aaron also wrote a blog post on ‘Where to Buy Native Plants in Oregon‘.

After a three-year field study, Aaron was able to identify 10 native plants which support a diversity of bee species. We developed an infographic to share this information with gardeners, and include lavender in the image, since many gardeners perceive lavender to be a pollinator-friendly plant (Bennett 2019).

Image 1: The number of estimated bee species associated with PNW native plants is shown in a yellow circle, above each bar. Lavender is shown as a comparison, since it is recognized as a pollinator-friendly plant by many gardeners.

Today, Oregon Flora’s garden resource page lists 10 nurseries where gardeners can find and purchase native plants (Oregon Flora 2025). I used their plant-finding tool, to see whether I could find the 10 native plants that we recommend to gardeners. None of the nurseries were listed as carrying all of these recommended plants: two nurseries were listed as carrying 6 species, three nurseries carried 5, two nurseries carried 4, and three nurseries carried 2. All of the 10 nurseries were listed as carrying Oregon sunshine (Eriophyllum lanatum). None were listed as carrying Farewell-to-spring (Clarkia amoena), varileaf phacelia (Phacelia heterophylla), or common madia (Madia elegans).

Farewell-to-Spring, a promising native nursery plant

The absence of farewell-to-spring from nursery shelves is particularly disappointing, because it has become a favorite in our lab group. Its native range spans the Bay Area of California, north through Oregon and Washington and into British Columbia. In Oregon, it grows west of the Cascades to the coast and is found in a variety of habitats including coastal prairie, grasslands and forested areas. It is an easy-to-grow annual plant with erect stems (5.4” maximum height), thin, green leaves and bright pink flowers. In our study plots, first bloom occurred anywhere between early June and early July and lasting through early August through late October, depending upon seasonal weather patterns and supplemental irrigation.

Farewell-to-spring attracts a diversity of beneficial insects. Aaron collected 14 bee species, 15 predatory insect taxa, and 12 parasitoid taxa from this wildflower (Anderson 2022, Anderson et al. 2022) documenting its ecological value for attracting pollinators, as well as natural enemies that promote the biological control of insect pests. In a separate, but related field study, Jen Hayes looked at the pollinator assemblages on eight species of wild-type native plants and 1-3 of their cultivars. Jen provided an overview of this study in the October 2020 issue of The Digger (Hayes and Langellotto 2020), and the full report of this study was recently published (Hayes et al. 2025) for folks wanting more detailed information.

Farewell-to-spring was one of the native plants in her field study of pollinators on native plants and native cultivars. The cultivars she used were ‘Aurora’ (dark pink blossoms with a cream center), ‘Dwarf White’ (white blossoms), and ‘Scarlet’ (red blossoms with a light pink center). She documented 32 total pollinator species from the wild-type plant (with an estimated 104 total pollinator species), 17 pollinators on ‘Aurora’ (28 species estimated), 23 pollinators on ‘Dwarf White’ (24 species estimated), and 9 pollinators on ‘Scarlet’ (13 species estimated). Furthermore, she found that specialist bees, which are picky about where they collect pollen, were either exclusively found on wild-type native plants (two species, Megachile gravita and Melissodes microstictus), or were found in higher abundance on wild-type plants compared to cultivars (two species, Melissodes lupinus and Melissodes clarkiae). Because specialist bees have relatively narrow diet preferences, including their preferred forage plants is an easy way to attract these unique bees into a garden, and to locally increase pollinator biodiversity.

In addition to the importance of wild-type Farewell-to-spring as a forage plant, Jen worked with Mallory Mead (a former undergraduate student in our lab) to document its importance for bee nest material. Many leafcutter bee species use leaves, mud, resin, sticks, pebbles, or petals when they build their nests. Jen documented two species of petal-cutting bees in her study plot, each of which had a significant association with Farewell-to-spring and its cultivars. Megachile montivaga had significant associations with the wild type native and ‘Dwarf White’. Megachile brevis was significantly associated with the wild type native, ‘Dwarf White’, and ‘Aurora’.

Image 2. A and B: Leafcutter bees cut discs from petals of a cultivar. C: A leafcutter bee carries a petal disc to its nest. D: A leafcutter bee nest in a sunflower stalk. Credits: Svea Bruslind (A), Devon Johnson (B), Mallory Mead (C), Heidi Nordijk (D), © Oregon State University

Although Jen found evidence that the leafcutting bees were significantly associated with two of the three cultivars she included in her study, Mallory documented a very strong preference for the wild-type native over the cultivars, when she documented foraging for nesting material. Because leafcutting bees leave a characteristic crescent cut in petals, Mallory could document foraging for nesting material by counting the number of petal cuts from each plant. Wild type native plants had 3-4X as many petal cuts than cultivars. Even when we controlled for bloom count per plant, the wild type native was significantly preferred over the cultivars.

Image 3: Number of petal cuts by bees on wild-type Farewell-to-spring, and 3 cultivars.

Native Cultivars Are Often Easier to Find and Buy

Given the high abundance and diversity of beneficial insects associated with Farewell-to-spring, as well as its unique association with specialist foragers and petal-cutting bees, we enthusiastically recommend this plant to ecologically-minded gardeners. However, the average gardener shopping for this species is more likely to encounter cultivars than wild-type plants. This is partly because the plethora of Farewell-to-spring cultivars are on the market. In addition to the three included in Jen’s study, gardeners can find ‘Double Azalea’ (pink, purple, red, white flowers), ‘Lilac’ (pink petals with dark red center spots), ‘Pink to Red’ (red petals with light pink edges), ‘White’ (white flowers), ‘Pink’ (light pink flowers with no other markings); and ‘Sugarplum’ (semi-double flowers, light pink with rose-colored center markings, dwarf, somewhat bushy).

As noted earlier, native plants can be difficult to source in the retail marketplace. Offerings may not reflect the regional species pool of plants (Zinnen and Matthews 2022), and in some areas, 77% of the native plants on market shelves are actually hybrids or cultivars (Coombs et al. 2020). However, multiple studies have found that gardeners are willing to pay higher prices for native plants and locally sourced plant materials.

Somewhat unexpectedly, in a recent survey of 719 gardeners (Hayes et al. in preparation), 81% report that they buy their native plants at pop-up plant sales hosted by Soil and Water Conservation Districts, Master Gardener groups, or other non-profits. A comparable percentage of gardeners (78%) said that they buy their native plants at retail plant nurseries. However, given the transient nature of pop-up plant sales, it was surprising to us that they were as or more popular than brick-and-mortar stores for native plant purchases. I think this speaks to the difficulty many gardeners have finding the plants they are seeking, and how non-profit plant sales are filling a market void. It also points to a market opportunity for the nursery industry, in general.

References:

Anderson, A. 2019. Native plant production and marketing. The Digger, April Issue, pp 33-36.

Anderson, A. (2022). Evaluating the Attractiveness of Pacific Northwest Native Plants to Insects and Gardeners [Dissertation submitted in partial fulfillment of Ph.D.] Oregon State University.

Anderson, A. G., Costner, L., Best, L., & Langellotto, G. A. (2022). The bee fauna associated with Pacific Northwest (USA) native plants for gardens. Conservation Science and Practice, 4(10), e12801.

Bennett L. 2019. Examining the gap between interest and understanding of provisioning for bees: A capstone project to support urban bee conservation [Thesis submitted in partial fulfillment of M.N.R.]. Oregon State University.

Coombs, G., Gilchrist, D., & Watson, P. (2020). An assessment of the native and invasive horticultural plants sold in the mid-Atlantic region. Native Plants Journal, 21(1), 74-82.

Hayes, J., Langellotto, G. 2020. Pollinator plant trials: researchers test the value of Willamette Valley natives and nativars. The Digger, October Issue, pp 33-37.

Hayes JJ-M, Bell NCS, Best LR, et al. 2025. Pacific Northwest native plants and native cultivars Part I: Pollinator visitation. Environ. Entomol. https://doi.org/10.1093/ee/nvae126.

Oregon Flora. 2025. Gardening with natives. https://oregonflora.org/garden/index.php, accessed January 29, 2025.

Zinnen, J., Matthews, J. W. 2022. Native species richness of commercial plant vendors in the Midwestern United States. Native Plants Journal, 23 (1) 4-15.

Garden Ecology Lab, Spring 2024 Update

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It has been a while since we last posted a lab update. Although we’ve been quiet on the blog, we have been busy! This post provides a brief update on some of our efforts, over the past several months.

We have a new website! The website serves as our running record of research projects, lab members, and resources for gardeners. Of particular note is the series of ten Garden Ecology Lab Briefs, that translate our research into a two-page document, that can be used by gardeners. Each brief is divided into three sections: 1) Our research, 2) What we found, and 3) How does this relate to your garden. We have briefs on the common bacteria you will find in garden soils, the flowers preferred by specialist bees, and which plants attract beneficial natural enemies to the garden. More briefs will be coming, soon! In addition to the Garden Ecology Lab briefs, we also have a short form infographic and a long form infographic that can help guide gardeners seeking to buy native plants. We hope that these are useful to you, and would love to hear your feedback on these resources and your suggestions for other resources you would like to see.

An example of a Garden Ecology Lab brief. These briefs were created to translate science to action in the garden.

Nicole Bell successfully defended her M.S. thesis, entitled ‘Urban garden bees: Global context and local perspectives’ in November of 2023. Her thesis consisted of a systematic review of the garden bee literature (which she published in the journal Frontiers in Sustainable Cities). The second part of her thesis consisted of an online iNaturalist guide and companion booklet (the Portland Bee Guide). Nicole recently started a pollinator outreach position with the University of Massachusetts, Amherst. Congratulations, Nicole!

The Portland Bee Guide represented one aspect of Nicole Bee’s M.S. thesis work.

Svea Bruslind graduated with an honors B.S., for her thesis entitled ‘Bee’s eye view: using multispectral photography to simulate bee’s view of flowers in natural settings‘. She graduated with a group art show (Confluences, at the Little Gallery at Oregon State University), and a solo art show (A Bee’s Eye View) at the Pine Meadows Ranch for Art and Agriculture.

Svea in front of her photographic array. She captured a garden over the course of a day, using filters that give viewers a glimpse of the colors a bee can see in a garden.

Nina Miller joined our lab group as an M.S. student with a passion for syrphid flies! Nina will be studying the syrphid fly communities of Portland- and Corvallis-area gardens. Specifically, she will document their biodiversity within garden spaces, and will be measuring their capacity for aphid management on kale, collards, mustard greens, and other brassicas. You can learn more about Nina’s study, from this recent blog post.

Anna Perry has joined the lab, to work on a Building-Integrated Agriculture project. Anna will be studying soil moisture and temperature fluctuations, in a 5-th floor urban agriculture array of 13 planter boxes that are part of the PAE Living Building, in Portland Oregon. The data will inform future plantings on this and other urban buildings.

There are 13 containers planted along the east and south windows of this building. Plants are challenged by hot temperatures in the summer, shade, and lack of consistent moisture.

Gail Langellotto worked with Nina Miller and an international group of designers and ecologists to produce a book chapter entitled ‘Supporting Galapagos Native Species via Ecological Landscape Design in Urban Greenspaces’. The chapter came out of the 2023 Association of Pacific Rim University Sustainable Cities and Landscape Conference, which was held in San Cristobal, Galapagos. This interdisciplinary conference coupled architects, designers, and ecologists, to work on urban issues. In the Galapagos, biodiversity drives tourism, but is also under threat from invasive plant species. We compiled a list of 130 native and endemic plant species, and created example landscape designs, to promote the use of native plantings in the urbanized areas of the islands.

Jen Hayes was quoted in this February 2024 Washington Post article about natives and nativars. Jen Hayes and Gail Langellotto were featured in this recent Pacific Horticulture, Voices of the West article. Jen is finishing up revisions to her manuscript reporting pollinator preferences for native plants and native cultivars. We’re excited to share the results with the scientific community, as well as with gardeners.

This is just a sampling of the our work over the last few months. Make sure to bookmark our new lab website, and to share the resources for gardeners with your gardening friends.

Gardeners Needed for a Native Plant Survey!

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Study: Native Plants & Native Cultivars: Understanding Pollinator Preference for Native Plants and their Cultivated Counterparts in the Pacific Northwest

Thank you for your interest our survey! We are done collecting survey responses at this time. If you previously took the survey and have any questions, please direct them to Gail.Langellotto@oregonstate.edu and/or Jen.Hayes@oregonstate.edu.

We’re Looking for Ecolawns!

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A group of five people are looking at a series of ecolawn study plots, while a female scientist is talking about ecolawns.
Ecolawn research plots at OSU’s Lewis Brown Turfgrass Research Farm in 2019.
Photo: Brooke Edmunds, Oregon State University

What is an ecolawn?

An ecological lawn, or ecolawn, is a reduced input alternative to a conventional mowed grass lawn. While numerous possibilities for an ecolawn exist, they all include multiple low-growing herbaceous plants that work well together and require less mowing, fertilizer and irrigation. In addition to reducing maintenance and resource utilization, they also provide important habitat for pollinators like bees and butterflies.

Help us find examples!

We are looking for examples of beautiful ecolawns throughout western Oregon. A few requirements:

  • Includes 3 or more different herbaceous broadleaf plants; additional grasses optional
  • Mutually compatible and ecologically stable when grown together
  • Installed for 2+ years (Spring 2021 or earlier)
  • All or most plants less than 1 foot in height
  • Looks good all year (and most of your neighbors would agree that it looks good 😊)
  • Needs little to no water to stay green through dry summer months
  • Little mowing (once per month to once per year)
  • Little or no fertilizer and no pesticides following installation

We want to find, understand and share your (or your neighbor’s) ecolawn. Ecolawns are part of a more sustainable future for Oregon. If you have a good example, please email 2-3 photos and contact information to Dr. Phil Allen, Visiting Professor in Horticulture at Oregon State University: allephil@oregonstate.edu

Petal-cutting Bees!

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A study of leafcutter bees and a PNW native flower, through the lens of iNaturalist.

The Clarkia Project team: Mallory Mead, Jen Hayes, Sarah Erskine, and Ali Filipovic

If you are a subscriber to our blog, you have likely seen our photos and videos of one of our favorite plant-pollinator interactions: the petals of Farewell-to-Spring (Clarkia amoena) being harvested by leafcutter bees!

After observing this eccentric harvest behavior in the research garden, we got curious about the bees behind the petal-nest craft, and how we could study this interaction further.

Leafcutter bee mid-petal-harvest! Photo by Devon Johnson.
Crescent-shaped petal-cuts left behind by leafcutter bees.

iNaturalist is a popular community-supported biodiversity database that the Garden Ecology Lab has been experimenting with in recent years. Jen realized that the leafcutter bees’ distinct crescent-shaped mark are visible in many iNaturalist observations of Clarkia amoena. She wondered how we could use the already sizeable iNaturalist database of Clarkia amoena observations to study the interaction over a wider geographic and chronological scale than that of the research garden. Jen and Gail agreed to mentor me in producing an undergraduate research thesis on this subject.

The study’s objective is to use iNaturalist’s data on Clarkia amoena to see if there is a difference in leafcutter bee usage of Clarkia amoena petals based on whether the flower is a native versus a cultivar type, and whether the flower is found in an urban or non-urban environment.

In this process we have found that iNaturalist is easy for anyone to contribute to, but the information it provides is limited compared to the wealth of contextual information gained when being in the actual, living presence of a specimen. So, to get a greater feel for the intricacies of this flower, I embarked on what we called “Ground-Truthing Field Trips” to check out some Clarkia amoena populations in the “real world”.

I went out during peak pollinator season, following the coordinates of recently posted iNaturalist observations. Each specimen I visited was incredibly different from the next. I found the delicate blossoms in natural areas, the borders of farmland, restoration sites, and gardens.

Data from these trips will not be published in my thesis because the contexts are not exactly comparable, and my sampling was exploratory rather than precise. Nonetheless, I gained contextual insight and inspiration watching diverse pollinator assemblages in beautiful meadows of pink.

Mallory at a meadow restoration site near Corvallis with Clarkia amoena and tarweed (Madia elegans).

The field trips have helped us more clearly see through the window of iNaturalist and have informed the methodology we use.

For example, I saw examples of hybridization between two species of Clarkia in a seeded restoration site, and cultivar-hybrid escapees in natural areas. It’s been important to navigate identification of cultivars and hybrids in iNaturalist.

In a restoration prairie seeded with two different Clarkia species, pollinators cross-pollinate them, giving rise to sterile hybrids (Lewis & Raven, 1958). Note the malformed stigma and anthers.

Simultaneously, our field crew recorded petal-cutting behavior on the Clarkia amoena natives and nativars at Jen’s research garden this summer. Below are the three cultivars in the garden, and if you look closely you can see “petal-cuts” which we counted and recorded weekly. We will analyze the difference in leafcutter usage between the cultivars and native type.

‘Aurora’
‘Scarlet’
‘Dwarf White’
This hot pink, stripy Clarkia doesn’t look like either the native or cultivars we had planted!

Clarkia amoena is an annual that reseeds itself effectively, so last year’s seeds gave rise to this season’s blooms. To our surprise, however, Clarkia amoena of all different colors started popping up in our research plots this Spring! Last season’s bees had combined pollen from the garden’s varieties bringing rise to all sorts of intermediate forms.

Clarkia amoena is prone to hybridization between members of the species or cultivars in the same proximity. These intraspecific hybrids are fertile. We seek to explore how cultivar genetics may be moving into natural populations.

Through the winter, our team is working with the iNaturalist data to quantify leafcutter bee petal usage. We expect to share our results in June 2023, so stick around to hear about our findings!

Work Cited:

Lewis, H., & Raven, P. H. (1958). Rapid Evolution in Clarkia. Society for the Study of Evolution, 12(3), 319–336.

2021 Field Update: Natives & Nativars

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Our second field season studying pollinator visitation to Oregon native plants and native cultivars spanned from April to late September of 2021, although if Douglas Aster had any say in the matter, we would likely still be sampling. The densely blooming Symphyotrichum subspicatum continued to produce a smattering of new flowers through November of last year, and we predict it will do the same this year, too!

Our field crew this summer included Tyler, Svea, Mallory and I. Together, we sampled on 33 different dates across the growing season, allowing us to collect around 2000 physical pollinator specimens, and observe 6,225 unique interactions between pollinators and our study plants! This season we conducted floral trait measurements (including the dimensions of flowers), took multispectral photos, and additionally collected pollen from a subset of our study plants.

From left to right: Mallory vacuum-sampling off of Douglas Aster 'Sauvie Snow', Tyler shaking a farewell-to-spring flower to get pollen off of it, and Svea photographing Baby Blue Eyes 'Penny Black'.

This year, we introduced a third cultivar for California poppy (Eschscholzia californica ‘Purple Gleam’), yarrow (Achillea millefolium ‘Moonshine’), and farewell-to-spring (Clarkia amoena ‘Scarlet’). The new cultivars were established in the spring, which resulted in a late bloom for the annuals, so we expect to see them blooming during their typical period in 2022. The Achillea ‘Moonshine’ replaced Achillea ‘Salmon Beauty’ in being the most abundant yarrow cultivar; it began blooming almost immediately as it was planted into our field site and is still continuing to push out blooms through October alongside the Douglas Asters. 

The plant groups in our study: the larger circles with orange text are the native plants, and the smaller circles and turquoise text are the cultivars. The top row contain the perennials yarrow, western red columbine, great camas, and Douglas aster. The bottom row shows the three annuals farewell-to-spring, California poppy, and baby blue eyes.

In addition to watching new plants bloom in the study garden, we had the opportunity to observe many incredible pollinators in the field this summer. We saw a hummingbird visit the Western Red Columbine, we tried to capture videos of leaf-cutter bees snipping little petal pieces off of farewell-to-spring, and at a neighboring plot we observed a male wool-carder bee section off an entire patch of Salvia for a female bee.

On the left: Farewell-to-spring 'Scarlet' with crescents cut out of the petals by leafcutter bees. Top right: A female wool-carder bee (Anthidium manicatum) collecting trichomes from Yarrow 'Calistoga'. Middle right: A leafcutter bee with a piece of petal from Farewell-to-spring 'Dwarf White'. Bottom right: A leaf cutter bee removing a piece of petal from Farewell-to-spring 'Aurora'.

We were also able to take a couple educational field trips this field season in order to learn about pollinator studies ongoing outside of Oak Creek. In June, we went up to the North Willamette Research and Extension Center in Aurora, OR to listen to three talks about pollinators at the Blueberry Field Day. We learned how to score the productivity of honeybee hives, how to properly don a the top of a bee suit, about blueberry’s best pollinators, and blueberry research projects at the University of Washington.

In August, we made a trip to Bend for a different kind of study… an artistic one! We travelled to the High Desert Museum in order to visit Jasna Guy and Lincoln Best’s exhibit “In Time’s Hum…”. Jasna is a brilliant artist inspired by pollinators, which translates into the subject of her pieces as well as her artistic media. Many of her pieces are made using encaustic (a method of painting using wax, bee’s wax in her case!), dipped directly into bee’s wax, or involve pollinators in some other format, including her color study of pollen, which attempts to replicate the colors of fresh pollen as well as the colors after bees have mixed them with nectar. In the center of exhibit were two cases filled with bees collected and identified by Linc, surrounding some of the dried plant specimens they forage on.

These field trips were a wonderful way to see what other pollinator work is happening in our broader community and to inspire future studies. It was especially exciting to see how Jasna and Linc combined art and science with their exhibit, which is something many of us in the Garden Ecology Lab are interested in. 

1. Mallory, Svea, and Jen at the blueberry Field Day. 2. Svea, Jen, Mallory, and Tyler at the High Desert Museum. 3. A panorama of the "... In Time's Hum ... " exhibit. 4-5. Art on the outside of the exhibit. 6. A snapshot of two pollen samples from Jasna Guy's pollen color study.

While we cannot make conclusions until we complete our final field season, we are excited to report some of the variation in visitation between native plants and native cultivars that we have observed in our first two field seasons. In the first field season, our observations of native bees foraging on the study plants revealed three plant groups to have variable amounts of visitation. Yarrow, farewell-to-spring, and California poppy all had at least one cultivar that received substantially less native bee visits than the native type. In our second year, all three of farewell-to-spring’s cultivars received less visitation than the native Clarkia amoena. Poppy had only one cultivar with less native bee activity than the native (Purple Gleam), and in the case of Douglas Aster, both of the cultivars actually had more visitation by native bees than the native. 

Figure 1: Average Abundance of Foraging Native Bees during 5-Min Observations in 2021. Individual plants are color-coded by genus. The naming scheme combines the first three letters of the genus and specific epithet; cultivars are denoted by an underscore and a 1-2 letter code to identify them. For example, AQUFOR is the native Aquilegia formosa, and AQUFOR_XT is Aquilegia  x ‘XeraTones’.

Five Scientific Studies that Changed the Way I Think About Gardens: Part 1

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[Preface: For the past few years, I have written a column for the Hardy Plant Society of Oregon’s (HPSO) Quarterly Magazine. It has been a wonderful experience, as the HPSO provides excellent editorial assistance. Below, I share my most recent article for the HPSO Quarterly, and thank Eloise Morgan and her team for helping to improve and elevate my writing.]

I spend my nights thinking about gardens: not about the plants that I want to purchase or the crops that I want to plant. Instead, I puzzle over how to study a system that is incredibly variable (from person to person, or even in the same person’s garden from year to year) and complex (with more plant species than just about any other system that has been studied). Gardens are both wild and managed, and unlike other systems I have worked, it is impossible to divorce human behavior from the ecology and evolution of the garden.

In this series, I wanted to share five scientific studies that have had a large role in shaping how I think about gardens. Because of space limitations, I will share the first study in this article. I will wrap up the remaining four studies, in subsequent issues. The five studies are:

Simberloff and Wilson (1969). This study commenced 54 years ago, and yet remains a ‘must read’ for any ecology student. In 1966, Dan Simberloff and Ed Wilson selected six small mangrove islands off the coast of Florida. The islands varied in distance from the mainland coast, from near to far (Figure 1a), as well as size, from small to large (Figure 1b)

Figure 1. In Simberloff and Wilson’s experiment, they selected mangrove islands that varied in their (a) distance from the mainland (the coastline of Florida) and (b) their size. Attribution: Hdelucalowell15 / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0)

Simberloff and Wilson constructed a scaffold that encircled the edge of each island, covered the scaffold with a tarp, and then proceeded to ‘defaunate’ each island with methyl bromide pesticide. In other words, they killed every arthropod on the islands. After removing their ‘death tents’, and over the course of the next year, they carefully monitored, cataloged, and counted every arthropod that arrived and survived on each island. What they discovered was formulated into the ‘Theory of Island Biogeography’, or a theory about how organisms colonize new habitat, and assemble into a biological community.

They found that islands that were closer to the mainland coast of Florida were colonized earlier, and accumulated species faster, compared to islands that were farther (Figure 2). They also found that species would accumulate on each island, over time, until a maximum peak is reached (not shown). Then, the number of species would begin to drop, as ecological interactions (such as competition for food) would allow some species to prosper, while others went locally extinct. They found that smaller islands were more prone to species extinctions, than larger islands (Figure 2).

Figure 2. Island size (small or large) and distance from the mainland coast (near or far) infuenced the dynamics of species colonization and extinctions on mangrove islands. Image Source: https://commons.wikimedia.org/wiki/File:Island-biogeography.jpg#file

Size, distance, age: those are the three things that Simberloff and Wilson predicted would govern the diversity and assembly of organisms within a habitat.

My first faculty position was at Fordham University in New York City, where I studied pollinators in 18 community gardens in Harlem and in the Bronx. During the course of this study, I was inspired by Simberloff and Wilson. I could not help but see the 600+ community gardens that dot the landscape of New York City as islands of green in a sea of concrete.

We expected that gardens that had been long-established would have more pollinator species than newer gardens. We expected that larger gardens would host more pollinator species than smaller gardens. And, we expected that gardens that were closer to ‘mainland’ sources of pollinators, such as Central Park or the New York Botanical Garden, would have more species of pollinator than those that were distant.

We were wrong on two out of three predictions (Matteson and Langellotto 2010). Larger gardens had more pollinator species than smaller gardens, but neither distance nor age had any impact. I was so disappointed that we did not find an effect of distance, or of garden age. I had visions of ‘revitalizing’ the Theory of Island Biogegraphy for urban landscapes, but it was not to be. If anything, our study suggested that the ‘sea of concrete’ was not exactly a wasteland, afterall. The street trees, potted plants, windowsill gardens, and patio gardens all provided resources for urban pollinators, even in one of the most densely populated and heavily developed cities in the world.

This study showed me that it will be much more difficult to track pollinator movements among urban gardens, than I had hoped. We tried to use a traditional mark-recpture approach (see Matteson and Langellotto 2012), but out of 476 marked butterflies we only found four in a garden other than which it was marked and released. We were searching for the ‘needle’ of small butterflies in the ‘haystack’ of the New York City landscape. My students tried to follow pollinators as they left our study gardens, and almost got hit by a car, as they were running across the street. We played around with the molecular markers of a few bumblebees (see Morath 2007), to see if there was evidence of genetic differentiation, but were stymied by a lack of reliable primers that could help us look for any genetic differences in bees from different gardens. And then I moved to the Willamette Valley, where gardens are islands of green in an ocean of green. Understanding what draws pollinators to particular gardens will be even more difficult in this landscape, where pollinators have so many other choices for finding nectar and pollen.

Based upon our initial results from our Portland Garden study (2017-2019), I think I have a new hypothesis as to what might draw pollinators to home and community gardens. Our second study year (2018) was characterized by a hot and dry summer. Our first sampling season was also dry, but the spring months were wet, and the summer was cooler. In 2018, we collected far more bees (abundance) and more types of bees (species) than we collected in 2017 or 2019. In 2018, the landscape of the Willamette Valley was toast! Almost all flowering plant materials seems to shut down photosynthesis, so that they could conserve pressure water that would otherwise escape through open stomates. In this type of situation, bees seemed to concentrate in home gardens, which seemed to be one of the few places where they could reliably find nectar and pollen.

If this is the case, gardens aren’t necessarily going to be an important source of floral resources across all years. In a good year, there should be other plants in bloom in the greater landscape that bees can use. But in a hot, dry year, gardens may become an even more important refuge for bees. Most gardeners provide irrigation, which extends the bloom season beyond what is natural in the valley. Or, gardeners select plants that can prosper and bloom without supplemental irrigation, such as goldenrod or Douglas aster. It’s important to note that, even in the hot, dry weather of 2018, we still collected more bees from gardens that used drip irrigation, rather than overhead sprinklers. I think that the overhead irrigation physically blocks bees from navigating through a garden, which lessens their abundance and diversity.

Ultimately, I hope that our studies can lead us to a more predictive model of the resource value of home gardens to pollinators. The goal isn’t necessarily to understand what gardeners should do to attract pollinators, but to describe the conditions where gardens become increasingly important to pollinator conservation. In addition, I’d love to describe the value of gardens, relative to other habitat types, to pollinators. And finally, I hope to better understand the direction and movement of pollinators between gardens and other habitat types.

 

Does Repeated, Lethal Sampling Contribute to Insect Declines?

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Over the past few months, I have shared data on bees and other insects that we have collected from Portland-area gardens. For every garden insect we study (except for butterflies, which can be identified to species by sight), we use lethal collection methods. This is because most insects can only be identified to species after close examination under the microscope. In fact, some insects require dissection before we can get them to species.

Bombus sitkensis male, with abdomen dissected, in order to make a species-level identification.

It seems odd that we kill bees in order to help understand how we can build gardens that can help to conserve bees. By collecting and killing bees and other insects, what role were we playing in promoting insect decline? How do projects, such as our own as well as the Oregon Bee Atlas, factor into bee declines?

That’s an excellent question, and one that we often ask ourselves. When we collect bees, we work to make sure that we are not needlessly causing harm. For example, our pan traps are good for collecting small bees, but are not good at collecting larger bees, including reproductive queens. When we hand-collect bees, we avoid taking queen bees. In fact, of the 2,716 bees that we collected in 2017-2019, only three were queens. We limited our sampling frequency to three times per year, and limited our sampling effort to 10 minutes of hand-collecting time and six pan traps, per garden. Even with these precautions, we are still faced with the question: does our research, or the research of others who collect and kill insects, harm the very species we are trying to conserve?

Water pan traps, used to collect garden bees and other small, flying insects. Insects are attracted to the color. When they land in the soapy water, they break the surface tension, drown, and die.

To address this question, I turn to the scientific literature. Gezon and colleagues set up an experiment to see whether lethal sampling for bees using pan traps and netting (the same methods we use in our research) has negative effects on bee abundance or bee diversity. For five years, they sampled nine sites every two weeks during the flowering season. They compared bee abundance and bee diversity in these repeatedly-sampled sites, to metrics from 17 comparable sites that were only sampled once. They found no significant difference in bee capture rate, bee species richness, or bee abundance between sites that were sampled repeatedly versus those that were sampled once. When they partitioned bees according to nesting habit (e.g. cavity, soil, wood, etc.), social structure (e.g. eusocial or not), and body size (e.g. small, medium, and large bees) they also found no significant differences in bee capture rates of single-sample versus repeat-sampled sites. They did catch more pollen specialists in repeated-sample sites than in single sample sites. However, the magnitude of the effect was relatively small, and did not represent a large change in catch rate between single-sample versus repeat-sampled sites. I suspect that the authors caught more pollen specialists at their repeat-sampled sites, because pollen specialists are fairly rare in time and in space. They drastically increased their odds of intercepting a pollen specialist on their repeatedly-sampled sites.

Gezon and colleagues suggest a few hypotheses that could explain why increased sampling effort had no significant effect on bee abundance or diversity. First, they suggest that reducing bee populations by sampling could benefit the bees that remain, by reducing competition for limited resources. If this is the case, bee populations can compensate for some losses due to sampling, by increasing reproduction in the bees that remain behind. Second, they note that if bees were sampled after they have mated and laid eggs, the overall impact of removing a bee from via sampling will be fairly small. Finally, they note that most bees are solitary, and that most solitary bees have short flight seasons. In this case, sampling every two weeks may not result in bee declines, if researchers are effectively collecting a new species during each sampling event.

I can breathe a bit easier. The data suggests that our research is not immediately responsible for documented bee declines. Still, I know that I can personally do more to help protect bees in my own garden. Even though our lab group studies native plants, I have not yet planted Aster subspicatus (Douglas’ Aster) in my own garden. This will be my mission for 2020: to find and plant this gorgeous perennial at home. In 2018 and 2019, it bloomed from mid June through mid November at our study plots in Aurora, OR, with peak bloom (75% or more of the plant in bloom) lasting one month! And, from 2017-2019, it was always a top five plant for native bee abundance. I give this Pacific Northwest native plant my highest recommendation for home gardens! There are plants that attract more native bees, such as Phacelia heterophylla. But, no other plant that we studied offers the triple threat of beauty, bees, and longevity.

Douglas’ aster (Aster subspicatus) is currently my favorite garden plant for bees.

Native Plants and Pollinator Survey

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Aaron Anderson is repeating his original survey on native plants and pollinators. This time, he is trying to understand how knowledge of a plant’s ecological function may alter impressions of native plants.

The survey takes about 25-30 minutes to complete. Folks who have taken the survey thus far have commented on how much they learned from taking the time to answer the questions.

If your time and interest allows, we would be extremely grateful if you could take the time to respond to this survey. The direct link to the survey is:

http://oregonstate.qualtrics.com/jfe/form/SV_9Alhv961rZX8Vs9

If you have friends or acquaintances who also might be interested in taking the survey, please feel free to share it with them.

A syrphid fly pays a visit to a California poppy at the North Willamette Research and Extension Center.

A bee visiting one of the Canada goldenrod plots in our Native Plant study.

Gilia capitata

Lotus unifoliolatus

PolliNation Podcast and Lab Update

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If you love bees, and you have not yet subscribed to PolliNation, you’re missing out! OSU Professor and PolliNation podcast host, Andony Melathopolous, does a wonderful job assembling a diverse array of guests to talk all things pollinator.

Aaron Anderson recently joined Andony on episode 94 of thePolliNation podcast, to talk about his research on native plants, different insect groups, and gardeners.

Aaron talks about the 100+ study plots that he manages (two of which you can see, below), as well as which plants were most attractive to bees (such as the California poppy, on the left) versus those that were more attractive to gardeners (such as the Oregon iris, on the right).

In other news, our lab group has been very busy. All of the 2017 and 2018 bees from our garden pollinator study have been identified to species (unless they are truly recalcitrant to being ID’d to the level of species).  Gabe has been working with Lincoln Best to identify the 2018 bees.  The 2017 were verified by Sara Kornbluth, and provided a great reference collection against which we could compare the 2018 bees. Gabe has been a short-time member of our lab group, but his expertise has been a huge benefit to our program. He leaves us at the end of April to start field work in the College of Forestry. After that, he heads to UC Davis to do his Ph.D.

For the garden bee project, we have >50 verified species of bees collected from Portland-area gardens, with a few more at the morpho-species level. This summer will be our final year of collections.

This summer will also be Aaron’s final year of field work at the North Willamette Research and Extension Center. This final year will help to resolve some of the differences we saw between his 2017 and 2018 data set.

After two years of amazing assistance in the lab and in the field, Isabella has started an independent research project on campus. She has planted some of Aaron’s study plants in gardens on campus, and is looking to see if bee visitation and bee communities markedly change, when you take them out of single-species plantings (like Aaron is studying) and put them into a garden setting.

Mykl is working to write up his urban soils data for publication. We are also hoping to do a side publication, comparing the soil types that we’re finding in home gardens, and seeing how they align with the types of soils that nesting bees prefer.

Lauren is writing up her capstone paper, and is preparing to defend this term. She surveyed gardeners to try to understand how well they can identify bees from other insects, and how well they knew bee-friendly plants from those that offered few or no nectar/pollen resources to bees.

Signe is taking the data that we are collecting, and working our findings into the online Master Gardener course. The best part of our work is being able to see gardeners put some of our research-based recommendations into action. Signe plays a huge role in translating our work for the general public.

Angelee is a relatively new member of the lab. She comes to us from the OSU STEM Leaders program. She’s learning lab protocols and lending a hand on just about every project. She has been a joy to work with.

Lucas has moved on from the lab, but still helps us with remote data-basing work, on occasion. He was a joy to work with, and I feel lucky that he stuck with us for a few years.

This fall, Jen will be joining our group as a new M.S. student. We will also be close to launching the first course in the online Urban Agriculture certificate program, which is being spear-headed by Mykl. We should also be pushing out a few more papers from our garden work, to join our first concept paper on the value of urban garden bees to urban and peri-urban agriculture.