Your garden soil contains millions to billions of individual microorganisms, including bacteria, fungi, viruses, and archaea, representing tens of thousands of different microbial species. Humans evolved for millenia in the presence of these environmental microbes associated with vegetation, soil, water, and wildlife. Our immune systems are not only adapted to coexist with the majority of these microbes, but may even require that interaction to function properly. Emerging scientific evidence suggests that exposure to soil microbes trains the immune system, reduces inflammation, and improves mental health (Rook, 2013). For example, the common soil bacterium Mycobacterium vaccae has been found to have positive impacts on stress tolerance and mental health (Matthews and Jenks, 2013), while other research has shown that children exposed to greater microbial diversity, such as that encountered in farming environments, tend to have lower prevalence of autoimmune disorders, including allergies and asthma, than their urban counterparts (Hanski et al., 2012).
The primary goal of the Garden(er) Microbiome Project was to understand how much microbial transfer from soil to skin occurs during gardening activities, what types of microorganisms are transferred, and how long they can persist on the skin. We are also interested in exploring how soil microbial communities vary with different management practices (e.g., organic vs. conventional) and geographic locations, as we know that microbes play critical roles in soil nutrient cycling, carbon sequestration, pollutant degradation, and, of course, crop health.
To accomplish this study, we recruited 40 gardeners to collect microbial samples from their garden soil and from the surface of their skin (hands). All samples were collected in July–September, 2020, and were equally distributed between the Willamette Valley and High Desert regions, as well as between self-reported organic and non-organic management practices. Each volunteer was asked to collect soil samples from three different garden beds and skin microbiome swabs before, after, ~12 hours after, and 24 hours after gardening (Figure 1). To identify bacterial taxa (different types of bacteria) present in the samples, we used Earth Microbiome Project protocols to sequence the V4 region of the bacterial 16S rRNA gene.
In garden soil samples, we observed over 8.5 million individual bacteria, representing about 45,000 different bacterial species. In skin microbiome samples, we observed over 6 million individual bacteria, representing almost 13,000 different bacterial species. Of all these bacterial species, there were just over 7,500 that were shared between garden soils and gardeners’ skin microbiomes over the course of the study (Figure 2).
Our initial hypothesis was that skin microbiome samples would be more similar to soil samples immediately after gardening, due to microbial transfer from soil to skin during direct contact. We also expected that the skin microbiome would return to baseline (before gardening) after a period of time, depending on individual behaviors, such as washing hands and bathing. It turned out that soil microbial communities were very different than those found on skin. Interestingly, skin microbiome samples tended to be dominated by a small number of taxa, though they were not always the same taxa at different sampling times. For many of the study participants, we did indeed see an increase in shared taxa for the skin samples collected immediately after gardening (Figure 3). However, soil microbes were generally transient on the skin and were no longer present after 12 hours. We note that the COVID-19 pandemic may have influenced hand-washing behaviors and use of hand sanitizers, which could have had additional unexpected impacts on the skin microbiome.
Though it was beyond the scope of the project to describe life history details about every type of bacteria that was found, we did investigate a handful of taxa that were highly abundant in many samples. In garden soil, many of the most abundant bacteria belonged to the genus Pseudomonas. In a recent paper, Sah and Singh (2016) state, “The genus Pseudomonas encompasses arguably one of the most complex, diverse, and ecologically significant group of bacteria on the planet. Members of the genus are found in large numbers in all the major natural environments (terrestrial, freshwater, and marine) and also form intimate associations with plants and animals.” Importantly for gardens, several species of Pseudomonas are able to promote plant growth, while others are well-known plant pathogens. Members of the genus Sphingomonas were also common soil inhabitants found in this study. Sphingomonads are broadly distributed in the environment, including soil, water, air, and plant leaves. Only one species of Sphingomonas is known to cause disease in humans, typically in hospital-acquired infections (Balkwill et al., 2006). A third genus of interest from garden soils was Streptomyces. This is a large genus with over 500 members that are ubiquitous in soils. They are known to form symbiotic relationships with plants and animals, and they are responsible for the production of over 2/3 of all known antibiotics (Antoraz et al., 2015). Streptomyces also produce the chemical compound geosmin, which gives soil its earthy smell (Seipke et al., 2012).
The composition of skin microbiome samples in this study varied wildly from individual to individual, and sometimes even for the same individual at different time points. Among the most abundant taxa we found were members of the genera Pantoea, Acinetobacter, Bacillus, and Klebsiella, as well as Pseudomonas, which was described above. Generally speaking, these are very diverse genera and are widespread in many environments, including soil and human skin. Some Pantoea species produce antimicrobial compounds that can help control fire blight in fruit trees (Walterson and Stavrinides, 2015). The genus Acinetobacter contains two species of interest for health reasons—A. baumannii is typically found in wet environments and is a notable opportunistic pathogen associated with hospital-acquired infections (Howard et al., 2012), whereas exposure to environmental sources of A. lwoffii is thought to protect against development of allergies, although it can also cause infection in immunocompromised individuals (Debarry et al., 2007). Members of the genus Bacillus have been explored for potential probiotics (Elshaghabee et al., 2017), and the genus Klebsiella is somewhat notorious for its human pathogenic members. However, Klebsiella, Pantoea, and several other members of the Enterobacteriaceae family have highly similar DNA sequences in the region that we targeted, so these composition results should be interpreted cautiously.
This study represents one of the very first investigations of garden soil microbiomes and, to our knowledge, the only one that explores the ability of soil microbes to transfer and persist on human skin after typical gardening activities. Overall, we found that garden soils tend to have far greater bacterial diversity than skin microbiome samples. Bacterial community composition was largely similar across different garden beds, whereas skin microbiome composition varied dramatically. Some soil microbes appeared to transfer onto skin during direct contact with soil, but they were generally gone within 12 hours, suggesting a low ability to permanently colonize skin. However, a daily gardening routine with repeated and extended contact with soil likely reinoculates the skin such that soil microbes are like a regular visitor during the growing season.
The specific ecological role of most microbes, both in soil and on skin, is a relatively new area of investigation garnering intense interest. However, few, if any, concrete recommendations are currently available to guide actions towards improving plant and human health. A primary goal of this study is to gather baseline data for future studies, which are needed to further explore the impact of daily soil contact over longer time periods (e.g. entire growing season), how changes in gardeners’ skin microbiomes compare with non-gardeners, and whether consumption of fresh garden produce affects the gut microbiome.
Written by Mallory Mead
My name is Mallory Mead, and I am new to the Garden Ecology Lab! I am an undergrad studying Horticulture and minoring in Entomology, and I started a few weeks ago as an assistant to Jen Hayes on her study of pollinator attraction to native plants and nativars.
I enrolled in Oregon State’s URSA Engage program, which gives undergrads a taste of research experience in the Winter and Spring of their first year, and joined a project studying how mason bees might be impacted by climate change with Dr. Jim Rivers of the department of Forest Ecosystems and Society. The study seeks to examine the effects of warming temperatures on mason bee behavior and the development of brood.
The Western US’s native species of mason bee, the Blue Orchard Bee (BOB) is known to be an excellent orchard pollinator. On many orchard crops they are more efficient at pollination than honey bees on a per individual basis, and so the commercial management of BOBs is being explored as honey bee colonies suffer management challenges and colony losses in recent years.
Mason bees have a short lifespan of 4 to 6 weeks. Emerging in the early spring, males die shortly after mating, while females build nests in holes in wood or reeds. They forage for pollen and nectar to form provision masses in which they lay their eggs. They also collect mud to form partitions between each provision mass and to cap the nest once it is full. Their offspring will feed on the provisions and metamorphose into cocooned adults to overwinter in their cells and emerge the following spring.
To ensure the bees had ample nutrient resources, the project was conducted next to the organic cherry orchard at OSU’s Lewis Brown Farm. Before the cherries bloomed, 6 nest structures were designed and constructed by Jim, Ron Spendal (a mason bee house conisuerrier) and Aaron Moore of Revolution Robotics.
Each structure has 3 shelves with 16 nest holes each, lined with paper straws so that the nests can be easily removed and examined. The structures are solar powered, and each shelf is heated to a different increment above the ambient temperature i.e. + 0°C , + 2°C, + 4°C, + 6°C, + 8°C, + 10 °C, and + 12°C. These differentials represent many potential warming outcomes of climate change.
- We predicted that female mason bees will select the warmer nests first, and that females will leave nests earlier in the morning to begin foraging because they will reach the critical internal temperature necessary for flight sooner.
- If heated bees have a greater window of foraging time, then we predict they’ll be able to construct nests at a faster rate in the warmer nests.
- With greater nest construction will come a greater production of offspring from the bees in the warmed nests.
- In terms of offspring quality, we predict that offspring of heated nests will emerge as weak individuals and mortality will be the highest for the heated brood.
…and we are pretty confident about this last prediction.
Insects are poikilothermic meaning their internal temperatures are determined by the environment. Past studies by researchers Bosch and Kemp have reported that mason bees who are overwintered at warm temperatures will “use up their metabolic reserves and are likely to die during the winter”. And a more recent study by researchers at the University of Arizona found that mason bees subjected to heating resulted in reduced body mass, fat content and high mortality of the mason bee offspring.
Our mason bees started hatching from cocoons in mid-April and began to colonize the nest structures. I captured video footage of the bees as they emerged in the morning to forage. If bees from heated nest sites emerge earlier, this will support our hypotheses that they reach their critical-for-flight temperature earlier, and get a leg-up on foraging compared to their neighbors.
I also conducted “nest checks” to track the rate of nest construction along with two other research assistants.
In the fall, the nest tubes will be extracted to examine the reproductive output, and in the following spring, offspring will be assessed for rates of mortality, offspring mass, and fat content.
Some of the challenges along the way have included dealing with insect pests. Spiders were easygoing inhabitants of the nest straws, for they only nested in empty straws, so we’d swap them out for a clean one. The earwigs were much more pervasive, and went for the already inhabited nests. As generalist foragers, the earwigs took advantage of provision balls of nectar and pollen that had not yet been sealed off by mud. Once I read that earwigs will indeed eat the mason bee eggs that are laid into the provision masses, I knew it was crucial to remove the earwigs from all nests, but these feisty creatures proved determined to stay. We ordered some tanglefoot, a sticky substance to trap the earwigs on their way up the structure post, and meanwhile I coaxed earwigs out with tiny pieces of grass. Jabbing them repeatedly would eventually provoke them to charge at the blade of grass and fall out from the straw.
Yellowjackets were another opportunistic nester. They’d sneak into the cocoon boxes to build nests, and always gave me a start when opening the tiny boxes. I removed their nests with an extended grabber tool and would destroy them in any way I could. I feel immensely lucky not to have been stung through this process.
The most terrifying surprise during the project was a fat snake that was living in the solar panel battery box. It popped out at me hissing while I conducted a routine check. Alas, I was too spooked to take on this unexpected visitor and let it leave on its own time.
Preliminary Findings & Observations
By mid-May, a pretty clear pattern was emerging. At each structure, the control shelf’s nests (+ 0 °C) were full and capped with mud, while the hottest shelves were almost completely empty. We will analyze nest check data to confirm that these patterns are not just arising by chance, but a study that was released this past April showed another species of mason bee in Poland following the same pattern of nest site preference and selection for cooler nest sites.
The mason bees’ unexpected behavior of avoiding the heated chambers may lead to trouble during the second part of the experiment because this means our sample size for heated offspring has become so tiny, but here it is important to note that this is mason bee project is a pilot study and so the data collected this year will simply influence more specific future research.
these preliminary findings make me think that mason bees have an ingrained sense to avoid warm nests, which might show mason bees’ adaptability in the face of climate change, that is, if they can manage to continue finding cool nests. People managing mason bees find that nests facing the morning sun are the most attractive to the bees, but I wonder how long it will be before temperatures rise and mason bees start avoiding these sunny nests.
By the end of May, I’d only see a few the mason bees per visit, so the season was clearly coming to an end. I wrapped up data collection and am now spending the summer extracting data from the video footage, and checking up on the bees to ensure they are safe and sound until Fall inspections.
I am wishing the best to both the wild bees in our region and those in our study, as the temperatures skyrocket this week but with this summer’s heat wave, I don’t think we need to simulate climate change; it is right here before us. Even though it is practically inevitable that temperatures will rise to dangerous heights in my generation’s lifetime, there is so much life to be saved, and there is no time to waste.
According to the staff at Oak Creek and many other gardeners and farmers I’ve had the opportunity to talk to, it appears that though 2020 was a difficult year for humans, it was truly a remarkable year for gophers and other rodents.
From left to right: wild type Great Camas, Camassia leichtlinii, the native cultivar ‘Sacajawea’, and the native cultivar ‘Caerulea Blue Heaven’.
Gophers & Camas
No matter how often a gopher was trapped and removed from Oak Creek last summer, the next week there would always be a mound of freshly turned soil on the grounds, indicating a new gopher had taken its place. While they seemed to enjoy popping up in some of the Organic Gardening Club’s beds, they had an extra fondness for my own experimental garden beds. Fresh gopher-turned soil was most commonly found in any plot growing our native Camassia leichtlinii (Great Camas) and the plots surrounding them.
We planted our 15 camas plots in the fall of 2019. Five plots were planted with the wild type camas species, Camassia leichtlinii (Great Camas). Five more were planted with the C. leichtlinii cultivar ‘Caerulea Blue Heaven’, and the final five were planted with C. leichtlinii ‘Sacajawea’. By the spring of 2020, the camas plots were relatively untouched, aside from some minor grazing by deer on a handful of plots. In April our three camas varieties began blooming in sequence (the native first, followed by ‘Blue Heaven’ and ‘Sacajawea’, respectively), and by mid June they had all gone to seed.
Though the gopher troubles seemed to really begin in June, there were signs of their activity that we did not heed. In spring of 2020 I was planting a Clarkia amoena cultivar plug. Upon removing some soil to make room for the plant, I found that the soil seemed to drop off into a massive hole beneath the plot I was planting. I shook some soil loose to fill the hole, planted my Clarkia, and moved on. Later in the season, a different Clarkia plant would be found dead, and upon its removal, another tunnel would be found beneath the top layer of soil.
By August, there had been so much gopher activity in our beds that I decided we needed to conduct a damage assessment. I asked Tyler to dig around in a Camas plot that seemed particularly ravaged by the gophers, to see if he could find any of the original 40 bulbs we had planted. His searching returned no bulbs.
I immediately went through each of the 15 camas plots and rated them with a visual assessment of the gopher activity that we would use to determine how many bulbs likely remained in the plots. The levels we decided on were “low/no damage” “Low damage”, “Moderate Damage”, “High Damage” and “Extreme Damage”. Plots with no damage were expected to have all 40 original planted bulbs. On the other end of the spectrum, plots labeled “Extreme” were expected to have no remaining bulbs.
At the end of our field season, we dug out the bulbs from each of the camas plots so we could assess the actual damage, and so we could install fencing to keep all future gophers out. During the bulb dig, we recorded the total number of bulbs found in each plot. In the table below, I have shared the visual damage rating for each plot, the estimated number of bulbs expected to be in the plots, and the actual number of bulbs we found.
|Rep #||Bulb Type||Visual Damage Rating||Estimated Remaining Bulbs||Actual Remaining Bulbs|
While our findings from this unexpected study of bulbs were unfortunate, they tell an interesting story. An important point to note is that many of the bulbs have divided since they were planted, which is why in a few cases we found more than the original 40 planted bulbs. Regardless, there is a clear preference for the native C. leichtlinii and native cultivar ‘Sacajawea’ bulbs over the ‘Blue Heaven’ cultivar. We also noticed that any bulbs that were planted more shallow than the recommended 2-3x the height of the bulb were missed by the gophers.
Finding the Gopher Stash
After the exploratory bulb digging, we excavated each of our camas plots to around 1 foot in depth to install fences to keep the gophers from returning to our plots. While digging out the excess soil, we would often find a bulb or two that weren’t located during the initial bulb removal (these numbers are not included in Table 1, as we did not record them). In one section where the three camas types were planted in a row, we excavated a huge section of the garden, and made an amazing discovery (extra Kudos to Tyler who did the bulk of the work on this section).
On one of the walls of the hole, we found a gopher food chamber with thick white roots sticking out of the bottom of it. We removed some soil from the entrance, and discovered a chamber filled with camas bulbs. We carefully removed them and found over 60 bulbs that had been stolen from our plots.
The 3 excavated plots, the food chamber, and the pile of 66 bulbs removed from the burrow.
Some of the bulbs were clearly the wild type great camas, identified by their characteristic long neck. The others we suspect to be ‘Sacajawea’ bulbs, as the burrow was found in what used to be a ‘Sacajawea’ plot. Any unknown bulbs were brought to my home and planted in a planter box to be identified in the next couple of months. The ‘Sacajawea’ bulbs have variegated foliage, making them easy to pick out once their shoots appear above the soil. We won’t know if the remaining mystery bulbs are ‘Blue Heaven’ or large wild type bulbs until they bloom in the spring.
On the left: Jen (me) building a gopher exclosure. On the right: Tyler finishing installing a gopher exclosure.
In November of 2020 we installed our fences, refilled the gaping holes with soil, and replanted all of the camas bulbs, including some supplemental purchased bulbs of each of the three varieties. The native Camas and ‘Blue Heaven’ were successfully replanted with 40 bulbs. We were only able to order enough ‘Sacajawea’ bulbs to achieve a density of 30 bulbs per plot, though they will receive additional geophytes if any of the mystery bulbs turn out to be variegated. The mystery bulbs have yet to push their shoots through the soil, but I will include an update on their identities when I have them.
Thank you to Tyler, Izzy, Max, and my fiancé Elliot for helping out in this laborious process. I absolutely would not have been able to safeguard the new camas plantings without your efforts and support in this process.
This past year presented challenge and change to the Garden Ecology Lab. COVID locked us out of the lab and out of the field for a period of time. We said goodbye to two lab members (Angelee graduated! Cliff decided to move on from graduate school), and said hello to new lab mates (Cara took over Cliff’s project; Gwynne started her post-doc; Tyler, Jay, and Max all joined the lab as undergraduate researchers and research assistants). In addition to COVID and personnel changes, I had orthopedic surgery that took me away from work for a little under a month.
But somehow, despite the challenges and changes, we managed to make progress on several research projects. Below, I present a partial reporting of the Garden Ecology Lab year in review for 2020. Besides each project heading is the name of the project lead(s).
1) Garden Bees of Portland (Gail & Isabella): Jason Gibbs’ group from the University of Manitoba provided final determinations for a particularly difficult group of bees to identify: the Lasioglossum sweat bees. In addition, Lincoln (Linc) Best provided determinations for garden bees collected in 2019. Isabella is entering in some of our last remaining specimens, and I am working through the database of over 2,700 collected specimens to ‘clean’ the data and double check data entry against specimens in hand. There are a few specimens that need to be re-examined by Linc, now that we have determinations from the University of Manitoba, the American Museum of Natural History (Sarah Kornbluth), and a graduate of Jim River’s lab (Gabe Foote).
Altogether, we collected between 76 and 84 species of bee across a combined acreage of 13.2 acres (sum total acreage of 25 gardens). The low end estimate conservatively assumes that each unique morphospecies (i.e. Sphecodes sp. 1 and Sphecodes sp. 2) are a single species, whereas the high end estimate assumes that each is a unique species. A few noteworthy specimens:
- We collected one specimen of Pseudoanthidum nanum, which is a non-native species to our area, which seems to be establishing and spreading in Portland. Stefanie Steele from Portland State University is writing a note on this apparent introduction, and is using data associated with our single specimen in her paper.
- We collected one specimen of Lasioglossum nr. cordleyi which might or might not be a new species. The notation nr. cordleyi means that this specimen looks similar to L. cordleyi, but that the morphology of this specimen is different enough than the normal ‘type’ for this species, that it catches your attention. Jason Gibbs’ group is retaining that specimen. Further study will be needed to determine if it is indeed a new species, or not.
- Some of the species we collected (as well as their ecological characteristics) suggest that gardens might be healthy habitat for bees. For example, we collected 72 specimens of Panurginus atriceps, which is a ground-nesting, spring-flying bee. Previous studies of garden bee fauna found ground-nesting and spring-flying bees to be relatively rare. We found them to be surprisingly (but relatively) common in our collections. We also collected seven putative species and 23 specimens of Sphecodes bees. This type of bee is a social parasite that does not collect nectar or pollen or construct a nest for their brood. Instead, they take advantage of the hard work of other bee species, by laying their eggs in the nest of another female. Parasitic bees are often used as bioindicators of habitat health. They would not be present on a site, unless the site also supported their obligate hosts.
- We collected two species of bee that are listed on the IUCN red list for threatened and endangered species: Bombus fervidus (18 specimens) and Bombus caliginosus (10 specimens). I am not yet sure if their presence in urban gardens suggests that these species are recovering, that these species might be urban-associates that would be expected to thrive in urban gardens, and/or if gardens might represent particularly good habitat for these species.
In 2021, I *hope* that I can complete gathering data for this study, so that I can begin to analyze data and write. I hope to make it out to every garden, one last time, to finalize garden maps that will be used to calculate the area allotted to ornamental plants, edible plants, hardscape, and unmanaged areas. Aaron has already mapped out the landscape surrounding each garden at radii of 500 and 1000 meters. Together, these data will be used to understand whether/how garden composition and the surrounding landscape interact to influence bee species richness.
2) Native Plants and Pollinators (Aaron Anderson): In February, Aaron successfully defended his dissertation proposal and passed his oral examination, and thus advanced to Ph.D. candidacy!! Since that time, he has been busy sorting, identifying, and counting three years’ of insect samples from his 140 study plots, representing five replicates plots of 23 native plants, four ornamental plants, and a control ~ a task that he finished two weeks ago! His bees have been identified to species by Linc. Aaron has identified the thousands of other insects in his samples to the taxonomic level of family. He is working through analysis of his massive data set, and is simultaneously working on two manuscripts: one focused on just the bees and the other covering all other insects. We plan to turn the key points of these two chapters into an infographic that can be used by gardeners and green industry professionals, to select native plants that support an abundant and diverse assemblage of beneficial insects.
Aaron recently submitted the first paper from his dissertation for publication consideration, to the journal HortTechnology ~ and it was accepted, pending revisions! This paper reports on his survey of gardeners’ impressions of the aesthetic value of his study plants, and includes five specific recommendations for native wildflowers that Pacific Northwest nurseries might consider growing and marketing as pollinator plants (e.g. Gilia capitata, Clarkia amoena, Eschscholzia californica, Madia elegans, and Sidalcea asprella virgata). These plants all fell within the ‘sweet spot’ of being attractive to both pollinators and to gardeners.
Aaron’s plots at the NWREC station remain in place. Although we are through collecting data for Aaron’s study, I am applying for grant funding to study how plant traits ~ both the reward that plants offer pollinators and the displays that they use to attract pollinators ~ change with plant breeding for specific aesthetic traits, and whether/how these changes affect pollinator visitation. We also hope to study how highly attractive pollinator plants function in mixed plantings and in garden settings.
3) Bees on Native Plants and Native Cultivars (Jen Hayes):
Jen successfully completed her first field season of research, which is a monumental accomplishment during this time of COVID restrictions on our work. In early 2020, Jen finalized her list of study plants, which included one native species and 1-2 hybrids or native cultivars. This, in and of itself, was a huge accomplishment. Although we started with a much broader list of potential study plants, so many native plants did not have native cultivars or appropriate hybrids available for sale.
Once Jen and her crew put the plants in the ground, a new set of challenges emerged. For example the native yarrow emerged with pink flowers, which was a clear signal that these plants were not true natives. In addition, the Sidalcea cultivars that Jen and her crew planted came up looking different than the Sidalcea native. This sent Jen on a journey to the OSU Herbarium, where she learned that the Willamette Valley’s native Sidalcea malviflora has been reclassified as Sidalcea asprella, and that the cultivars we purchased were hybrids of Sidalcea malviflora (native to SW Oregon and California). This all suggests a need to work with local nurseries and/or growers of native plants, to see whether or not there needs to be or can be standards for sale of native plants. Should native species and native cultivars be verified or share provenance? Should gardeners be asking for this information? I don’t know, but I think that they’re important questions to consider.
With one field season’s worth of data in hand, the native cultivars were more attractive to all bees (with overall patterns being driven by the abundance of the European honey bee) for all floral sets, except California poppy. When we excluded honey bees from the analysis, to look at (mostly) native bees, no clear pattern of visitation on native plants versus native cultivars emerged. Native California poppy was most attractive to native bees. But, native cultivars of Sidalcea were more attractive to native bees (keeping in mind that in 2020, our native cultivars were not cultivars of our regionally appropriate native plant). For all other plants, there was no difference. We look forward to collecting additional data in 2021 and 2022, to see if the lack of difference in bee visits to native plants versus native cultivars holds up. Particularly for the perennials, we are finding that bee visits change so much from year to year, as the plant becomes established.
4) Garden Microbes in Soil and on Skin (Dr. Gwynne Mhuireach): Dr. Mhuireach successfully recruited 40 gardeners to participate in this study: 20 from western Oregon and 20 from the high desert. She has received and processed all soil samples and all skin swab samples for PCR (genotyping), which will be used to infer the diversity and identity of the soil microbial community in garden soils and on gardeners’ skin. She has also received survey responses from all study participants, so that she can characterize gardeners’ crop types, time in the garden, and gardening practices (e.g. organic, conventional, or mixed).
Dr. Mhuireach then sent me the soil samples, so that I could process them for submission to OSU’s Soil Health Lab. The Soil Health Lab is currently performing the chemical and physical analyses on each soil sample, so that we can determine if there is any relationship between soil characteristics, gardening region (e.g. western Oregon or high desert), crop choices, management practices, and the microbes that can be found in garden soils and/or on gardeners’ skin. Gwynne just received the first data back from the PCR analyses ~ and we can’t wait to share some of the intriguing findings with you, after we’ve had some time to process and digest the data!
Because of COVID-19 lab closures, we are a bit behind where we had hoped to be at this point. We anticipate receiving all data from each service lab by the end of January or in early February. You can read more about Gwynne’s project, here.
Beyond these four studies, Tyler started his BioResource Research project (costs and yield of container grown and intercropped tomotoes), and Isabella worked on her thesis (parasitoids in Portland area gardens). We also collaborated with OSU Computer Science students to turn a database of first frost / last freeze dates that Angelee compiled, into a web-based app (the app is still in beta-testing, but we hope to release it, soon!). I will detail those studies, in another post. But for now, I’m getting excited for the smell of carnitas that is filling the house, and that will go on top of the New Years’ nachos that will help us ring in 2021! I hope that you all have a very Happy New Year, and that 2021 brings health, and happiness, and joy to all.
This article is the third in a five part series that I am writing for the Hardy Plant Society of Oregon (HPSO) Quarterly Magazine. I am grateful to the team at HPSO for their editorial skills and feedback. Part 1 (overview, and gardens as ‘islands’ in an urban ‘ocean’), and Part 2 (putting a price on nature) of this series can be found in earlier blog posts.
I distinctly remember the day that I decided I wanted to study wild bees. I was sitting in a darkened auditorium at the American Museum of Natural History in New York City, listening to Claire Kremen deliver the plenary address in a symposium focused on invertebrate conservation.
In her address, Dr. Kremen shared the results of her research on watermelon farms in California’s Central Valley. Like all cucurbits, watermelon requires insect pollination to set fruit. Watermelon, in particular, has a high pollination requirement: it takes at least eight bee visits to deposit the 500-1,000 viable pollen grains needed to set harvestable fruit in seeded watermelons. Seedless watermelons require between 16 and 24 visits by a bee in order to set fruit. Most growers meet the high pollination requirement of melons by renting and placing honey bee hives in fields. Dr. Kremen’s research suggested that a different approach might be possible.
Dr. Kremen and her colleagues studied three types of watermelon fields that varied in their pest management practices (organic or conventional) and their proximity (near or far) to native habitat in the foothills of the California coast range. These fields were: organic near, organic far, and conventional far. Watermelon fields that used conventional pest management practices and that were located near the foothills were not included in this study because this type of farm did not exist in the region. The team determined the number of pollen grains that different bee species deposited on watermelon, by presenting different bees with a single watermelon blossom that had yet to receive any insect visits. After a blossom was visited by a single bee, the flower was bagged and tagged accordingly, and the number of pollen grains deposited on the stigma by that single bee was counted in the lab. They repeated this process for 13 different bee species.
Next, the team sat in watermelon fields and observed what types of bees visited watermelon blossoms, in different types of farm fields. Watermelon flowers are only receptive to pollination visits for a single day. They recorded the sex and species of each bee visitor to the blossoms. Based upon these species specific counts, combined with the pollen deposition data (above), they were able to assess how much each particular bee species contributed to the production of harvest-ready watermelon.
Dr. Kremen found that pollination surpassed 1,000 pollen grains needed to set harvestable fruit per flower in the organic near fields but not in the organic far or the conventional far field (Fig 1, part A). Furthermore, she found that this outcome could be tied to the greater diversity and abundance of bees in organic near fields, compared to the other two types of fields (Fig 1, part B).
Dr. Kremen also found that, even though no single species of wild bee was as effective as managed honey bees, the collective group of wild bees surpassed the effectiveness of honey bees in organic near fields (Figure 2). Interestingly, honey bees were most effective as crop pollinators in the conventional far fields and least effective as crop pollinators in the organic near fields. This may be because few other flowers were in bloom in the conventional far fields, so that honey bees concentrated their attention on the crop at hand. In the organic near fields, a greater diversity of flowering plants likely competed for the pollination services of honey bees.
Wild bees were able to fully satisfy the pollination requirements of a crop with an extremely high pollination requirement because broad spectrum insecticides were not used, and the foothills provided year-round and protected habitat for the bees. This story blew my mind!
Prior to that conference, I had never given wild bees much thought. They’re mostly solitary nesters, with small bodies, that only forage for a few days to a few weeks. They tend to be inefficient foragers, particularly when compared to the juggernaut of a honey bee hive. Whereas wild bees are akin to a single vendor on Etsy, honey bees seemed the unbeatable Amazon!
Dr. Kremen’s work showed the potential value that wild bees have to agriculture. And her work was published just prior to the global onset of colony collapse disorder in honey bees in 2006. It set off a worldwide discussion about what to do about honey bee losses. Should scientists put time and effort into saving a single, non-native species (the honey bee), or should we work to conserve or build habitat around farm fields while also reducing insecticide use?
I was incredibly hopeful that the simultaneous threat to honey bees and promise of wild bees might promote heavier investments in agroecology, including the conservation of bee-friendly habitat around farms. During this time period, I was also in the early stages of documenting wild bee biodiversity in community and residential gardens, and I was surprised that abundance and diversity of garden bees was much higher than I had anticipated.
Back in 2004, I started to see gardens, and the abundance and diversity of wild bees that they host, as a potential solution to the problem of colony collapse disorder. Although I continue to be fascinated by the potential role of home and community gardens as a safe haven for bees from agricultural stresses, the urgency of this question has faded. Colony collapse disorder does not currently plague honey bees, due in large part to federal investments in studying, understanding, and mediating the factors that contribute to failing hives. With honey bees doing much better, attention has somewhat faded on the potential role of wild bees as crop pollinators. Still, work in this area continues and may rise to renewed importance, should colony collapse disorder again present a major challenge to United States agriculture.
Kremen, Williams, Thorp. 2002. Crop pollination from native bees at risk from agricultural intensification. Proc. Natl. Acad. Sci. 99: 16812-26816. DOI: 10.1073/pnas.262413599.
As part of Master Gardener Week at the end of October, I had the opportunity to view “Five Seasons: The Gardens of Piet Oudolf” and participate in a discussion afterwards. This recently-released film has brought renewed attention to the gardens and landscapes created by this internationally-renowned designer. His popular public garden designs, and several books, have had a profound impact on the design of public spaces, as well as private gardens.
Oudolf’s gardens have been described as spontaneous, immersive and naturalistic, and rely heavily on grasses and structural perennials to maintain visual interest well into the winter. They evoke flower-filled meadows and prairies, and seem at first glance like places that could, indeed, have occurred spontaneously. Oudolf himself acknowledges, though, that they require a certain amount of “interference”, and his design process is comprehensive and very specific. He has a palette of plants that he has tested over time for durability and effect.
During the bloom season, one imagines these gardens will be buzzing with pollinators, and be places of lively, hungry activity. When it comes to pollinators, it seems, almost any garden is better than no garden at all, and a garden doesn’t need to be designed especially for pollinators in order to offer benefits to them. As research in this lab has shown, though, a garden designed specifically to be pollinator friendly has an outsized impact.
So I wondered, how pollinator-friendly are Oudolf’s naturalistic gardens, really?
On the positive side:
• Lots of flowers. From early season to late, things are blooming. Plants are left standing well into winter, providing seed and shelter.
• Little or no use of pesticides.
• Native plants are often included, though there is no particular emphasis on them.
On the negative side:
• Maintenance involves cutting everything to the ground in late winter. This destroys the winter homes of cavity-nesting bees that use the stems. At the Lurie garden in Chicago, this problem was recognized and steps were taken to leave some stems standing.
• Lack of layering. The iconic Oudolf garden is composed almost entirely of herbaceous perennials, with trees and large shrubs lacking. This limits the provision of food and habitat for a variety of creatures.
I believe pollinators could be better supported by Oudolf-style gardens with three simple changes.
• Keep mowed areas to a minimum. Group plants with good winter nesting stems, and leave them standing until they are covered by new growth.
• Include and group small groups of larger plants such as suitable small trees and shrubs.
• Prioritize native plants where possible.
If you would like to know more about Piet Oudolf’s gardens, plant choices, and design process, here are some reference materials. And if you get the chance, watch the film “Five Seasons: The Gardens of Piet Oudolf”.
Dream Plants for the Natural Garden by Henk Gerritsen and Piet Oudolf, Timber Press 2000
Essentially a catalog (although not all plants are pictured) of plants that Oudolf has culled to be “reliable plants that, over the years, can be maintained in an average garden without too much in the way of artificial props and bolstering”. Many of them “look good dead”, too. These are the plants he uses in his designs. They are divided into categories of Tough Perennials (the longest section by far), Playful Biennials and Annuals, Troublesome Invasive Plants, and Troublesome Capricious Plants – hardly the usual categories!
If you are an experienced gardener and want an invaluable reference for plants that will enhance your natural garden without requiring loads of work, this book is for you.
Planting Design: Gardens in Time and Space by Piet Oudolf and Noel Kingsbury, Timber Press 2005
On the other hand, if you are not an experienced gardener, this book might be a better place to start. It is a thrifty introduction to the concepts of how gardens fit into nature, and vice versa, and how plants can be used through space – and time! – to create the desired outcomes. There are many lists of plants for specific purposes, such as Small Trees to combine with perennials, and Biennials for self-sowing, and a short but useful section on how to prepare for, implement, and maintain a planting of this sort.
Planting: A New Perspective by Piet Oudolf and Noel Kingsbury, Timber Press 2013
This book builds on the previous two, offering a detailed look at the techniques and philosophy Oudolf uses to design his gardens, as well as specific ways in which he uses plants in them. A season-by-season guide dissects various effects and combinations, and a chart towards the end concisely organizes many of the plants used. One of the most interesting concepts is that of matrix planting.
For more detail on the creation of specific gardens by Piet Oudolf, there are also books on Hummelo, the High Line, and Durslade Farm.
The Self-Sustaining Garden by Peter Thompson, Timber Press 2007
In this book matrix planting is presented in great detail. This is an effective and efficient way of designing intermingled plantings without having to specify the location of each and every plant. The matrix (often grasses) may be made up of several plant species, and serves as a stage for other, showier compatible plants embedded in it.
Dramatic Effects with Architectural Plants by Noel Kingsbury, Overlook Press, 1997
Oudolf’s chief writing partner has produced many noteworthy books himself. As the title describes, this book focuses on plants with strong and dramatic architecture. Having some of these in the mix is a key technique that makes Oudolf’s designs work.
Naturalistic Planting Design by Nigel Dunnett, filbert press 2019
With a foreword by, who else, Piet Oudolf, this is one of the most recent entries in the category of books focusing on natural or naturalistic design. It’s a dense book with at least as much text as photography, covering garden lore from historic, through contemporary, and looking to the future. Basic design principles, as they pertain to a naturalistic design, are also presented, along with a series of case studies illustrated by seasonal photos.
Gardening with Native Plants of the Pacific Northwest by Arthur Kruckeberg and Linda Chalker-Scott, University of Washington Press, 2019.
And finally, if you want to use PNW native plants to achieve Oudolf-like effects in your garden, this recent book is an accessible, thorough, well-illustrated guide to those plants. You will find it easy to browse through for plants that have the look you want. Symbols by each photo give a hint as to each plant’s cultural requirements.
The blog Gardenista has several lovely entries on aspects of Oudolf’s designs. https://www.gardenista.com/posts/?t=oudolf#search
Piet talks about current projects in this recent interview: https://www.hauserwirth.com/ursula/29413-attached-world-piet-oudolf-garden-life
If you want LOTS of pictures to look at, try Piet Oudolf’s Flickr photostream, https://www.flickr.com/photos/10470961@N03/
Or his own website https://oudolf.com/
I’m pleased to present the work of my very first field season as a master’s student here at OSU. My project centers around presumptive sterile cultivars of Buddleja, or butterfly bush. Over the next few years, I will be studying how breeding for sterility affects pollinator attraction, pollinator nutrition, and if this breeding is truly effective in slowing the invasiveness of this particular plant. The hope is that this research will be able to serve as a framework for assessing putative sterile varieties of other potentially economically lucrative, but invasive, ornamentals.
Buddleja davidii was designated as a B-list noxious weed in 2004, and was placed in quarantine in conjunction with this designation. Since then, the ODA (Oregon Department of Agriculture) has begun to allow sale of B. davidii cultivars that display a 98% reduction in fertility in comparison to fully fertile ‘old school’ cultivars such as ‘Black Knight’ or ‘Nanho Blue’. At the moment, 14 cultivars of Buddleja davidii are legal to sell, propagate, transport or import in Oregon though no science has been conducted to assess how a reduction in fertility actually translates to reduced weediness.
The other questions I am researching are how pollinators behave around these new, ‘sterile’ cultivars in comparison to how they interact with fertile ones, and what kind of nutrition pollinators can obtain from sterile varieties. These are ever more important questions as we continue to put pollinator health at the forefront of plant selection decisions. To that end the team has been conducting timed pollinator counts through the summer in the test plot.
The test plot is located at Lewis-Brown Horticulture Farm, in the beautiful countryside surrounding Corvallis, Oregon. There, we have randomly allocated six to nine replicant plantings of six fertile cultivars and 28 putative sterile cultivars. Working in this gorgeously fragranced field (seriously-think notes of honey, spice, and fruit) has been a true delight all summer. Cultivars of Buddleja run the gambit in terms of color, plant habit, and floriferousness. There is everything from Buddleja ‘Purple Haze’, a prostrate variety with blue-violet flowers, to my personal favorite, Buddleja x weyeriana ‘Honeycomb’, an absolutely uprightly enormous variety with unique yellow blooms.
Once a week, I go to the field and determine which of the 204 plants are at maximum flower. These plants are slated for our weekly pollinator counts. To conduct a pollinator count, we simply set a timer for 5 minutes and watch the plant for visitors. These visitors are identified to morpho-type in the field (i.e. Honeybee, Bumblebee, Syrphid fly, Butterfly…). Here are the full counts for this season:
You may notice that there are less than 34 cultivars on this graphic! That is because we are in possession of several cultivars that have yet to be released to the general public, so unfortunately, I cannot share them here with you today. It does seem clear, for this season at least, that honeybees are the most prevalent visitor of butterfly bush. Though we can’t draw conclusions from this season’s data alone, we hope that with a few more seasons of data we will be able to identify patterns of attraction and biodiversity. Until then I will be back in classes and working on other aspects of my research-looking forward, of course, to next field season.
Our colleague, Brooke Edmunds, was kind enough to shoot and edit this short video on two of our current lab projects: Jen Hayes’ study of native plants and nativars and Tyler Spofford’s study of the economic costs and benefits of growing vegetables in bucket gardens.
As we near the end of our 2020 field season, stay tuned for research updates.
Five Scientific Studies that Changed the Way I Think About Gardens: Part 2, Putting a Price on Nature
This is the second is a series of articles that I am writing for the Hardy Plant Society of Oregon Quarterly Magazine. I extend my thanks to the HPSO editorial team for improvements to my narrative.
Humans benefit from the natural world in many ways. These benefits include the products (such as food, fiber, or timber) that we can harvest from nature, or the processes (such as pollination, biological control, or nutrient cycling) that make earth such a nice place to live. Whether people recognize the importance of these so-called “ecosystem services” to our health and well-being varies considerably as a function of education, past experiences with nature, and other socio-economic factors. In fact, some people find abundant ecosystem disservices in nature. For example, some people view natural areas as dangerous places that should be avoided.
In an increasingly urbanized world, where many people lack meaningful interaction with the natural world, how can we help ensure that the importance of nature is recognized and valued? As Robert Michael Pyle wrote in his book The Thunder Tree: Lessons from an Urban Wildland (1998: Oregon State University Press), “What is the extinction of a condor to a child who has never seen a wren?”
One approach to helping society value the natural world is to put a dollar value on it, and that’s just what Robert Costanza and 12 colleagues did over the course of a five-day workshop hosted by the National Center for Ecological Analysis and Synthesis in 1996. A few months later, they published the second global accounting of the monetary value of the ecosystem goods and services of our planet1.
The authors found over 100 studies that valued one or more ecosystem services. They standardized the dollar value of each ecosystem service as the 1995 dollar value per hectare. They noted the location of each study and categorized the biome where the study occurred. They also generated novel estimates of the dollar value of various ecosystem services in various biomes by constructing what were essentially supply and demand curves. With these curves, they mathematically asked questions such as “How much more valuable would pollinators be, if they were endangered?” In this way, they were able to mathematically manipulate supply and demand curves and estimate what is known as the “marginal value” of each ecosystem service. In short, they used a lot of math. On a global map, they measured the area taken up by each biome. They multiplied the dollar value of each ecosystem service per unit area by the area taken up by each biome and developed a global map of sum-total value of ecosystem services.
The authors estimated that the value of the earth’s ecosystem services averaged $33 trillion dollars per year (1995 dollar value), which was 1.8 times the global gross national product. Nutrient cycling represented the highest valued ecosystem service, at $17 trillion per year. Coastal systems were identified as the most valuable biome, at $12 trillion per year.
Urban and suburban areas were included in the study. What struck me about this paper, however, was that the dollar value of ecosystem services of urban areas was not listed. Instead, the authors noted that ecosystem services in urban areas (like desert, rocks, tundra) “do not occur or are known to be negligible.”
When I read this paper as a young Ph.D. student in 1997, I was incensed. My family grew food and raised chickens and rabbits in the backyard of our Baltimore rowhouse (ecosystem service = food). As a child, I captured water striders, turtles, and tadpoles from urban streams (ecosystem service = habitat). As an undergraduate, I loved exploring the urban forests of Patapsco Valley State Park for exercise and stress management (ecosystem service = recreation). Did urban areas really deserve a zero? This paper made me want to study the ecosystem services of cities, just to prove the authors wrong!
In 2002 I started to study the ecology of urban areas, as an assistant professor of biology at Fordham University in New York City. I collaborated with doctoral student Kevin Matteson to study the value of urban gardens as wildlife habitat and pollinator conservatories. We found that 18 small gardens dotting one of the most urbanized landscapes on earth were used by a diversity of insects, including 24 species of butterfly and 54 species of bee. At this same time, others were also documenting the ecosystem services of urban areas. For example, The New School’s Timon McPhearson estimated that raised bed gardens in New York City annually helped to retain and manage 12 million gallons of stormwater from flooding city streets. Karin Burghardt, as a University of Delaware undergraduate studying with Doug Tallamy, showed how plant choices can increase bird abundance and diversity in suburban gardens in Pennsylvania.
In fact, the early 2000s were a heyday for urban ecology research, due in large part to National Science Foundation funding of urban long-term ecological research efforts in Phoenix, Arizona, and Baltimore, Maryland. Whereas less than one-half of one percent of all papers published in nine leading ecological journals between 1995 and 2000 focused on urban systems or urban species (Collins et al. 2000), by 2016 over 1,000 articles, books, and book chapters have been published; and over 130 students have been trained in urban ecology by the Phoenix and Baltimore programs, alone (McPhearson et al. 2016). Despite these advances, the field of urban ecology is still relatively young, and much remains to be discovered.
In 2014, Costanza and colleagues published a new paper, with an updated estimate for the value of our globe’s ecosystem services.2 They estimated that natural systems annually provided $125 trillion (2011 US$ value) in ecosystem services to humanity. At least part of this increase is due to improved documentation of the portfolio of ecosystem services provided by different biomes (see table). And this time, ecosystem services provided by urban areas were valued at $2.3 trillion dollars, or $2.9 trillion in inflation-adjusted dollars for 2020.
”Hmph,” I thought. “At least it’s a start.”
1Robert Costanza et al. (1997): “The value of the world’s ecosystem services and natural capital.” Nature 387: 253-260.
2Costanza (2014): “Changes in the global value of ecosystem services.” Global Environmental Change 26: 152-158.
Table 1. The Value And Ecosystem Services Provided By Various Biomes On Earth. All dollar values have been inflation adjusted to 2020 dollar values, and are reported as TRILLIONS of dollars. Red Text: Identified as a service in Costanza et al., 1997, but not 2014; Green Text: Identified as a service in Costanza et al., 2014, but not 1997; Black Text: identified as a service across both papers.
|Biome||Value from 1997 Paper||Value from 2014 Paper||Ecosystem Services|
|Open Ocean||$14.8||$27.9||Gas regulation, Cultural, Climate regulation, Genetic resources, Recreation, Nutrient cycling, Biocontrol, Food|
|Coastal||$22.1||$35.3||Climate regulation, Erosion control, Genetic resources, Disturbance regulation, Nutrient cycling, Biocontrol, Waste treatment, Habitat, Food, Raw materials, Recreation, Cultural|
|Forest||$8.3||$20.7||Gas regulation, Pollination, Habitat, Climate regulation, Disturbance regulation, Water regulation, Water supply, Erosion control, Soil formation, Nutrient cycling, Waste treatment, Biocontrol, Food, Raw materials, Genetic resources, Recreation, Cultural|
|Grassland||$1.5||$23.5||Climate regulation, Water supply, Habitat, Raw materials, Genetic resources, Cultural, Gas regulation, Water regulation, Erosion control, Soil formation, Waste treatment, Pollination, Biocontrol, Food, Recreation|
|Wetlands||$8.5||$33.65||Gas regulation, Climate regulation, Erosion control, Nutrient cycling, Biocontrol, Genetic resources, Disturbance regulation, Water regulation, Waste treatment, Habitat, Food, Raw materials, Recreation, Cultural|
|Lakes/Rivers||$2.9||$3.1||Water regulation, Water supply, Waste treatment, Food, Recreation|
|Cropland||$0.3||$11.9||Climate regulation, Water supply, Erosion control, Soil formation, Waste treatment, Raw materials, Genetic resources, Recreation, Pollination, Biocontrol, Food,|
|Urban||$0||$2.9||Climate regulation, Water regulation, Recreation|
[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). Experimental Zoogeography of Islands: The Colonization of Empty Islands. Ecology 50: 278-296.
- Costanza et al. (1997). The value of the world’s ecosystem services and natural capital. Nature 387: 253-260.
- Kremen et al. (2002). Crop pollination from native bees at risk from agricultural intensification. PNAS 99: 16812-16816.
- Burghardt et al. 2009. Impact of native plants on bird and butterfly biodiversity in suburban landscapes. Conservation Biology 23:219–224.
- Lowenstein et al. (2014). Humans, bees, and pollination services in the city: The case of Chicago, IL (USA). Biodiversity and Conservation 23: 2857–2874.
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)
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).
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.