Highlights from the Western Society of Weed Science Annual Meeting

Earlier this month, I went to Garden Grove, California to attend the 71st annual meeting of the Western Society of Weed Science. My trip was funded by an Education and Enrichment Award presented by the Pahove Chapter of the Idaho Native Plant Society. It was a great opportunity for a weeds-obsessed plant geek like myself to hang out with a bunch of weed scientists and learn about their latest research. What follows are a few highlights and takeaways from the meeting.

General Session

Apart from opening remarks and news/business-y stuff, the general session featured two invited speakers: soil ecologist Lydia Jennings and historian David Marley. Lydia’s talk was titled “Land Acknowledgement and Indigenous Knowledge in Science.” She started by sharing a website called Native Land, which features an image of the Earth overlayed with known “borders” of indigenous territories. By entering your address, you can see a list of the tribes that historically used the land you now inhabit. It is important for us to consider the history of the land we currently live and work on. Lydia then compared aspects of western science and indigenous science, pointing out ways they differ as well as ways they can be used in tandem. By collaborating with tribal nations, weed scientists can benefit from traditional ecological knowledge. Such knowledge, which has historically gone largely unrecognized in the scientific community, should receive more attention and acknowledgement.

David Marley was the comic relief. Well-versed in the history of Disneyland, he humorously presented a series of stories involving its creation. Little of what he had to say related to weed science, which he openly admitted along the way; however, one weeds related story stood out. Due to a lack of funds, the early years of Tomorrowland featured few landscape plants. To make up for that, Walt Disney had signs with fake Latin names created for some of the weeds.

Weeds of Range and Natural Areas

I spent the last half of the first day in the “Weeds of Range and Natural Areas” session where I learned about herbicide ballistic technology (i.e. killing plants from a helicopter with a paintball gun loaded with herbicide). This is one of the ways that Miconia calvescens invasions in Hawaii are being addressed. I also learned about research involving plant debris left over after logging. When heavy amounts of debris are left in place, scotch broom (Cytisus scoparius) infestations are thwarted. There was also a talk about controlling escaped garden loosestrife (Lysimachia punctata) populations in the Seattle area, as well as a few talks about efforts to control annual grasses like cheatgrass (Bromus tectorum) in sagebrush steppes. Clearly there are lots of weed issues in natural areas, as that only covers about half the talks.

Basic Biology and Ecology

On the morning of the second day, the “Basic Biology and Ecology” session held a discussion about weeds and climate change. As climate changes, weeds will adapt and find new locations to invade. Perhaps some weeds won’t be as problematic in certain areas, but other species are sure to take their place. Understanding the changes that are afoot and the ways that weeds will respond to them is paramount to successful weed management. This means documenting the traits of every weed species, including variations between and among populations of each species, so that predictions can be made about their behavior. It also means anticipating new weed species and determining ways in which weeds might exploit new conditions.

No doubt there is much to learn in order to adequately manage weeds in a changing climate. An idea brought up during the discussion that I was particularly intrigued by was using citizen scientists to help gather data about weeds. Similar to other organizations that collect phenological data from the public on a variety of species, a website could be set up for citizen scientists to report information about weeds in their area, perhaps something like this project in New Zealand. Of course, there are already a series of apps available in North America for citizen scientists to report invasive species sightings, so it seems this is already happening to some degree.

Teaching and Technology Transfer

A highlight of the afternoon’s “Teaching and Technology Transfer” session was learning about the Wyoming Restoration Challenge hosted by University of Wyoming Extension. This was a three year long contest in which thirteen teams were given a quarter-acre plot dominated by cheatgrass with the challenge to restore the plant community to a more productive and diverse state. Each team developed and carried out their own strategy and in the end were judged on a series of criteria including cheatgrass and other weed control, plant diversity, forage production, education and outreach, and scalability. Preliminary results can be seen here; read more about the challenge here and here.

And so much more…

Because multiple sessions were held simultaneously, I was unable to attend every talk. I also had to leave early on the third day, so I missed those talks as well. However, I did get a chance to sit in on a discussion about an increasingly troubling topic, herbicide-resistant weeds, which included a summary of regional listening sessions that have been taking place in order to bring more attention to the subject and establish a dialog with those most affected by it.

One final highlight was getting to meet up with Heather Olsen and talk to her briefly about her work in updating the Noxious Weed Field Guide for Utah. This work was aided by the Invasive Plant Inventory and Early Detection Prioritization Tool, which is something I hope to explore further.

If you are at all interested in weeds of the western states, the Western Society of Weed Science is a group you should meet. They are fun and friendly people who really know their weeds.

See Also: Highlights from the Alaska Invasive Species Workshop 

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Moving Your Ecosystem Forward – An Arborist’s Application of Ecological Principles in the Urban Landscape

This is a guest post by Jeremiah Sandler.

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Ecosystems are everywhere – interconnected and interdependent systems of biology, climate, ecology, and geography. The inside of your house is an ecosystem with its own micro-climate, life (including but not limited to you), and topography. Everywhere you go, you’re in some kind of ecosystem.

The same is more obviously true about your landscape. In my area of the U.S. (southeast Michigan), forests and wetlands are often removed to build suburbs. Both the appropriate soil and ecologically relevant plants are removed from the site. After construction, these areas are re-planted with genetically inadequate plants in poor soil. The ecosystem is modified at a rate faster than most organisms can adapt. Landscape designs common in the suburbs are inadequate in maintaining biodiversity and healthy, natural ecosystems.

In some lucky areas, there are communities doing their best to maintain a strong and natural forest canopy. Leaving secondary forests relatively untouched during construction should be the standard when developing areas for humans.

Ecosystems evolve and change, and one can argue that human-caused mass deforestation is simply another driver of ecosystem evolution. While this may be true, it is a driver that influences the ecosystem at a much greater magnitude than other factors. It just so happens to be mitigable or avoidable altogether.

What can cause an ecosystem to change?

Let’s use the trees in a natural forest ecosystem as an example. Disturbances in any ecosystem drive biological adaptation and behavioral changes in the organisms within it. Disturbances such as fire, wind events, floods, drought, and pathogens alter the forest canopy. Fire may kill smaller trees and wind events can blow trees over. Such disturbances open the canopy and allow dormant seeds to germinate in the new sunlight, which gives additional genetic material a shot in the world.

Ecological disturbance is vital to plants, animals, and microbes because it keeps their genetic material up-to-date with evolving pathogens and changing environments. Up-to-date trees need less work. They are more prepared for their environment and its diseases, as evidenced by their parents successfully reproducing.

We can’t control all ecological disturbances, but in the urban environment we do our best to avoid major ones. Understandably, right? We aren’t fond of wildfire, nor do we want flooding anywhere near our homes.

Applied ecosystem principles on the job

Oftentimes in large, human constructed landscapes, only upper and middle canopies exist; sub-canopy layers are missing. This is surprisingly common in forest ecosystems, especially in suburban areas. Forests like this are considered to have a closed canopy.

Closed-canopy forests are naturally occurring and are not necessarily bad. The thick shade cast by the upper canopy is very dense and prevents most understory growth. Over time closed-canopy forests will evolve and change – large trees or limbs come down in the wind, flooding occurs, lightning strikes, or diseases are introduced. Whatever the disturbance, the newly opened canopy once again helps move the ecosystem forward.

Disturbance by pruning

A client of ours lives on a beautiful property in a dry-mesic southern forest (a closed-canopy forest). Due to all the trees on the property, this client sought advice from arborists. The client’s smart choice lead us to an important solution.

Various large species of both white and red oaks dominate the overstory and upper emergent layers of the canopy. The trunks of these towering trees are far apart. Below these titan trees are some slightly shorter oaks, an american beech, and a few hickory species residing in the midstory. About 40 feet below are various types of moss, some stunted sedges, violets, forest grasses – a sparse herbaceous understory. Beyond that there were several patient serviceberries here and there, and a single red maple, about 1.5 inches in diameter and 15 feet tall at most.

Allegheny serviceberry (Amelanchier laevis) – via wikimedia commons

The area has been undisturbed for a long time (it doesn’t even get mowed), and with the presence of oak wilt in southeast Michigan, we steered away from planting anywhere in the root zone, as it poses a risk for oak wilt infection. Sure, we could plant an over-designed landscape to be manicured, but we had other ideas in mind.

Direct application with two solutions

We asked the client how long ago the red maple and serviceberries volunteered themselves into their landscape. Together we traced the germination back to a wind event that knocked a large limb down years ago. The red maple and serviceberries popped up as a result of new sunlight, yet according to the client, these plants hadn’t grown much in height during the last decade or so. Why might this be? A mature plant can close holes in the canopy faster than lower story plants can, so they no longer receive as much light as they once had.

The next time a limb falls, the maple and serviceberries will have another explosive growth spurt. There are also other dormant seeds to germinate every time a disturbance like that occurs. This is an example of another natural phenomenon called forest succession. It is another way forest ecosystems change.

Planting foreign species in place of the native ones takes away important food sources and habitat for surrounding wildlife. So rather than planting cultivar clones and ecologically useless plants – plants that don’t support other lifeforms – into the existing ecosystem, we proposed we could either do strategic crown thinning or just wait for mother nature to do it for them.

Course of action

My associates and I operate on a “less is more” approach. Not touching this ecosystem is our alternative to modifying the canopy. Like a human patient undergoing surgery, cutting open any organism exposes it to infection. In time, either a natural disturbance will come through to modify the canopy, or the trees will naturally shed lower limbs on their own – a process called cladoptosis.

Strategic branch removal will open up the canopy, allowing more sunlight to the ground below, while keeping the trees looking true to their natural form. The climbing team would be using a type of pruning called refracturing. The openings will simulate a wind event disturbance. As a result, the plants that germinate will be the most competitive, hardy, resistant, and genetically up-to-date plants. This truly is “right plant, right place,” provided no invasive buckthorns pop up.

If the customer does want to go forward with disturbance-by-pruning, the proposal is to open the canopy during winter, as most of the canopy are oak trees. The risk of infecting these trees is reduced significantly by pruning in the winter when the vectors for oak wilt are dormant.

The canopy holes would be placed where the homeowner wants more trees. One benefit of pruning the trees is that disturbance is controlled, rather than a wind disturbance causing a chaotic breakage into the house, for example.

Observation would begin early the following spring. We will watch for germination; it’s expected that the plants that do germinate won’t survive the competition.

What’s important about any of this?

The arborist-homeowner relationship highlighted above is an exemplar of proper arboriculture. We offered expertise along with our services. The exchange saved the homeowner hundreds of upfront costs from the installation of a landscape, as well as future maintenance costs.

Assuming it isn’t under human-induced stress, no forest needs human intervention. In this project, we would want to see natural phenomena form the landscape in this client’s yard. It is our preference to leave the current closed-canopy forest alone.

The benefits of using naturally occurring trees are plentiful. In general, up-to-date trees are more prepared for your ecosystem and support the wildlife that co-evolved with them. An ever-increasingly displaced wildlife population will happily occupy new habitat; they’re here too, after all.

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Jeremiah Sandler lives in southeast Michigan, has a degree in horticultural sciences, and is an ISA certified arborist. Follow him on Instagram: @jeremiahsandler

Lettuce Gone Wild, part two

The lettuce we eat is a close relative to the lettuce we weed out of our gardens. Last week we discussed the potential that wild relatives may have for improving cultivated lettuce. But if wild lettuce can be crossed with cultivated lettuce to create new cultivars, can cultivated lettuce cross with wild lettuce to make it more weedy?

Because so many of our crops are closely related to some of the weeds found along with them or the plants growing in nearby natural areas, the creation of crop-wild hybrids has long been a concern. This concern is heightened in the age of transgenic crops (also known as GMOs), for fear that hybrids between weeds and such crops could create super weeds – fast spreading or highly adapted weeds resistant to traditional control methods such as certain herbicides. To reduce this risk, extensive research is necessary before such crops are released for commercial use.

flowers of prickly lettuce (Lactuca serriola)

There are no commercially available, genetically modified varieties of cultivated lettuce, so this is not a concern when it comes to crop-wild hybrids; however, due to how prevalent weedy species like prickly lettuce (Lactuca serriola) are, hybridization with cultivated lettuce is still a concern. So, it is important to understand what the consequences might be when hybridization occurs.

In a paper published in Journal of Applied Ecology in 2005, Hooftman et al. examined a group of second-generation hybrids (L. sativa x L. serriola), and found that the hybrids behaved and appeared very similarly to non-hybrid prickly lettuce. They also found that the seeds produced by the hybrids had a significantly higher germination rate than non-hybrid plants. This is an example of hybrid vigor. Thus, “if hybridization does occur, this could lead to better performing and thus potentially more invasive (hybrid) genotypes.” However, the authors cautioned that “better performing genotypes do not automatically result in higher invasiveness,” and that much depends on the conditions they are found in, the level of human disturbance, etc.

Another thing to consider is that hybrids are not stable. In an article published in Nature Reviews Genetics in 2003, Stewart et al. adress the “misunderstanding that can arise through the confusion of hybridization and … introgression.” It is wrong to assume that hybrids between crops and wild relatives will automatically lead to super weeds. For this to occur, repeated crosses with parental lines (also known as backcrossing) must occur, and “backcross generations to the wild relative must progress to the point at which the transgene [or other gene(s) in question] is incorporated into the genome of the wild relative.” That is what is meant by “introgression.” This may happen quickly or over many generations or it may never happen at all. Each case is different.

prickly leaf of prickly lettuce (Lactuca serriola)

In a paper published in Journal of Applied Ecology in 2007, Hooftman et al. observe the breakdown of crop-wild lettuce hybrids. They note that “fitness surplus through [hybrid vigor] will often be reduced over few generations,” which is what was seen in the hybrids they observed. One possible reason why this occurs is that lettuce is predominantly a self-crossing species; outcrossing is rare, occurring 1 – 5% of the time thanks to pollinating insects. But that doesn’t mean that a stable, aggressive genotype could never develop. Again, much depends on environmental conditions, as well as rates of outcrossing and other factors relating to population dynamics.

A significant expansion of prickly lettuce across parts of Europe led some to hypothesize that crop-wild hybrids were partly to blame. In a paper published in Molecular Ecology in 2012 Uwimana et al. ran population genetic analyses on extensive data sets to determine the role that hybridization had in the expansion. They concluded that, at a level of only 7% in wild habitats, crop-wild hybrids were not having a significant impact. They observed greater fitness in the hybrids, as has been observed in other studies (including the one above), but they acknowledged the instability of hybrids, especially in self-pollinating annuals like lettuce.

seed head of prickly lettuce (Lactuca serriola)

It is more likely that the expansion of prickly lettuce in Europe is due to “the expansion of favorable habitat as a result of climate warming and anthropogenic habitat disturbance and to seed dispersal because of transportation of goods.” Uwimana et al. did warn, however, that “the occurrence of 7% crop-wild hybrids among natural L. serriola populations is relatively high [for a predominantly self-pollinating species] and reveals a potential [for] transgene movement from crop to wild relatives [in] self-pollinating crops.”

Lettuce Gone Wild, part one

Lettuce, domesticated about six thousand years ago in a region referred to as the Fertile Crescent, bears little resemblance to its wild ancestors. Hundreds of years of cultivation and artificial selection eliminated spines from the leaves, reduced the latex content and bitter flavor, shortened stem internodes for a more compact, leafy plant, and increased seed size, among several other things. The resulting plant even has a different name, Lactuca sativa (in Latin, sativa means cultivated). However, cultivated lettuce remains closely related to its progenitors, with whom it can cross to produce wild-domestic hybrids. For this reason, there is great interest in the wild relatives of lettuce and the beneficial traits they offer.

image credit: wikimedia commons

Crop wild relatives are a hot topic these days. That’s because feeding a growing population in an increasingly globalized world with the threat of climate change looming requires creative strategies. Utilizing wild relatives of crops in breeding programs is a potential way to improve yields and address issues like pests and diseases, drought, and climate change. While this isn’t necessarily a new strategy, it is increasingly important as the loss of biodiversity around the globe threatens many crop wild relatives. Securing them now is imperative.

There are about 100 species in the genus Lactuca. Most of them are found in Asia and Africa, with the greatest diversity distributed across Southwest Asia and the Mediterranean Basin. The genus consists of annual, biennial, and perennial species, a few of which are shrubs or vines. Prickly lettuce (L. serriola), willowleaf lettuce (L. saligna), and bitter lettuce (L. virosa) are weedy species with a wide distribution outside of their native range. Prickly lettuce is particularly common in North America, occurring in the diverse habitats of urban areas, natural areas, and agricultural fields. It is also the species considered to be the main ancestor of today’s cultivated lettuce.

In a paper published in European Journal of Plant Pathology in 2014. Lebeda et al. discuss using wild relatives in lettuce breeding and list some of the known cultivars derived from crosses with wild species. They write that in the last thirty years, “significant progress has been made in germplasm enhancement and the introduction of novel traits in cultivated lettuce.” Traditionally, Lactuca serriola has been the primary source for novel traits, but breeders are increasingly looking to other species of wild lettuce.

bitter lettuce (Lactuca virosa) – image credit: wikimedia commons

Resistance to disease is one of the main aims of lettuce breeders. Resistance genes can be found among populations of cultivated lettuce, but as “extensive screening” for such genes leads to “diminishing returns in terms of new resistance,” breeders look to wild lettuce species as “sources of new beneficial alleles.” The problem is that there are large gaps in our knowledge when it comes to wild lettuce species and their interactions with pests and pathogens. Finding the genes we are looking for will require “screening large collections of well defined wild Lactuca germplasm.” But first we must develop such collections.

In a separate paper (published in Euphytica in 2009), Lebeda et al. discuss just how large the gaps in our understanding of the genus Lactuca are. Beginning with our present collections they found “serious taxonomic discrepancies” as well as significant redundancy and unnecessary duplicates in and among gene banks. They also pointed out that “over 90% of wild collections are represented by only three species” [the three weedy species named above], and they urged gene banks to “rapidly [acquire] lettuce progenitors and wild relatives from the probable center of origin of lettuce and from those areas with the highest genetic diversity of Lactuca species” as their potential for improving cultivated lettuce is too important to neglect.

Lactuca is a highly variable genus; species can differ substantially in their growth and phenology from individual to individual. Lebeda et al. write, “developmental stages of plants, as influenced through selective processes under the eco-geographic conditions where they evolved, can persist when plants are cultivated under common environmental conditions and may be fixed genetically.” For this reason it is important to collect numerous individuals of each species from across their entire range in order to obtain the broadest possible suite of traits to select from.

One such trait is root development and the related ability to access water and nutrients and tolerate drought. Through selection, cultivated lettuce has become a very shallow-rooted plant, reliant on regular irrigation and fertilizer applications. In an issue of Theoretical and Applied Genetics published in 2000, Johnson et al. demonstrate the potential that Lactuca serriola, with its deep taproot and ability to tolerate drought, has for developing lettuce cultivars that are more drought tolerant and more efficient at using soil nutrients.

willowleaf lettuce (Lactuca saligna) – image credit: wikimedia commons

Clearly we have long way to go in developing improved lettuce cultivars using wild relatives, but the potential is there. As Lebeda et al. write in the European Journal of Plant Pathology, “Lettuce is one of the main horticultural crops where a strategy of wild related germplasm exploitation and utilization in breeding programs is most commonly used with very high practical impact.”

Coming Up in Part Two: Can cultivated lettuce cross with wild lettuce to create super weeds?

Book Review: Good Weed Bad Weed

Distinguishing weeds from desirable plants is a skill that takes years of experience. If you’re not an avid gardener or a practiced naturalist, the distinction between the two groups may be blurry. There are weed identification guides aplenty, but even those aren’t always the most user-friendly and can often leave a person with more questions than answers. One of those questions may be, “Why is this plant considered a weed and not that one?” Through her book, Good Weed Bad Weed, Nancy Gift attempts to answer that question, offering much needed nuance to a regularly vilified group of plants.

In the introduction, Gift acknowledges that the term “good weed” sounds like an oxymoron. A weed, by definition, is an unwanted plant, an interloper and a troublemaker, without value or merit. What could be good about that? Gift, on the other hand, asserts that “it is a weakness of the English language that weeds are universally unwanted.” We need a word that describes plants that may have weedy characteristics but some redeeming qualities as well. For now, Gift uses “volunteer” – “a plant that comes up without being planted or encouraged” – suspending judgement until its performance can be fairly assessed.

Good Weed Bad Weed is a weed identification guide designed for beginners, for those wondering if their yard is “infested or blessed.” It is specifically concerned with weeds commonly found in lawns and garden beds, and “not meant to apply to farm fields or any other landscape.” It sets itself apart from other identification guides by organizing weeds into three categories: Bad Weeds, Not-So-Bad Weeds, and Good Weeds. Each plant profile includes a description, notes about benefits as well as problems, and some recommendations for control. Assigning good/bad designations to these plants is bound to cause some heated debate and outright disagreement, and Gift acknowledges that; however, we all have our “unique judgement” about the plants we encounter in our landscapes, so as “weed-lovers-in-training,” Gift hopes that we can “make a few new friends in the plant kingdom” and, perhaps, a few less enemies.

For the ten plants that make the Bad Weeds list, the reasoning is pretty clear. They are highly competitive and difficult to control [foxtail (Setaria spp.), garlic mustard (Alliaria petiolata), and Canada thistle (Cirsium arvense)], they are poisonous to humans despite being beneficial to wildlife [poison ivy (Toxicodendron radicans ) and poison hemlock (Conium maculatum)], they are known allergens and otherwise unattractive [common ragweed (Ambrosia artemisiifolia)], or, like Japanese knotweed (Fallopia japonica), they are on the list of top 100 worst invasive species.

The other two categories are where more personal judgement comes into play. The twelve plants considered Not-So-Bad Weeds are said to have “admirable qualities despite some negatives.” Prostrate knotweed (Polygonum aviculare) provides excellent erosion control. Orange hawkweed (Hieracium aurantiacum), bull thistle (Cirsium vulgare), and musk thistle (Carduus nutans) are quite beautiful and highly beneficial to pollinators and other wildlife. Nutsedge (Cyperus spp.) is edible and easy to keep in check if you stay on top of it. Bindweeds (Convolvulus arvensis and Calystegia sepium) avoid the Bad Weeds list because their flowers are so appealing. Aesthetics really matter to Gift, which is made clear with the entry for common fleabane (Erigeron philadelphicus), which could have made the Good Weeds list were it not for its disappointing and forgettable floral display.

field bindweed (Convolvulus arvensis)

As for the Goods Weeds list, more plant species find themselves in this category than the other two categories combined. That being said, those who have strong, negative opinions about weeds should probably avoid this section of the book, lest they experience an unsafe rise in blood pressure upon reading it. But be advised that making the Good Weeds list doesn’t mean that there are no negatives associated with having these plants in your yard; it’s just that the positive qualities tend to overshadow the negatives.

Positive qualities include edible, medicinal, low growing, slow growing, easy to control, beneficial to wildlife, not a bully, hardly noticeable, uncommon, and soil building. Certain weeds are desirable in lawns because they are soft to walk on, like ground ivy (Glechoma hederacea), yarrow (Achillea millefolium), and moss. Other weeds, like self-heal (Prunella vulgaris), stay green year-round and don’t leave ugly, brown patches when they die or go dormant. Still others, like bird’s-foot trefoil (Lotus corniculatus), black medic (Medicago lupulina), and clovers (Trifolium spp.) fix nitrogen, providing free fertilizer. Gift notes that, for those who keep chickens, weeds like common sorrel (Rumex acetosa) and cuckooflower (Cardamine pratensis) are great chicken feed.

Speaking of eating weeds, Gift concludes her book with four pages of recipes. The “Weedy Foxtail Tabouli” is particularly intriguing to me. Reading this book definitely requires an open mind, and some people simply won’t agree that any weed should ever be called “good.” Gift seems okay with that. She calls herself a “heretical weed scientist,” insisting that “a weed is in the eye of the beholder.” As “beholders,” I hope we can all be a little more like Nancy Gift.

A weedy lawn (photo credit: wikimedia commons)

More Book Reviews on Awkward Botany:

What Bugs Can Tell Us About the Value of Vacant Urban Land

Back in October 2017, we discussed some potential benefits of spontaneous urban vegetation (commonly referred to as weeds) and the abandoned or undeveloped urban spaces they inhabit. There is much to learn about the role these plant communities play in the ecology of cities and their contribution to vital ecosystem services. In a review published in the December 2013 issue of Environmental Entomology, researchers from Ohio State University discuss how studying arthropod communities on vacant lands can help “advance our ecological understanding of the functional role” these habitats may have in our cities.

Arthropods were selected as the subject of study because their “populations respond quickly to changes in the urban environment, making them key indicators of how land use change influences biodiversity.” Urban-dwelling arthropods “are diverse and occupy multiple trophic levels” and are “easy to sample.” Additionally, many of the services that vacant, unmanaged land offers are “arthropod-mediated,” including “pollination, decomposition, nutrient cycling, and biological pest control.”

photo credit: wikimedia commons

Vacant land was selected as the study site because “understanding [its] ecological value is important to the advancement of urban ecology and ecosystem management,” and even though such areas are often overlooked in conservation planning, studies have shown that they “have the potential to be valuable reservoirs of biodiversity.” In order to determine just how valuable vacant land might be, more research is needed comparing these spaces to other parts of the city. In addition, vacant lots are generally ephemeral and in due time may be developed. Whether this means that a building or parking lot takes their place or that they are converted into a park, garden, or urban farm, it is important to understand what these land use changes mean for urban biodiversity and ecological functions.

Urbanization is often measured by comparing the amount of built area to the remaining green space. Where there is a high degree of urbanization, there is a low degree of green space comparatively. As urbanization increases, so does habitat fragmentation, pollution, and the urban heat island. In the meantime, biodiversity suffers. The authors cite a number of studies demonstrating that increased urbanization negatively impacted beneficial insect populations. For example, a study in the United Kingdom found that bumblebee diversity in gardens “decreased with increasing urbanization of the surrounding landscapes.” Similar results were found in a study we wrote about.

photo credit: wikimedia commons

Together with remnant natural areas, parks, private and public gardens, greenways, and commercial landscapes, vacant lots are part of a mosaic of urban green space. Each of these areas “experience different levels of disturbance and harbor varying plant species,” which, in turn, “influence arthropods and the services they can supply within and between patches.” Because vacant lots can remain undisturbed and virtually unmanaged for long periods of time, they help provide a contrast to the homogeneous, highly managed green spaces that are common in cities. By their very nature, they “have the potential to aid conservation and enhance green space quality and connectivity within city centers.”

It’s one thing to recognize the value of vacant lots; it’s another thing to change the negative perception of them. Aesthetics are important, and to many people vacant lots are an eyesore and a sign of neglect. Some management may be necessary in order to retain their important ecological value and assuage the feelings of the public. The authors present a number of ways that vacant lots can be and have been managed in order to achieve this goal. They also consider how certain management strategies (mowing, removing and/or introducing plant species) can impact arthropod populations for better or worse. Yet, where vacant lots are left alone and allowed to advance in the stages of ecological succession, changes in arthropod diversity and ecosystem function also occur. For this reason, “the regional species pool of a city requires a mosaic of all successional stages of vacant land patches.”

photo credit: wikimedia commons

Finally, the authors discuss the conversion of vacant land to urban agriculture. Even this land use change can have dramatic effects on the arthropod community. For example, undisturbed or unmanaged areas are a habitat requirement for cavity and soil nesting bees, and regular disturbance associated with farming may interfere with this. Also where pesticides are used or plant diversity is minimized, the arthropod community will be affected.

Thus, “the study of vacant land ecology necessitates a transdisciplinary approach” in order to determine how changes in vacant, urban land “will affect diverse ecosystem functions and services.” A variety of management strategies are required, and land managers must “determine the most appropriate strategies for improving the sustainability of cities from a connected landscape perspective.” It is clear that vacant lots have a role to play. The extent of their role and our approaches to managing them requires careful investigation.

One thing is certain – for biodiversity’s sake – don’t pave over vacant lots to put up parking lots.

When Urban Pollinator Gardens Meet Native Plant Communities

Public concern about the state of bees and other pollinating insects has led to increased interest in pollinator gardens. Planting a pollinator garden is often promoted as an excellent way for the average person to help protect pollinators. And it is! However, as with anything in life, there can be downsides.

In many urban areas, populations of native plants remain on undeveloped or abandoned land, in parks or reserves, or simply as part of the developed landscape. Urban areas may also share borders with natural areas, the edges of which are particularly prone to invasions by non-native plants. Due to human activity and habitat fragmentation, many native plant populations are now threatened. Urban areas are home to the last remaining populations of some of these plants.

Concern for native plant populations in and around urban areas prompted researchers at University of Pittsburgh to review some of the impacts that urban pollinator gardens may have and to develop a “roadmap for research” going forward. Their report was published earlier this year in New Phytologist.

Planting a wildflower seed mix is a simple way to establish a pollinator garden, and such mixes are sold commercially for this purpose. Governmental and non-governmental organizations also issue recommendations for wildflower, pollinator, or meadow seed mixes. With this in mind, the researchers selected 30 seed mixes “targeted for urban settings in the northeastern or mid-Atlantic USA” to determine what species are being recommended for or commonly planted in pollinator gardens in this region. They also developed a “species impact index” to assess “the likelihood a species would impact remnant wild urban plant populations.”

A total of 230 species were represented in the 30 seed mixes. The researchers selected the 45 most common species for evaluation. Most of these species (75%) have generalized pollination systems, suggesting that there is potential for sharing pollinators with remnant native plants. Two-thirds of the species had native ranges that overlapped with the targeted region; however, the remaining one-third originated from Europe or western North America. The native species all had “generalized pollination systems, strong dispersal and colonization ability, and broad environmental tolerances,” all traits that could have “high impacts” either directly or indirectly on remnant native plants. Other species were found to have either high dispersal ability but low chance of survival or low dispersal ability but high chance of survival.

This led the researchers to conclude that “the majority of planted wildflower species have a high potential to interact with native species via pollinators but also have the ability to disperse and survive outside of the garden.” Sharing pollinators is especially likely due to super-generalists like the honeybee, which “utilizes flowers from many habitat types.” Considering this, the researchers outlined “four pollinator-mediated interactions that can affect remnant native plants and their communities,” including how these interactions can be exacerbated when wildflower species escape gardens and invade remnant plant communities.

photo credit: wikimedia commons

The first interaction involves the quantity of pollinator visits. The concern is that native plants may be “outcompeted for pollinators” due to the “dense, high-resource displays” of pollinator gardens. Whether pollinator visits will increase or decrease depends on many things, including the location of the gardens and their proximity to native plant communities. Pollinator sharing between the two has been observed; however, “the consequences of this for effective pollination of natives are not yet understood.”

The second interaction involves the quality of pollinator visits. Because pollinators are shared between native plant communities and pollinator gardens, there is a risk that the pollen from one species will be transferred to another species. High quantities of this “heterospecific pollen” can result in reduced seed production. “Low-quality pollination in terms of heterospecific pollen from wildflower plantings may be especially detrimental for wild remnant species.”

The third interaction involves gene flow between pollinator gardens and native plant communities. Pollen that is transferred from closely related species (or even individuals of the same species but from a different location) can have undesired consequences. In some cases, it can increase genetic variation and help address problems associated with inbreeding depression. In other cases, it can introduce traits that are detrimental to native plant populations, particularly traits that disrupt adaptations that are beneficial to surviving in urban environments, like seed dispersal and flowering time. Whether gene flow between the two groups will be positive or negative is difficult to predict, and “the likelihood of genetic extinction versus genetic rescue will depend on remnant population size, genetic diversity, and degree of urban adaptation relative to the planted wildflowers.”

The fourth interaction involves pathogen transmission via shared pollinators. “Both bacterial and viral pathogens can be transmitted via pollen, and bacterial pathogens can be passed from one pollinator to another.” In this way, pollinators can act as “hubs for pathogen exchange,” which is especially concerning when the diseases being transmitted are ones for which the native plants have not adapted defenses.

photo credit: wikimedia commons

All of these interactions become more direct once wildflowers escape gardens and establish themselves among the native plants. And because the species in wildflower seed mixes are selected for their tolerance of urban conditions, “they may be particularly strong competitors with wild remnant populations,” outcompeting them for space and resources. On the other hand, the authors note that, depending on the species, they may also “provide biotic resistance to more noxious invaders.”

All of these interactions require further investigation. In their conclusion, the authors affirm, “While there is a clear potential for positive effects of urban wildflower plantings on remnant plant biodiversity, there is also a strong likelihood for unintended consequences.” They then suggest future research topics that will help us answer many of these questions. In the meantime, pollinator gardens should not be discouraged, but the plants (and their origins) should be carefully considered. One place to start is with wildflower seed mixes, which can be ‘fine-tuned’ so that they benefit our urban pollinators as well as our remnant native plants. Read more about plant selection for pollinators here.