Introducing the Summer of Weeds

I spent the first five months of this year posting almost exclusively about invasive species. There is still plenty more to say on the topic, and I’m sure I will get back to that. However, it is time now to dive into the topic that I really want to explore. Weeds.

There is definitely crossover between the two topics – many weeds are invasive species – but there are clear distinctions, too. Oftentimes, weeds as a category of plants are unfairly and unjustly lumped under the title “invasive,” but any plant can be a weed at any moment in time if a human says so. That’s the difference. A plant does not have to prove that it is causing any sort of ecological or economic damage to be called a “weed;” it just has to be growing where a human doesn’t want it to. Yet, too quickly a plant “out of place” is cursed at using words like “invasive” or “noxious” regardless of its origin or behavior. I know I’m being overly semantic about this, but it seems unfair (and incorrect) to lump any and all plants that are bothering us for whatever reason into categories that have legal definitions.

If you can’t already tell, I am obsessed with weeds. It’s a topic I have been thinking about fairly consistently for much of my adult life. For one thing, as part of my career I spend a huge portion of my time killing and controlling weeds. I comprehend fully the visceral reaction of seeing a garden overcome by weeds – the vile thoughts one can have towards a group of plants that are soiling what could otherwise be a beautiful landscape – and I know very well the backbreaking work and countless hours that go into removing uninvited plants (cursing the intruders along the way). I get why weeds are a problem, and I understand why they are a subject of so much vitriol. Yet, over the years I have developed a respect – even a love – for weeds (despite the fact that I still must remove them and that removing them continues to be an overwhelming task).

Unwanted plants have been following us around and getting in our way for millenia. Essentially, we are partners in crime. We intentionally and unintentionally bring plants from various parts of the world on our travels, and through disturbance we create conditions where introduced plants can settle in and thrive. Over time, some once beloved plants grow out of favor and transition from desirable to weedy. As our cycles of disturbance continue, we give early successional, opportunistic plant species a chance to perpetuate themselves, guaranteeing that we will keep such “weeds” with us forever. We reap what we sow; even though we generally don’t plant weeds on purpose, other actions ensure that they will be our constant companions.

The importance of weed control goes beyond the aesthetic. In horticulture and agriculture, weeds compete with crops for light, space, water, and nutrients. They also harbor pests and diseases, and their seeds can contaminate crops. In pastures and rangelands, some weeds poison livestock. Certain weeds are harmful to people, too. Other weeds are simply disruptive – getting tangled up in machinery, damaging infrastructure, blocking our vision along roadways, and even giving cyclists flat tires. Apart from all that, even if all weeds did was make our gardens look unsightly, I imagine we would still be pretty angry with them.

I am interested in weeds wherever they are, but the weeds that fascinate me the most are those that thrive in urban environments. Not necessarily the weeds in our yards, but the weeds that have escaped our fences and property lines; the ones in the margins. We see them in abandoned lots, along roadways, near irrigation channels, and in other neglected spaces. They pop up in the cracks of sidewalks, on rooftops, in the middle of decaying buildings, and anywhere else that people haven’t paid attention to in a while. Urban areas have, for the most part, been scraped of their native flora. Introduced species move in to fill that void. As Richard Mabey writes in his book about weeds, these plants “insinuate the idea of wild nature into places otherwise quite shorn of it;” they are “the very essence of wildness.” Novel ecosystems, like those created by urbanization and human development, are with us whether we like it or not. There is a “wildness” to them that is unlike other cultivated and manicured areas maintained by humans. These urban wild places are worth a closer look.

So, what is the Summer of Weeds?

Put simply, it’s an exploration of weeds. Throughout the summer I will be profiling some of the weeds I come across in my daily life. I will include photos, a brief description, and some interesting facts about each species. I will also include quotes about weeds from various sources, as well as videos, links, resources, and whatever else I come across that seems worth sharing. I hope you enjoy it. If you have anything to add along the way – specifically any personal thoughts or stories to share about weeds – please do. You can contact me via the usual ways: in the comment section below, through the Contact page, or on Twitter, Tumblr, Facebook, or Instagram. Happy Summer!

Love and Hate – The Story of Purple Loosestrife

In the early 1800’s, seeds of purple loosestrife found their way to North America. They arrived from Europe several times by various means – accidentally embedded in the ballast of ships, inadvertently tucked in sheep’s wool, and purposely carried in the hands of humans. Native to much of Europe and parts of Asia and commonly found growing in wetlands and other riparian areas, purple loosestrife’s appealing spikes of magenta flowers, sturdy, upright growth habit, and ease of propagation made it a prized ornamental; its abundant nectar made it a favorite of beekeepers.

During its first 150 years or so in North America, purple loosestrife became naturalized in ditches, wet meadows, and the banks of streams, rivers, lakes, and ponds while also enjoying a place in our gardens. Concern about its spread was raised in the first half of the twentieth century, but it wasn’t until the 1980’s after an extensive survey was done and a special report was issued by the U.S. Fish and Wildlife Service that attitudes about purple loosestrife shifted dramatically. At that point, it was no longer a benign invader and welcome garden companion. It was, instead, a biological menace that needed to be destroyed.

Lytrhrum salicaria – commonly known as purple loosestrife, spiked willow-herb, long purples, rainbow weed, etc. – is an herbaceous perennial in the family Lythraceae. It reaches up to two meters tall; has square or angular stems with lance-shaped, stalkless leaves up to ten centimeters long; and ends in dense, towering spikes of pink-purple, 5-7 petaled flowers. The flowers attract a wide variety of pollinating insects – mostly bees – and afterwards produce small capsules full of tiny, red-brown seeds. Charles Darwin thoroughly studied the flowers of purple loosestrife; he was intrigued by the plant for many reasons, including its heterostyly (a topic for another post).

Lythrum salicaria (purple loosestrife) – image credit: wikimedia commons

Purple loosestrife seeds remain viable for up to 20 years and are transported by wind, water, and in mud stuck to the feet of birds. Apart from seeds, populations expand clonally as root crowns grow larger each year and produce increasingly more stems. Broken stem pieces also take root in mud, creating new plants. Purple loosestrife’s ability to form expansive populations in a quick manner, pushing other plants aside and forming what appears to be a dense monoculture, is part of the reason it has earned itself a place among the International Union for Conservation of Nature’s list of 100 World’s Worst Invasive Alien Species.

But is this ranking justified? In a paper published in Biological Invasions in 2010, Claude Lavoie compares news reports about purple loosestrife around the turn of the century with data presented in scientific papers and finds that the reports largely exaggerate the evidence. Purple loosestrife was being accused of all manner of crimes against nature and was being condemned before there was sound evidence to justify such actions.

It began with the U.S. Fish and Wildlife Service’s special report published in 1987. According to Lavoie, “a long list of the impacts of the species on wetland flora and fauna [was] presented,” but the claims were not supported by observational or experimental data – “the impacts [were] only suspected.” Regardless, wetland managers began campaigns against purple loosestrife in order to convince the public that it was a Beautiful Killer. News outlets were quick to spread the word about this “killer” plant. When biological control programs began in the 1990’s, news outlets reported on their success. Little empirical evidence had been published on either topic, and debates about purple loosestrife’s impacts remained unsettled in the scientific community.

The flowers of purple loosestrife (Lythrum salicaria) – photo credit: wikimedia commons

Around this time, five reviews were published examining the evidence against purple loosestrife. Lavoie reports that all but one of them “rely on a relatively high number of sources that have not been published in peer-reviewed journals.” After examining the reviews, Lavoie concludes: “although each review provided valuable information on purple loosestrife, most were somewhat biased and relied on a substantial amount of information that was anecdotal or not screened by reviewers during a formal evaluation process. Only one review was impartial, and this one painted an inconclusive picture of the species.”

Research has continued regarding the impacts of purple loosestrife, and so Lavoie examined 34 studies that were published during the 2000’s in search of conclusive evidence that the plant is as destructive to wetlands and wildlife as has been claimed. Upon examination he concludes that “stating that this plant has ‘large negative impacts’ on wetlands is probably exaggerated.” The most common accusation – that purple loosestrife crowds out native plants and forms a monoculture – “is controversial and has not been observed in nature (with maybe one exception).” Lavoie finds that there is “certainly no evidence that purple loosestrife ‘kills wetlands’ or ‘creates biological deserts,'” and “there are no published studies [in peer-reviewed journals] demonstrating that purple loosestrife has an impact on waterfowl or fishes.” All other negative claims against purple loosestrife “have not been the object of a study,” except for its impact on amphibians, which had at that time only been tested on two species, one “reacting negatively.” Certain claims – such as purple loosestrife’s impact on wetland hydrology – should be studied more in depth “considering the apparent public consensus on the detrimental effects of purple loosestrife” on wetland ecosystems.

Lavoie agrees that it is reasonable to control purple loosestrife when the intention is to reduce additional pressures on an ecosystem that is already highly threatened. However, he warns that “focusing on purple loosestrife instead of on other invasive species or on wetland losses to agriculture or urban sprawl could divert the attention of environmental managers from more urgent protection needs.” There is mounting evidence that purple loosestrife invasions are disturbance-dependent and are “an indicator of anthropogenic disturbances.” In order to protect our wetlands, we must first protect them against undue disturbance. Lavoie supports using the Precautionary Principle when dealing with introduced species; however, he finds the approach “much more valuable for newcomers than for invaders coexisting with native species for more than a century.”

A field of purple loosestrife in Massachusetts – photo credit: wikimedia commons

Purple loosestrife has found its way to nearly every state in America and most of the Canadian provinces. Peter Del Tredici writes in Wild Urban Plants of the Northeast, “Conservationists despise purple loosestrife, despite its beauty, and it is listed as an invasive species in most of the states where it grows.” By listing a plant as a noxious weed, landowners are obligated to remove it. Care must be taken though, as removal of purple loosestrife can result in a secondary invasion by noxious weeds with an even worse track record, such as common reed or reed canary grass. “Hardly a gain from the biodiversity point of view,” quips Lavoie.

Claude Lavoie’s paper and the papers he references are definitely worth reading. It is important that we continue to study purple loosestrife and species like it in order to fully understand the impact that introduced species are having on natural areas, especially since it is unlikely that we will ever completely eliminate them. On that note, I’ll leave you with this passage from The Book of Swamp and Bog by John Eastman:

The situation is easy for environmentalists to deplore. This plant, like few others, stirs our alien prejudice. Our native cattails, for example, are almost as rudely aggressive and competitive in many wetland areas as purple loosestrife. Yet, because cattails obvioulsy ‘belong here,’ they seldom evoke the same outraged feelings against their existence. … With the spread of purple loosestrife, we have new opportunities to witness the phases of an ever-recurring ecological process. We can watch it affect, change, adapt, and refit both its own elements and those of invaded communities into new arrangements of energy efficiency. The point is that we might as well study this process rather than simply deplore it; we have few alternatives.

Field Trip: Chico Hot Springs and Yellowstone National Park

Thanks to an invitation from my girlfriend Sierra and her family, I spent the first weekend in May exploring Yellowstone National Park by way of Chico Hot Springs in Pray, Montana. The weather was perfect, and there were more plants in bloom than I had expected. During our hikes, my eyes were practically glued to the ground looking for both familiar and unfamiliar plant life. Most of the plants in bloom were short and easily overlooked. Many were non-native. Regardless, the amateur botanist in me was thrilled to be able to spend time with each one, whether I was able to identify it or not. I tried to remind myself to look up as often as I was looking down. Both views were remarkable.

On our first day there, we hiked in the hills above Chico Hot Springs. The trail brought us to a place called Trout Pond. There were lots of little plants to see along the way.

Trout Pond (a.k.a. Chico Pond) near Chico Hot Springs in Pray, Montana

mountain bluebells (Mertensia longifolia)

shooting star (Dodecantheon pulchellum)

western stoneseed (Lithospermum ruderale)

western wallflower (Erysimum capitatum)

The next day we drove into Yellowstone. From the north entrance we headed east towards Lamar Valley. Wildlife viewing was plentiful. Elk, bison, bighorn sheep, pronghorn, black bears, red foxes, and even – if you can believe it – Canada geese.

Sierra looks through the binoculars.

Perhaps she was looking for this red-tailed hawk.

Daniel looks at a tiny plant growing in the rocks.

Still not sure what this tiny plant is…

On our third day there, we headed south to see some geysers. We made it to the Norris Geyser Basin and then decided to head east to see the Grand Canyon of the Yellowstone. This was our geology leg of the tour. But that doesn’t mean we didn’t stop to look at a plant or two along the way.

Nuttall’s violet (Viola nuttallii) near the petrified tree in Yellowstone National Park

Wild strawberry (Fragaria sp.) at Norris Geyser Basin in Yellowstone National Park

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Photos of Lamar Valley, red-tailed hawk, Daniel looking at a tiny plant, mystery plant, and Grand Canyon of the Yellowstone were taken by Sierra Laverty. The rest were taken by Daniel Murphy.

Speaking of Sierra, she is the founder and keeper of Awkward Botany’s Facebook page and Instagram account. Please check them out and like, follow, etc. for Awkward Botany extras.

Campaigns Against Invasive Species, part two

Happy American Wetlands Month!

One of the biggest threats to wetland ecosystems is, of course, invasive species. In last week’s post I shared a selection of videos that were produced by a variety of organizations to inform the public about invasive species. Many such videos specifically address invasives in wetlands and waterways. Here are a few of those videos.

Invasive Species of Idaho reminds you to “Clean, Drain, Dry” to avoid transporting aquatic hitchhikers:

Purple loosestrife is a “very wicked plant:”

Commander Ben vs. the Saltcedar Bandits:

Michigan’s Department of Environmental Quality urges hunters not to use Phragmites australis to make duck blinds:

More information about Phragmites by National Geographic:

Texas Parks and Wildlife and the Attack of the Zebra Mussels:

The story of Eurasian milfoil told by students at George Williams College:

Water hyacinth – another “very wicked plant”:

Water hyacinth invasion in Africa:

Attack of the Killer Algae by TED-Ed:

Campaigns Against Invasive Species, part one

I have been posting almost exclusively about invasive species for four months now. If you have made it this far, I salute you. It is neither the most exciting nor the most encouraging topic, but it is the journey I am on (for whatever reason), and I am pleased to have you along.

In the battle against invasive species, citizen awareness and participation is imperative. The public and private sectors can try as they may, but if individual citizens are acting in ways that help introduce or spread invasives, then much of this effort can be for naught. Thus, campaigns to educate the public are regularly launched.

One popular way to spread the word is through video. Often, the goal of these videos is to both educate and entertain. Some achieve this better than others, while some are downright dull or simply baffling. Speculating on the effectiveness of these videos is not the purpose of this post. Rather, I just thought I would take a break from the usual text heavy posts and share a few videos that I found interesting and/or entertaining. If you have a favorite invasive species video, please share it in the comment section below.

Invasive species explained:

Introducing Bob Noxious from Invasive Species of Idaho:

And here is the particularly creepy, Vin Vasive, from USDA APHIS:

Invaders! in British Columbia:

In Namibia, “Cacti must die!”:

Eco Sapien and the story of Japanese knotweed in the UK:

What happened when American minks, brought to Europe for the fur trade, escaped into natural areas?:

Michigan’s Department of Environmental Quality explains how invasive species spread:

Pennsylvania’s Wild Resource Conservation Program teaches kids about invasive species:

MinuteEarth‘s take on invasive species:

Also, check out these five TEDx talks:

Screening for Invasive Plants at Botanical Gardens and Arboreta

As discussed in last week’s post, many of the invasive species that we find in our natural areas were first introduced to North America via the horticulture trade. As awareness of this phenomenon grows, steps are being taken by the horticulture industry to address this issue. The concluding remarks by Sarah Reichard and Peter White in their 2001 article in BioScience describe some recommended actions. One of them involves the leadership role that botanical gardens can play by both stopping the introduction and spread of invasive species and by presenting or promoting public education programs.

Reichard and White offer North Carolina Botanical Garden as an example, citing their “Chapel Hill Challenge,” which urges botanical gardens to “do no harm to plant diversity and natural areas.” Reichard and White also encourage botanical gardens and nurseries to adopt a code of conservation ethics addressing invasive species and other conservation issues. Codes of conduct for invasive species have since been developed for the botanical garden community and are endorsed by the American Public Gardens Association.

 

Botanical gardens that adopt this code have a number of responsibilities, one of which is to “establish an invasive plant assessment procedure,” preferably one that predicts the risks of plant species that are new to the gardens. In other words, botanical gardens are encouraged to screen the plants that are currently in their collections, as well as plants that are being added, to determine whether these plants currently exhibit invasive behavior or have the potential to become invasive. Many botanical gardens now have such programs in place, and while they may not be able to predict all invasions, they are a step in the right direction.

In an article published in Weed Technology (2004), staff members at Chicago Botanic Garden (CBG) describe the process they went through to determine a screening process that would work for them. CBG has an active plant exploration program, collecting plants in Asia, Europe, and other parts of North America. Apart from adding plants to their collection, one of the goals of this program is to find plants with horticulture potential and, through their Ornamental Plant Development department, prepare these plants to be introduced to the nursery industry in the Chicago region. As their concern about invasive species has grown, CBG (guided by a robust Invasive Plant Policy) has expanded and strengthened its screening process.

In order to do this, CBG first evaluated three common weed risk assessment models. The models were modified slightly in order to adapt them to the Chicago region. Forty exotic species (20 known invasives and 20 known non-invasives) were selected for testing. Each invasive was matched with a noninvasive from the same genus, family, or growth form in order to “minimize ‘noise’ associated with phylogenetic differences.” The selected species also included an even distribution of forbs, vines, shrubs, and trees.

Weed risk assessment models are used to quickly determine the potential of a plant species to become invasive by asking a series of questions about the plant’s attributes and life history traits, as well as its native climate and geography. A plant species can be accepted, rejected, or require further evaluation depending on how the questions are answered. For example, if a plant is known to be invasive elsewhere and/or if it displays traits commonly found in other invasive species, it receives a high score and is either rejected or evaluated further. Such models offer a quick and affordable way to weed out incoming invasives; however, they are not likely to spot every potential invasive species, and they may also lead to the rejection of species that ultimately would not have become invasive.

After testing the three models, CBG settled on the IOWA-modified Reichard and Hamilton model “because it was extensively tested in a climatic zone reasonably analogous to … Illinois,” and because it is easy to use and limits the possibility of a plant being falsely accepted or rejected. The selected model was then tested on 208 plants that were collected in the Republic of Georgia. Because few details were known about some of the plants, many of the questions posed by the model could not be answered. This lead CBG to modify their model to allow for such plants to be grown out in quarantined garden plots. This way pertinent information can be gathered, such as “duration to maturity; self-compatibility; fruit type and potential methods of seed or fruit dispersal; seed production, viability, and longevity in the field; and vegetative spread.” CBG believes that evaluations such as this will help them modify their model over time and give them more confidence in their screening efforts.

More about botanical gardens and invasive species: Botanic Gardens Conservation International – Invasive Alien Species

More about weed risk assessment models: Weed Risk Assessment – A way forward or a waste of time? by Philip E. Hulme

Horticulture’s Role in the Spread of Invasive Plants

I live in the city of Boise – a bustling metropolis by Idaho’s standards. It is located in the high desert of the Intermountain Northwest in a region called the sagebrush steppe. Our summers are hot and dry, and our native flora reflects this.

When I leave my apartment I am greeted by a flowering quince (Chaenomeles sp.). At this time of year it is in full bloom and looking amazing. It originated in East Asia. To my left I see a tree of heaven (Ailanthus altissima), a common urban tree that came to America from China via Europe. To my right there is a row of Norway maples (Acer platanoides), another popular urban tree. As its common name suggests, it is a European species that is distributed across large portions of eastern and central Europe. None of these plants are native to the sagebrush steppe, nor would they survive the harsh conditions without supplemental irrigation. All are horticultural introductions.

Tree of Heaven (Ailanthus altissima) – photo credit: wikimedia commons

But there is another thing that at least two of these species have in common. Tree of heaven and Norway maple are considered invasive species in North America due to their propensity to spread into natural areas and disrupt native ecosystems. They also have a reputation of being pesky urban weeds.

My experience isn’t unique. Yards across North America are planted largely with species that are not native to this continent, and while most species stay where we plant them, a significant portion of them have leaped out of our tidy landscapes and disseminated themselves across natural areas, earning them the title invasive species.

In a paper published in BioScience (2001), Sarah Hayden Reichard and Peter White discuss the role that horticulture has played in introducing invasive species to the United States. Humans have a long history of moving plants from one part of the world to another for food, fuel, and fiber. However, collecting plants from around the world and organizing them into gardens for aesthetic purposes is, by comparison, a more recent thing. Species used for ornamental horticulture are what Reichard and White are concerned about.

As an introduction, Reichard and White offer a quick history of the beginnings of ornamental horticulture in the United States. This period is summed up well in an article by Richard Mack and Mark Lonsdale in the same issue of BioScience:

As colonists became more secure in their new environments, they began to import ornamental species from their homelands and elsewhere, in simultaneous quests for both familiar and unfamiliar plants. These plant importations sprang from deep-seated or primal aspects of human behavior shared by people in former colonies and homelands alike. … Many needed to be reassured with familiar plants from home, and they also had seemingly antithetical desires to experience novel, exotic ornamental plants.

Today, plant explorations continue throughout the world, often with the goal of introducing new plant species to the horticulture trade, and avid gardeners remain eager to find something new and interesting to add to their yards. There is nothing inherently wrong with this. Nor is there anything inherently wrong with filling our yards with exotic plants. The trouble comes when these plants escape cultivation and cause problems in neighboring ecosystems. Bringing awareness to this darker side of ornamental horticulture is what Reichard and White endeavor to do.

“Thomas Jefferson, an avid horticulturist, also introduced several species. He may have been the first person to introduce Cytisus scoparius (Scotch broom) as an ornamental species; that plant is now an invasive species in many parts of North America.” — Reichard and White (2001) [photo credit: www.eol.org]

Major players involved in the global movement of horticultural specimens include botanical gardens and arboreta, nurseries, garden clubs and horticultural societies, and the seed trade industry. The motives for transporting species vary among the groups, as do their roles in addressing the invasive species issue. Many botanical gardens have extensive plant exploration programs, which today are often more conservation focused than they were in the past; however, some of the species acquired during these explorations are released to the public, often without certainty that they won’t spread.

Even though most nurseries don’t have active plant exploration programs, they may acquire plants from nurseries or other institutions that do. For business reasons, plants may be sold before they have been properly screened for invasive-ness. Some retail nurseries make an effort to not sell plants that are known invasives in their regions. However, there are plenty of mail order nurseries that may not be aware of or may simply ignore the fact that they are shipping plants to regions where they are invasive. Seed exchanges between garden clubs and botanical societies, as well as the seed trade industry, are also responsible for shipping species to areas where they are currently or may become invasive.

“Uninformed people sometimes dump their aquarium water and plants into local water sources, and many of the aquarium plants survive and multiply. Hydrilla verticillata, a very aggressive aquatic weed in the South, was probably introduced to provide a domestic source of this plant for the aquarium trade.” — Reichard and White (2001) [photo credit: wikimedia commons]

Plant exploration will continue, and many new plants will be introduced to the public through the horticulture trade. Rules and regulations help restrict some plant movement, but in a capitalist society such restrictions will ultimately be, as Reichard and White write, “a compromise between ideal invasive plant exclusion and trade facilitation.” Plants can be screened for invasivibility, but it is difficult to know if, when, and where a species may become invasive. Furthermore, given enough time, a species that appeared to stay put can suddenly start to spread (or could have been spreading all along unnoticed).

Reichard and White acknowledge that “the burden of finding a solution to the problems posed by invasive plants does not necessarily fall on the shoulders of [the horticulture] industry.” Various groups from broad disciplines will have to come to together to work towards a solution. Reichard and White offer some suggestions for working together. For example, invasive species biologists can share their research with the horticulture industry which can, in turn, communicate this information to the public through garden writers and speakers. Botanical gardens can take a leadership role by vowing to “first do no harm to plant diversity and natural areas” and by providing public education about the issue.

Efforts can be made to ban the sale of problematic plants and to encourage proper screening of new introductions, but public demand for certain plants may remain. So, “better communication from ecologists to the public about which species are causing problems will discourage people from buying them.” Involving the public in eradication efforts can also help raise awareness, as people can see first hand that plants in their yards have invaded the wild.