Wildflower is published quarterly by the Wildflower Center. Its content is national in scope with articles about the conservation and use of native plants as well as news from the Wildflower Center. A subscription is provided to Wildflower Center members as a benefit of membership.
Invasive Procedure - Spring 2012
Garlic mustard (Alliaria petiolata) is a native of Europe and poses a problem for forested areas across the country, most recently the Northwest. It is one of the few non-natives able to invade and dominate the understory of North American forests. Photo by Chris Evans, River to river CWMA, Bugwood.org.
How invasive plants wreck our gardens
NATIVE PLANTS ARE BY DEFINITION LOCAL, so on the surface it would seem as though native plant gardeners on one coast have little in common with those on the other. However, a couple of big things stand out to unite us: We want our gardens and natural areas to grow with the plants best suited to where we live. And we want to keep destructive exotic invasive plants from taking over. Three authors – from East Coast to West – share their experiences about why and how we do that.
One Homeowner's Crusade
WHEN I MOVED INTO MY HOUSE in Seattle a few years ago, I knew I would have my work cut out for me, literally. The backyard was large and woodsy and could have been beautiful if it wasn't overrun by two of Seattle's most infamous invasives, Himalayan blackberry and English ivy. These plants, introduced here more than a century ago by oblivious gardeners, have become regional scourges, choking out native plants and wildlife. As I hacked and cleared and dug and mulched – filling up a 12-squarefoot parking pad with a mountain of weedy yard waste – I never imagined that I was still harboring one of the most insidious of invasive plants in Seattle, garlic mustard.
But with the mail one morning came a letter from Karen Peterson of the King County Noxious Weed Control Program informing me that she had identified an outbreak of garlic mustard (Alliaria petiolata) – apparently the new "it" invasive in the Northwest – on my property. She went on to say that I was obliged under state law to control this fast-growing and worrisome weed.
"The reason we are so aggressive about this weed is because it poses a serious threat to natural areas," Peterson's letter continued. "It not only flourishes in the shade, where many of our native plants and animals reside, but it inhibits nutrient uptake of other, desirable plants and disturbs the life cycles of a variety of other organisms." She added that the plant thrives in our climate and may be more invasive here than in other parts of the U.S. where it's already problematic.
In response, I called Peterson and scheduled a time for her to come out and show me exactly what garlic mustard looked like, where I could find it on my land and how to remove it. A few days later she came over and gave me a tour of the flora of my property, pointing out which plants were native as well as which non-natives – including copious stands of garlic mustard – were worth removing. Although the notion of harboring a noxious weed on my property was unsettling, she reassured me that I was not alone. In King County, more than 100 different plant species have been classified as "noxious weeds." These innocuous-looking invasive plants are a serious nuisance to society in both environmental and economic terms, degrading natural areas and crowding out food sources and habitat for native wildlife while causing farmers and gardeners to use billions of dollars worth of harsh synthetic chemicals to keep them in check.
LEFT The author's Seattle yard after he removed the invasive garlic mustard. CENTER The tools and materials that were needed for the job. RIGHT Layers of woodchips in the author's garden now serve to keep invasives from taking hold again and seal in moisture for these native ferns. Photos by Roddy Scheer.
Given my sympathy with Peterson's mission – I already had cleared a busload of blackberry and ivy – I was more than willing to cooperate with this new task. She reported that my best hope of eradicating garlic mustard would be via sheet-mulching, which involves spreading a layer of cardboard or newspaper over weed-prone ground and then covering it with a substantial amount of mulch or wood chips. The idea is to starve the weeds below of light and therein cut off photosynthesis. Over the course of a few years the paper/cardboard and wood chips break down into loamy virgin soil.
So I got to work raiding friends' recycling bins for newspapers and cardboard, and I secured a dump truck load of wood chips from an arborist working on a tree removal down the block. Armed with a pair of work gloves, a shovel and a wheelbarrow, I began the arduous process of hand-pulling garlic mustard from the quarter-acre hillside in question, spreading out newspaper and cardboard and then covering it all with a two-foot layer of wood chips. Working steadily for a couple of hours every afternoon, I sheet-mulched the entire hillside within a week.
Of course, sheet-mulching such a large area was labor-intensive and time-consuming – and still takes some scouring for rogue weeds now and again – but in retrospect I wouldn't have done it any differently given the money saved, chemical harm averted, and overall effectiveness at keeping garlic mustard and other invasives at bay. Now my biggest gardening issue is what to plant next.
Roddy Scheer is a Seattle-based freelance writer and photographer specializing in outdoors, nature, environment and travel. Check out more of his work at his website, roddyscheer.com.
An infestation by Japanese climbing fern, which often invades disturbed areas such as roadsides and ditches but can also invade natural areas. Photo by Chuck Bargeron, University of Georgia, bugwood.org
A Closer Look
THIS PAST SPRING, I discovered an invader creeping along the side of my Austin house. I hadn't landscaped the side yard yet, and it blended in with the rest of the greenery. But one day, I took a closer look. What I found was a thicket of tough stems with branches of waxy green leaves. It was an invasive tree called ligustrum, also known as privet. As it happened, I had just spent a Saturday with a volunteer group clearing hundreds of these out of a park. Left to its own devices, ligustrum grows so thick that it blocks out virtually any other plant from growing around it. Now here it was, invading my own territory and staunchly resisting removal. Looking over the fence, I saw that my neighbors have a full-grown ligustrum shading their backyard.
I had a feeling that, unlike my unwelcome new tree, the ligustrum next door was intentionally planted. Many plants with invasive characteristics – including ligustrum (Ligustrum spp.), heavenly bamboo (Nandina domestica) and Chinaberry (Melia azedarach) – are perfectly legal to propagate and sell at nurseries. That means that while thousands of dollars and volunteer hours go toward fighting invasive plants every year, homeowners are planting their reinforcements.
An invasive plant is commonly defined as a non-native species whose introduction potentially harms the environment, the economy or human health. In Texas, an invasive plant is defined by its inclusion on an "official" state list of 30 species that are illegal to traffic and sell. Popular landscaping plants are notably excluded. To address the need for consumers to know about invasives sold in nurseries, entities like the Wildflower Center have created their own lists of invasive plants. That didn't sit well with the nursery and landscaping industry, whichprofits from the plants that consumers are discouraged from purchasing. During the last legislative session, industry lobbyists introduced a bill to require a disclaimer on unofficial lists, informing consumers that these lists provide only recommendations and have no legal status.
Damon Waitt, senior botanist at the Wildflower Center, was involved in the debate on the bill. He told me it spotlighted the inadequacies of the official list. By the end of negotiations, conservationists and the industry agreed that more plants deserved a spot on it. The Texas Department of Agriculture, which maintains the list, laid out a path for adding new plants.
This was a big step forward, because previously the process was undefined. Waitt is now on a committee to propose new invasive plants to the list, and he says they plan to start with the less popular species. He gave the example of Japanese climbing fern (Lygodium japonicum), which creates a dangerous path for wildfires to burn up to forest canopies. "We can document that it is a threat to our environment, but it's not economically important. There should be no barriers to adding it to the list."
LEFT The foliage of glossy privet (Ligustrum lucidum) on left compared to that of Chinese privet (Ligustrum sinense) on right. Photo by James H Miller & Ted Bodner, Southern Weed Science Society, Bugwood.org. RIGHT Japanese climbing fern (Lygodium japonicum) in a pine straw bale. It can form dense mats that smother understory vegetation, shrubs and trees. Photo by Dennis Teague/bugwood.org
Outlawing a plant like ligustrum is a bigger challenge. "What it's going to come down to is: Are the environmental negatives of that plant great enough to outweigh the economic benefits that plant provides to the state of Texas?" Waitt said. He said that the best approach would be finding alternatives to best-selling invasive plants and having nurseries slowly phase out those species on their own.
Concerned gardeners can find out which nursery plants are considered invasive by finding "unofficial lists" in their area. In Texas, texasinvasives.org has a comprehensive database of invasive plants and native alternatives. The website also has information about how to get trained to detect the arrival of new invasive species.
Lindsay Patterson is an Austin-based science writer and gardener. She blogs about science at lindsayjpatterson.com and contributes to various publications and radio programs.
TOP Many "harmless" exotic ornamentals, such as this popular English ivy (Hedera helix), invade and devastate established landscapes, requiring tremendous energy to control. English ivy has been officially labeled a "noxious weed" in 46 states, and it is banned from sale in Oregon. BOTTOM Norway maples (Acer platanoides) – distinguishable here by their bright-green early foliage – thrive in the Northeast by leafing out a month earlier, and holding their foliage a month later, than the native trees. The resulting forest is a dark, impoverished habitat. Photos by Sue Reed.
How Invasive Plants Steal Energy
AS A LANDSCAPE DESIGNER IN WESTERN MASSACHUSETTS for the past 25 years, I rarely have encountered a project site that didn't contain at least a few invasive plants. Some contained many. Oh, the disappointed clients I have faced! What to do now? How serious is this? How much time and effort will be required, and what's the best solution? And, er, do we really have to do it?
My own property is no exception. Ten years ago, when we bought our 4-acre lot, one of the first things I did was hand-pull colonies of barberry and burning bush (which mostly have not come back) and countless bittersweet vines (which continue to pop up everywhere!). By far our worst problem, though, was a huge stand – 80' wide – of Morrow's honeysuckle. Some trunks were 10" across. This thicket was choking our little stream and creating a mucky, impenetrable mess. Fixing this problem required serious effort: a chain-saw just to get past the outer edges and a tractor to pull the stumps.
Sweating my way through this project, I suddenly realized a whole new reason not to like invasive plants. Beyond the harm they cause to the environment – reduced diversity, displaced natives, simplified ecosystems, for example – invasive plants actually interfere with our work, as individuals and as a society, to save energy. I've now come to see that, no matter where they grow, invasive plants steal our fossilfuel energy in three basic ways.
INVASIVE PLANTS TAKE ENERGY TO REMOVE. Opinions differ about what to do after aggressive non-natives have become well-established in a site, but most ecologists and environmentally aware gardeners believe we should make an effort to remove them. This effort might involve large teams cleaning out acres of buckthorn, barberry or autumn olive. Or it could be a neighborhood group tackling yet another stand of Japanese knotweed. Or perhaps it's just a single homeowner pushing back, week after week, against the insidious creep of Japanese stiltgrass.
No matter how big or small, every removal job consumes energy. Fuel to transport people and supplies. Gas and oil for the equipment. Energy spent on manufacturing the chemicals and tools. Electricity for researching best solutions. Some of these are immediate expenses while others are hidden or dispersed costs, but together they add up to big losses.
INVASIVE PLANTS NEGATE INVESTMENTS. Shade trees, abundant foliage, windbreaks, lawn alternatives, hedges and groves, semi-wild patches – all these (and many more) will reduce a building's utility costs and/or its landscaping energy costs. If unnoticed or left alone, invasive plants can wipe out these savings. They might overwhelm or tear down some plants; they might slow or prevent the establishment of others. What's lost then are both the energy costs of the work already done and the future energy-saving benefits.
INVASIVE PLANTS HARM ECOSYSTEM SERVICES. We are beginning to understand that ecosystems provide "services" that are essential to our human comfort and survival. Many ecosystem services – such as water-purification, cycling of nutrients or carbon sequestration – might occur equally well in any sort of plant community, native or non-native. However, other essential services only can come from ecosystems full of diverse native plants.
The most important of these involves insects. Yep, humble bugs. Insects assist humans in several vitally important ways, including controlling/ consuming other insect pests and pollinating many flowering plants (the USDA Natural Resources Conservation Service lists 1,700 links just on the subject of native pollinators). Perhaps insects' greatest service, though, is that they convert the sun's energy stored in plants into the protein of their own bodies. This protein is then consumed by larger and larger creatures. In essence, insects form the foundation of every food chain.
Japanese stiltgrass (Microstegium vimineum) has taken over this upstate New York forest and now flows, relentless as a river, across nearby yards and gardens. A relative newcomer in the Northeast, this little plant looks so harmless that few people recognize its destructive potential until too late. Photo by Sue Reed.
The vast majority of insect species' larvae are able to eat the foliage of just a few, or sometimes only one, plant genus. When invasive plants displace native plants, biodiversity declines, habitats vanish and insect populations plummet. And here is invasive plants' biggest theft: as a society, we then must spend energy to replace or compensate for basic services that the insects in healthy, diverse ecosystems once gave us, for free.
Thinking back to my honeysuckle thicket and the thousands of other invasive plants that I've advised property owners to pull, whack, burn, smother and otherwise get rid of ... I do realize that the issue is complex. But it's important to remember that invasive plants do more than just harm the natural world. Right now, when saving energy is more important than ever before, we should realize that invasive plants also rob our increasingly precious energy resources.
Author of "Energy-Wise Landscape Design," Sue Reed is a registered landscape architect who specializes in designing sustainable landscapes that are ecologically rich and energy efficient. Her lively talks have received rave reviews from landscape professionals, design students, botanic gardens and master gardeners. Visit www.energywiselandscape.com to find out more, or read her blog posts at www.nativeplantwildlifegarden.com.