What’s All This About Weeds?
Clockwise from top left: Houndstongue, Spotted Knapweed, Leafy spurge, Hoary allysum, Tansy, Canada thistle
INVASIVE SPECIES
A species -- plant, fish, insect, mammal, bird, or disease -- is invasive when it is both nonnative to the ecosystem in which it is found and capable of causing environmental, economic, or human harm. Invasive species often compete so successfully in new ecosystems that they displace native species and disrupt important ecosystem processes. Considered by scientists as one of the single largest threats to our nation's natural resources, invasive species may:
Decrease biodiversity
Further imperil endangered and threatened species.
Displace native plants that wildlife and fish depend on for food
Increase soil erosion and the frequency and risk of wildfires
Reduce agricultural production and property values.
NOXIOUS WEEDS
A weed is a plant out of place. It is a plant growing where it is not wanted by humans. Ralph Waldo Emerson considered a weed “a plant whose virtues have yet to be discovered,” i.e., a plant in need of a publicist.
For land managers, a weed is a plant that interferes with the management objectives of a given area at a given point in time. In Montana, a weed is elevated from this overly broad category to “noxious” when they are plants of foreign origin that can directly or indirectly injure agriculture, navigation, fish or wildlife, or public health. Currently there are 35 plant species on the statewide noxious weed list in Montana that collectively infest millions of acres. In addition, counties can add additional species of concern.
The concern about “foreign origin” is not a form of floral xenophobia, but rather recognition of a pattern that alien species, inadvertently or otherwise imported into North America, are generally regulated only by abiotic factors (climate, fire, flooding, etc.) which are insufficient to keep their populations in balance. Biotic factors, such as insect predators and plant pathogens, that evolved with the species in their native lands are typically not present, and therefore not a control. Spotted knapweed and leafy spurge are two examples of plant species that are exotic and invasive.
The impacts from noxious weeds, like that of invasive species in general, include:
Potential to dominate plant communities, form monocultures, displace native and desired forage species.
Alter water cycles and cause erosion: for example, areas infested with spotted knapweed incurred 56% higher runoff and 192% higher sediment yield compared to those dominated by native bunchgrass in western Montana.
Cause economic loss: for example, cost of leafy spurge to grazing lands and wildlands in the upper Great Plains including the states of Montana, North and South Dakota, and Wyoming is estimated at $129.5 million annually and represents a potential loss of 1,433 jobs.
Endanger livestock. Hoary alyssum, an exotic rapidly expanding its range and densities, is poisonous to horses.
The rate of introduction and spread of noxious weeds has increased dramatically over the past 50 years thanks to increased human activities, trade, and climate change. For example, spotted knapweed was first recorded in the state in the early 1920’s. Since that time, it has spread to infest more than four million acres in the state, and continues to spread.
Certain weeds have earned county, state, and federal notoriety. They are blacklisted as “noxious”, “invasive”, and “alien.” They are depicted on wanted posters just like Jesse James and Ma Barker. At the same time, many non-native species (aka weeds) have become part of our landscape with little or no fanfare. White clover, yellow sweet clover, chicory, and bittersweet nightshade are a few examples. While some might cast them as outsiders, in general there was been no public campaign against them. In fact, many people enjoy their presence on a daily basis.
Every year more “invasive aliens” are added to our watch lists. With the specter of climate change and increased globalization, where should our battle against weeds go? Emma Marris in the Rambunctious Garden notes that we have grown fond of clinging to fragments of “virgin” landscapes and “intact ecosystems”. But like slivers of soap, they shrink and slip through our fingers. Rather than mourn the passing of “pre-human” nature, however, Marris takes a more optimistic approach that recognizes that while today’s nature is decidedly not pristine, it is abundant and it should be embraced for what it is rather than some fossilized view of nature past. So what to do about weeds in and around the Upper Yellowstone Watershed?
Know your weeds. Most weeds are spread as a result of ignorance or non-action. For example, resist the temptation to “pluck and chuck” the Velcro-like seeds of Houndstongue as that helps spread them.
Prevent infestations of new noxious species. It is relatively easy to control and even eradicate small populations of noxious weeds. Best yet prevent the introduction of new species and populations in the first place by practicing #3.
Control spread of existing noxious weeds. Clothing, horses, and off-road vehicles are three effective vectors for transport of noxious weed seeds from an existing population to a new one. Clean before you move.
Keep an eye on the rest. Guilty of being non-native immigrants (like many residents of Montana), the vast majority of weeds are part of the landscape and their behaviors don’t rise to the level of harm -- which raises the fifth point
Know what is not a noxious weed. Increasingly there is ample evidence that weed spraying programs can cause more harm than good when the spray wand is in the hands of applicators who don’t recognize that every broad-leaved plant is not a weed. Fields that once abounded with prairie smoke, anemones, and other flora, have been reduced to stands of non-native pasture grasses. In the name of controlling noxious weeds, we are attacking our native plant life.
For more information:
Montana’s Noxious Weeds (PDF download)
Statewide Noxious Weeds-Montana Field Guide
Park County Weed Control District
Noxious Weed Monitoring, Park Country Environmental Council
Invasive Species Action Network