Invasives Expand Ranges Much Faster Than Native Species
Native species also can’t move fast enough to avoid climate-driven chaos
July 22, 2024
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An international team of scientists recently discovered that nonnative species are expanding their ranges up to 1,000 times faster than native ones, in large part due to human help.
For instance, the sale of invasive Japanese barberry is allowed in Rhode Island. In fact, the Ocean State is the only New England state that doesn’t have a complete list of invasive plants. While the other five states have a long list of invasive species that are banned or at least identified in Connecticut’s case, the Rhode Island Department of Environmental Management’s invasive plants webpage notes the damage inflicted by nonnative species but only mentions one: phragmites, which aren’t sold at nurseries and garden centers.
Many other nonnative species, however, are sold commercially in Rhode Island.
Barberry was brought to the United States from Japan and eastern Asia in the late 1800s. The ornamental is still used in residential and commercial landscapes because of its fall coloring and deer resistance. But the prickly shrub easily spreads into woodlands, pastures, and meadows, where, like many invasives imported from faraway lands, it strangles native species.
The researchers found that even seemingly sedentary nonnative plants are moving at three times the speed of their native counterparts in a race where, because of the rapid pace of climate change and its effect on habitat, speed matters.
To survive, the article’s authors noted plants and animals need to be shifting their ranges a few miles a year just to keep up with the increasing temperatures and associated climactic shifts — a speed, they said, native species can’t manage without human help.
Led by scientists at the University of Massachusetts Amherst, the team includes researchers from New Jersey, Michigan, Colorado and Hawaii, and Sevilla and Zaragoza in Spain. The article was recently published in Annual Reviews of Ecology, Evolution and Systematics.
“We know that the numbers of invasive plant species are increasing exponentially worldwide,” said Bethany Bradley, professor of environmental conservation at UMass Amherst and the paper’s lead author. “We also know that plant nurseries are exacerbating the climate-driven spread of invasives and that confronting invasives is one of the best ways to prepare for climate change. What we wanted to find out is how fast both native and nonnative species are moving right now, and how far could they go.”
To figure out how fast species are moving, Bradley and her colleagues comprehensively surveyed a vast trove of previously published papers and publicly available datasets on how far and how fast both native and nonnative species, representing different taxa and various ecosystems, have been moving.
An important subset of this search, according to Bradley, was to compile data showing how humans are helping to accelerate the spread of nonnative species, either accidentally, such as when a particular species finds itself in a shipping container that travels between continents, or intentionally, when a gardener buys an invasive ornamental from a nursery.
The conclusion that Bradley and colleagues reached is that land-based species, including plants, need to be moving about 2 miles a year if they want to stay ahead of climate change, while marine species need to be moving 1.7 miles annually. They found native species are only managing to move an average of 1.1 miles a year.
They also found nonnative species are spreading at about 22 miles a year on their own. When the human role in spreading invasive species is taken into account, then the rate jumps to an “astronomical” 1,170 miles per year — 1,000 times faster than the rate at which native species are spreading.
“Essentially, there’s no chance for native species to keep up with climate change without human help,” Bradley said. “It’s really clear that people are very good at moving species, and this is one of the biggest advantages that nonnative species have. We need to seriously consider and begin implementing assisted migration [the practice of deliberately helping native species move to more suitable locations] if our native plants and animals are to stand a chance.”
We have a vine with thorns that grows rampant, sun or shade, and twists around other plants, choking them to death! I have to cut them to the ground weekly! The root system cannot be dug out either.
An evolutionary aproach to this topic would focus on Asia, as ecosystems in Asia are so close to each other, often with simply verticsl spacing rather than horizontal. The competition is fierce. This makes anything brought from Asia to other places likely to be a fiercer competitor than natives elsewhere in the world.
“An important subset of this search, according to Bradley, was to compile data showing how humans are helping to accelerate the spread of nonnative species, either accidentally, such as when a particular species finds itself in a shipping container that travels between continents, or intentionally, when a gardener buys an invasive ornamental from a nursery.”
This paragraph tells us a couple of ways humans bring exotic plants to new places, but not how humans have allowed these species to spread from the point of introduction. Gardeners may be responsible for planting the invasive in the first place, but have little to do with how it spreads from the garden. The rate of spread will depend on where the gardener’s yard is – in a 50-acre forest, or a 50-acre old field.
The basic thing to know about exotics is their affinity for disturbed land, and there has been no time in New England’s past when there was more disturbed land than at the peak of deforestation in the mid-1800s. Much of the vast expanse of open land was converted to pasture and cropland dominated by European grasses and a host of weeds that came along for the ride. Many of these plants (dandelion, plantain, dock, purslane, white clover, red clover, mustards, celandine, horn poppy, timothy, orchard grass, etc., etc.) have been here so long that most people think of them as natives.
As the forest returned in the mid 19th C. many of the exotics were knocked back, but all that changed as the forest became fragmented by new highways, powerlines, subdivisions, malls, and all the rest that not only provided a plethora of new permanent habitats, but a network of migration pathways. The most successful exotics produce large amounts of seed that are transported by the prevailing winds, in the berries birds consume, and the burrs attached to animal fur. But they are also transported in the mud on hiker’s boots, campers, and logging skidders.
Not mentioned in the article as a way in which humans are aiding the spread of invasives is by mismanagement of the land. I am currently involved in a study in the Green Mountain National Forest where the Forest Service is implementing plans to log over 17,000 acres of forest (some of it over 160 years old) to create early successional habitat, or as they describe it, the “regenerating forest class of 0-9 years of age.” And, highly disturbed sites ripe for exotic infestation.
Our study is inventorying the plant communities in and around sites already logged and planned for logging, and also along access roads throughout the National Forest. In less than two months, we have found exotic plants to be widespread throughout the GMNF. At the Chittenden campground, a smaller remote site over two miles from a main road, over 15 exotic plants were found, several (wild chervil, purple loosestrife, and bird’s-foot trefoil) officially listed as invasive. It should be noted that this campground is also the trailhead for more remote sections of the Forest, including several designated natural areas.
The Forest Service speaks highly of their efforts to keep invasives (the “official ones”) under control, but that control is accomplished solely through the application of herbicides, primarily glyphosate.
These results should be disheartening to Rhode Islanders. As the second-most densely populated state, it has rapidly become an invasive species heaven and a biodiversity nightmare. No wonder there are no legal restrictions on invasive species – it doesn’t much matter anymore. Plus, you have state natural resource agencies who want to cut down more forest to create more disturbed land for early successional species, and to “help the forest be more resilient to the effects of climate change”. Just like the Forest Service encourages them to do.
What can be done in the face of such stupidity?