17. CREEPERS AND INVASIVES AND THE EFFECTS OF CLIMATE CHANGE
Winter Creeper - Sometimes you have to block an unsightly view or need a creeper to cover a bank. Winter creeper (Eponymous fortunei) is a nice choice, and newer varieties on the market sport colorful leaves.
Most creeping perennial vines in the North don't hold onto their leaves in winter, making them limited options for screening a foundation or view. However, winter creeper holds its leaves in all but the severest winters (in Zone 4 at least). Not only can it be trained up a fence or trellis, but it can also be grown as a ground cover, too. They come in a variety of leaf colors beyond green, including green and gold, white and gold, and even some with a tinge of pink.
Unlike more aggressive vines such a Boston ivy, winter creeper needs to be attached to a fence, trellis or wall to grow vertically. I grew it once on some lattice along my foundation to hide the concrete. If grown along the ground, it will root, so winter creeper can also be a good choice for banks where you don't want to mow.
Fall is a good time to control exotic invasives that threaten to take over your yard. In the Northeast, shrubs and vines such as burning bush, Japanese honeysuckle, barberry, multiflora rose, oriental bittersweet and buckthorn have taken over forests and fields, choking out native plants. Even native plants such as Virginia creeper, can get out of control if you’re not diligent. They love my backyard and community garden.
INVASIVES AND CLIMATE CHANGE
Not only are there more invasives in a warm climate, but non-native species appear to have a more plastic response to temperature changes. Researchers used information dating back to the 1850s, when Henry David Thoreau recorded when flowers bloomed for 10 years at Walden Pond. During the last 160 years, the climate of Concord has warmed by almost 2.5 degrees Celsius.
The researchers found that across all sites, the exotic species flowered earlier than native species. More than that, they adjusted their flowering time depending on the temperature — in warmer years they flowered earlier, while in cooler years they flowered later.
Native species tended to flower at the same time every year, regardless of the rising temperatures. In Concord, invasive species flowered 11 days earlier than native species and nine days earlier than non-native species that weren’t classified as invasive. The research team found that the inflexibility of the native species was linked to declines in the abundance of those species.
Dangerous Invasives - Poison parsnip is a plant with broad, low leaves and yellow flowers on a tall stalk. Touch the sap, expose it to sunlight, and — ouch — the plant sap reacts with sunlight and burns your skin.
There are a lot of plant newcomers in Vermont these days, some of which, like poison parsnip, are considered noxious weeds. Some scientists say climate change will help noxious weeds spread and thrive, while making it harder for many native species to make a living. Others aren’t ready to take a stand.
Lewis Ziska, a plant physiologist with the U.S. Department of Agriculture, says weeds in general will do better in a warmer world — there will be more weeds, bigger weeds, different kinds of weeds.
“The factors in climate change that are relevant here are really related to carbon dioxide and temperature. In that context, and I’m speaking in very broad terms, what we see is that weeds tend to respond more to the carbon dioxide that has already occurred and is projected to occur in this century,” he said.
Ziska says Vermonters should watch out for weeds that are already major problems in the South: kudzu, pale swallowwort, Japanese barberry, and giant hogweed, which causes phytophotodermatitis many times worse than poison parsnip. Ziska also says we can expect more poison ivy.
Until recently, state officials didn’t have many weeds to worry about. Vermont’s cold winters kept many of them at bay.
“What we’re seeing is not just for weeds, but for a range of different animals and a range of different plant species, that one of the things that keeps species where they normally are is cold winters,” said Ziska. “As the winters warm, it expands the range that species can move into.”
Kudzu - Oftentimes, the species that do take advantage of that are invasive species. Those are the species that tend to move very rapidly when there’s a shift in the climate.” Kudzu, a fast-growing vine that covers forests and farm fields in the South, has already been found in Massachusetts and Ontario.
When Massachusetts state officials first visited a property in Needham that had a kudzu infestation, they estimated the plant to cover 150 square feet. When they came back a week later, the plant — what they believe is a single individual — had grown noticeably.
“Seeing it like that gives you an idea of how bad it could get if you let it go,” said Jennifer Forman-Orth, state plant pest survey coordinator with the Massachusetts Department of Agricultural
The site in Needham is just one of four kudzu infestations that various government agencies are battling in Massachusetts. Though they are small compared to the acres of kudzu-choked forests you can find in the South, these patches represent the forerunners of an expanding threat.
Kudzu, native to Japan, is among a number of noxious weeds that some scientists say will likely prosper thanks to climate change. A 2010 study by researchers at Princeton found that kudzu’s bioclimatic envelope — the conditions in which it can survive — will include Vermont by the year 2100.
Research also shows that kudzu has growth spurts when the air around it is enriched with carbon dioxide, according to the Northeast Climate Impact Assessment, a hefty report that outlines major predictions for climate, ecology, agriculture, and business for the Northeast.
Other invaders of concern include mile-a-minute vine and Japanese stilt grass, both of which cut off sunlight to surrounding plants.
“There are a bunch of species that are poised to make their ways up this way and they’ll probably do a little bit better in Vermont than they would have otherwise,” said Marangelo.
Crop Loss - $58 billion worth of crops are lost to invasives, disease, and weeds each year. A full quarter of U.S. agricultural production is lost to invasive species each year. The link between climate change and invasion for many species is not always clear. Take Japanese knotweed. This hollow-stemmed ornamental plant spreads by underground stem and when it’s torn apart by floods, pieces of the stem wash into new areas. These grow into monocultures of knotweed, crowding out native species. The floods of Tropical Storm Irene in Vermont certainly spread knotweed further afield, but it was spreading anyway.
Non-Native Species - Though many non-native species never change their new habitat substantially, a few do. The species that do, called invasive species, can wreak ecological, economic, or public health havoc in their new home. Invasive species may be relatively tame in their home habitats, but when released into a new place without natural predators, they get out of control.
Some invasives don’t change a whole community, they merely remove a member. Dutch elm disease wiped out the fountain-shaped elms that formed arcing galleries along Vermont’s riverbanks. Chestnut blight took out the American chestnut, so that now it exists largely as resprouted shrub-like trees.
That doesn’t mean invasives are always detrimental. Ariel Lugo, director of the International Institute of Tropical Forestry, has published a number of scientific papers suggesting that invasive species may in some cases be ecologically beneficial. Invasive trees helped speed reforestation in Puerto Rico, for example. In the desert Southwest, an endangered bird called the Southwestern willow flycatcher now nests in the invasive tamarisk tree that took over its riverside habitat. Sometimes, urban biological diversity is made up largely of non-native species.
Regardless of whether they harm or help, by definition invasives are game-changers, and they’re on the rise. Forman-Orth says Massachusetts is dealing with the kudzu infestations early so they spend less later on. “Massachusetts has limited resources to take care of invasive plants — that’s true for every state,” she said. “We’re focusing on early detection and rapid response to smaller infestations that lets us utilize our limited resources in a smarter way.
Farm Effects - Increased carbon dioxide concentration in the atmosphere appears to reduce the effectiveness of certain herbicides, like Roundup. Southern farmers consistently lose more of their crops to weeds. So, more weeds plus fewer effective means of control equals more losses. And even though all plants put on more growth with an atmosphere richer in carbon dioxide, as far as scientists can tell that’s not enough to compensate for the negatives.