What many people see as agricultural pests, are actually powerful indicators of ecological change. Trinity Western University Biologist David Clements, Ph.D., has found that understanding weeds’ well-honed coping mechanisms could inform strategies for ecological management in the face of climate change.
In a new study, "Predicting Weed Invasion in Canada Under Climate Change: Evaluating Evolutionary Potential," published in the Canadian Journal of Plant Science, Clements, along with Cornell University Weed Ecologist Antonio DiTommaso, Ph.D., uncovers the missing link in models that predict how weeds will react to climate change.
“Our research points to differences between weeds as being genetic, not just due to environmental differences as once thought,” said Clements. “The missing link is evolution.”
Many weeds are capable of relatively rapid genetic change, further enhancing their ability to colonize new areas. While other species are expected to suffer from environmental fluctuations, changes in temperature may help invasive weeds expand their ranges.
The study looks at four different weed species—Himalayan balsam, velvetleaf, Japanese knotweed and johnsongrass—that were expanding their ranges northward within North America. The researchers observed evidence for potential evolutionary responses to climate change in each species, despite population genetic differences.
The standard modeling approach treats weeds like static entities. In the ‘70s, researchers developed the idea of the all-purpose genotype of a weed. There was an assumption among biologists at that time that weeds wouldn’t change genetically. Part of that assumption came from a long-held misunderstanding of how weeds behave, said Clements.
What worries weed scientists today, is their resistance to glyphosate—a broad-spectrum systemic herbicide used to kill weeds, which was brought to market by Monsanto in the ‘70s under the trade name “Roundup.” For years, researchers thought weeds couldn’t develop resistance. However, as the chaos theorist in the movie Jurassic Park warned: “Nature will find a way.” Or as Clements puts it, “Weeds will find a way.”
“Plants don’t follow the same rules as animals,” said Clements. In their study they found interspecies crossing and gene flow from one species to another. With two species coming together, the range of expansion that they could occupy could be greater.
Terho Hyvönen, Ph.D., Principal Research Scientist with MTT Agrifood Research in Finland, has taken notice of their work and has sought funding approval for a potential partnership in an international research project comparing weeds from North America and Europe.
Next up, Clements would like to explore what’s happening at the edge of the species range. “Evolution is always a response to stress,” he said. “I’d like to look at how weeds respond to the stressful environments they face at the northern edge of their range, which often falls right here in Canada.” This should provide important clues as to how weeds will respond to climate change.
As President of the Canadian Weed Science Society, Clements has been involved in a trend of bringing ecology into weed science. He conducts much of his field work in the Crow’s Nest Ecological Research area on Salt Spring Island. In addition to local research, Clements is the editor of a series about invasive species in the Pacific Islands, published in the Journal of Pacific Science, and teaches a botany course featuring invasive weeds every other year in Hawaii.