Climate may keep purple loosestrife in check

As the rampant invasive plant purple loosestrife spreads across North America, it might be facing a natural barrier, according to researchers at the University of Toronto.

Lythrum salicaria, a  beautiful but highly destructive plant, has been heading north since it was first introduced from Europe to the eastern seaboard 150 years ago, the university says in a news statement. ‘This exotic invader chokes out native species and has dramatically altered wetland habitats in North America.”

purple loosestrife photo 1.jpg

NPS photo

Purple loosestrife’s native range is throughout the UK, and across central and southern Europe to central Russia, Japan, China, southeast Asia and northern India, according to the U.S. National Park Service.

“Purple loosestrife adapts readily to natural and disturbed wetlands. As it establishes and expands, it outcompetes and replaces native grasses, sedges, and other flowering plants that provide a higher quality source of nutrition for wildlife. The highly invasive nature of purple loosestrife allows it to form dense, homogeneous stands that restrict native wetland plant species, including some federally endangered orchids, and reduce habitat for waterfowl,” NPS says on its Web site.

According to the U.S. Fish and Wildlife Service, purple loosestrife now occurs in every state except Florida.


Wanted: Dead, Not Alive! Purple Loosestrife poster distributed for public information

California Department of Food and Agriculture image

Purple loosestrife destroys wildlife habitats by displacing native vegetation that provides food, shelter, and breeding areas for wildlife, Toronto University said.

“In urban areas, it invades ditches where it can block or disrupt water flow. It has few pests and diseases, resists various control methods, and plants can produce as many as 3 million seeds a year.”  

But it turns out it may have a vulnerability after all: the northern climate.

As this invasive plant has spread north it has run into challenges posed by a shorter growing season, according to a study conducted by Robert Colautti, who recently obtained his Ph.D. from the University of Toronto’s Department of Ecology and Evolutionary Biology.

The results are published online last week in the Proceedings of the Royal Society of London, series B and published in the journal Nature.

The scientists have found that adapting to the Great White North carries a severe reproductive penalty that may limit its spread, the University of Toronto explained.

“The authors used modeling and experimental studies of 20 purple loosestrife populations along a 1,200 kilometer [750-mile] latitudinal gradient from Maryland to Timmins, Ontario, representing a one-month difference in growing season.

“They found that northern populations have become locally adapted and flower earlier in response to a shorter growing season,” the university said.

“However, early flowering plants suffer a cost in terms of smaller size and reduced seed production. The reason: a genetic constraint,” the university said.

“Genes that cause early flowering also reduce plant size, so early flowering and small size evolve together,”  Colautti said. “Smaller size results in lower seed production, which is likely to limit the spread of purple loosestrife in northern regions.”

But isn’t that only while the northern climate remains cool?

Co-authors of the study are Colautti’s supervisor Professor Spencer Barrett of the Department of Ecology and Evolutionary Biology and Christopher Eckert of Queen’s University. The research was funded by the Natural Sciences and Engineering Research Council of Canada, an Ontario Graduate Scholarship and a Premier’s Discovery Award from the Ontario Government.

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