Warming climate opens door to new forest pests

By JESSICA BATANIAN

Capital News Service

LANSING – The mimosa webworm was nowhere to be found on honeylocusts at Michigan State University 20 years ago.

mimosa webworm

Credit: Joe Boggs, via Buckeye Yard and Garden Online

But within the past decade, warming temperatures made the campus an appealing home for this destructive bug.

“It was the canary in the coal mine,” said Deborah McCullough, an MSU entomologist who witnessed the honeylocusts disappear from campus as temperatures warmed and the mimosa webworm moved north into Michigan.

It’s a phenomenon not confined to webworms and honeylocusts as the Earth’s temperature rises and the variability of climate increases, experts say.

Climate change will increase the frequency of droughts, increase the severity of snowstorms and rain storms and make frosts occur later, said Sophan Chhin, an assistant professor of forestry at MSU. As climate changes and growing seasons are interrupted by drought and frost, trees are preoccupied with regaining their strength and become more vulnerable to insects and disease.

The hemlock woolly adelgid is another insect of concern for the Great Lakes region. It attacks a type of conifer called hemlock and hasn’t breached the northern parts of Michigan and Wisconsin because of colder temperatures – yet.

“Currently, Wisconsin is a little too cold but that may become less of a case with climate change,” said Ken Raffa, a professor of entomology at the University of Wisconsin in Madison.

Insects are moving farther north than they ever have in the past, he said.

McCullough said the mountain pine beetle is the “one that scares all of us.” It’s native to the Rocky Mountains, with a range spanning from Canada all the way south into Mexico, and is naturally controlled by colder temperatures.

Warmer winters have allowed the mountain pine beetle to move farther north and to higher altitudes, McCullough said. And that’s created the opportunity for the insect to move east across Canada into areas like Manitoba and target lodgepole and jack pines.

Jack pines are an important species to the Great Lakes region mainly because of the ecological benefits they offer and the diverse habitats they create.

“If mountain pine beetle successfully attacks jack pines in Canada, which it probably will, it could continue moving east into our jack pine forests in this region,” said McCullough. “The consequences of continued mountain pine beetle spread to eastern North America could be pretty devastating.”

An increase in pine mortality as a result of mountain pine beetle could mean forests in northern parts of the Great Lakes states would be at higher risk for forest fires, said McCullough.

Raffa said that cold weather used to be a line of defense for trees. However, warming temperatures are forcing trees to move north, which in some cases is impossible.

Chhin said that’s especially the case in Michigan where the majority of the upper half of the state is made up of sandy soils. Although certain trees need to move north to remain in their preferred colder habitat, some cannot grow successfully because of other environmental features like soil and water availability.

Other trees will simply not exist in the region anymore because of warming temperatures and loss of natural habitat, he said.

“The rate of climate change exceeds the rate of migration,” he said. “In the future, people aren’t going to get to see those types of forests. They will just have to cross the border” into Canada.

There are significant threats to the future of forests in the Great Lakes region as a result of climate change. However, some trees may be able to turn the consequences of climate change into short-term advantages for growth, according to Chhin.

For example, the growing season will get longer as temperatures warm overt ime. Trees in Michigan grow into October now, but that could change in the future. Apart from an extended growing season, atmospheric gases that contribute to the global greenhouse effect may also have a positive impact on trees.

Global warming is the result of the accumulation of greenhouse gases like water vapor, carbon dioxide, methane and nitrous oxide. Carbon dioxide, the most abundant greenhouse gas globally, is released into the atmosphere through deforestation and burning of fossil fuels like coal, oil and natural gas.

All that carbon dioxide has a fertilization effect, Chhin said. Trees take carbon dioxide out of the atmosphere through photosynthesis. Excess carbon dioxide available because of pollution makes them more efficient with their water supply. Trees then use that reserved energy to grow more successfully..

Even though the extended growing season and the use of excess carbon dioxide benefit forests, they are only short-term advantages that don’t accurately depict the larger impacts of climate change, Chhin said.

Researchers are working on long-term management and early identification practices of region-specific insects, like the emerald ash borer, and beech bark disease to try and reverse or slow the future effects of warming temperatures on forests.

Raffa said, “Uncertainty is the biggest outcome of climate change. We need to start thinking about the different processes involved in order to solve the problem.”

Jessica Batanian writes for Great Lakes Echo.

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