Lake Superior Basin feeling heat, Part 2: June 2007

HOUGHTON -- This year, the ongoing wolf-moose study at Isle Royale National Park counted the lowest number of moose ever in its nearly five-decade history. The study -- the world’s longest running predator-prey research, according to Park Superintendent Phyllis Green -- found only about 385 moose on the island, down from 1100 in 2002.

"That’s a pretty dramatic drop, much of which is related to warmer weather," says Green.

Not only moose but also birds, mice and a range of other animals and plants, researchers say, have started to show the effects of recent climate shifts around Lake Superior. The region’s average air temperatures have risen over the last few decades, and Lake Superior’s surface waters have warmed even faster.*

These changes parallel global trends reported this year by the International Panel on Climate Change (IPCC), whose latest assessments say it is "very likely" the planet is warming as a consequence of adding human-generated greenhouse gases to the atmosphere. As the IPCC has issued its reports, scientists around Lake Superior have been documenting ways in which rising average temperatures already appear to be affecting this region.

One of the more striking changes is the moose decline found by the Isle Royale wolf-moose study, co-directed by Michigan Technological University (MTU) faculty Rolf Peterson and John Vucetich. Peterson explains that moose are heat sensitive and are affected in a few different ways by warmer temperatures.

Cluster of winter ticks on moose hide. Click for larger version. (Photo © 2007 John Vucetich. Reprinted with permission.)

"The warm springs and warm autumns tend to promote a winter tick population, and those are pretty hard on moose," Peterson says. "We’ve had several years in a row now of peak tick infestation of moose."

Isle Royale moose shows areas of skin rubbed bare due to tick infestation. (Photo © 2007 John Vucetich. Reprinted with permission.)

This photo of an Isle Royale moose shows areas of skin rubbed bare due to tick infestation. Moose lose fur when they rub against trees in an attempt to remove ticks. Warmer temperatures favor ticks and make moose more vulnerable to winter tick infestations. Small photo, above, left: Cluster of winter ticks (Dermacenter albepictus), also called moose ticks, on moose hide. These ticks do not affect humans. Click on small photo for larger version. (Photos © 2007 John Vucetich. Reprinted with permission.)

"When it’s hot, moose just don’t forage, or they forage less than they would otherwise," says Peterson. "So they go into winter with less fat, and that sets them up for trouble."

These stresses, Peterson explains, make moose more vulnerable to predation by wolves. Peterson says moose also sometimes die directly from heat, especially since they don’t sweat.

"They have trouble cooling off because their only means to do so is to breathe faster," he explains. "And if you’re going to increase your respiration rate you’ve got to have heart, lungs and kidneys all working perfectly."

Just as older people are more susceptible to overheating, Peterson adds, so are older moose. He has examined at least a couple of moose who apparently died of heat stress at Isle Royale.

"One died in ‘05, summer, right in the middle of a hot spell in July," Peterson recalls. "Showed up dead in the water."

Another was reported to him during the hot summer of 1998 by some Isle Royale visitors who watched a cow moose immerse herself in water and just stand there for a couple of days until she died.

Small mammals: shifting ecological cornerstones

Climate change appears to be affecting smaller mammals, too. Phil Myers, associate professor of ecology and evolutionary biology at the University of Michigan, says there have already been shifts across the Upper Peninsula for seven species: Opossums, white-footed mice, eastern chipmunks and southern flying squirrels are moving in from the south; and woodland deer mice, least chipmunks and northern flying squirrels are retreating to the north.

Until recently, for instance, the woodland deer mouse was the dominant mouse found in the Upper Peninsula. As of the 1930s, white-footed mice lived just in Menominee County. Then in the 1990s, some were documented in Delta County; and now they’ve spread from the Wisconsin border in the west all the way to I75 in the east. As white-footed mice have spread, woodland deer mice -- though still common -- have declined.

Woodland deer mouse. (Photo © 2007 Phil Myers. Reprinted with permission.)

White-footed mouse. (Photo © 2007 Phil Myers. Reprinted with permission.)

Woodland deer mice (left) have started to be displaced by white-footed mice (right) across the U.P. Researchers believe climate warming is the reason. (Photo © 2007 Phil Myers. Reprinted with permission.)

After studying several possible causes for these shifts, Myers believes they are due to a warming climate.

"The speed of change has been remarkable, especially in the U.P.," Myers says. "All this has happened in 30 years."

That kind of quick change is usually only seen when exotic species are introduced, he explains.

"The change is a little frightening to me because we can’t predict where it will lead," Myers notes.

Many small mammals are ecological cornerstones, dispersing seeds, eating insects and keeping them in check, while serving as food for carnivores such as hawks or foxes. It’s not known, Myers says, what replacing one such species with another will do to the balance of ecological communities.

"Because the species are so common and ecologically significant, the potential for a substantial impact on our communities, one that may not be to our liking, is there," he notes.

Birds moving north

Warmer springs and falls have also shifted some bird ranges, says Associate Professor David Flaspohler of the MTU School of Forest Resources and Environmental Science.

"The trend is toward birds breeding further north than they used to," Flaspohler says.

He cites an important study by Professor Terry Root, formerly of the University of Michigan and now at Stanford. Among a number of bird range shifts correlating with temperature increases, the study found that 43 percent of warblers had shifted their breeding ranges to the north over 20 years.

Many warblers come to the U.P. for the mixed conifer-hardwood or boreal forest habitat, Flaspohler explains.

"The vast majority of warblers that are breeding in Michigan are breeding in the Upper Peninsula," he says.

In response to rising temperatures, these birds can shift their ranges faster than forests; but ultimately boreal forest trees such as spruce, cedar and fir are expected to move as well, Flaspohler adds. When they do, the birds could change further.

"We’re probably going to lose species of birds that are associated with those conifers and pick up species that have a more southern breeding distribution, like mockingbirds and tufted titmice and things like these that nobody ever used to see in the U.P.," he says.

These species are already showing up here more often, and some are arriving earlier in spring or leaving later in fall, he adds.

"We don’t know if that’s all climate-change related, but there’s certainly lots of anecdotal evidence of robins or cardinals -- of a lot of birds that people weren’t commonly seeing in the winters -- now routinely over-wintering," he notes.

An increase in backyard feeders could also be a reason for an increase in birds like cardinals, Flaspohler says.

Northern mockingbird at Manitou Island, spring 2006. (Photo © 2006 Joe Kaplan. Reprinted with permission.)

Northern mockingbird at Manitou Island, spring 2006. A warming climate trend may be responsible for an increase in the number of mockingbirds seen in the Copper Country since the early 1990s. (Photo © 2006 Joe Kaplan. Reprinted with permission.)

Nancy Auer, associate professor in the MTU Biological Sciences Department and a member of Copper Country Audubon, says the club has documented some of these changes in its annual Christmas Bird Count.

"We have started to see more and more southern species each Christmas," says Auer.

The red-bellied woodpecker is another such bird now seen more often in the Copper Country, she adds.

Auer is a fish biologist; and lately, though she can’t link this definitively to climate change, she has observed more early spawning in the lake sturgeon she has studied for two decades.

"The last few years have been pretty interesting with the fish coming into the streams earlier because the snow has melted," she says. "We expect it again this year -- that we’ll see some really early spawning." Auer notes that recently she has recorded sturgeon spawning as much as three weeks earlier than normal.

Forests show longer growing season

Studies that do document statistically significant changes linked to climate tend to be decades long. Phil Myers’ data on small mammals span the 20-plus years of his own studies, as well as historical records going back to the mid-1800s. The Isle Royale wolf-moose study started in 1958 and will celebrate its 50th anniversary next year.**

Another research project showing a statistically significant shift that correlates with temperature increases actually had set out to measure something different. Research Associate Professor Andy Burton of MTU’s School of Forest Resources and Environmental Science says a 20-year study of the effects of nitrogen deposition in hardwood forests ended up documenting a change in the average length of the growing season.

"What we’ve seen over time is that the growing season is getting longer, probably by at least a week and a half," Burton says.

This particular study collects data from four forest sites dominated by sugar maples, three in lower Michigan and one in the U.P. near Twin Lakes. Data from all the sites show a trend toward both earlier spring leaf-out -- the date when leaves are half-expanded in the spring -- and later leaf fall in the autumn. These changes correlate very well with rises in temperature, Burton says.

Burton sees the possibility for a positive change from this shift: it could stimulate trees to grow more and lead to higher productivity in the forests, as long as water is adequate. If climate change means continued drought, however, the forests might grow less.

Continued drought might in fact be what climate change means here, says Apostle Islands National Lakeshore Superintendent Bob Krumenaker. He has studied the climate change issue recently to aid in Park Service planning, and says global climate models predict for a long term the same conditions that we are seeing in the region now, including warmer, dryer summers and warmer, shorter winters.

Krumenaker, too, cites the likelihood of boreal forests moving if continued warmer air degrades habitat for cold-loving trees like spruce, fir and cedar.

"We’re kind of at the southern edge of the boreal forest and if warming continues, that edge will retreat further north," he says. But, he adds, "That migration of forest patterns is not necessarily going to be smooth. You’re going to have a lot of dead trees out there at some point, and therefore scientists are predicting an increased fire frequency in our area as well."

At Apostle Islands, Krumenaker has seen another impact on forests that, while not caused by climate change, might be affected by warmer temperatures.

"The Gypsy moth last year defoliated a notable part of the Apostle Islands for the first time," Krumenaker reports, noting that the summer of 2006 when the damage occurred was particularly hot.

Gypsy moths were coming anyway, but Krumenaker says he wonders how much warmer temperatures might be aiding their spread. "Warmer weather and stress to the forests certainly makes pest infestations that much more likely," he says.

Tiny plankton, big effects

Climate change might also be responsible for several shifts that are too microscopic to see. But just because they’re not visible to us doesn’t mean they aren’t important, researchers say.

Take, for instance, the recent discovery of a cold-weather phytoplankton "doughnut" in the southern basin of Lake Michigan -- a finding that has implications for Lake Superior. The "doughnut" is a large cylinder-shaped concentration of microscopic plankton, extending from the top to the bottom of the lake and circulating in a huge counterclockwise current. A research team including Charles Kerfoot, professor in MTU’s Biological Sciences Department, spotted the formation in satellite imagery. It’s the first time such a bloom has been seen in winter or early spring, Kerfoot explains.

"You can pick it up as early as January or February, but then it becomes really pronounced in March and April," he reports.

Satellite image of phytoplankton "doughnut" in southern Lake Michigan. (Image courtesy W. Charles Kerfoot. Reprinted with permission.)

Satellite image of phytoplankton "doughnut" in southern Lake Michigan. Researchers suspect similar phenomena related to warming temperatures could be found in Lake Superior and the other Great Lakes. (Image courtesy W. Charles Kerfoot. Reprinted with permission.)

Kerfoot and his team postulate that four things have contributed to the phenomenon: warmer temperatures, less ice cover, more frequent storms and more severity of storms -- all of which have been documented in the region. The increased frequency and severity of storms, Kerfoot says, has been confirmed in a study of municipal water intakes around Lake Michigan, which track the turbidity (or cloudiness) of the water they take from the lake.

"When you have the winter storms, the water gets turbid," he says. "You can clearly see over the last 40 years, from the water intake records, that there’s now a greater frequency of winter storms and that the severity is also increased."

These more frequent and severe storms generate stronger currents, says Kerfoot, with water rotating counterclockwise in a huge circle in southern Lake Michigan, and clockwise to the north. They also stir up nutrients more readily. And with climate change reducing ice cover, Kerfoot’s team believes, there might be more nutrients out in the lake to stir up.
Kerfoot explains that ice shelves generally trap organic matter and nutrients like phosphorus and carbon, holding them close to the shore.

"With global climate warming and the loss of that ice shelf, you’ve lost that trapping and storage effect," he says. "This material then is being entrained into the coastal currents and moved out to the center where it’s causing the doughnut phenomenon."

In Lake Michigan, this has had ramifications for the entire food web, Kerfoot says. His team has found a change in the distribution of zooplankton and fish, which now tend to cluster around the inner ring-edge of the doughnut. Kerfoot suspects that similar phytoplankton blooms -- and changes in fish distribution -- might be found in the other Great Lakes, including Lake Superior.

A change already seen along Superior’s shores, Kerfoot notes, is the increase in what are called jellies. These are a type of Holopedium, a small zooplankton that produces a gelatinous ball around itself. As their numbers have increased, these micro-crustaceans have become more noticeable as they wash up on Lake Superior beaches in late August and early September.

"We can clearly show in the sediment cores that there is this major increase of them over the last 50 years," Kerfoot says.

Unseen changes in soil

Even harder to see than plankton in the lake is the world of soil microbes. But, says Dave Toczydlowski, research scientist with MTU’s Biological Sciences Department, over 95% of an ecosystem’s biodiversity might be found in the soil.

Toczydlowski works with a research team that studies biogeochemical cycles at a network of national park research sites, including one at Isle Royale. Led by Robert Stottlemyer of the U.S. Geological Survey, the team looks at carbon and nitrogen cycling in soil and through ecosystems -- and at how that cycling might be affected by global change. So far, this research indicates a trend toward more loss of carbon and nitrogen from the soil as average temperatures get warmer.

Wallace Lake drainage in Lake Superior's Isle Royale National Park. (Photo © 2007 Dave Toczydlowski. Reprinted with permission.)

This photo by Dave Toczydlowski shows Wallace Lake drainage in Lake Superior's Isle Royale National Park. Toczydlowski is part of a research team that studies biogeochemical cycles at a network of national park research sites. (Photo © 2007 Dave Toczydlowski. Reprinted with permission.)

This is not necessarily a straight-line process. Lately, Toczydlowski reports, warm autumns have more frequently left the ground bare of its usual blanket of insulating snow. That allows the soil to freeze more deeply; and it freezes more soil microbes, too, causing them to burst open.

The burst microbes release nitrogen and carbon into the soil, which in turn sends more of those nutrients as runoff into lakes and streams. With less insulating snowpack, more soil microbes freeze and burst; and more nutrients are washed out of the soil and into waterways.

"These ecosystems here have evolved over thousands of years to have that snowpack," Toczydlowski explains.

Dave Toczydlowski monitors snow depth and moisture content of the snowpack on Isle Royale. (Photo © 2007 Dave Toczydlowski. Reprinted with permission.)

Without the autumn snow, he says, shifts are occurring in soil biology and chemistry that can ripple from the base of the food chain through the rest of an ecosystem. For instance, loss of nitrogen from soil might increase weedy plant species that can more easily store excess nitrogen. An increase in weeds might then affect animals -- and people -- in turn.

From microbes to moose, questions remain

From single-celled microbes to six-foot moose, questions remain about how shifts in climate might affect Lake Superior’s biological future.

For moose at Isle Royale, Rolf Peterson can’t yet say if the recent population drop can be chalked up entirely to a warming climate, or if it will continue. For comparison, he cites a recent study of the near-disappearance of moose in northwestern Minnesota. In that area, moose numbers have dropped 90 percent over 20 years due to warming temperatures, which made those moose more prone to infestations of parasites like ticks, flukes and brainworm.

The fate of moose at Isle Royale, and just how much their dwindling numbers are due to warming, should be easier to specify in the next two or three years, he says.

"If moose don’t pop out of this decline once wolf numbers go down -- and they [wolf numbers] have started that already -- then I’m inclined to think it’s a climate issue," he says.

Recently, the Isle Royale wolf population has been on the high side, with 30 individuals counted last year; and that puts more predation pressure on moose. But this year the number of wolves dropped to 21 -- a 30 percent reduction.

"That might be enough to stop the decline in moose," Peterson says. "One would hope. But there’s no guarantee."

NEXT IN THIS SERIES: Winter biking and wind energy -- indicators of our possible future? How warming temperatures around Lake Superior are affecting business and culture.

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Read more about the author of this article, Katie Alvord, on her Keweenaw Now contributor page.

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