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Science

Northern forests are changing fast -- and no one knows what it will mean

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  • Updated: September 28, 2016
  • Published September 7, 2015

FAIRBANKS -- It didn't take long this year before Alaska State Forester Chris Maisch was reminded of the record wildfire season of 2004.

The snow cover melted earlier than usual this year, and with little rain or cloud cover, the sun relentlessly scorched Alaska's forests, creating especially dry conditions. Desiccated black spruce trees across the millions of acres of land that Maisch supervises were ripe for conflagration.

"We knew we were in very high fire risk because all of May and early June we kind of cooked the fuels and had very low rainfall," Maisch said. "So we knew things were really prepared to burn -- and we have indices to tell us that."

Then in late June, right after the summer solstice, a major lighting storm struck Interior Alaska. The fire service's sensors detected 10,000 to 15,000 lightning strikes a day for three days, sparking more than 300 wildfires.

Many tore through remote reaches of the state and would contribute to a season that -- while not yet over -- already has a place in Alaska record books as the second-worst.

Warmer and drier weather patterns in northern latitudes are driving the trend toward more severe fire seasons. In turn, wildfires, along with other factors such as insect infestations, are transforming the world's boreal forest ecosystem -- the vast northern forests that stretch from Interior Alaska through Canada, Northern Europe and Russia.

"My concern is whether the forest will be resilient enough to adapt to the change," Maisch said.

The journal Science devoted an article in a recent issue to reviewing research on the forests, and from dozens of studies, drew the conclusion that "projected environmental changes of unprecedented speed and amplitude pose a substantial threat to their health."

As the atmosphere warms over the course of the century, the regions closer to the poles are projected to see higher temperature rises. Models that show an average 4-degree increase overall anticipate an "extreme" increase of up to 11 degrees in the boreal regions.

Much of Science's review focused on the future of the boreal from a resource management perspective. About two-thirds of the northern latitude forests are under management, mostly for industrial wood production. Sustainable harvesting practices and policies exist but "current international agreements and regional market mechanisms fail to provide incentives or opportunities to fully implement the existing options."

Predicting the future of the forest

In the United States, many of the researchers who are working to decipher how climate change will impact the Arctic and subarctic forests -- forests that cover 17 percent of the terrestrial area of the earth -- are based at the University of Alaska Fairbanks.

Largely avoiding the public debate between climate deniers and doomsayers, these professors have been for decades meticulously studying everything from the thick and bouncy mat of vegetation that makes up the forest floor to the birds that fly above the canopy of spruce.

Scott Rupp, director of Scenarios Network for Alaska and Arctic Planning, a research center based at UAF, is working on ecosystem modeling.

Self-described "data hogs," Rupp's team digests information about the forest's past -- precipitation levels and temperatures, for example -- and tries to make predictions about its future.

SNAP undertakes research based on the needs of various stakeholders, from communities facing environmental challenges to fire managers such as Maisch.

"Fire managers are the best people to work with on modeling," Rupp said "They are used to working with uncertainty. They know what they are getting is imperfect."

But if the projections from year to year are not exact, the longer-term trends are clear.

"All the climate models we have used suggest warming, and in all cases we see increases in fire activity, in particular for the next 20-30 years," Rupp said.

Typically, wildfires prefer mature forests, where dead plant matter provides ready-made fuel. Younger areas that burned in the previous seasons are spared, maintaining a balance between old and new forest. This patchwork fire pattern fosters diverse wildlife habitats. Moose like to to slurp up the leaves of saplings, for example, while woodpeckers feed on the bugs lodged in the bark of fully grown trees.

Scientists refer to the regeneration pattern after a fire as succession. The grasses and herbs are first to grow from the ashes. Then come the shrubs and deciduous trees, followed finally by the evergreen spruce.

Succession, however, can be interrupted by a variety of factors such as weather, changing water flow, and the early return of fire. In the past, fires recurred to a given forest area in Alaska every 196 years on average. Now, that period has shrunk to 144 years, according to a UAF summary on wildfires and climate change. A shorter fire return period can jeopardize the ability of spruce trees to mature and reproduce.

Longer and warmer fire seasons are also driving a specific kind of burn. The forest floor, made of dense organic layers of moss, lichen, and grass can act as a buffer against the fire. But when snow melts earlier, the ground will lose its moisture sooner, making it more susceptible to the penetration of flames.

Studies show that the deeper the burn, the harder it is for the prevalent species, spruce trees, to seed and return.

What tends to grow in their stead are broadleaf trees such as birch.

'Facing a biome shift'

Warmer weather does not just prompt severe fire seasons; it also has a direct effect on the health of trees.

Glenn Juday, a forest ecology professor at UAF, has been studying a group of white spruce for nearly 30 years as part of the Bonanza Creek Long Term Ecological Research Site.

Hiking down to the study area in a forest south of Fairbanks, he warns not to lean on the trunks of spruce along the way because some are dead and could easily be tipped over.

Successive droughts over recent decades have weakened many trees, inviting pests that kill them by various means.

Six outbreaks of spruce budworm in 30 years, for example, have contributed to defoliation. In the worst cases, trees lose so much of the photosynthetic tissue -- leaves and needles -- that they die.

Wood-boring beetles kill a tree by a different mechanism. Burrowing into the trunk to lay their larvae, the beetles introduce fungus spores into sensitive layers of wood. The fungi grow and expand, plugging up the circuitry that carries water from the roots to the branches.

Insect outbreaks are normal and natural in boreal forests but in changing climate conditions they can overwhelm the ability of the forest to recover. Insects thrive under the same warm and dry weather that weakens the trees.

The forests around Fairbanks are some of the best studied, but the problems plaguing them are prevalent in other places as well.

"In cold-climate conifer forests all over the world you see insect outbreaks and big fires," he said. "Accelerated tree mortality can be seen all over the world, but the rate is higher in these types of forests."

There's still some good news for the white spruce, which dominates much of Alaska's boreal forest. The shifting climate is creating hospitable conditions for the species in new areas. A recent study authored by Juday shows white spruce migrating north and west into regions that are traditionally tundra.

"Trees near the outer tree line are doing fantastically well while the ones in the interior are growing more slowly," he said.

Because the changes to the vast boreal forest are hard for the untrained eye to see, guides like Juday regularly take reporters on forays into the woods. He points out the dynamic interplay between plants, insects and wildlife on a granular level. Zooming out, he explains how the activity observed connects the forest near Fairbanks to an entire circumpolar system, known in science as a biome.

Without fail, every reporter who has interviewed Juday has asked him why readers and viewers should care about a bunch of trees. His answer? "I am not in the business of making people care. I am in the business of finding out about the world."

But what he is learning about is certainly worrying him. "We are facing a biome shift," he said. "This entire forest is collapsing due to various stresses, many of them due to climate change."

A change on the scale Juday is suggesting raises questions about the continued ability of the boreal to provide one of its most important ecological services: storing massive amounts of carbon.

The trees and vegetation suck carbon dioxide, a greenhouse gas, out of the air. The forest floor, and especially the frozen soils below, represent organic deposited over thousands of years.

According to some estimates, the circumpolar boreal forest may be a larger reservoir of carbon than the tropical forests.

The fear is that a warming globe will unlock the carbon through a shift in vegetation and the thawing of the organic rich soils -- along with it's more spectacular release that occurs each fire season. And unless that carbon is reabsorbed into the earth somehow, it will increase the greenhouse effect and warm the forest further, in what's known as a positive feedback loop.

At this point there are too many variables -- how quickly the boreal is changing, for example, or what biome might come to replace it -- for conclusions.

Rupp has tried to model carbon cycle under changing climate conditions, but "whether the Arctic will be a flux or a sink for carbon, that is uncertain."

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