Hansen has said that if we reach 3C, we’ll have a
new planet. Even now, though, it’s easy to argue
that we already have one. And it’s not exactly
looking favorable for C sequestration by forests.
“In the past, Interior forests have generally
grown back in predictable ways after fires.”
“The plant succession is different from what we
might have expected 10 or 20 years ago.”
“…if the warming continues, the forests could
eventually become grasslands, according to
“‘The climate is getting closer and closer to
what you might expect for grassland,’ he said
July 29, 2008
Alaska forests hit with more wildfires, infestations as climate changes
By Stefan Milkowski
BONANZA CREEK – It was just getting cool when
Glenn Juday went out to see his trees. The leaves
were still on the birch and aspen, and the summer
growing season was lingering. But it was already
October, and gathering data would be much harder
once it snowed. So Juday had to hurry.
“I’ll work till dark,” he had declared that
morning in his office at the University of Alaska
Fairbanks, where he teaches forest ecology.
“We’re seriously behind.”
Now Juday was about 20 miles from the university
– down the George Parks Highway, across a rutted
dirt road and down a worn footpath crossed by the
fallen trunks of old white spruce.
He’s been here every year since 1988.
Juday has come to know trees almost like
children. He knows, for instance, exactly how old
each tree is, how tall and thick it is, how much
it has grown over the last year and whether it’s
getting pestered by bugs.
This time he came with a graduate student from
Germany and a lab technician he had hired.
The lab tech carried a small metal case with
papers showing the research plots and the
individual white spruce trees in them.
There were 2,200 trees in all.
Juday started in section 2.05 with tree No. 36.
He measured its height – it was tiny – and its
circumference at the base, then looked around for
signs of a bud-eating insect that’s been showing
up more and more in white spruce trees in
“This one is budworm free,” he said, not quite believing it.
Juday checked again.
“No, sorry, very light.”
The lab tech wrote down the new figures, and Juday moved on to the next tree.
Juday started his research 20 years ago to unlock
the secrets of the boreal forest, as he says. He
chose a site in the Bonanza Creek Experimental
Forest that had recently burned so that he could
track new trees from seedling to maturity. He
learned a lot, published papers on his research,
and could have stopped at any time.
He didn’t stop, and over the years climate change
worked its way into his research and another
finding emerged – things are not looking good for
white spruce in the Interior.
“We’re in the biggest period of change that has
happened in this part of the world for several
centuries at least,” Juday said. “No matter what
you do, or what interest you have in this part of
the world, it’s very likely to be affected.”
Alaska’s forests have looked relatively the same
for thousands of years. Tree species shifted in
range and elevation as the climate warmed and
cooled, but the same species stuck around.
Now the climate is changing again – at least in
part because of human-induced climate change –
and the forests are responding.
Changes in temperature and precipitation are
favoring some species over others, and
weather-related threats like wildfires and insect
infestations are becoming more common.
According to Juday, the warming is already
stressing many Interior trees and could bring
them to the limits of their survival within
“It’s not just one species, it’s all species,” he
said. “And it’s not just some places, it’s most
A forest to match the climate
Climate change is affecting Alaska’s forests in a
number of ways, many of them complex and
indirect. But warming temperatures themselves are
also affecting forests and are likely to cause
the most dramatic impacts in the future.
As the climate warms, Alaska’s trees are expected
to gradually shift their ranges to cooler areas
but also give way to species more suited to the
If white spruce start to die in upland areas,
deciduous trees could start to take over in
Interior forests, says Terry Chapin, a professor
of ecology at the University of Alaska Fairbanks.
Some south-facing slopes with lots of sun already
resemble the aspen woodlands more common to
Saskatchewan and Alberta, and if the warming
continues, the forests could eventually become
grasslands, according to Chapin.
“The climate is getting closer and closer to what
you might expect for grassland,” he said last
According to Juday, the birch and white and black
spruce that dominate the boreal forest could all
be eliminated from the Interior as the climate
Consider white spruce, the trees Juday monitors
at Bonanza Creek. By studying temperature records
and tree ring data, as well as his own trees,
Juday has figured out how white spruce respond to
In general, they like it cold and wet. In fact,
the colder and wetter, the better. A graph
plotting growth against temperature should look
something like a bell, with an ideal temperature
in the middle and less and less growth if it’s
too warm or too cold. But in the 20 years Juday
has been keeping track, he’s only seen one side
of the bell.
That is, it’s already warmer and drier than ideal.
None of Juday’s trees have died from the heat –
most of the trees that have died were killed when
standing, fire-killed trees collapsed on them –
but in 2004 and 2005, when it was hot and dry for
months at a time, some trees came close. Tree
growth during those two summers was less than
half the long-term average, and, judging by tree
ring width, some trees grew about a fifth as much
as they would normally.
Black spruce also tend to struggle in the heat,
and some birch already seem to be stressed and
dying from warm, dry conditions, according to
If temperatures rise as climate models predict,
Juday figures all three boreal forest species
could be eliminated from vast portions of the
Interior by the end of the century.
“Essentially the trees come to a point where they
just won’t grow anymore,” said Val Barber, who
studied with Juday and now teaches at the
University of Alaska Fairbanks. “We’re actually
predicting that our trees aren’t going to be able
to make it here in Alaska.”
Other impacts are less direct.
Warming temperatures are degrading permafrost,
altering the hydrology over wide areas, and
causing some places to get wetter and others to
dry out. In the Tanana Flats southwest of
Fairbanks, the changes have already killed stands
of birch, according to Chapin.
“Those forests have drowned, basically, and are
turning into wetlands,” he said.
In the rainforests of Southeast Alaska,
scientists are blaming the widespread decline of
yellow cedar on a changing climate. During the
last century, trees that started growing hundreds
of years ago in a cooler climate have been dying
across roughly 500,000 acres of coastal
rainforest – from north of Sitka to Ketchikan.
In an ironic twist, researchers from UAF and the
U.S. Forest Service believe the trees are
essentially freezing to death. February and March
temperatures have warmed over the last 100 years,
but there are just as many late-winter frosts.
(Snowfall at low elevations has also decreased in
the last 50 years.)
It’s more common now for the air to warm up, melt
the snow insulating the ground, and then drop
below freezing again. Scientists figure the
thaw-freeze combination is killing the trees by
freezing their roots after warm weather has
jump-started tree growth.
“It’s kind of one of those things you would not
have expected,” said Paul Hennon, a forest
pathologist with the Forest Service.
Wildfires on the way
A week after Juday went to measure his trees,
snow started to fall in the Interior.
On a chilly October morning, Marc Lee drove south
from Fairbanks to check on a wildfire mitigation
project he was overseeing for the state’s
Division of Forestry.
He took a detour down a dirt road and studied the
landscape. A few houses sat at the top of a
valley filled with highly flammable black spruce.
“Those homes are toast, basically,” he said.
Lee turned off the road and drove down a hill
through patches of white spruce and birch. He
parked in a stand of black spruce and walked
along an icy trail to a giant clearing in the
woods – a fuel break covering 320 acres.
Piles of cut trees crackled with flames, and a
tower of gray smoke rose thousands of feet in the
air. Two men lit more piles on fire with a giant
torch spitting gelled diesel fuel.
Wildfires are a natural part of the ecosystem,
and they’re common enough in the Interior that
they burn just about everything every few hundred
But as temperatures have warmed in recent
decades, fires have increased in number and
intensity, threatening communities and altering
ecosystems. Fire seasons are starting earlier in
the year, and big fire years are more common.
“Things are changing, there’s no doubt about
that,” said Lee, who’s worked for the Division of
Forestry for 27 years. “We’re seeing it in the
In 2004, fires consumed more than 6 million acres
of forests across Interior Alaska, more than in
any year since records began in 1950. In 2005,
roughly 4 million acres of forests burned, making
that year the third worst on record.
Increased fires are already adding to the costs
of fighting fires, threatening homes and other
infrastructure, and posing health risks for
people with respiratory problems.
“It was pretty awful for people with problems,”
James Conner, the Fairbanks North Star Borough’s
air quality specialist, said of the thick smoke
in 2004 and 2005.
It’s hard to pin any specific event on climate
change, but warmer temperatures tend to result in
more fires. When scientists at UAF studied the
factors contributing to big fire years, they
found a strong correlation between the area
burned in any given year and how and dry the
summer was. The number of fires started by people
doesn’t seem to be a large factor.
The summers of 2004 and 2005 were unusually warm
and dry and, according to Lee, never got the
rains that normally come in July and August.
As the climate warms, researchers at UAF expect
fires to increase in the Interior. Climate models
project that Alaska will generally get more
precipitation in the future, but warmer
temperatures could dry out forests and even
tundra by increasing evaporation. Last fall, a
rare tundra fire spread across more than 220,000
acres north of the Brooks Range, sending smoke as
far north as Barrow.
In part because of the increased fire risk, Lee
said, the state is working with the Fairbanks
borough on an ambitious wildfire protection plan
that involves clearing wide swaths of flammable
trees in key locations around the city. The goal
is to cut of fires completely or at least allow
firefighters a place to get in and fight.
The break Lee checked on was meant to stop fires
rolling up the Goldstream Valley toward Fairbanks.
In addition to their direct impacts, wildfires
also have the potential to reshape the forests
themselves in connection with a warming climate.
In the past, Interior forests have generally
grown back in predictable ways after fires.
Willow, alder, and poplar dominate at first, then
birch and aspen, and finally, in upland areas,
white spruce. In cold and wet areas, the forest
might go straight from willow to black spruce.
But now that process is changing. Fires are
burning hotter, destroying organic matter in the
soils and thawing permafrost deep into the
ground. According to Chapin, a burn area might
come back as birch or aspen and transition very
slowly – or not at all – to white or black spruce.
“The plant succession is different from what we
might have expected 10 or 20 years ago,” he said.
A race against bugs
Juday grabbed the branch of a small white spruce
near his research plot and studied the tip. It
was brown, and bits of debris were nestled in the
needles – budworm.
Spruce budworm caterpillars spin silken nests in
tree needles in the summer and come out the next
spring, Juday explained. If the spring is a cool
one, the tree buds have a good chance to grow
before the caterpillars emerge. If it’s warm, the
caterpillars will hatch early and eat the buds,
stunting the tree’s growth.
“It’s a race,” Juday said. “And that race is
controlled by temperature – when it’s warm, the
Spruce budworm is just one of the insects
affecting Alaska’s forests. Spruce bark beetles
and engraver beetles also attack spruce trees;
leaf miners feed on aspen and birch.
Each insect has its own life cycle and preferred
host tree, but scientists say many of the bugs
are already doing more damage as temperatures
rise and will likely have a bigger and bigger
impact in the future.
Warmer temperatures allow the insects to thrive
while also stressing trees, making them more
susceptible to damage.
The most devastating of the insects so far has been the spruce bark beetle.
Between 1989 and 2002, bark beetles killed white,
Sitka, and Lutz (a cross between white and Sitka)
spruce trees across more than 3 million acres in
Southcentral Alaska, including roughly half of
the forested land on the Kenai Peninsula.
It was the biggest single insect infestation
recorded in North America until scientists this
year documented an even larger outbreak of pine
beetle in British Columbia.
Ed Berg, who has worked as the Kenai National
Wildlife Refuge’s ecologist for the last 15
years, studied the outbreak on the Kenai. By
looking at past outbreaks, he found that beetles
thrived when the average summer temperature
stayed above 51 degrees Fahrenheit for two or
more years in a row. (The warmer temperatures can
shorten the beetles’ life cycle from two years to
Before the outbreak in the late 1980s, warm
summers were typically offset by cool summers,
keeping the outbreaks in check, he said recently.
But starting in 1987, summer temperatures went
into “overdrive” and stayed warm for 11 years in
“Basically the beetles just kept building until
they ate themselves out of house and home,” Berg
said. “We’ve had warm summers since then, but
there’s not much for the beetles to eat.”
In recent years, beetles have infested trees on
the Kenai Peninsula that were too young and small
during the main outbreak but have since matured.
In 2006, beetles attacked tens of thousands of
acres in Katmai National Park & Preserve in
Other insects are affecting forests in the Interior.
Infestations of aspen leaf miner were hardly
noticeable before 1999 but have ballooned in
recent years. In 2005, insects affected aspen
trees across more than 650,000 acres of Interior
forests, according to the state’s Division of
Forestry. In some cases, the bugs contributed to
the death of trees already stressed by warm and
An outbreak of spruce budworm in the early 1990s
defoliated trees across roughly 280,000 acres of
forest along the Tanana and Yukon rivers.
The outbreak died down, but the insects returned.
In 2006, the bugs were “horrendous,” Juday said.
Aerial surveys showed damage along ridges near
Fairbanks – the Nenana, Parks, and Chena Ridges –
and in the northern foothills of the Alaska
Range. The outbreaks were so bad they spilled
over from white spruce to black spruce.
Last year, budworm showed up in the spruce around Juday’s house.
A changing ecosystem
The extent to which climate change affects
Alaska’s forests will depend on how fast things
change and how various impacts play out together.
While disturbances like fires and bugs are a
natural part of the ecosystem, a dramatic
increase in the extent of those disturbances
could overwhelm existing species, according to
Juday. Black spruce forests could turn to white
spruce, or lodgepole pine could extend into
More severe fires could also change which trees
grow in a given area, and severe droughts could
make trees more susceptible to insect damage.
Invasive plants and insects could pose additional
threats to the species here now.
Juday is still trying to figure out exactly what
climate change will mean for his 2,200 white
The tallest spruce in the plots is about 25 feet,
and countless birch already rise well above that
Fifty years ago, the white spruce almost
certainly would have won out on this south-facing
hillside above the Tanana River.
But things are different now, and Juday figures
the birch could possibly win out this time.
In 2007, Juday’s trees did OK. Tree growth wasn’t
back to normal, but the trees were recovering
from the warm summers of 2004 and 2005, thanks in
part to cool weather in 2006. Most trees had some
sign of budworm, but the insect damage was less
than the year before.
Juday crawled under the bows of one of his
bushier trees. He wrapped a special tape measure
around its trunk – converting from circumference
to diameter – and called out numbers to his lab
The trees’ fate wouldn’t be clear for years or
decades, and Juday had work to do now.
He climbed over thick logs of white spruce felled
by the fire 30 years ago and measured another
tree. There were still well more than 1,000 to
go, and winter was coming.