Tree line changes on the Kenai
By Ned Rozell
January 07, 2008
The late Yule Kilcher, a Swiss homesteader who knew the landscape
around Homer better than anyone, once told ecologist Ed Berg
that during Kilcher's half century of observing the natural world
around him, trees in the area had crept "at least several
hundred feet" up the hills.
Two students at Alaska Pacific University recently confirmed
at least part of Kilcher's observation. They looked for changes
in the tree line of the western Kenai Peninsula and found it
has risen about a yard each year since 1951 on north-facing slopes.
Tree line didn't change much on south-facing slopes, but trees
and bushes got denser there.
Tree line is on the
move in many areas of Alaska.
Photo by Ned Rozell
Katrina Timm and Alissa McMahon compared photos of the western
Kenai hills from the 1950s to photos of the same area taken in
1996 to see the changes in tree line, which is among the most
gradual and spotty indicators of warming. In comparing the photos
and hiking into the hills to sample trees and take detailed measurements,
the pair also found that 20 percent of the alpine tundra that
existed in 1951 had become shrubbery or open woodlands by 1996.
They wrote up their results in the Journal of Geological Research.
The gradual change in tree line is one of many that people have
noticed on the Kenai Peninsula in recent years. The most obvious
is the 1980s-to-1990s Spruce bark beetle invasion, during which
the insects killed 30 million mature spruce trees on the Kenai
and a wide swath of southern Alaska. Harding Icefield, coating
the high country of the peninsula with tendrils of glacier reaching
toward the sea, also has shrunk more than 70 feet in elevation
during the last half century, and kettle ponds on the peninsula
are drying up.
Ed Berg, an ecologist with the Kenai National Wildlife Refuge
for the past 15 years, has noticed other subtle changes in the
trees of the Kenai. Since Yule Kilcher alerted him to what he
perceived to be a fast-moving tree line, Berg kept his eye on
the trees growing at the edge of alpine areas. He noticed that
gnarled dwarf evergreens up high were becoming a rarity. These
trees, called "krummholz" ("twisted wood"
in German) by foresters, have lush growth near the ground where
snow protects them from wind-driven ice crystals. They are quite
small for their age; Kenai krummholz hemlock six inches in diameter
have been alive since the 1500s, Berg wrote in a 2004 article
for the Kenai National Wildlife Refuge. In the article, he wrote
of the major change he noticed in the forest of "twisted
gnomes," possibly due to less extreme weather.
"Kenai mountain hemlocks aren't doing krummholz anymore,"
Berg wrote. "Baby hemlocks now grow straight up at tree
line, and have probably been doing so for much of the 20th century,
to judge from the upright saplings growing amidst the krummholz
The changes in Kenai Peninsula trees might be due to the milder
weather the peninsula, along with most of Alaska, has experienced
since about 1977, when ocean-surface temperatures in the North
Pacific warmed. Climatologists with the Alaska Climate Research
Center report that the Homer area warmed 4.2 degrees Fahrenheit
on average from 1949 to 2007.
As for the near future, people can expect to see more changes
in the area, according to Roman Dial, a professor at Alaska Pacific
University and the advisor to Timm and McMahon.
"Even if the climate were to reverse itself today, the changes
we have already seen during the last 50 to 100 years would likely
take more than that length of time to reverse themselves,"
Dial wrote in an article for the
newspaper, Peninsula Clarion.
This column is provided
as a public service by the Geophysical Institute,
University of Alaska Fairbanks, in cooperation with the UAF research
community. Ned Rozell is a science writer at the institute.
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