The tree line is crawling up on north slopes
on the Kenai Peninsula.
Phtoto by Ned Rozell
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.
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.
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.
Their results — Changes in the alpine forest-tundra ecotone commensurate with recent warming in southcentral Alaska: Evidence from orthophotos and field plots — appeared in December in the Journal of Geophysical 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. (See Berg on beetles.)