New Maps Chart Old-Growth Forests in Alaska, B.C

Mature and old-growth forests are vital for biodiversity, carbon storage, cultural traditions and economic activity. But in Alaska and British Columbia, these rich resources haven't been reliably mapped, leaving much unknown about what land is protected.

Now, University of Oregon researchers are leading a comprehensive mapping effort that sheds light on the location, makeup and conservation status of old-growth forests across the region.

Their data show that more than 40% of mature and old growth forests in the study area are in places that lack permanent legislative protection. These forests also store the most carbon in the study area.

"Our goal was to better capture where old-growth forests exist, how and where they're being conserved and what the different vulnerabilities are based on the policies that govern conservation efforts," said study lead author James Lamping. The study was recently published in the journal Ecosystems.

Mapping old growth

Old-growth forests in Alaska and British Columbia are protected through a range of land classifications, including national parks, national monuments and wilderness areas. But by far the greatest area of old-growth forest was found in "Inventoried Roadless Areas" in Alaska.

Inventoried Roadless Areas lack the permanent legislative protections found in places like national parks or monuments. Instead, they're governed by the federal administration.

For over 20 years, the 2001 Roadless Area Conservation Rule has prohibited road construction or timber harvests in these areas. But changes in administrative priorities can alter the protections given to Inventoried Roadless Areas without going through Congress.

"One of the biggest takeaways from our research is that the highest amount of old-growth forests are in Inventoried Roadless Areas, which happen to be the most vulnerable to changes in the policies that govern these forests," said Melissa Lucash, UO geographer and co-author of the study. "The mapping effort showed just how much old growth, and how much carbon storage, exists in areas that are more vulnerable to these types of policy changes." 

The researchers don't call for policy changes or conservation protections in their paper. Instead, they provide the status of old-growth forests in Alaska and British Columbia, which can be used to track changes and guide policy. 

In Alaska, they found 3,720 square kilometers (roughly 1,400 square miles) of old-growth forests in Inventoried Roadless Areas, compared to 1,560 square kilometers in national monuments and 730 in national parks.

In Oregon, Washington, and northern California, land managers have used this kind of data to inform the Northwest Forest Plan, which dictates land use and management on federal lands in the Pacific Northwest.

But in Alaska and British Columbia, there have only been piecemeal snapshots of old-growth forests, or global maps that lack precise information about their location and makeup, the researchers said.

Mapping this data for Alaska and British Columbia was particularly challenging because the area spans international borders.

"It's been hard to get a good idea about how much old growth there is in Alaska and British Columbia because different agencies apply different definitions for old-growth forests, and these maps are often artificially dissected by borders," Lucash said. "We wanted to create a consistent framework that offers confidence in the maps that we produced."

Lamping started with forest inventory plots that contain data about the makeup of forests, including tree species, vegetation and structure. He linked those measurements to satellite imagery, climate variables and topographic data to create a detailed map, making inferences based on how similar a given spot's environmental conditions were to places that have been measured on the ground.

The group mapped the different species in each forest, the type of forest, the amount of carbon storage and what percentage of each area is classified as mature or old growth.

Knowing the makeup of the forest helps land managers better understand where conservation efforts could significantly enhance biodiversity and carbon storage.

The group's methodology can also be used to track changes in the forests over time.

"The Northwest Forest Plan highlights how important old growth is and how much we need strong and consistent data for policy decisions," Lamping said. "But this data is just as important in Alaska and British Columbia. The Pacific Northwest's temperate rainforests are all connected, so it's vital that we have maps and continued monitoring for mature and old growth forests across the entire region."