FAIRBANKS — The Fairbanks area is experiencing its annual melt-off this month, but the typical sight of dirty snow has been accentuated with a distinctive shade of rusty brown.

The culprit is a massive crop of birch seeds, which have accumulated on the canopy beneath local birch forests and along roadsides throughout the winter. As snow melts, the layers of seeds and their scales have merged into a thick blanket.

Jan Dawe, an assistant professor of forest science at the University of Alaska Fairbanks, said both anecdotal reports and a limited number of samples seem to verify this is an uncommonly strong crop. 

She examined branches from several trees on campus on Thursday, and noted they were loaded with the seed-filled remnants of female flowers. The trees’ male catkins, which create pollen, were either underdeveloped or completely absent.

It’s no accident. Dawe said the pattern began early last summer, when the combination of warmth and moisture was ideal for local birch trees. When the trees have a good, healthy spring, they typically focus more on making flowers than catkins.

“Energetically, it’s a lot more costly to make seeds,” Dawe said. “But when the conditions are right, you want to make a bumper crop.”

The development isn’t just a boon for birch trees. Their shift toward producing seeds last summer rather than catkins should bring some relief to local allergy sufferers. If the seed-heavy response is consistent throughout the area, pollen production should be down significantly this spring after several heavy years.

The trend also has provided an abundant food source for a variety of local birds, including chickadees, grouse, and most significantly, redpolls. 

Mark Ross, a wildlife biologist for the Alaska Department of Fish and Game, figures the Fairbanks area has seen the biggest influx of March redpolls in the past 7-10 years. That huge population received a big boost this year by the birch seed boom.

“That’s the primary thing they feed on this time of year,” Ross said. “I’ve seen them actually make short tunnels through the snow to get to the different layers.”

Scientists have eyed birch trees as a possible loser as Alaska’s climate gradually warms. UAF forestry professor Glenn Juday, who is now retired, declared two years ago the birch population was in “terrible shape” after several hot, dry summers and the recent migration of birch leaf miner insects to the Interior.

The warming weather also has lengthened the summer growing season by about 45 percent in the past century, however, giving surviving birch trees a boost when conditions are good. Some 4-year-old birch trees at a UAF test plot already are producing seeds, an occurrence that would normally be expected at 12 years old or later among wild trees, Dawe said.

She said the key for any species during a time of rapid change is to make genetic adaptations. An enormous crop of birch seeds, like the one seen this year, can help provide more variety to withstand a variety of conditions.

“The big question with climate change is can a species produce enough seeds in nature that genetically they’re adapting,” she said.

Contact staff writer Jeff Richardson at 459-7518. Follow him on Twitter: @FDNMbusiness.