FAIRBANKS, Alaska (KTUU/KTVF) – As spring-like conditions come to Fairbanks and the winter snow continues to melt, community members are waiting for “green up,” an annual occasion where the boreal forest seems to turn green over a day.
Rick Thoman, Climate Specialist with the Alaska Center for Climate Assessment and Policy at the University of Alaska Fairbanks (UAF), has been keeping track of data related to green-up season since the early 1990s.
He said these measurements are done by looking with the human eye from the West Ridge area on campus to the boreal forest hillside at Chena Ridge.
“It’s not infrequent that Chena Ridge will be brown in the morning and then by late afternoon it’s all green,” Thoman said, noting there are sometimes disagreements within a day or two of when it happens.
He said the National Weather Service at the university’s Akasofu building has become the official record-keeper of green-up.
Over the years that green-up has been measured, the day it happens ranges from the last week of April to May 26-28, with May 8 as the average, according to Thoman.
“No surprise, the earliest green-ups are very warm springs,” said Thoman, “and the latest green-ups are where it stays cold … through April and even right into early May.”
This year, he said, experts predict May 8-10.
While Thoman noted that various factors, including how much sunlight hits the region and how quickly the snow melts, play into when green-up happens, he primarily uses spring temperatures to predict when it will happen.
By analyzing Fairbanks climate data going back to before World War I, researchers have attempted to reconstruct when green-up likely happened each year since that time.
Using these estimates, Thoman said it appears that green-up is happening, on average, about a week earlier in the year than it used to.
However, he noted that since observations began about 50 years ago, there has not been a statistically significant shift, with green-up being cyclical, with a period of several years where it’s happening earlier, followed by a similar timeframe when it’s happening later in the season.
Green-up is usually preceded by sap running in the birch trees, and these trees release their pollen around the same time green-up happens.
Afternoon humidity, Thoman said, also increases in the Fairbanks area around this time.
UAF Faculty and Staff member Toni Abbey said green-up season serves as a reminder of the imminent 24-hour daylight months, which she finds exhausting.
However, she enjoys the spring smells, which to her indicate the change of the season.
“Part of that smell is also the chokecherry trees that are around town, and unfortunately, I know they’re not indigenous and they’re bad for moose, but they create a wonderful smell in the springtime, that just adds to that natural change in the air that happens over the springtime,” Abbey added.
She gauges the onset of the green up season by the development of birch trees and cottonwood trees.
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