Alaska Science Forum

May 18, 2011

Greenup hits, so does pollen

Article #2064

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.

Greenup — the great, silent collective explosion of freed tree buds that had been frozen all winter like a clenched fist — happened yesterday in interior Alaska. I know this because it’s a phenomenon that’s easy to notice here in Fairbanks, which is locked up in black-and-white for much of the year. And because Rick Thoman just told me.

Thoman, who works for the National Weather Service in Fairbanks, called it the most dramatic greenup in years, and the latest since 2002. His colleague Ted Fathauer, who has recorded greenup at his home on Chena Ridge since 1986, also declared yesterday, May 17, as the day “leaf buds in birch and aspen open just enough to produce a faint, but distinct green flush through the forest canopy.”

That description of greenup is from the late Jim Anderson, a librarian here on the West Ridge of the University of Alaska Fairbanks campus who chronicled the event beginning in 1974 until his death in 2007.

Anderson, who found his hobby was also an interesting way to measure short-term climate change, noticed the greenup date fluctuate by about a month, with a slight trend toward earlier greenups. The earliest Fairbanks greenup he measured was in 1993, when the hills changed on April 30. The latest greenup occurred on May 25, 1992, when the average temperature for the month was 41.8 Fahrenheit degrees, more than six degrees colder than normal.

The new neon-bright leaves increase humidity a bit as they complete a pathway in which deciduous trees pull water from the ground and emit water vapor. One would also think moose must be happy to have some fresh greens after a winter of chewing frozen twigs. Jim Anderson pointed out another consequence of greenup — a rise in the amount of pollen in the air. He for years measured pollen concentrations in the air with a device mounted on top of the building that houses the library in which he worked. Anderson, who did not suffer from allergies, created charts for people who did. Birch pollen gives people the most problems, followed to a much lesser degree by alder and willow.

Using pollen and greenup data, Anderson determined that birch trees start to release pollen about two days before greenup. He found that birch pollen reaches its maximum concentration—3,000 pollen grains per cubic meter of air—about three days after greenup. On one busy day, he measured more than 4,500 grains of birch pollen per cubic meter.

As I wrote in this space in 1999, grains of tree pollen are small enough that eight of them would fit on the period at the end of this sentence. The air is heavy with these dots because trees do their hit-and-miss mating in springtime. The first step in a tree’s reproductive mission is to release sperm, held in the center of a pollen grain. Trees release a staggering amount of pollen to improve the odds of finding a female flower. One birch catkin (the cluster of tiny flowers that looks like a caterpillar) can release millions of pollen grains.

Allergy sufferers are hit hardest by birch pollen because it contains irritating proteins. Each grain of pollen consists of a center containing the male genetic material, surrounded by a protective wall called the exine (which was not coincidentally the word featured on the license plate of Anderson’s van). When pollen comes in contact with moisture, such as that on the nose's mucous membranes or the lining of the eyelid, protein molecules from the exine leach into a person’s tissues. An allergic person's immune system produces antibodies against the protein molecules. Antibodies then trigger the release of histamines and other potent substances, leading to cold-like symptoms.

Anderson discovered that, in the Fairbanks area, poplar and aspen release pollen first. Birch, alder, spruce and grasses follow. But all things end, even pollen season, and according to pollen calendars Anderson made for Fairbanks and Anchorage, birch trees typically shed the largest amounts of pollen May 10th through the 20th, and then they are done for another year.           

A parachute and a rocket payload as seen from a small aircraft over northern Alaska the same day the rocket launched from Poker Flat Research Range in Chatanika, Alaska, 170 miles away.

Photo by Ned Rozell.

Chris Christenson of NASA helps attach a rocket payload to a helicopter sling near a small arctic creek 170 miles north of Chatanika, Alaska, from where the rocket launched a few days before.

Photo by Nick Cranor of NASA.