Green up is getting close

ANCHORAGE, Alaska (KTUU) - Anchorage is on the verge of “green up,” that period of time when the trees and grass shift from brown to green. Rick Thoman, climate specialist with the Alaska Center for Climate Assessment and Policy, has forecasted green up for some time between May 6 and 10.

Fairbanks is just a day or two behind that.

Green up was defined by forest ecologists at the University of Alaska-Fairbanks many years ago, looking at the greening of the boreal forest. One thing Thoman was very specific about is that green up is a large-scale phenomenon.

“It’s not when the very first leaf on the very first trees appear,” Thoman said. “It’s not when every single tree is leafed out. It’s a larger scale view and that general green tinge.”

The green up forecast is also focused on birch and aspen trees.

Why care about a green up forecast?

A lot happens when green up occurs, so having some warning can help.

For people who tap birch trees to turn the sap into syrup or other products, the green up forecast can give them a warning as to when the season might end.

“That sap is really only usable for that purpose in the time before green up occurs,” Thoman said. “As green up occurs, it starts to use the sugars in that sap, so it’s not useful for tapping, for making stuff — so tappers are very interested in getting an indication of when they’ll have to stop.”

Green up also leads to an explosion of tree pollen.

“People with asthma and other types of sensitivities to that, we can give them potentially a heads up for when that will occur,” Thoman said. “Because that usually occurs within a day or two of green up, that the pollen levels really go up.”

Last year in Anchorage, the tree pollen was in the moderate category on May 5, according to data from the Allergy, Asthma and Immunology Center of Alaska. Two days before green up, the level had jumped to 609, putting it in the high category. Green up occurred last year on May 9th. By May 14, the tree pollen levels were at 1,210, again in the high category.

The fire danger also falls as green up occurs. Right now, the grass is dry and burns easily.

“Once that snow melts off that dead dry grass, all that is a really flashy, fine fuel,” said Tim Mowry with the Alaska Division of Forestry Wildland Fire and Aviation program. “All it takes is a spark to ignite that grass.”

Mowry said the division has seen grass fires in the Matanuska-Susitna Borough, on the Kenai Peninsula and the the Copper River Basin. They are seeing specific kinds of fires, he said.

“Grass fires from escaped debris burns, grass fires from escaped burn barrels,” Mowry said. “This weekend we saw a grass fire in the Valley caused by a hot lawn mower parked over dry grass which is really indicative of how dry things are right now. That’s our concern right now.”

Mowry said another concern is that many of these fires are starting near houses.

“These are all human caused fires that we’re getting now. There’s no lightning,” said Mowry. “The thing that make this so dangerous is the fires these people are burning right now, debris burns, burn barrels, things like that, they’re typically close to homes. Once you get a spark in the grass, it just takes off if there’s any wind behind it, and it can be licking at the side of a house within seconds. And that’s what people really need to be aware of, is how quickly these fires can happen and spread at this time of year.”

Green up helps because those leaves opening up will put more moisture in the air.

“Green leaves and green grass, that’s the big thing,” Mowry said. “Once you get the green grass and the green leaves, there’s just a lot more moisture in green than brown. It’s just harder for a fire to catch and then spread.”

Of course, green up doesn’t make the fire danger disappear immediately.

“Just be careful and use common sense and just realize that anything you do that can create a spark can cause a fire,” Mowry said. “And that can be a lawnmower blade on a rock, that can be if you’re recreational shooting a spark on a ricochet. It could be setting a hot chainsaw down on dry grass. And it’s not just this time of year. Even when we get green up, we still want people to be careful.”

How to forecast green up

Forecasting green up is done by looking at daytime highs above freezing temperatures starting in March, but it’s not a simple mathematical formula. Days later in spring get more influence than those in the early part of the season.

“The same temperature in early May seems to be worth more, if you will, than in mid-March, that makes sense from the tree point of view,” Thoman said. “The sun’s much higher in May than it is in March so that’s somewhat accounting for that additional solar factor.”

Really warm temperatures — like in the 60s or 70s — have a dramatic influence on green up, so those get calculated in.

“It’s all based on the high temperatures above freezing, but with these date and high temperature adjustments,” Thoman said.

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