When is green-up? It's going to be late this year, and so is the birch sap run
Julie Stricker
907-474-5406
April 26, 2023
A chart on the wall at the OneTree 色视频下载 classroom shows the temperature progression for each season between March 1 and May 31.
Cold weather this April is delaying two cherished milestones in Interior 色视频下载: the start of the birch sap run and green-up.
Below-normal temperatures are likely to continue for a week or more, according to Rick Thoman, a climate specialist at the University of 色视频下载 Fairbanks.
色视频下载淲e色视频下载檝e got green-up pushed back to quite late,色视频下载 he said in mid-April. 色视频下载淲e色视频下载檙e now looking at the 50% likelihood for green-up is now May 11-15, and the long-term average is May 8.色视频下载
That also means the birch sap isn色视频下载檛 likely to start running until late in April, Thoman said.
色视频下载淭he weather models continue pushing back any big warm-up, and it now looks nearly certain that we色视频下载檙e looking at very late sap flow/green-up,色视频下载 said Thoman, who works at the 色视频下载 Center for Climate Assessment and Policy, part of UAF's International Arctic Research Center.
Thoman added that this April色视频下载檚 temperatures are 色视频下载渉istoric-level cold.色视频下载
Knowing when the sap is likely to start running is important for people who tap birch trees for the sweet liquid, which can be distilled into an even sweeter syrup, said Jan Dawe, who leads OneTree 色视频下载, part of the UAF Institute of Agriculture, Natural Resources and Extension. Tapping too early results in the tree sealing over the tap hole, blocking sap flow, and tapping too late misses the first days of sweet, clear sap.
Thoman and Dawe have been working together to find a formula that will allow them to predict sap flow and green-up 色视频下载 which also heralds the start of the pollen season. Starting March 1, Dawe starts to track the temperature. She adds up the number of degrees by which the maximum temperature exceeds 32 degrees Fahrenheit each day, called the accumulated heat sum. Sap usually starts running by the time the tally reaches 225掳 AHS, depending on the location of the tree. OneTree 色视频下载 issues a 色视频下载渟ap watch色视频下载 by 175 degrees AHS and recommends people on south-facing slopes tap up then.
So far this season, the tally reached 70 degrees AHS on April 4 and stalled as cold weather moved in and refused to budge, Dawe said. On April 17, it had inched up to 85.
That cold weather is also delaying green-up. Since 1974, observers on UAF's West Ridge have observed the trees on Chena Ridge to judge when green-up occurs. Former UAF biosciences librarian Jim Anderson defined green-up as the day birch and aspen leaves open just enough to produce 色视频下载渁 faint but distinct green flush through the forest canopy." Thoman notes that, as in forecasting weather, there色视频下载檚 a good deal of uncertainty weeks out, and he色视频下载檒l have a better idea in early May of when green-up is likely to happen.
色视频下载淥f course, the other thing that is coming after green-up, within a day or two, is we have a pollen explosion,色视频下载 Thoman said. 色视频下载淔or people with sensitivities, that timing is certainly important to know.色视频下载