Tuesday, April 3, 2012

What a warm March we have had!

Crabapples put on a spectacular display almost a month early in Berthoud, Colorado

Today there are a lot of articles in newspapers and on the web about what an exceptionally warm March we have had all across the country. This past March has been a great opportunity to learn how adaptable our plants are to changes in weather. Here in northern Colorado the average daily temperature in March is normally 50 degrees F, but this year it actually averaged 58.6, and there were many days with high temperatures in the 80's! What was remarkable about this past March was it was so warm not only here in the Rockies but all across the country. We have been getting all kinds of reports to Project BudBurst especially from the midwest and east, of flowers appearing a month or more early this year. Climatologists say that such an unusual warm spring has not occurred like this since 1910, so it is an exceptional year indeed. In a northern climate to have flowers appearing a month early is pretty amazing. That is a huge change in the growing season!

Here in Colorado our warm March has resulted in some of the earliest records of flowering since Project BudBurst started 5 years ago. Just looking at where I make observations on a 1 mile loop around my town it has been quite an amazing pattern to see. Most plants that I have records for have flowers that appeared 15-28 days early this spring. This is consistent with some studies of how plants respond to changes in temperature. A particularly detailed study from Europe from the 1800's to the present showed that plants should put out flowers about 4 days early for every 1 degree C increase in temperature. For my area near Loveland, CO this comes out to about 19 days earlier, or right about the average for the plants I have been observing here (my average is 20.4 days).

Like many other topics in science you learn as much from the exceptions as the general rule. Here the exceptions to this rule, at least this year, are Quaking aspen which is only 7 days early, dandelions only 5 days early, and silver maple which flowered at exactly the same day last year and this year. Why? No clear answers yet but Project BudBurst data from here and places all over the country should provide scientists with lots of clues and puzzles to work on!

Paul Alaback

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