Wednesday, May 12, 2010

Rapid changes in plant phenology in the Rockies

Spring finally came to the northern Rockies in Missoula,
Montana in early May. Serviceberry and maples are in full bloom.

As mentioned in our blog a few weeks ago, spring has been coming early across the country over the past several decades. How early spring has advanced depends on what species (and what phenophases) you are looking at or where you are. Spring has advanced so rapidly in some places that it appears to be causing stress for some native plant species. A study just published in the Proceedings of the National Academy of Sciences even documents a bird species in Europe that has increasing numbers of its populations that have apparently quit migrating, in response to warming spring and winter weather (!). Recent studies have documented that plant species that are most flexible and that are changing dates of first flowers or first leaves emerging tend to be doing better than species that are not changing their dates of their phenological stages (phenophases). (spring creep). This effect varies by species and location, so is an active area of scientific research. Scientists still do not clearly understand the causes of this variation by species or location (see Korner and Basler, March 10, 2010 issue of Science )

A recent study (Lesica In Press, Journal of Arid Environments) documented that in semi-arid or dry areas, like here in the Missoula valley of western Montana spring may be advancing even more rapidly than what we have seen in the Midwest and East. Most studies have documented that spring wildflowers are appearing an average of 3 days earlier each decade for the past 30 years or so, or an average of about 10 days earlier than historical records. Most of these studies have been done in humid climates in the eastern US and northern Europe. The Lesica study, and budburst data in this region show that spring is advancing at a rate of 7 or more days per decade for the earliest species, or more than twice what has been reported in most other regions.

Sagebrush buttercups are local sign of spring in our area. They put out leaves in the fall, usually in response to fall rains. Then they put out more leaves and the first flowers usually within a week or so of consistent warm temperatures, usually in the middle of March. In just the past 14 years, Lesica found that these flowers are emerging an average of 1.6 days earlier each year, or more than two weeks over the study. More than seven years of data were available for thirty-two species, 75% of which are flowering earlier. The most rapid advance in dates of first flowers were noted for 10 of the earliest flowering herbs. Comparing budburst data with my monitoring data for these foothills around Missoula, many plant species are flowering earlier even in the summer or fall, another result that is much more dramatic than for many humid sites in the East.

This study highlights the importance of what we are trying to do with our network of volunteers in Project Budburst. While there are general trends of how plants are responding to changes in climate, there are significant differences in some regions. Scientists really need better information on how all parts of the country are changing in response to changes in weather and climate, and how changes vary by species and phenophase.

Keep those observations coming!

Budburst News

Over 10,000 observations submitted by Budburst volunteers! We broke this threshold in early May. Keep up the good work! It is especially valuable when you can make observations on the same sites and species from year to year.

Top 10 wanted! Also check if any of our top 10 species or closely related species occur in your area. These data are especially useful to us in documenting how phenology is changing for these species across the country.

Paul Alaback

Photos: Top-Mount Sentinel, Near Missoula, Montana on April 25th. The cool spring has extended the length of the flowering period for both western serviceberry (Amelanchier alnifolia) and for Norway maple (Acer platanoides)
Middle: Sagebrush buttercup (Ranunculus glaberrimus) in flower on Mt. Sentinel.
Bottom: Yellow Puccoon or yellow gromwell (Lithospermum ruderale), one of the herbs found to be flowering weeks earlier that was recorded in the early 1990's.

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