Weather Window: Sierra butterflies waiting for Spring
June 23, 2011
TAHOE/TRUCKEE and#8212; The snowpack is melting quickly at the lower elevations, but a thick frozen mantle persists up top and in the north and east-facing basins. Several local ski areas will take advantage the unusual conditions to run chairlifts over the Fourth of July weekend for anyone jonesing for more turns or angling for bragging rights and a T-shirt.
July is right around the corner, but Lake Tahoe’s surface water temperatures are still chilly, ranging in the mid 50s (a little colder in Tahoe Vista), which makes for bracing water sports. More importantly, Tahoe’s surface elevation is now above 6,227 feet and rising, good news for water supplies, boating enthusiasts and the Truckee River ecosystem.
The late season snowpack is impacting the area and human and animal behavior. To avoid snow, mountain bikers and hikers are staying east of the main Sierra range or heading for the lower elevations to enjoy their sports. Engorged streams and rivers are running cold and fast, with flood advisories, watches and warnings currently posted on many regional water courses. Snowmelt has been manageable so far and available upstream water storage has mitigated most potential flooding risks.
Something more subtle most people won’t notice is the cold spring has delayed butterfly emergence on Donner Pass. Professor Art Shapiro, a renowned world-class entomologist and ecologist with the University of California, Davis, has monitored butterflies in the area for more than 35 years. I met him recently at Norm Saylor’s Donner Summit Historical Society in Soda Springs. Shapiro said in his 35 years studying butterflies in the area, this is the latest date none have been observed flittering about.
Truckee has a long history associated with butterflies. Town patriarch Charles F. McGlashan, an author, attorney, teacher and noted entomologist, was well known for his extensive collection and expert field knowledge of the fascinating insects. McGlashan was in the right spot. According to Dr. Shapiro, with more than 100 distinct species the Donner Summit area boasts such diversity the site ranks as one of the and#8220;richest butterfly faunas documented in North America, north of Mexico.and#8221;
Dr. Shapiro recently published a major paper on his remarkable butterfly research that uncovered the negative impacts urban development and climate change are having on butterfly diversity at his 11 study sites. Species diversity at all his sites, including near sea level, the central valley and Sierra foothills, is declining rapidly. In the mountains the loss is slower, while at the highest elevation monitoring sites near tree line butterfly diversity is actually increasing as lower-elevation species escape the warming climate by moving upslope to cooler regions. Diversity is decreasing, however, for those butterflies adapted to the coolest air at the highest elevations as temperatures there also increase (http://butterfly.ucdavis.edu).
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With all the snow above 7,000 feet, it’s no surprise butterflies are taking their time emerging for the summer. Just a few weeks ago the snowpack at the Central Sierra Snow Laboratory near Soda Springs was nearly 8 feet deep, the greatest depth of record for the date at their study site. The nearly 54 feet of snow that fell at the Snow Lab during winter 2011 is third greatest since World War II, behind only 1952 (812 inches/67.7 feet) and 1983 (671 inches/56 feet), two iconic winters that had tremendous impact on the region.
After enduring such a long and stormy winter, you can’t blame the butterflies for being gun-shy about leaving the safety of their protected nests.
and#8212; Tahoe weather historian Mark McLaughlin is a nationally published author and professional speaker. His award-winning books are available at local stores or at http://www.thestormking.com. You can reach him at firstname.lastname@example.org
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