For avid tree peepers, the state聮s quaking aspen colors should be glorious this fall, according to a University of Colorado at Boulder professor.
"The summer moisture and recent evening cooling patterns should make for excellent aspen viewing," said Michael Grant, a professor in the environmental, population and organismic biology department. He predicted the aspens at higher elevations may begin to turn during the second week of September, those at mid-elevations should be in their prime in the third week and those at lower elevations likely will peak during the last week of the month.
Although the gold, yellow and red pigments seen in the aspen leaves each fall are present throughout the spring and summer, they are overshadowed by the green chlorophyll, the primary food-manufacturing pigment in the trees. When the chlorophyll is retracted from the leaves in autumn in preparation for winter dormancy, the brilliant pigments remaining in the leaves shine in full glory.
The only major tree species that changes color in the high country, quaking aspen begin to turn color on north-facing slopes first, said Grant, who also is CU-Boulder聮s associate vice chancellor for undergraduate education. The colors of aspen leaves primarily vary because of their genes, much like hair color in people, he said.
In the arid West, quaking aspens reproduce asexually through a cloning process, generating many underground runners from a single root that sends stems, or trees, to the surface reaching heights of 50 feet. This causes individual patches of trees belonging to the same clone to turn the same color at about the same time, he said.
In 1992, Grant, along with EPO biology Professors Jeffry Mitton and Yan Linhart, identified a clone of aspen trees in the Wasatch Mountains west of Salt Lake City as the most probable candidate for the world聮s largest living organism. Working from a description of the giant aspen clone published in the journal Forest Science, the CU-Boulder professor calculated the clone weighed about 13.2 million pounds.
Their paper, published in the weekly international science journal Nature, estimated the clone was 60 times heavier than the world聮s previously known largest living organism, a gigantic fungus located in a Michigan hardwood forest. The aspen clone, estimated to be about 33 times heavier than a blue whale (the largest living animal on earth) and three times heavier than the world聮s largest sequoia tree, is now listed in the Guinness Book of World Records.
Researchers can usually identify aspen trees belonging to the same clone through similarities in leaf shape, bark color, time of bud production and the angle of branches protruding from the stem. But direct genetic testing is the most reliable method, said Grant.
Some of the best quaking aspen viewing along the Front Range west of Boulder this fall should be on the Peak to Peak Highway (Highway 72) linking the Central City-Blackhawk area to Nederland and north to Allenspark. Along Interstate 70, large aspen stands between Vail and Avon provide good viewing and the area around Ouray in southwest Colorado sometimes has spectacular displays.
For those who prefer to view the autumn glow of aspen off the beaten path, Grant recommends the gravel road running from just west of Nederland to the old mining town of Caribou and the gravel road running west of Rollinsville toward East Portal and the Moffatt Tunnel.
The most serious aspen aficionados with the time and resources could conceivably stretch the aspen viewing season to seven weeks by following the Rocky Mountain corridor and accompanying aspen clones from Alaska to Mexico, he said.