DENVER — With about three and a half weeks left of summer, fall foliage will soon attract both residents and visitors to hundreds of beloved places around Colorado.
Denver7's Chief Meteorologist Mike Nelson says it looks like we should see our peak color on schedule this year. The best color over the northern mountains should begin around Sept. 12 and last through the 24th. The central mountains will be about five days behind, with the southern mountain areas rounding out the last days of the month and the first five days of October.
The turning of leaves, mostly aspens in the high country, while on the larger scale, is indeed affected by latitude (leaves turn earlier in Montana than Colorado, in general).
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Aspen trees in a given area vary in timing, due to genetic differences, perhaps. Some are past peak while the same type of tree nearby may still be changing from green to yellow. Soil moisture also plays a role — stressed trees may turn earlier.
Altitude is important mostly in the variation of nighttime temperatures. Plants tell time, it is believed, by a combination of temperature and daylength.
Perhaps the most appealing part of autumn is the gold found in the mountains each year. Not the gold sought by prospectors over a century ago, but rather the gilded glory of Colorado's famous aspen trees. The decrease in sunlight switches off the mechanism in the leaves that creates chlorophyll — the green color in the leaf. As the green fades, the gold color dominates until the dying leaf flutters to the ground.
The best years for aspen viewing are those with well-timed rains and no major fall storms. A too-dry summer will send the leaves falling quickly, while a wet summer tends to make them darken to brown or black. The most brilliant display of aspen occurs when we have a mild late summer and periodic gentle rain, combined with a dry September that includes few big windstorms or early snows.
Usually the first signs of aspen gold begin in mid to late August over the higher forests of central and northern Colorado. By the second and third week of September, many aspen groves are well worth a day's drive. Usually the peak time to view aspen is around the last weekend of September. After that, early snows will knock down the leaves and others drop away by themselves.
Aspen color does not vary nearly as much as the rich reds and purple leaves of the Midwest and East, but there is something about gold leaves against a backdrop of rich evergreen and deep blue sky that makes our fall mountains special.
Populus tremuloides — or the quaking aspen — can be found in all 11 of Colorado's national forests.
Aspen trees naturally propagate in areas where hardier trees have been damaged or destroyed. This was the case in Colorado, where the slender trees grew in after logging stripped trees from mountain areas. Characterized by their elaborate root systems, aspen reproduce by sending up suckers from the roots to create "clone" stands of trees. These clones, connected underground at the root, are genetically identical to the mother tree. The identical nature of a clone stand is most obvious in springs, when each tree in the stand leafs at the same time, and in fall, when each tree turns the same shade of gold.
Historically, native tribes used the aspen bark to make medicinal teas to alleviate fever. The inner bark was sometimes eaten raw in the spring, and the outer bark occasionally produces a powder that was used as a sunscreen. Aspen is a favorite of Colorado wildlife too. Beavers use aspen for food and building; elk, moose, and deer eat the twigs and foliage. Other names for quaking aspen are golden aspen, mountain aspen, popple, poplar and trembling poplar.
Despite Coloradans' affinity for aspen, these delicate trees are not highly recommended for residential landscaping, especially at lower elevations of the state. Aspens are susceptible to many diseases, their convoluted root systems often grow into sewage drainage systems, and they generally last no longer than about 10 years out of their native habitat.
