Other October events

Western rattlesnakes converge on communal hibernating sites in rocky hillsides and prairie dog colonies.

Elk continue bugling in mountain meadows. Visit Rocky Mountain National Park's Moraine Park or Upper Beaver Meadows at dusk to enjoy the spectacle (weeknights recommended).

Bottle gentians, gumweed and asters continue to bloom in the foothills.

Marmots, ground squirrels and meadow jumping mice enter hibernation.

An Arapaho legend tells how stars in the sky really come from the Earth. The stars move up through the roots of cottonwoods into the branches and wait until the night spirit asks the wind spirit to provide more stars. Winds blow, trees thrash and twigs break off to release the stars. If you snap off a twig that's neither too old nor too young, you will see a starburst at the node.

Just as aspens fade in the high country, cottonwoods come into their full golden glory on the plains.

Carotene and xanthophyll, yellow pigments that have been in the leaves all summer, make for a golden autumn. When photosynthesis shuts down, the green chlorophyll that masks other pigments is no longer replenished, and the underlying yellows are revealed.

As autumn progresses, the leaves turn brown and rustle rhythmically together "applauding the tune of the wind." In April, male and female flowers, borne on different trees, bloom.

The male flower resembles a red chenille tassel, whereas the female flower looks like a string of pale green beads. Later, the female catkin fluffs up into an elongated powder puff that fills the air with flying cotton like a spring snowstorm -- an efficient method of seed dispersal.

Until it died earlier this year, this plains cottonwood along Crane Hollow Road in Boulder County held the title of the largest in the United States.
Until it died earlier this year, this plains cottonwood along Crane Hollow Road in Boulder County held the title of the largest in the United States. (Photo by Glenn Cushman)

Cottonwoods sustain many creatures. Their "gallery forests" line waterways and have enabled many eastern species, such as blue jays, opossums and white-tailed deer, to spread westward. In spring, warblers flit through cottonwood branches searching for insects, and Bullock's orioles favor these trees for their pendulous nests. Great horned, screech and barn owls often raise young in cottonwood cavities, and bald eagles favor sturdy cottonwoods to support their large nests.

Plains Indians ate the bark and buds, which contain salicin and populin similar to substances in aspirin, to relieve pain. They also made a yellow dye from the leaf buds, and their children made toy tepees from the leaves. Cowboys and westering pioneers watched eagerly for cottonwoods, a welcome sign of water. They scraped the inner pulp for its sweetness and called it "cottonwood ice cream" -- a treat also enjoyed by Plains Indians and by horses.

There are more cottonwoods on the plains now than during pre-settlement times when prairie fires, irregular streamflows and trampling by bison herds limited their growth. Recently, however, many streams have been channelized and wetlands drained.

Cottonwoods, which need periodic floods to scarify their seeds, are not reproducing well. In many places they are beset by overgrazing and by the spread of introduced species such as Russian olive and tamarisk, which shade out seedlings, impede flooding and soak up groundwater.

Once started, cottonwoods grow fast and become enormous. According to the National Register of Big Trees, the largest plains cottonwood (Populus deltoides) in the United States grew on Boulder County open space until it died earlier this year. This champion cottonwood that reigned for 45 years measured 105 feet tall and more than 35 feet in circumference. The dead tree on Crane Hollow Road will continue to provide homes for wildlife for many years.

Plains cottonwoods have deeply furrowed, gray bark and deltoid or heart-shaped leaves -- sort of like a golden valentine for Halloween. Other Boulder County cottonwood species include the narrowleaf cottonwood (P. angustifolia); lanceleaf cottonwood (P. deltoides X P. angustifolia), a natural hybrid between the plains and the narrowleaf cottonwood; and balsam poplar (P. balsamifera), a possible relict of the glacial period.
