I tell time by watching the seasons. I know it's spring when buds come up on the lilac bushes. Hummingbirds, as they dart across my yard, announce summer. Fall begins when the rabbit brush has gone to seed, and winter when the last leaf has fallen off the cottonwood trees. Some plants don't seem to notice the change in weather, but others, like the aspen, have a new outfit for each season.
My family and I enjoy hiking the Mount Taylor Ranger District of Cibola National Forest. We usually hike one of three trails near Wingate, New Mexico: Strawberry Canyon, Milk Ranch Canyon, or the Look Out Tower trail, but in May 2001 we tried camping and hiking at a new spot that a friend recommended. We camped next to a pond called Lost Lake. The land around the lake looked like much of Cibola National Forest: ponderosa pine, gambel oak, pion pine, and juniper circled the pond. At night we heard spadefoot toads croaking, and in the morning we saw tadpoles and goldfish in the pond. We found several trails near the pond and decided to try all three. At the beginning of one trail, only 100 yards from our tent, we found fresh bear tracks in the mud.
Everyone in my family ran in different directions when we heard a rattlesnake under my dad's feet. Our third hike also provided a surprise, though a subtle one. After hiking one mile, we reached an aspen grove in a valley. I was surprised because there are few aspens in our ranger district. I had seen aspens in the cooler, higher mountains of Colorado, but aspens are scarce here. The aspen grove was long and narrow; it filled an entire valley. Ponderosa, pion, and juniper grew on the sides of the valley, but none grew in the valley with the aspens. Not even the scrub-like gambel oak grew in the aspen grove. I wondered why aspens grew in this one spot but not in the rest of the forest. Is it cooler in the valley? Does this valley get more rainwater and melting snow? Or is the grove an island left over from a cooler, moister period in the forest's history? I hiked to the aspen grove several times in 2001 but never tried to answer my questions. But this summer (2002), I decided to act.
August 11, 2002: Lost Lake
Today we went to the aspen grove near Lost Lake. Near the Look Out Trail, we saw a doe and her fawn. They stood still for a minute, but ran through the trees when I got my camera out. Two cowboys and a herd of about 30 cows crossed our road, so we stopped for a few minutes while the cows walked past. Some cows left the trail and the cowboys had to chase them back.
We got out of the car when we reached Lost Lake and took the trail to the aspen grove. The aspen grove was warmer and drier than I had expected. At 3:35 pm it was 83°F and sunny. There was a light breeze and the air felt dry. I think of the aspen grove as being moister than the rest of the forest, but I couldn't feel or see any difference today. I marked off a randomly chosen area about 50 yards by 50 yards. I chose four trees to mark the boundaries and tied pink parachute string around the four chosen trunks. Three trees were carved with graffiti; one was dark and chipped. The land in and around my box is filled with tall aspens. The aspens grow down here at the bottom of a canyon on flat ground. But where the land rises and the walls of the canyon begin, there are no aspens. The canyon walls grow only conifers typical to the rest of the forest: junipers, pions, and ponderosas. Inside the box I found two kinds of mushrooms, various flowering plants, one lizard, cow pies, deer scat, and one leaf from a gambel oak. I was surprised because there are no gambel oaks growing in the valley. Now I know that an acorn could blow into the canyon and sprout, but there are no oaks growing here now.We saw a hummingbird drinking from an Indian paintbrush. Another hummingbird was attracted by my dad's bright red licorice. It was disappointed when the licorice disappeared down my dad's throat.
I still had questions after this hike. I wondered why aspens predominate in the valley near Lost Lake. The aspen grove differs from the rest of the forest, which is a mixture of pion, ponderosa, and juniper. I saw no obvious solution to why aspens should grow in this one spot. I decided to compare my box at the aspen grove to a control area at Milk Ranch Canyon. What environmental characteristics favor the growth of aspens near Lost Lake? I thought that higher altitudes and cooler temperatures would probably create a good climate for aspen. I also thought that the extra water that ran into the valley would make it an ideal area for aspens.
After my expedition of August 11, I decided I needed tools: a pedometer to measure the size of the aspen grove, an altimeter to measure altitude, and a psychrometer to measure humidity. I predicted that the altitude at the aspen grove would be higher than the altitude at Milk Ranch Canyon. I also predicted that the aspen grove would have a higher humidity than the control area at Milk Ranch Canyon.
September 7, 2002: Lost Lake
Today we hiked 0.8 of a mile from Lost Lake to the aspen grove. We saw some flowering scarlet gilia. The gilia look like bright red shooting stars. We got to the aspen grove at 11:40 am. It was 73°F, with 55 percent humidity, and the sky was partly cloudy. The altimeter read 8,900 feet above sea level. After identifying the trees that marked the corners of my box, I explored inside it. I looked on the ground first. Today I saw more Indian paintbrush than I did on August 11. I found several bushes with yellow flowers; the bushes look like a species of cliff rose. The aspen leaves are beginning to turn yellow.
Some aspens had patches of bark missing. The first layer of bark was scraped away, revealing a layer of green chlorophyll. The trees were scraped between my shoulder and eye level. On a few of the scraped trees, I found short brown and white hairs. Elk must have scraped the trees, trying to reach the inside bark of the trees. Walking back to the car, I saw a horned lizard and scarlet gilia.
I was interested in the green chlorophyll I saw underneath the aspen bark. At home, I consulted Ann Zwinger's Aspen: Blazon of the High Country, from which I learned that while most trees collect energy only through their leaves, aspens also use their bark to collect the sun's energy. "The ability of aspen to photosynthesize almost year-round, even at temperatures below freezing, adds about 2 percent to the tree's net photosynthesis" (p. 4). Photosynthetic bark helps aspens recover from insect damage and frosts, and allows aspens to grow in coniferous ecosystems where other deciduous trees cannot grow.
Even in years of drought prickly pear cacti bloom profusely. The cacti store water so that they can bloom and be pollinated even in dry years.
I also wondered about wildlife benefiting from aspens. In Colorado, on a vacation, I once saw an abandoned beaver lodge surrounded by felled aspens. I wondered why the beavers had cut so many trees. Since then, I have read that beavers eat aspen bark, but cut down twice as many trees as they can gather food from. Cutting trees not only feeds the beavers but also files down their ever-growing teeth. Deer and elk also benefit from aspens. Both deer and elk graze on aspen leaves when the aspens are young and small. Elk also "bark" aspen, scraping the outer bark with their teeth in search of the green chlorophyll. "Elk and aspen are almost synonymous in the West," writes Zwinger, "and aspen stands on the first day of hunting season are not good places for hikers to be" (p. 24).
The summer of 2002 was a summer of drought. I knew the elk had survived the drought when I found elk tracks and saw the damage caused by elk "barking" aspen trunks. Since I have not seen any bear tracks or bear scat this summer, I wonder whether the bears survived the drought. I hope they found a corridor to a moister valley.
September 16, 2002: Milk Ranch Canyon
Today it took 20 minutes to hike one mile to Milk Ranch Canyon. In the muddy spots of the trail I saw both deer and elk tracks. In one spot I saw dog prints and small tracks that look like raccoon tracks.
At Milk Ranch Canyon, in a randomly chosen area, I marked off a box 50 yards square. A tall ponderosa, two junipers, and a cliff rose formed its corners. At 2:23 pm, I checked the temperature, humidity, and elevation. It was 64°F, with 30 percent humidity, and the elevation was 7,500 feet. The sky was clear and sunny.
Pion, juniper, ponderosa, and cliff rose are the main flora in my box at Milk Ranch Canyon. Ponderosas are my favorite. Their bark smells like cream soda. Other flora in this box includes: scarlet gilia, a purple flower, yellow flowers, blue grama grass, prickly pear cactus, several types of lichens, Spanish moss (growing on pion), gambel oak, and Indian paintbrush. At Milk Ranch Canyon, no one species predominates.The soil at Milk Ranch is sandy, dry, and red-brown. Lizards hide so well I see them only when they streak. I glimpsed one lizard. A scarlet gilia attracted a hummingbird.Surprisingly, Milk Ranch Canyon exhibits greater biodiversity than the aspen grove. I still need to identify some of the flowers I photographed at Milk Ranch. Even my Boy Scouts of America Philmont Fieldguide, specific to northern New Mexico, failed me here.
September 22, 2002: Lost Lake
We went to the aspen grove at Lost Lake today. With a pedometer, I measured the length of the aspen grove: it is 50 yards wide and half a mile long. Walking the length of the aspen grove, I heard a couple of gunshots.The aspens have green leaves; only a few leaves are yellow. Scarlet gilia, Indian paintbrush, and goldeneye are still blooming.
Walking back to the car, a single turkey crossed our trail. I had only seen wild turkeys in groups before today. Perhaps this turkey was scared away from its companions by hunters.As we approached Wingate, a fox dashed across the road. Here I also noticed aspens at a halfway point between Lost Lake and Milk Ranch Canyon. These aspens have gold leaves. Are their leaves turning yellow faster because they get more sun than the aspens near Lost Lake?
Comparing Aspen Grove to Milk Canyon Ranch
|Aspen Grove||Milk Ranch Canyon|
|Altitude||8,900 feet||7,500 feet|
|Date||Sept. 7, 2002||Sept. 16, 2002|
blue grama grass
prickly pear cactus
With this expedition, I had "discovered" a second aspen island in the forest of pion and juniper. The question of what conditions favor aspen growth persisted. I knew melting snow could make the aspen groves quite marshy. Could it be that aspens tolerate marshy periods but ponderosas and other conifers do not?
Gambel oaks grow from acorns, pions grow from their nuts, but I didn't know how aspens handled reproduction. The cottonwoods in my backyard send sprouts up from their roots as a way of reproducing, so I thought aspens might send up shoots as well. I turned to my references and found that aspens, in fact, use both forms of reproduction. While aspens do release seeds, they prefer to send up shoots from the roots of a parent tree. Many aspens in one grove are clones of another aspen. Aspens that start as ramets, or suckers, from another tree's roots, will share characteristics with the "parent" tree. The aspen clone has the same sex, bark color, and branching habit, and breaks dormancy at the same time. Some aspens grow from seed, but this is rare.
In The Sagebrush Ocean, photographer Stephen Trimble describes aspen groves in the arid West as island communities, remnants of the Pleistocene era. At the end of the last Ice Age, New Mexico had a cooler, wetter climate than it does now. Today, 10,000 years after the last Ice Age, aspen groves survive where conditions permit. The aspen groves I explored could be two of these islands.
Many aspen groves, Trimble explains, consist of one clone in which all the aspens are genetically identical. Unlike aspen clones, "laboratory" clones of sheep and cats aren't true clones; they retain only 90 percent of their parents' DNA (Discover, January 2003, p. 31). One aspen may live only 60 years, but the trees from its suckers will continue to grow and reproduce. An aspen clone can grow for thousands of years, withstanding even fire. Is the single aspen trunk an individual, or do its multiple clones form one individual?On October 4, 2002, I visited the gully where I had seen aspens 12 days earlier. I measured its altitude at 7,100 feet. I counted three dozen aspens in the gully, all turning gold. I was surprised - very surprised - to find aspens at this lower elevation, but guessed that rainwater floods the gully. Extra water would encourage aspen growth.
Aspens here prefer high elevations. The first aspen grove I explored has an altitude of 8,900 feet. But I also found aspens growing at 7,100 feet. Milk Ranch Canyon, at 7,500 feet, has no aspens. Higher elevations, with cooler temperatures, encourage aspen growth. Yet aspens survive in a moist microenvironment at a lower elevation. Are these 10,000-year-old aspens remnants of the last Ice Age? The soil at Milk Ranch Canyon is dry and sandy; at the first aspen grove, it is thick and dark. Canyon walls skirt around both aspen groves, and water runs into these canyons. Aspens here grow in valleys with a moist microclimate. Though elevation is a factor in aspen growth, water makes all the difference.In winter, aspens are bare. They look like giant icicles pointing to the sky. Spring brings pale green leaves that grow into the dark green of summer. Fall exhibits the aspens crowned with gold leaves. The aspens know intuitively what to do. They have practiced for years.
I measure time in seasons and years. I remember that in the winter of 1998, we had lots of snow and went sledding every week. The following autumn, I picked pions off trees and ate them raw. Each summer, I look forward to the July monsoons when I can smell rain in the air. From where I stand, I can't see the emerging patterns in my life. I only remember moments and short seasons. But aspens look back 10,000 years and see what has changed. I am dwarfed by tall trees with long memories.
Bowers, Janice Emily. The Mountains Next Door. Tucson: University of Arizona Press, 1991.
Petrides, George A. and Olivia. Western Trees. Boston: Houghton Mifflin Company, 1992.
Shaw, Daniel and Mary Stuever. Philmont Fieldguide. Philmont Scout Ranch, Cimarron, New Mexico: Boy Scouts of America, 1985.
Trimble, Stephen. The Sagebrush Ocean. Reno, Nevada: University of Nevada Press, 1989.
Tweit, Susan J. The Great Southwest Nature Factbook. Portland: Alaska Northwest Books, 1992.
U.S. Department of Agriculture. Trees Native to the Forests of Colorado. Durango, Colorado: San Juan Mountains Association, 1999.
Wheelwright, Jeff. "2002: The Year of Cloning." Discover, January 2003, pp. 28-31.
Zwinger, Ann. Beyond the Aspen Grove. Tucson: University of Arizona Press, 1981.
Zwinger, Ann and Barbara Sparks. Aspen: Blazon of the High Country. Salt Lake City: Peregrine Smith Books, 1991.
More About This Resource...
This winning entry in the museum's Young Naturalist Awards 2003 examines a surprising aspen grove. Elspeth's narrative essay, with illustrations and photographs, includes:
- how the discovery of an aspen grove in a valley prompted her to find out why the trees existed in this one spot when they didn't in the rest of the forest
- her initial hypotheses about what environmental characteristics favored the aspen growth
- field journal entries that detail the similarities and differences she found between this aspen grove and a control area she selected
Less than 1 period.
Supplement a study of biology with an activity drawn from this winning student essay.
- Send students to this online article, or print copies of the essay for them to read.
- Explain what a biodiversity index is to students. Then ask them to calculate one for both Aspen Grove and Milk Ranch Canyon based on the species list on page four of her essay.
OriginYoung Naturalist Awards