24 THE IMPORTANCE OF ASPEN

THE IMPORTANCE OF ASPEN

THE IMPORTANCE OF ASPEN

Aspen trees are described as a "keystone species," that is, a species on which other species in an ecosystem largely depend, such that if it were removed the ecosystem would change drastically. Aspen trees are the most visible of western North American hardwoods providing understory biodiversity, wildlife habitat, livestock forage, specialty forest products, fire protection and highly desirable scenery.

An abundance of forage grows in this forest type, 10 times that associated with coniferous forests within the same region. A variety of birds rely on the aspen for nesting sites and food. Elk, pronghorn, mule deer and other ungulates heavily rely on aspen stand for grazing. The same is true of cattle and sheep. Aspen habitat can be important during calving

The quaking aspen (Populus tremuloides), growing up to 80 feet tall, is the most widely dispersed tree in North America, found from Canada to Central Mexico. Along with its broad distribution, the tree is noteworthy as the largest living organism on Earth. Aspen grow in clonal colonies. Because these trees typically reproduce through their root sprouts, via offshoots called “suckers,” each and every tree is a clone of the former and all trees are connected within the broader colony. Pando, also called “The Trembling Giant,” is a massive aspen stand in Utah’s Fishlake National Forest, spanning 106 acres, aged at roughly 80,000 years and estimated to weigh roughly 13 million pounds, making it the heaviest organism in the world.

BEAVER

season for elk, providing critical cover and forage. During the spring upslope migration, pregnant cows break off on their own several days before giving birth. For some weeks after calving, cows and calves remain in the mid-elevation forest zone—a zone often dominated by aspen—before joining the herd.

As symbiotic as the relationship between wildlife and aspen is, it is equally precarious. Heavy browsing from elk, deer and livestock during the early sapling stage can prevent or greatly reduce aspen growth. Beaver favor aspen for dam building and flooding. Cutting trees can stimulate regeneration, but if aspen stand within the newly flooded zone, they will not regenerate. Aspen is also sensitive to its bark being stripped. Unlike many tree species which grow thick protective bark, aspen have a thin, living bark which is easily harmed by elk, deer, rabbits, mice, voles and porcupines as they strip bark for food. Too much bark removal may kill a tree.

MOUNTAIN BLUEBIRD

ANATOMY OF AN ASPEN STAND Walk under an aspen canopy and sit down for a spell. With the smallest breeze, every leaf is set to tremble in a shudder of white noise, much like that of the ocean and with the same quieting effect on the mind.

ELK

BLACK-CAPPED CHICKADEE

DOUGLAS FIR

ASPEN & FIRE

Aspen rely on disturbance, such as cutting or fire, to reproduce. The species is often associated with the Douglas fir timber type and is a pioneer tree after a burn or logging. Fire triggers aspen to release a chemical in their roots (called cytokinins) thereby triggering the growth of suckers from the root. Up to 50,000 to 100,000 suckers may sprout and grow on a single acre following a fire. Fire

additionally kills invading conifers growing within aspen stands. Aspen withstand fire due to their moist leaves and thick twigs which do not catch fire easily, unlike the dry needles of conifers.

After a fire, aspen will dominate a site because it grows quickly. Many aspen stands across an area are the same age and can be traced to a singular instance of fire or other disturbance. Without disturbance, aspen stands are often overtaken by coniferous species. The shade of the taller conifer overstory eventually chokes out aspen.

INDIAN PAINTBRUSH

BLACK-HEADED GROSBEAK

ASPEN IN DECLINE

Aspen face great challenges today. In recent years, scientists have documented large-scale die-off of thousands of acres of trees. In spite of the species’ historically broad distribution, quaking aspen stands are vanishing across the American West (Arizona -96%, Colorado -49%, Utah-51%, Wyoming -53% and Montana -64%).

Fire suppression and elk browsing are the primary culprits. Due to heavy-handed fire suppression policies in the 20th Century, combined with drought and changing climate conditions, aspen began their current decline. When a new grove does sprout up, ungulates devour the saplings. There are more ungulates on the landscape now than ever (primarily elk), due to the loss of their natural predators. Hunting can only manage elk, deer and other ungulates to a certain extent.

The loss of aspen stands means loss of biodiversity and thereby loss of habitat to many species. Aspen conserve water and

without them, snow melts faster, increasing flooding and creating challenges for ranchers and populated areas whose water supply depends on slowly melting snowpack. Finally, loss of aspen means loss of a fire buffer, leading to more intense, unchecked wildfires.

Land managers are equipped with a toolkit to address aspen regeneration. Most of these techniques create some kind of disturbance to stimulate root growth, from controlled burns to selectively cutting trees. Managers may also protect trees from grazing wildlife and livestock by erecting high fences. One method is to remove encroaching conifers from inside an aspen stand and use them to build a matchstick barrier around the stand’s perimeter. Stories of aspen regeneration success exist, but to resuscitate declining stands across the American West will require long-term sustained effort.

SOLUTIONS

RED-WINGED BLACK BIRD

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