The Valley Harrier (Page 5)

THE VALLEY HARRIER

Newsletter of the

ARKANSAS VALLEY

AUDUBON SOCIETY

(Colorado)

Volume XXVIII Issue 6

October, 2002

Page 1 2 3 4 5

Table of Contents

Nature’s World: Aspen by Susan Tweit

Over the past few weeks, I’ve watched as the hints of gold on the mountainsides above town grew to splatters and then splotches and then whole patches. The aspen leaves are changing color early this year, and they’re doing it more quickly too.

Where usually the shift from summer’s green to autumn’s lemon, gold, and orange happens gradually, this year it seems that all the aspen are in a hurry. It’s as if they received the “it’s autumn” signal at the same time and just like that, shut down for the year.

Aspen trees “know” that it’s the end of summer by a combination of cues, including lessening day length and decreasing soil moisture. In this extraordinary drought year, the leaves are changing colors in a shorter span of time because soils are so parched that the trees must either quit producing food or risk injury due to dehydration.

The color change of the leaves is a natural chemical process: first, the trees stop producing chlorophyll, the green pigment essential to making sugars and starches from sunlight. Then, as the existing chlorophyll decays, it leaches out of the leaves, revealing yellow and orange pigments formerly masked by the green.

Aspen are remarkable plants. Each tree in a given grove is actually connected to every other tree in the grove, sharing food and water through a common root system. In fact, each tree is genetically identical to the other trees in the same grove, sprouted from a bud of their common parent.

Aspen groves or “clones” are examples of super-organisms, living beings composed of many identical, interconnected individuals. Fungi such as mushrooms are another example of super-organisms.

In an aspen clone the dozens, hundreds, or thousands of trees in a grove are all part of the same plant; large clones may spread over hundreds of acres. (The world’s largest aspen clone is thought to be in western Colorado.)

The trees within each clone are all alike: all top out at about the same height, their bark is the same color (varying from creamy white to olive green), and the same texture, either smooth or marked with the bumpy black calligraphy of a fungus specific to aspen. All grow either straight as an arrow-shaft or crooked as a lightning bolt.

The trees in adjacent clones, however, may look entirely different, and in fact, often leaf out and turn colors on different schedules.

Thus, changing seasons trace aspen grove boundaries like a colored map: Spring paints one clone pale green with new leaves, while a neighboring clone is still bare, the trees ghostly gray. In autumn, each clone flames a distinct shade of gold on its own schedule, regardless of its neighbor’s calendar.

Aspens are as dependent on wildfire as fish are on water. Fire clears out the shady overstory of a forest, baring the soil and fertilizing it by recycling the nutrients contained in the dead wood and living plants.

Aspens spring up quickly after a fire, either from seeds or from the root systems of old clones. As the aspen grove matures, seedlings of shade-loving evergreen trees—Douglas firs, true firs and spruces—germinate in the cooler, moist microclimate created by the aspens.

These taller, longer-lived trees eventually shade out and replace the clone that nurtured them. Because hormones manufactured by the standing aspen trunks keep the sprouts from growing tall, no new trees grow until all the old trunks fall.

Nearly hidden by the evergreen trees, a scattering of aspens may persist for a long time—the trunks can live up to 250 years—a reminder of the long-ago fire that created the clone. When the root system finally runs out of energy, the trees die and fall within a few years of each other, the clone disappearing as abruptly as it sprouted.

After the fires in Yellowstone National Park in 1988, aspens sprouted in places no one remembered seeing them in a hundred years. The fires of 2002 will no doubt also conjure aspen as if by magic.

The mountainsides I watch above town haven’t known wildfire in a long time. I wonder, as I admire the flecks and splotches of gold, how much longer these aspens will survive.

Susan will be teaching a day-long workshop called “Reading Western Landscapes” on October 27th at Tattered Cover Bookstore in Denver. For more information, people can call Tattered Cover Lodo at (303) 436-1070.

© 2002 Susan J. Tweit