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A Day Mending Aspen Fence24 July 2010 Photos by Tom Bean. Text by Susan Lamb.
Two dozen volunteers and USFS staff assemble to repair fences that protect young aspen from browsing animals near Hart Prairie, on the west side of the San Francisco Peaks in the Coconino National Forest. The crew includes members of Friends of Northern Arizona Forests (FoNAF), a volunteer organization dedicated to supporting the USDA Forest Service mission of "caring for the land and serving the people” through projects that sustain the forests and cultural sites of northern Arizona. Other volunteers represent Friends of the Forest (FOF), a similar organization committed to maintaining, protecting, and restoring the scenic beauty of National Forest lands in the Sedona area. To help with the labor-intensive but vital task of repairing and maintaining the fences, FoNAF has obtained a grant from the National Forest Foundation for start-up funds to initiate a long-term commitment to erect, improve, protect, and maintain exclosure fences in the greater Hart Prairie area. (The grant stems from a collaboration between the National Forest Foundation and the National Association of Forest Service Retirees.) A fund established in memory of Kenneth Lawrence, who loved the forests around Flagstaff, provided matching funds for the National Forest Foundation grant. The combined funding paid for tools and equipment such as ladders and fence stretchers, for metal signs explaining the project, and for ten-foot metal T-posts to make fences high enough to prevent elk from jumping over them.
Coconino National Forest silviculturalist Patty Ringle explains the day’s work. The group will divide into crews to repair and improve the fences, remove fallen trees that have damaged them, cut down dead or dying trees that are likely to fall on them in the future, and post signs explaining the purpose of the exclosures. Volunteers will also return periodically to check on the condition of the fences. Why are these fences here? In 2000, the Forest Service conducted a prescribed burn in the area, creating openings among the ponderosa pines to enable aspen to regenerate naturally. At the time, crews built “exclosure” fences around two of these openings to prevent elk, deer, and cattle from eating the sprouting aspen, stripping bark from mature trees with their teeth, and scraping their antlers on the fragile bark of the trunks. Since then, dead trees have fallen and crushed parts of the fences. For reasons that are unclear, members of the public have cut through them as well. Repairing the fences would prevent animals from browsing the aspen shoots again, undoing the work of a decade, and threatening the long-term survival of the trees.
Aspens favor snowy winters but crave sunlight. Even their bark is composed of living cells that photosynthesize nourishment in the form of carbohydrates, using the sun’s energy to process carbon dioxide and water. Aspens are fairly short-lived trees, partly because pine, spruce, and fir sprout at their feet and eventually grow tall enough to starve them of light. After the aspens die back, their roots lie dormant until a disturbance — fire, avalanche, or rockslide — allows sunlight to stimulate the sprouting of ramets once again. New aspens may emerge from tiny seeds but, usually, shoots called ramets sprout from a mass of roots that already exist. Some of these root masses may be thousands of years old. They are capable of producing half a million shoots per acre and can extend considerable distances. They create forests of genetically identical tree-clones and enable them to exchange moisture and nutrients with one another to support expansion into less favorable areas. Protected by an exclosure, this aspen clone’s spindly ramets are regenerating successfully. Aspen groves are biologically diverse, providing habitat for myriad plants and a marvelous array of creatures. Their crowns admit enough dappled light to foster layers of life from small trees to shrubs, wildflowers to grasses. Countless insects thrive in the cool, moist environment of the groves, pollinating flowers and sustaining a wide variety of birds. Hawks, goshawks, and owls swoop among the aspens while woodpeckers, flickers, and sapsuckers tap on their trunks. Snags shelter nests of mountain bluebirds, violet-green swallows, and house wrens. Mammals — from rabbits to porcupines to bear — feed on their buds, bark, and leaves.
A ponderosa pine makes a sturdy corner post for the exclosure fence. Volunteers first stretch the fence line with brute strength, then ratchet it tight around pieces of wood placed to cushion the pine tree from the strangling pressure of the wire. Pines have increased exponentially in numbers and density over the past century, largely due to suppression of the natural fires that once swept through the forest every few years. Ponderosas now encroach on grassy areas and in moist draws. Once rich in plants that sustained insects, birds, and other animals, these grassy openings and damp drainages are losing biodiversity under the conifers’ shade and thick blanket of discarded needles. Dense stands of pines are unhealthy in their own right, as their competition for moisture and nutrients makes them more vulnerable to insects and disease. They also pose the threat of larger and more intense fires much more destructive than the low-intensity fires that burned through the area in the past. Concerns about these dire conditions and about the health of the nearby Bebb willow community prompted USDA forest scientists to propose the Hart Prairie Fuels Reduction and Forest Health Restoration Project in 2009. Covering almost 13,000 acres, the Hart Prairie project includes restoration of aspens on about 3,200 acres by removing encroaching conifers, conducting prescribed fires, severing roots in the interiors of aspen clones to stimulate new growth, clearfell- coppicing (removing all aspens to create an opening), some planting, and excluding browsing animals from the clones.
Volunteers stretch and attach wire to repair a fence that was most likely damaged by elk pushing and leaning over it to reach the sprouting aspens. Protected from elk, the spindly aspen ramets will grow taller and develop thicker trunks over the next few decades. With continued maintenance of the fence, the aspen will regenerate successfully to become a healthy, vigorous, sustainable and long-lived clone. Other work in the Hart Prairie project will decrease the number and density of conifers and open up the forest to more potential aspen groves. The scorched bark of a ponderosa pine is evidence of the prescribed burn conducted here in 2000. Aspen is adapted to fire, which sweeps away other plants that compete for nutrients and kills aging overstory trees, opening up the ground to sunlight. Fire restores nutrients to the soil, and sunlight warms soil blackened by fire more efficiently than it heats up ground covered in plants, creating better conditions for young aspen to thrive. Nevertheless, a layer of pine needles already carpets the ground here, inhibiting the growth of wildflowers and grasses. On the other hand, aspens drop leaves that decompose much more readily than pine needles, restoring nutrients to create more favorable soil for other plants.
Elk can jump over a six-foot fence with ease. Using cylindrical metal post drivers, volunteers pound in 10-foot-tall fence posts in a series of ringing whacks. They string single wires at the tops of these new posts and move the wire mesh higher up on the shorter posts, knowing that elk and deer will not go under the wire. The fence is at a distance from the aspen clone, protecting ramets sprouting in the sunny area around its edge. Shade cast by the larger trees at the heart of the clone inhibits the sprouting of young aspen. In addition, the upper branches of mature aspens produce auxin, a chemical that flows to the aspens’ roots and suppresses the sprouting of ramets close to a large tree. Under natural conditions, disturbances such as fire or rockslides damage the root systems of aspen clones, interrupting the flow of auxin and allowing young ramets to sprout. To imitate this effect, one of several strategies in the Hart Prairie project is ripping: severing roots within aspen clones to stimulate new growth.
Volunteers stretch and re-attach mesh and add another row of wire at the top of the fence. Altogether about 40 aspen groves in the Coconino National Forest, from the Hochderffer Hills north of the San Francisco Peaks to five miles south of Mormon Lake, have been fenced to exclude elk, deer, and livestock. Fences around young aspen must be maintained for up to 30 years to protect young aspen from browsers. Why such an urgent need for fences? Despite their remarkable ability to regenerate from their ancient and massive networks of roots, aspens have dwindled rapidly in the Southwest over the past fifty years. Decades of fire suppression reduced sunny openings in the forest that were necessary for young aspen to sprout. Successive years of drought stressed mature trees, making them more vulnerable to insects and disease. In June of 1999, a catastrophic frost defoliated the aspens on the San Francisco Peaks, accelerating their decline. According to the proposal for the Hart Prairie project, “There is little evidence on the San Francisco Peaks of successful aspen recruitment over the last several decades due in large part to browsing by elk. Loss of aspen at a landscape scale signifies a tremendous loss of biodiversity, with aspen decline cascading into losses of vertebrate species, vascular plants, and likely other groups of organisms.”
A volunteer detaches wire mesh in order to stretch and re-attach a section of the fence where fallen tree pulled it loose. Although the dead tree must be removed in order to finish repairing the fence, the trunk may be left nearby to create an obstacle to browsing animals. Efforts to protect aspen often include felling trees in a random pattern to create an obstacle to browsers, a technique known as “jack-straw.” Bands of aspen follow mountain ranges throughout North America, making them the most widely distributed tree on the continent. In the Southwest, stands of aspens usually occur between 7,500 and about 10,000 feet. Yet some thrive well outside this elevational range on cool north-facing slopes down to 5,600 feet, or on sunny south-facing slopes up to 11,500 feet. Aspen are dioecious trees, meaning that all the flowers on a tree are either male or female. Being genetically identical, all the members of a clone are of the same gender. Male clones are more common at the harsher, higher elevations while females are generally in more favorable conditions down slope. The frequency of the genders balances out overall.
Volunteers cope with a tricky situation. Two downed aspens lie at an angle, one on top of the other. The top one is threaded through two huge dead aspens that need to come out because they will soon fall and damage the fence. John Nelson, retired US Forest Service ranger and a founding member of FoNAF, describes this as a very dangerous ���classic setup to get kickback.” After a thorough discussion of how to solve the problem, the crew determines where to cut which trunk and in what order. They begin by clearing away sticks and chunks of wood that confuse the situation and could flip up and strike someone when stepped on or when the big trunks are sawn apart. They use a stout branch to lever up the top tree and roll away a piece of wood that braces it. Then they saw straight down through it, right where it crosses the trunk underneath. The top log breaks almost in two with a loud, reverberating snap. Two volunteers finish cutting it apart and the pieces are dragged out of the way.
After the site is cleared of debris, the crew considers the best way to fell each of the two dead trees still standing in order to prevent them from crushing the fence when they eventually fall on their own. They know they will need to “take ‘em with the lean,” to cut them so they will fall in the direction they are already inclined. Everyone makes sure they have a clear route of escape, a 45-degree safety zone in case things don’t go as planned. Felling a tree — especially in circumstances like these — is dangerous, difficult, and most of all... unpredictable. John Nelson and Ralph Baierlein, who is the founder and president of Friends of Northern Arizona Forests, use John’s crosscut saw to make a “pie cut” — a deep notch — in one of the dead aspens. This deceptively simple-looking task requires considerable skill and constant attention. Plastic wedges are driven around the cut and the sides are chopped with an ax to further weaken the tree. All the while, birds noisily chatter in the surrounding pines. Finally, a concussive crack like a gunshot echoes through the forest and the tree keels over.
For whatever reasons, people have been cutting the fences that protect young trees, especially in the Hart Prairie area. Perhaps the mysterious fence cutters assumed the fences were intended to restrict access to areas of the forest. Maybe people who saw elk or deer inside the exclosures assumed that the animals were trapped. Whatever the reason, cutting the fences is threatening the present and future wellbeing of aspen groves and the plants and animals that depend on them. The volunteers and Forest Service staff hope that signs explaining the purpose of the exclosures will prevent deliberate human damage of these fences. FoNAF president Ralph Baierlein attaches a sign to the exclosure fence using 3⁄4” metal crimps originally designed for the sausage trade. Over 250 of these signs will be attached to fences to explain the purpose of the exclosures. The metal signs bear the logos of the National Forest Foundation, the National Association of Forest Service Retirees, the USDA Forest Service, the Arizona Game and Fish Department, and Coconino Sportsmen.
After a successful day learning new and challenging skills and making new friends, volunteers and Forest Service staff look forward to the next opportunity to work outdoors together to conserve a precious natural amenity for people and wildlife. |
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