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Trail Construction and Maintenance Notebook

Trail Corridor

The trail corridor includes the trail's tread and the area above and to the sides of the tread. Trail standards typically define the edges of the trail corridor as the clearing limits (figure 21). Vegetation is trimmed back and obstacles, such as boulders and fallen trees, are removed from the trail corridor to make it possible to ride or walk on the tread.

Drawing of two trees around a trail explaining clearing limits. Text in the drwaing reads, Clearing Limits, clearing limit uphill, clearing limit downhill, trailway, trailbed, and saw branches flush with trunk rather than cutting into the tree. Arrows are used to show the height of the listed limits.
Figure 21—Terms describing the trail corridor clearing limits. You need to
understand these terms to clear a trail to specifications.

The dimensions of the corridor are determined by the needs of the target users and the challenge of the trail. For example, in the Northern Rockies, trail corridors for traditional packstock are cleared 2.5 meters (8 feet) wide and 3 meters (10 feet) high. Hiking trails are cleared 2 meters (6 feet) wide and 2.5 meters (8 feet) high. Check with your local trail manager to determine the appropriate dimensions for each of your trails.

Clearing and Brushing

Working to wipe out your trail is no less than that great nuclear furnace in the sky—Old Sol, the sun. Old Sol and the mad scientist, Dr. Photosynthesis, convert dirt and water into a gravity-defying artifice called a plant. Seasoned trail workers will attest to the singular will and incredible power of plants. No sooner is a trail corridor cleared of plants than new ones rush toward this avenue of sunlight.

Plants growing into trail corridors or trees falling across them are a significant threat to a trail's integrity. Brush is a major culprit. Other encroaching plants such as thistles or dense ferns may make travel unpleasant or even hide the trail completely. If people have trouble traveling the trail tread, they'll move over, usually along the lower edge, or make their own trail. Cut this veggie stuff out (figure 22)!

In level terrain, the corridor is cleared an equal distance on either side of the tread's centerline. For a hiking trail, this means that the corridor is cleared for a distance of 1 meter (3 feet) either side of center. Within 300 millimeters (1 foot) of the edge of the tread, plant material and debris should be cleared all the way to the ground. Farther than 500 millimeters (1.5 feet) from the trail edge, plants do not have to be cleared unless they are taller than 500 millimeters (1.5 feet) or so. Fallen logs usually are removed to the clearing limit.

Photo of a trail with heavy vegetation.
Figure 22—This trail needs to be brushed.
Cut the veggie stuff out.

On moderate to steep sideslopes, a different strategy may be useful. Travel along the lower (outer) edge of the tread is a common cause of tread failure. You can use trailside material to help hold traffic to the center of the tread. A downed log cut nearly flush with the downhill edge of the trail will encourage travelers to move up to avoid it. Rocks, limbed trees, and the like can all be left near the lower edge of the tread to guide traffic back to the center so long as the guide material doesn't prevent water from draining off the trail (figure 23).

Photo of a trail winding up a hill.
Figure 23—Rocks and logs help to keep the trail
in place. Remember, this is a path through
nature, not a monument to Attila the Hun.

The key is to make sure that this guide material does not interfere with travel on the center of the tread and does not block drainage. For example, bikers need enough room for their pedals to clear the backslope on one side of the trail and the guide materials on the other.

Something's Gotta Go

If time and budgets are tight, consider brushing only the uphill side of the trail. This approach keeps users off the trail's downhill edge and keeps the trail in place.

On the uphill side of the trail, cut and remove material farther from the centerline. For instance, on slopes steeper than 50 percent you may want to cut fallen logs or protruding branches within 2 meters (6½ feet) or more from the centerline (horizontal distance). This is particularly true if you're dealing with packstock because they tend to shy away from objects at the level of their head.

Clearing a movable corridor rather than clearing to a fixed height and width takes some thought. Doing so may be difficult for inexperienced crews.

Finally, remember that the scorched earth look created by a corridor with straight edges is not very pleasing to the eye. Work with natural vegetation patterns to feather or meander the edges of your clearing work so you don't leave straight lines. Cut intruding brush back at the base of the plant rather than in midair at the clearing limit boundary. Cut all plant stems close to the ground. Scatter the resulting debris as far as practical. Toss stems and branches so the cut ends lie away from the trail (they'll sail farther through brush as well). Don't windrow the debris unless you really and truly commit to burn or otherwise remove it (and do this out of sight of the trail).

Rubbing the cut ends of trailside logs or stumps with soil reduces the brightness of a fresh saw cut. In especially sensitive areas, cut stumps flush with the ground and cover them with dirt, pine needles, or moss. Rub dirt on stobs or bury them. Here's where you can use your creativity. A carefully trimmed corridor can give a trail a special look, one that encourages users to return.

Some trails may have to be brushed several times a year, some once every few years. Doing a little corridor maintenance when it is needed is a lot easier than waiting until plant growth causes expensive problems.

Removing Trees

Usually, trees growing within the corridor should be removed. Remember that those cute little seedlings eventually grow into pack-snagging adolescent trees. They are a lot easier to pull up by the roots when they are small than they are to lop when they grow up.

Prune limbs close to the tree trunk. For a clean cut, make a shallow undercut first, then follow with the top cut. This prevents the limb from peeling bark off the tree as it falls. Do not use an ax for pruning.

If more than half of the tree needs pruning, it is usually better to cut it down (figure 24). Cut trees off at ground level and do not leave pointed stobs.

Drawing of two excessivly pruned trees along a trail.
Figure 24—Something's wrong with these trees! Cut trees
out when they need excessive pruning.

Logging out a trail means cutting away trees that have fallen across it. The work can be hazardous. The size of the trees you are dealing with, restrictions on motorized equipment, and your skill and training determine whether chain saws, crosscut saws, bow saws, or axes are used. Safety first!

You need training to operate a chain saw or a crosscut saw. Your training, experience, and level of certification can allow you to buck trees already on the ground or to undertake the more advanced (and hazardous) business of felling standing trees. Be sure you are properly trained and certified before cutting standing or fallen trees. Using an ax to cut standing or fallen trees poses similar hazards. Some trees may be felled more safely by blasting. Check with a certified blaster to learn where blasting is feasible.

Removing fallen trees is a thinking person's game. The required training will help you think through problems, so we won't relate the details here.

Cut fallen trees out as wide as your normal clearing limits on the uphill side, but closer to the trail on the downhill side. Roll the log pieces off the trail and outside the clearing limits on the downhill side. Never leave them across ditches or waterbar outflows. If you leave logs on the uphill side of the trail, turn or bury them so they won't roll or slide onto the trail.

Sometimes you'll find a fallen tree lying parallel with the trail. If the trunk of the tree is not within the clearing limits and you decide to leave it in place, prune the limbs flush with the trunk. Limbing the tree so it rests on the ground helps the trunk decay faster.

It is hard to decide whether or not to remove leaners, trees that have not fallen but are leaning across the trail. If a leaner is within the trail clearing zone, it should be removed. Beyond that, it is a matter of discretion whether a leaner needs to be cut. You need to consider the amount of use on the trail, how long it will be before the trail is maintained again, the soundness of the tree, and the potential hazard the leaner is creating (figure 25). Felling a leaner, especially one that is hung up in other trees, can be very hazardous. Only highly qualified sawyers should work on leaners. Blasting is another way to remove leaners safely. When in doubt, tie flagging around the leaner and notify your supervisor.

Based on injury statistics, felling standing trees (including snags) is one of the most dangerous activities for trail workers. Do not even consider felling trees unless you have been formally trained and certified. Bringing in a trained sawyer is cheaper than bringing in a coroner.

Photo of a man assessing two trees that need to be felled near a trail.
Figure 25—If you are uncomfortable with your
ability to safely cut a tree because of the
hazards or your lack of experience,
walk away.