Naturalizing Abandoned Trails
Naturalizing abandoned trails requires as much attention and planning as constructing new trail.
The goal is to reduce the impact human trails have on the landscape. Simple restoration may consist of blocking new shortcuts and allowing the vegetation to recover. Complex restoration projects include obliterating the trail, recontouring, and planting genetically appropriate species. Careful monitoring and followup are necessary to ensure that almost all evidence of the trail is gone. Thus, restoration ranges from simple and relatively inexpensive to complex and costly (Figure 72).
Figure 72--Candidate trail for a causeway
or rerouting, combined with naturalization.
Past practices of trail abandonment have left permanent scars on the land. If you've worked in trails awhile, you probably know of abandoned trails that had a few logs and rocks dragged into the tread and trenches. Decades later, those same trails are still visible, still eroding, still ugly, and sometimes, still carrying visitor traffic!
Naturalization strategies include: closure, stabilization, recontouring, revegetation, and monitoring. Restoration needs to be carefully planned. The consequences of each strategy should be examined. Consult with a hydrologist and soil and plant specialists when planning a naturalization project.
Each abandoned trail should be closed (Figure 73). This is true whether an entire trail is abandoned or a segment with multiple trails is being narrowed back to one tread. If the trail is not blocked to prevent further use, the trail may persist indefinitely. Closure is particularly important if stabilization and revegetation are being attempted. The abandoned tread should be blocked to all traffic, recontoured, and disguised to prevent users from being tempted to take it. This work should be accomplished for all segments visible from trails that remain open.
Figure 73--Abondoned trails need to be blocked
off effectively, and with sensitivity.
Stabilize abandoned tread to prevent further erosion. This will promote natural revegetation in some instances. Trails break natural drainage patterns and collect and concentrate surface water flows. Restoring the natural contour of the slope reestablishes the local drainage patterns and reduces the likelihood of erosion. Recontouring usually eliminates any temptation to use the old trail and facilitates revegetation efforts. Pull any fillslope material back into the cut and use additional material to rebuild the slope, if necessary.
Remove culverts and replace them with ditches. Loosen the soil with hand tools, stock and harrow, or heavy equipment to speed revegetation.
Check dams are used on pieces of abandoned, trenched tread to arrest further erosion and to hold material placed during site restoration. Sometimes check dams are appropriate for trails in active use. Check dams are intended to slow and hold surface water long enough to deposit transported sediment. They should be used with drainage structures to reduce overall erosion from the abandoned tread (Figure 74).
Figure 74--Check dams or retainer bars allow
soil to rebuild on eroded trails.
Check dams are best used as holding structures for fill used to recontour the old tread. The material used in the dam should be seated in an excavated footing that extends into the sides of the trench. As material behind the dam naturally builds up, successive levels can be added to the dam with enough batter to offer stability against the pressure of the fill. The top of the dam should be level or slightly higher than the trench walls. For watertightness, chinking and tamped fill should be used to complete the uphill face of the dam. Fill is then added behind the dam to finish the process. It generally takes a long time for these trenches to fill up. Most never do. If they do, add fill below the dam to finish the process.
Spacing between dams depends on the steepness of the old grade and the degree of restoration desired. If the check dam is intended only to slow down erosion, then relatively wide spacing is sufficient (every 20 m (65 ft) on a 25-percent grade). If the intent is for half of the old trench to be filled back in, the bottom of each dam should be level with the top of the next lower dam. On steeper grades the dams need to be closer together. If the intent is to approach complete recontouring of the trench, the dams should be closer still, especially on grades above 25 percent. A point of diminishing returns is reached on grades above 40 percent. Check dams would have to be built right on top of each other to retain soil at the full depth of the trench.
Revegetation can be accomplished passively or actively. Passive revegetation allows surrounding vegetation to colonize the abandoned trail. This works when erosion has been stopped, adequate precipitation occurs, and adjacent vegetation spreads and grows rapidly. Active revegetation ranges from transplanting onsite vegetation to importing genetically appropriate seed or propagated plants. Successful revegetation almost never happens in a single season. Plan carefully for best results.
There are no cookbook answers for returning abandoned trails to their natural condition. Each site should be evaluated for its potential to regrow and heal. On sites that are moist and relatively flat, it may be possible to block off the trail and allow rehabilitation to proceed naturally. Dry, steep sites will take a lot of work.