Repairing trailside erosion

The winter soil-bioengineering season has come to an end, and spring is everywhere. The landscape displays every imaginable shade of green. This is when we start to see the benefits of our winter work pay off. The living structures we built are leafing out, which means their roots are already deeply rooted in the soil. This is good news for this old trail, and the creek that flows beside it. I walked it today; there are newts in the pools and the air is filled with the sound of birds and falling water.

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Trail cutting imposes particular stressors on a landscape. It alters the grade on both the upslope and downslope sides, changes hydrology patterns and soil stratification, and disturbs soil microorganisms, affecting soil cohesiveness. Old trails, particularly those cut prior to the advent of park master planning and mandated environmental assessment, will show their age in the form of damaging erosion patterns, aged fencing, and deferred maintenance of all sorts.

What’s the deal with this particular trail? First of all, it’s one of the oldest in the Bay Area. Second, it’s situated directly adjacent to a creek; urban stream drainages are notoriously erosive and unstable environments and generally not good places to site trails. Third, this is an off-leash trail. As evidenced by the lack of vegetation on the trailside streambank, trampling is constant and damaging, resulting in a stream bank almost totally devoid of living plant matter. Hundreds of dogs per day leap through the fence slats and down into the creek, then back up again. All of these factors spell trouble for a creek and the critters that live there.

What is to be done? There will be no decommissioning of the trail at this point in its life; it is well established and loved by the large community living in nearby cities. It’s a cornerstone of the park system here, connecting dozens of trailheads and recreational features. And most of the trail is in fine shape.

So, we compromise. By combining the efforts of local youth with the knowledge and tools of park staff, we can accomplish a great amount of work to remediate damage. In 2015 hundreds of feet of fencing were replaced and several dozen square feet of living willow structures built to take the pressure off the riparian ecosystem and help it begin to recover. We successfully decommissioned at least five bootleg trails (non-sanctioned trails caused by users ignoring park rules and going wherever they please).

Here are six willow wattle structures installed parallel to the slope to capture sediment from a new trail dip we built to channel water:


Here’s our structure today, at about 2 months old:


These leaves are all from individual willow whips sprouting even on this dry slope. The structure has already captured a large enough amount of sediment that it’s partially buried. That’s all sediment that isn’t going into the creek!

Just up the trail, behind the new fencing and slash we piled to discourage off-trail activity, the native vegetation is beginning to recover. This area was bare and compacted before we started work. It’s amazing how much nature can recover simply by removing a stressor.


To users of the the bootleg trail, it doesn’t look like your steps are doing any damage; but that’s because your steps are merely perpetuating the damage done by others before you. As long as the steps continue, the native vegetation can’t establish, and soil quality degrades. There is a purpose for all that trail planning! Part of the job of maintaining public parks is to ensure that the park benefits wildlife as well as people-and that means limiting human use.

Decommissioning a trail is an art, and not always simple to do. Many users believe they have a right to use the park in whatever way they choose. Unfortunately this attitude harms both nature and other users.

This bootleg was a veritable staircase leading right up to another bootleg trail, and so worn that it looked like it was supposed to be a trail. It was so heavily used that oak roots that used to be underground were now exposed:


And here’s the trail after our work:


The critical trick is to make the trail disappear. This discourages most users simply because the trail no longer looks like a trail. At first, people tried to continue climbing the trail, throwing brush aside and blazing a trail. But we persisted in replacing it. Four months after the work was performed, the native ferns and snowberry are coming back. Decommissioning of this sort is really an ideal approach, because it doesn’t involve changing policy or policing users. The trick is to change the trail from an inviting place to a place one wouldn’t think of going. I love low-tech solutions like this.

Despite the fencing and the signs advising owners to keep their dogs out of the creek, of course, I watched dogs romping through the creek on at least five different occasions today. This work that we do is largely to protect the ecosystem from those who don’t care or know any better, because the data indicate that around half of the trail users fall into one of those two categories. It’s unfortunate, but that’s the reality of maintaining a public park: undoing the damage caused by the public. Along with removing litter and clearing downed trees, repairing physical damage is a main mission of rangers. They, of course, are thrilled to have a crew helping them to get done all this work that they need to do, and the crew gains training in natural resource management. I hope that some of them will be rangers here someday.

These results are very encouraging for the first year of this project and I’m looking forward to spreading word of the positive results and getting more work done! I’ll post more before and after results soon.



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