Mud, Feet, and Somme

This is a Somme Specific version of a broader mud post at Strategies for Stewards.

In the healthy ecosystem, soil is clothed with diverse plants. Underneath is a dense network of rootlets and other soil biota, tangled and supportive. We walk on it just fine. 

Our trails are not "all weather" trails. At Somme, Forest Preserve staff and volunteers are experimenting with "soft tech" approaches. Rules on the Forest Preserve website state: "“Trail usage is prohibited in muddy conditions.” Some people stay home when the trails are wet (Thank you). But, many people do not know the rules, and may come from some distance on a precious day off, and are looking forward eagerly to the balm of nature. We find that most people do not turn around and go back when they reach a muddy section of the trail. So we follow design principles and sometimes harden trails to save biota.

The photo below shows an imperfect but functioning path:

This example is from Somme Prairie Grove, which is visited mostly by people who come to appreciate its wild plants and animals. These folks tend to be careful, respectful, even reverent to some degree.  

In the above photo, the tree-trunk “pavers” are easily visible and not entirely comfortable to walk on. They are either too thick, too far apart, or perhaps just not yet as "settled in" as they will be after a year or two of foot traffic. 

We work to make Somme preserves accessible during spring – the most challenging time for trails. We have tried to locate the trails such that they traverse drier slopes as much as possible (See Endnote 1: Trail Design). We reinforce trails wherever and whenever mud starts to form. A more successful trail in spring is shown below:

The savanna turf here (with its many rare and endangered plant species) is untrampled outside the footpath. The trail surface itself is carpeted with a plant called Path Rush – which in fact grows only in animal-created (including human-created) paths. There are pavers here too. But they are narrower, appropriate to this less-wet area. And those narrower pavers have sunk below the path-rush-and-soil surface. No one notices that this trail has a crafted structure. Preferably, footpath composition should be invisible, or minimally so, for example with path rush growing between the pavers, and not bumpy to walk on. 

You can help maintain these trails just by walking. Here are some basic principles:

1. On wet days, if the path-rush surface is breaking down, perhaps it’s too wet to walk that path. Turn around, and come back another day. Or walk on the vegetated edge of the trail. Natural footpaths here are about 8 inches wide. If you walk eight inches to the right or left of the existing path, that area too may become vegetated by path rush. Such a path, that is twice as wide, could handle twice the foot traffic as the original. (But don't walk it if that's breaking down too. Go back.)
2. If you walk on that eight-inch trail edge, walk on the uphill side of the trail. Our trails have a long-term tendency to migrate downhill, as it's slightly easier, as the vegetation bumps into you more from the uphill side. Walking the uphill edge will curb that counter-productive tendency. (Perhaps this point is too complicated, before the 'graduate level' - but it's true. For more on this, in the unlikely event that you want it, see Highly Obscure Endnote 1.5.) 
3. For people to pass each other, the slower walker (or the more careful, or the smaller group) should step just off the trail and let the other(s) pass. This courtesy should have a minor impact on the ecosystem.

Crossing small streams is another challenge. 

This photo shows a bridge over a stream that is a rushing torrent after heavy rains. Rot-resistant black locust logs are held in place by stakes driven into the muck. Passers-by who don't quite understand how this works best have added miscellaneous wood. That seems to be a fact of nature, in this case human nature. If they work okay, we leave them. 

This approach is sometimes used to cross wider wet swales. In this case, a less functional crossing was replaced when a large oak fell across the trail and needed to be cleaned up. 

At the Somme preserves, we spend most of our stewardship time restoring biodiversity directly. But we want people to appreciate and care, so we spend what time on trails as we can. (We sometimes hope to have more folks focusing on the trails.) Might you be interested? Might the photos below make sense to you?

In the foreground, the path is thickly vegetated by path rush and in great shape. But see those two whitish patches ahead, as we approach the oak grove? Close up of them in next photo:

Here two wet swales had been muddy messes. Pavers here are two- to four-inch bur oak trunks - quite a luxurious building material, but an "appropriate resource" as we were thinning bur oaks to improve the structure of the woodland and benefit other trees. They make a good surface, but the trail sections before and after them are still mud. More work is needed here, if we have time.  

Further into the grove we find this area:

One-inch buckthorn pavers are doing okay, protecting a stretch that had been bad mud. They're well sunk into the soil and don't look uncomfortable to walk on. They're mostly keeping feet and hooves from sinking in too far. Some additional pavers in between seem like they'd help. And where's the path rush? Perhaps in a growing season or two it will get a chance to recover.

Above is what a savanna or prairie footpath looks like later in the year. 

Then, further on down the path, a broad view. Visitors don't think about the trail. They are immersed in the ecosystem - and happy to be a part. Do we think the work is worth it? Oh yes we do. 

Endnotes

Endnote 1: Trail Design

There are many good trail-design references, though most focus on wider and more-heavy-duty trails. We've appreciated a great little book, The Indiana Trails Construction and Maintenance Manual published by the Department of Natural Resources, as its geared to our kinds of trails. Other good practical guides to narrow trails are put out by mountain-bike groups. 

In any case, one of the most basic principles is that trails should "traverse" slopes obliquely enough that rain water crosses the trail - rather that running down it and turning the path into an eroding stream. Trails should not go directly up or down slopes. They should cross slopes on an angle and frequently go up, then down, at least a little bit, so that water will flow off frequently. 

Highly Obscure Endnote 1.5

We first noticed this unexpected trail tendency when there was a little stump on the side of the path which, over the years, moved into the middle of the path. A few years later, it had moved completely to the other side of the path. Of course, the stump didn't move. It was just the indicator that showed us that the path was moving downhill.  

Endnote 2: How to Install Pavers

 
Although we’ve tried to route our trails through dry ground as much as possible, the trails necessarily cross some soil that turns to mud under foot traffic. This problem is especially severe in spring, often during the height of bloom of the spring flora.  We want people to learn to love Somme. Walking through deep mud is a bad experience for people. It also wrecks the trail and kills adjacent quality ecosystem, which we'd hope people would be able to walk next to. 
 
“Paving” wet stretches of trail with a “corduroy” log surface solves that problem, but it takes some care to do it in a way that will be effective and will last for years or decades. Well-installed corduroy logs won’t be kicked aside or be uncomfortable to walk on, as they’ll be embedded in the soil. 
 
When to install the logs
 
The time to install the log “pavers” is when the ground is as wet as it gets. This is typically in spring. 
 
If the soil isn’t wet enough, the tendency will be to use logs that are too narrow, and then when the trail gets wetter, the logs will sink lower, and there will be an inch or two of mud on top of them, and people will move their steps to the side, and when the ends are stepped on, the other end will pop up, and a subsequent walker will kick it out of the way, and the work will have been wasted. 
 
What kind of wood to use
 
The best species is black locust. It lasts for many decades. Unfortunately, it’s hard to get a great many straight pieces of locust. The best logs to use – that we have the most of – are buckthorn and maple. (We're restoring an oak woodland, and maple is often the major invasive that we must control.) If they’re being thinned for restoration, red oak, hickory, and hop hornbeam are also good. 
 
The worst logs are spongy basswood or any dead and starting-to-rot logs. They’ll last just a year or less.  
 
How much curve can the paver logs have?
 
Branches and curvature result in logs being kicked out, tripping people, and the corduroy surface starting to fail.
 
What happens with curves is that the center of the log will get pushed down by feet – and the curved ends will stick up a bit. Then someone's subsequent steps will land on the sticking-up end, and the log will get levered up and later get kicked out.
 
See below illustration below:

How thick should the paver logs be? 
 
The only way to determine this is to put the logs into maximally wet soil. The surface of the log should be just above the soil surface. (Over time the logs may be pushed down as people walk over them. Just barely below this soil surface is a great place for the pavers to end up. The trail seems like just a “naturally non-muddy” trail.)
 
Normally, the logs should be thickest in the center of the wet patch and thinner toward the edges. See below:

How close together should the paver logs be put?
 
They can be so close together that they touch. However, it’s time consuming to cut all those paver logs. Feet are supported just fine by logs two to three inches apart. 
 
How long should the paver logs be?
 
The longer they are, the more stable the trail will be. But longer logs have more chance of running afoul roots and thus not sinking down into the wet earth, the way you want them to. Also, it’s more time consuming to find and prepare long logs than short. So, a foot or two or three often seems like the best length. 
 
Tree roots
 
Often tree roots are in the trail. They can make it difficult to get a log to settle into the soil as far as you want. On the other hand, roots at the surface may make a good contribution to the stability of the trail.  
 
Path rush
 
One advantage of spaces between the logs is that they allow path rush to grow. For not-too-heavily-used trails, path rush is a great surface. It’s the “path version of a lawn.” It’s soft, flexible, alive, solar powered, and holds the soil. Path rush will spring up before long on any trail used by any feet. But we sometimes speed up the process by harvesting seeds and scattering them along new trails.