Anyone who has spent time hiking or walking in the woods has probably come across a trail that has been deeply eroded to the point of becoming a streambed full of large, unstable rocks. It’s an unpleasant experience – your feet get wet, the footing is bad, and you know that whoever designed the trail did not intend for their lovely path to turn into a washed-out gully.
It doesn’t have to be this way, of course – trails can be designed in such a way that they last indefinitely with a minimum of regular maintenance. Whether you’re a landowner thinking of putting in a trail or two on your land, or a volunteer with one of the groups that maintains trails across New Hampshire and Vermont, or simply an interested trail enthusiast, here is a quick overview of the two key concepts of ecological trail design.
The first concept is water management. Depending on a trail’s use, feet, horse hooves, or tires soon trample the vegetation and compact the soil, creating a shallow yet continuous groove in the earth. This groove is a natural place for water to gather during spring melt or a rainstorm, and it quickly starts to move downhill, gaining both volume and velocity. As water runs down the groove, it picks up soil and small stones and begins the process of erosion.
Erosion is what turns a soft footpath into a washed-out gully. The longer the water runs down the trail, the faster it moves; the faster it moves, the sooner it destroys the trail. A trail running straight down a steep slope, for example, with no way for the water to escape the footpath groove, may not even survive its first summer thunderstorm.
Erosion is an easy problem to avoid when the trail is being designed: simply minimize the grade and keep the trail off the fall line, which is the path of least resistance for anything moving down a slope. Imagine yourself with a bowling ball at the top of a hill. If you drop the bowling ball, it will follow the fall line (gathering velocity when it can) until it reaches the bottom of the hill. If a trail is designed to follow the contour of the hill instead of the fall line, gradually descending, then water – just like the bowling ball – won’t be interested in staying on the trail. A good contour trail, built with water bars that channel rainwater and runoff away from the trail and back to the fall line, is a trail built to last.
Even with a well-designed trail, however, some erosion will still occur as users compact the treadway. Trail designers should leave a buffer strip of 50 or more feet between a trail and any streams, ponds, and lakes in order to minimize any damage that a 100-year flood or other extreme weather event might create. Soil that is carried into a water body via erosion creates sediment, raises water temperature, and has other ill effects on the creatures that live there. Ecological trail design also avoids vernal pools and other delicate habitats that are vital to species other than ourselves.
The second key concept in ecological trail design is to cut as few large trees as possible in order to maintain a closed tree canopy overhead. Increased sunlight on a trail means increased plant growth, which means you’ll need to spend time pruning out all the new growth to keep your trail open. Some of this new growth is likely to come from unwanted, invasive plants that like lots of sun and thrive on disturbed soil. These species do well on sunny trailsides, and the trail helps them colonize areas of forests that they otherwise wouldn’t be able to penetrate. Seeds can travel miles in the soles of hiking boots or knobs of bike tires.
Maintaining a closed forest canopy also keeps the soil moist for all the salamanders, wood frogs, and other amphibians that inhabit our deep woods. Increased sunlight can dry out the land on both sides of a trail and create an effective barrier that amphibians, which must remain moist in order to survive, cannot cross. What looks like a trail to us ends up looking more like a wall to them. Keeping the canopy intact over a trail avoids this problem; after all, it’s their home – we are just visiting.
Whether you are out on the trails this summer as a trail builder or a trail user, keep an eye on the details of how water and sunlight affect the path. Good trail design provides both a pleasant experience today and a good trail long into the future.