Trails sustain our mountain biking experience. Without them all we would have is some really expensive fat-tire bicycles with nowhere to go. To preserve our experience we need to conserve our trails. Below is a very cursory look at some techniques that make for good trails and which you can apply to existing trails to prolong their excellence.
Keep the Water Off the Trail
Despite what some people say trail users, be it mountain bikes or horses or hikers, don't create erosion. What causes the bulk of erosion is water. However, the impact of trail users can exacerbate water’s effect on trails.
Standing water on trails creates an unpleasant experience. Water allowed to run down trails creates a disagreeable riding surface but more than that, can greatly shorten the lifespan of a trail. Water, when allowed to flow continually downhill increases in velocity and mass, creating a more powerful erosive effect. The trick is to get the water off the trail before it can create a nuisance. When building a trail or increasing the longevity of an existing trail there are several fundamental techniques to keep the water off the trail.
One of the most effective way to move water off the trail and prevent excessive erosion is to create grade reversals. These are changes in the gradient of the trail, from negative to positive and vice versa. If located at suitable intervals and with terrain appropriate dimensions then it prevents water from flowing down the trail. They can also create a more interesting and enjoyable riding experience.
Outslope is when a slight outward tilt is created on the trail so that water sheds off the trail rather than running down the trail. It does not need to be a severe angle, in fact, when done well the angle is nearly imperceptible to trail users.
Nicks, gutters, boxes, gullies, culverts, channels, ditches, trenches, any of these work. They have to be selected depending on the specifics of the local terrain and applying the appropriate technique.
Keep the Rider on the Trail
Sinewy, snaking brown ribbons of trail are what we look for. The singletrack experience is what we look for, which is why almost all new trail is built narrow and why we should defend existing singletrack from rider generated broadening.
Cutting corners might make you faster on Strava but your cheeky inside line becomes braids that forever change the character of a trail, might negatively impact the drainage system of a trail and widen the trail tread, which is an environmental and social problem.
To avoid this a trail could be built or retrofitted with as many natural and artificial choking devices as necessary. Trees, boulders, rock piles, bushes, debris, etc., can be used to create chokes, blocks and gates which keep riders on the trail.
The fall line goes down the gradient of a slope. Although often fun to ride, trails that run down the fall line are prone to erosion, therefore shortening their lifespan. Instead, trails should have an average grade of under 10 percent and have a maximum grade of 15 percent (with exceptions for natural or built rock structures)
Most people assume trails are created and maintained with the use of shovels, picks, diggers and back breaking work. However, one of the often overlooked tools is the clinometer. Although expensive, this little device will prevent poor alignment of trails and help identify the degree to which sections of trail may be trouble spots. If you think you can spot good alignment with your own eyes, and many people are too stubborn to accept the use of this implement, then why don't you just use one to confirm your thoughts.
Measure twice, cut once.
Essentially, the only real way that trails can be preserved is to educate and involve yourself. Sure, reading this or the textbooks out there (highly recommended is IMBA's Trail Solutions: A Guide to Building Sweet Singletrack, which was written by Bike Magazine web editor, Vernon Felton) can help get a better understanding of the subtleties but the real learning comes on the trail. Join in with local trail maintenance days, not just for karmic credit but to learn from experienced builders. It's not rocket science and it's not all about heavy labor. Sometimes the most effective work is that which is less intensive – replanting vegetation, cutting back foliage, or even scratching, digging and moving dirt and rock doesn't always have to be too back breaking. All that matters is identifying appropriate projects, coming up with an efficient plan to accomplish them, and donating a little bit of time.
Remember, there are no such things as trail fairies/gnomes/elves and if you say you haven't got time to donate to the trails you ride but you still ride them, then I curse you with a thousand flat tires.