Archive for January, 2010


Saturday, January 30th, 2010

Recently I’ve had a lot of time on my hands (a lot of time on my hands) and one of the things I’ve been doing had been watching an embarrassing amount of “Mythbusters”. In the unlikely event you don’t know who the Mythbusters are they are a crew of special effects experts who have several design studios dotted around the Bay Area and use them to test popular myths for the Discovery Network.

I applaud their efforts in so many ways that I can’t even began to count them but most importantly they make science and empirical research fun and accessible to a wide audience; that and they get paid to blow stuff up.

By this point you may be asking what does this have to do with mountain biking. Good question. I’d love to see them do an episode on trail impact by different user groups.

Soil samples could be set up test for how different soil mixtures set at common trail pitches and moisture content levels. Weigh each box so you have a baseline for comparisons later. Having different users repeatedly walk and ride over the samples could run test then have the soil samples then doused with water in order to simulate rain run off.  Next, count how many ruts that form, measure the amount of soil and water run off in a catch basin, use a ruler to gauge the depths of the ruts in the samples as they form then finally weigh each box of soil to see how each user group’s impact affects soil density.

Set a couple of control boxes aside so they won’t be affected by user impact but subject them to the same amount of water run off.

Granted, it wouldn’t be a “Mythbusters” episode unless you can count on Tory Belleci hurting injuring in the process of testing an experiment, Grant Imahara making some cool robot, or Adam Savage finding some way to set up some blast shields and blow the whole thing up.

That said, I had stumbled across some interesting impact studies:

There was an interesting passage in the Wildland CPR study that effectively demonstrated a pretty comprehensive control experiment on the relative impact of both hiking and biking and said:

“Thurston and Reader (2001) applied five different intensities of experimental use to test lanes in Boyne Valley Provincial Park, Ontario, Canada. The intensities of treatments were 0, 25, 75, 200, and 500 passes each for hiking and mountain bicycling. Before and after these treatments they measured plant stem density, species richness, and soil exposure. They made follow up measurements of these endpoints at two weeks and one year after treatment. They found no significant differences between the mountain biking and hiking plots. Both stem density and species richness were reduced by nearly 100% at the highest treatment intensities, but recovered within the study period to pre-treatment levels. From this they conclude that both mountain biking and hiking impose fairly similar short-term damage and that vegetation recovers quickly once either use is halted”.

A 1995 study did indicate that the greatest amount of trail damage that sustained by bikes is largely due to heavy braking:

“Wheels also apply both compaction and shearing damage, but they do so in different ways (Cessford, 1995). Wheels apply a constant swath of compaction, unlike feet, which apply an interrupted series of localized compactions. However, wheels apply shearing force to the ground either during acceleration or braking (Cessford, 1995). In this, mountain bikes and motorcycles will differ greatly as a motor has the ability to exert sustain shearing force over time and uphill. Such loss of traction for a mountain bike causes a halt to forward progress and cannot be sustained meaningfully”.

The article I found on the AmericanTrails website authored by Woody Keen, a professional trail builder, did discuss the impact that equestrians have on trails:

“A trail impact study from the Aldo Leopold Wilderness Research Institute comparing hiking impacts to horses and llamas noted: “Horse traffic resulted in statistically significant higher sediment yields (the primary indicator of trail deterioration) than either hiker or llama traffic. The low level (250 passes) horse treatment caused more impact than the high level (1000 passes) llama treatments, suggesting that horses can cause at least four times as much impact to trails under the conditions simulated in this experiment. In addition, under dry trail conditions horse traffic caused significant reductions in soil bulk density (a measure of how compacted the soil is) compared to llama and hiker traffic. Horse traffic also caused significant increases in soil roughness compared with the other 2 users. This suggests that the greater impacts of horses on trails is a result of soil loosening of trail surfaces that are otherwise compacted, thereby increasing the detachability of soil particles and increasing sediment yield and erosion.” (Llamas, Horses, and Hikers: Do They Cause Different Amounts of Impact? – Thomas Deluca (University of Montana) and David Cole (USFS – Wilderness Research Institute) 1998 study)”.

From what I’ve been able to gather is all trail users have an impact.  Responsible trail users have lower impacts. No one user group can automatically look down at another group and with a self assured sense of superiority, wag their finger and say, “Shame on you!”

Obviously having a better knowledge concerning user impact on trails will not by itself end user conflicts any time soon.  But it’s good to know we aren’t the monsters that other user groups make us out to be.