I have recently returned from a successful round of field work in Yosemite National Park. The main goal of my work this summer was to train a new graduate student in my lab on GPS-tracking methodologies and to help her set up a trampling study. Trampling studies are the quintessential controlled experiment in Recreation Ecology. The purpose of a trampling study is to mimic visitor impact (visitors hiking off-trail) to determine the resistance, resilience, and tolerance of particular vegetation types to being stomped on. Resistance is a vegetation types ability to resist being altered by trampling. Resilient vegetation types are those that can bounce back or recover more easily after trampling has stopped. Resistance and resilience can be combined into a single indicator of vegetation vulnerability called tolerance. Basically, the results of a trampling study can tell park managers which types of vegetation and which plant communities may be more susceptible to damage from off-trail visitor use.
Trampling studies go like this:
1) Pick your vegetation type(s) of interest and set up your experimental plots. In Yosemite we looked at a forest understory plant community and a meadow community.
2) Take premeasures of percent vegetation cover (total and by species type), percent bare ground, and vegetation height by species.
3) Pace back and forth over the trampling lanes repeatedly to mimic visitor impact (it’s very handy to have your ipod during this phase of the experiment – my labmate and I each walked 3 kilometers while trampling). The treatments typically used are 0 passes (control), 25 passes, 75 passes, 200 passes, and 500 passes (or more if the vegetation is particularly resistant).
4) Repeat measures of percent cover, bare ground, and vegetation height.
5) Wait 1 year and return to measure percent cover, bear ground, and vegetation height again.
The results of trampling studies are often displayed in these eloquent curves which recreation ecologists call “Use-Impact Curves”. The use-impact curve is the closet thing to a theory that we have in the field of recreation ecology. Use-impact curves are curvilinear in nature and often show a threshold effect (a point at which the vegetation has been so damaged that further impact no longer causes much change).
Our hope is that the findings from trampling experiments can tell managers “Well, this vegetation type/plant community is really susceptible to trampling so you probably want to try to prevent visitors from going here. However, this vegetation is more tolerant of being stepped on repeatedly, so try to confine people to these areas when visitors are traveling off-trail.”
Standard Trampling Procedures:
Cole, D.N., Bayfield, N.G., 1993. Recreational trampling of vegetation: standard experimental procedures. Biol. Conserv. 63, 209-215.