The science strongly indicates a curvilinear relationship between use and environmental effects; regardless of the type of activity that occurs, the most detrimental environmental effects (especially to soils and vegetation) occurs when a trail is first constructed.
Though the effects on soil of wheeled travel are notably different than those of recreationists travelling on feet or hooves, it seems difficult to determine whether one mode of travel is universally more damaging than the other. The amount of erosion, compaction, and sediment damage that occurs is highly variable and depends
oThe ecosystem and resulting soil characteristics in which the activity is taking place.
o The amount of moisture in or on the soil.
o The steepness of the slope, its orientation in relation to the fall line, and the direction of travel (ascending or descending) of the user.
o The behaviour of the user (whether or not best practices are known/applied).
o The design of the trail (including mitigative infrastructure) and the recreational use for which it is intended.
Effects on vegetation are highly commensurate with effects on soil, and are similarly difficult to assess universally in terms of types of recreation that are comparatively more or less detrimental. Vegetation is removed from a trail as part of its design, and activities that follow trails should not appreciably increase the amount of vegetation that has been removed. Certain invasive species seem to react favourably to the presence of mountain biking, but others prefer the vectors provided by other activities.
There is support in the literature for the hypothesis that the effects on some species of wildlife are more pronounced with mountain bikes than they are with other forms of recreation (primarily related to the 'sudden encounter' effect), but again these effects are highly dependent on the species being considered and other factors.
Recreation ecology, similar to other kinds of field ecology, is fraught with the challenges of conducting statistically valid research. “Most studies are deficient in any number of ways: they may be too short in duration, not have adequate controls or replications, be anecdotal in nature, or have too many potentially confounding variables” (Knight and Cole 1995).