Trampling

Abstract: There have been many recent observations of trampling and its effect on bone surfaces1–8 as well as some experimental investigation of the process9–14. Although there is known to be a relationship between trampling and scratches on bones, there has been no detailed microscopic comparison with marks made by stone tools. As distinguishing cutmarks from other types of surface features is important in interpreting early hominid behaviour9,14–18 and the entry of humans into the New World7,19–20, we have examined possible mimics caused by trampling in an attempt to define diagnostic criteria for cutmarks. We find that microscopic features alone are not sufficient evidence to distinguish human-generated cutmarks from the results of trampling. We suggest different lines of evidence which together may achieve this goal.

Abstract: Disturbance can profoundly affect the cover, species composition, and the physiological functioning of biological soil crusts. The disturbances we discuss include air pollution; exposure to oil, herbicides, and pesticides; invasion by annual exotic weeds; mechanical disturbances such as human and livestock trampling (see Chap. 29), off-road driving, mining, and hiking; and, briefly, wildfire (for extensive discussion, see Chap. 28). Studies on disturbance have generally been limited to the western US and Australia, with some additional work done in China, Israel, South Africa, and Zimbabwe.

Abstract: Biological soil crusts (biocrusts)—communities of mosses, lichens, cyanobacteria, and heterotrophs living at the soil surface—are fundamental components of drylands worldwide, and destruction of biocrusts dramatically alters biogeochemical processes, hydrology, surface energy balance, and vegetation cover. Although there has been long-standing concern over impacts of physical disturbances on biocrusts (e.g., trampling by livestock, damage from vehicles), there is increasing concern over the potential for climate change to alter biocrust community structure. Using long-term data from the Colorado Plateau, we examined the effects of 10 y of experimental warming and altered precipitation (in full-factorial design) on biocrust communities and compared the effects of altered climate with those of long-term physical disturbance (>10 y of replicated human trampling). Surprisingly, altered climate and physical disturbance treatments had similar effects on biocrust community structure. Warming, altered precipitation frequency [an increase of small (1.2 mm) summer rainfall events], and physical disturbance from trampling all promoted early successional community states marked by dramatic declines in moss cover and increases in cyanobacteria cover, with more variable effects on lichens. Although the pace of community change varied significantly among treatments, our results suggest that multiple aspects of climate change will affect biocrusts to the same degree as physical disturbance. This is particularly disconcerting in the context of warming, as temperatures for drylands are projected to increase beyond those imposed as treatments in our study.