As we have seen so far, the geomorphological effects of animals are both indirect and direct. The indirect effects of mammals, as well as other animals, are biotic, through the destruction of vegetation cover and litter, in turn altering community structure and possibly reducing ground cover, leading to enhanced erosion rates (McNaughton, Ruess, and Seagle 1988; Naiman 1988; Thomas 1988). Direct, abiotic effects (terminology from Thomas 1988) include those associated with digging, wallowing, trampling, and drinking. I have already described the extensive geomorphological results of mammals excavating for, and caching, food. The geomorphological results of digging for denning and habitation construction are examined in Chapter 7. In the present chapter, I focus on the geomorphic effects of trampling, wallowing, and geophagy.

It is difficult to separate the geomorphological effects associated with these processes. In order to drink, mammals may trample the landscape around a waterhole. In the process, the waterhole-fringe soils become compacted, leading to subsequent surface ponding of rainfall and enhancement of the waterhole, in turn attracting more animals. These animals in turn may wallow in the mud around the fringes of the waterhole, and/or consume parts of saline–laden soils surrounding waterholes that seasonally dry up. As the following sections are encountered, readers are urged to remember the complex interactions (sensu McNaughton et al. [1988] and Whicker and Detling [1988a] for indirect actions, and Thomas [1988] for direct) of these individual processes.

Trampling

Trampling by animals can lead directly or indirectly to erosion.