Stefan Wirtz Vom Fachbereich VI (Geographie/Geowissenschaften ...

Experimentelle Rinnenerosionsforschung vs. Modellkonzepte – Quantifizierung der hydraulischen und erosiven Wirksamkeit von Rinnen
Furthermore, the article points out the vulnerability of these shrublands against grazinginduced
erosion.
Basically, two main theses on the impacts of grazing can be found in literature. The studies
with a more ecological or botanical focus regard grazing animals as ‘ecosystem engineers’
and emphasize the increased biodiversity of grazing areas with different biospheres for other
biota, as compared with non-grazing areas (e.g. JONES et al. 1994, SCHAICH 2007, STAVI
et al. 2009). The more soil scientific, geomorphologic and hydrologic studies point out the
physical compaction phenomena and, accordingly, the reduced infiltration rates of the soils
(MULHOLLAND & FULLEN 1991, PARIENTE 2002, PIETOLA et al. 2005, PROFFITT et
al. 1995, STAVI et al. 2008a, b, STAVI et al. 2009, STEWART & CAMERON 1992,
TABOADA & LAVADO 1993, MWENDERA & SALEEM 1997a).
In contrast to that, the immediate influence of the trampling of sheep and goat hooves on the
soil surface are overlooked. The destruction of crusts and the loosening and mobilization of
soil material for further transport through wind and water are possible effects. Correlating
geomorphologic rates are also unknown, so far. Only few studies suggest that the impact of
animal trampling is significant and should not be neglected any more (e.g. UNGAR et al.
2009, RIES 2005, 2010).
The issue of rock fragment translocation is treated in even fewer publications. GOVERS &
POESEN (1998) investigate the translocation of rock fragments by sheep and goat trampling
in a study area with steep, debris-covered slopes in Turkey, and discovered significant rock
fragment movements. Particularly, the long-term effects of animal trampling on debriscovered
slopes should be subject to further investigation (GOVERS & POESEN 1998).
UNGAR et al. (2009) determine considerable rock fragment movement regardless of their
size on grazed areas as opposed to the reference area without grazing influence in the Negev
desert. The vegetation cover is regarded to be the most important factor influencing rockfragment
movement by animal trampling. On existing trails more rock fragments are moved
than on densely vegetation-covered areas. NYSSEN et al. (2006) emphasize rock fall and
material movement as being the most important geomorphologic process induced by animal
trampling in Ethiopia. On grazed test-areas, up to 95 % of the rock fragments on the soil
surface were moved in the course of 20 months.
Only a small number of experimental studies focus on the influence of grazing on vegetation
cover and geomorphodynamics (RIES et al. 2003, ELDRIDGE 1998, MWENDERA &
MOHAMED SALEEM 1997a). RIES et al. (2003) observe that sheep and goat trails in dense
Matorral with intensive grazing can be regarded as the most active surfaces due to the
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