Introduction

In his introduction to the vegetation and erosion conference session at the European Geosciences Union's General Assembly 2009, John Thornes (2008), known internationally for his research in soil erosion and desertification processes particularly in semi-arid areas (Thornes, 1990), asserted that vegetation cover long has been accepted as a key factor for controlling overland flow, runoff, and soil erosion. Since the 1940s, in fact, empirical, experimental, and modelling studies have confirmed the general relationship of vegetation cover and the intensity and extent of geomorphodynamic processes and have investigated the roles of changing land use, various agricultural crops, and grazing behavior.

Based on the work by Elwell and Stocking (1974), numerous studies recording and evaluating land degradation have implicitly assumed a "clear" relationship between vegetation and erosion (Ries, 2000). Their interdependence, which was established mainly for cropland and grassland, needs, however, to be seen more differentiated in the case of Mediterranean fallow land, abandoned fields, and shrubland (e.g., GarcĂ­a-Ruiz et al., 1996; Molinillo et al., 1997; Ries, 2002). In these environments, the small-scale variability and heterogeneity as well as the substantial change of vegetation cover associated with land-use change and vegetation succession (Fig. 16-1) give rise to a high complexity of geomorphological processes.

FIGURE 16-1 Abandoned fields and gully erosion near Maria de Huerva, Province of Zaragoza, Spain. The terraced fields in the upper part of the image were abandoned in the 1930s, while the former cereal field in the upper right corner has lain fallow for only six years. Vegetation cover is patchy to extremely low on both areas following a period of several years with precipitation below average. Drought, grazing, soil sealing, and crusting (and to a trivial extent geographers clearing their tent pitches) are among the factors that keep vegetation cover sparse. The large gully, which drains into the Val de las Lenas, is among those monitored for many years in another study by the authors (see Chapter 13). Hot-air blimp photograph by IM and JBR, April 1996.

FIGURE 16-1 Abandoned fields and gully erosion near Maria de Huerva, Province of Zaragoza, Spain. The terraced fields in the upper part of the image were abandoned in the 1930s, while the former cereal field in the upper right corner has lain fallow for only six years. Vegetation cover is patchy to extremely low on both areas following a period of several years with precipitation below average. Drought, grazing, soil sealing, and crusting (and to a trivial extent geographers clearing their tent pitches) are among the factors that keep vegetation cover sparse. The large gully, which drains into the Val de las Lenas, is among those monitored for many years in another study by the authors (see Chapter 13). Hot-air blimp photograph by IM and JBR, April 1996.

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