Coupling Landscape Patterns and Ecological Processes - Landscape Ecology for Sustainable Environment and Culture - page 13

evapotranspiration than south-facing slopes, which is favorable to soil water
retention. Studies on the Loess Plateau in China indicated that soil water storage is
highest on the north-facing slope, followed by west-facing and south-facing slopes
(Chen and Shao 2003 ). Micro-topography drives water redistribution at the slope
scale. Generally, the central and lower parts of a slope are more active in water
exchange and have larger soil water storage capacity (Jiang 1997 ). (2) Human land
use strategies affect vegetation patterns and soil properties strongly at the slope
scale, leading to net loss of matter (Ludwig et al. 2005 ; Wilcox et al. 2003 ), and
such damage results in severe disturbance over long periods of time. (3) The
frequency of runoff and erosion varies depending on the spatio-temporal scales.
Wilcox et al. ( 2003 ) found that the erosion happened more frequently at patch scale
than slope scale.
1.4.3 Landscape Pattern and Soil Erosion Processes
at the Watershed Scale
Watershed, as the basic unit of hydrological response, is an ideal scale to study
landscape patterns and soil loss processes (Wang et al. 2001 ). Most watersheds
used in ecosystem studies are relatively small, first order streams with drainage
areas of 10-50 ha. The interaction between landscape patterns and most eco-
hydrological processes (except the nutrient cycling or flooding, which is fairly
straightforward) at watershed scales is complex and subject to multiple factors: (1)
Climate, particularly the spatial/temporal pattern of precipitation, affects riparian
water conditions, runoff, sediment, and vegetation patterns; (2) Land use strategies
affect vegetation, water and nutrient cycling. For example, in the Loess Plateau in
China, forest and grassland, as well as terraced fields, can effectively prevent soil
loss, while bare land (particularly slope cropland) generates runoff. The arrange-
ment of farmland, forest and grassland determines the generation or interception of
runoff, and decides the extent of soil loss (Wang et al. 2000 ). (3) Configuration
patterns of soil properties and vegetation at larger scales are important factors. In
semi-arid areas characterized by over-infiltration runoff, barren land is the major
generator of surface runoff, while vegetated areas absorb rainfall. The mosaic
patterns of vegetation patch and soil properties affect the sediment concentration
of the watershed, flood peak flow and runoff at the estuary (Zhang et al. 2006 ). (4)
Human activities, particularly imprudent ones, often intensify the watershed's soil
erosion by affecting the landscape pattern, resulting in soil loss and desertification,
as well as altering river flow modes. For example, in Little Karoo, South Africa,
inappropriate agricultural practices such as overgrazing, cultivation, and irrigation
have led to the disruption of landscape linkages (e.g., hydrological flows, organic
matter recycling), resulting in decreasing infiltration and increasing runoff yield).
In addition, after each individual rainfall, the disturbed river has larger water flow
and more frequent rip currents than the undisturbed river, which causes more