Coupling Landscape Patterns and Ecological Processes - Landscape Ecology for Sustainable Environment and Culture - page 12

environment for the growth of other organisms. Soil property is a key factor
affecting erosion. High water content, infiltration rate, and surface roughness can
increase sediment and nutrient retention, and greatly improve vegetation growth.
Soil property, vegetation type and their interactions jointly regulate water cycling
and micro-climate.
In addition to vegetation type and soil properties, other factors are also involved
in the soil erosion process: (1) Patch characteristics of vegetation (shape, size, and
density) play key roles in rainfall interception, runoff storage, and soil erosion
processes. Ludwig et al. ( 1999 , 2005 ) compared the capacity of different shapes of
vegetation patches in intercepting runoff, sediment and nutrients, and found that
banded patterns (stripes or strands) captured about 8 % more rainfall as soil water
than did stippled patterns, and increased plant productivity by about 10 %. (2)
Meteorological factors such as rainfall, temperature, radiation, wind speed, etc.,
significantly affect vegetation biomass (Hao et al. 2008 ) and water soil content
(Huang et al. 2005 ) at patch scales. In semi-arid areas, water is a limiting factor for
plant growth, and precipitation serves as the primary water source. Precipitation in
semi-arid areas is characterized by ''impulsiveness'' at the patch scale; rainfall,
rain intensity, and rain frequency exert profound influences on the magnitude and
intensity of runoff and on the vegetation distribution in each patch. (3) The dis-
turbances of human activities, such as crop growth and grazing, are important
factors for soil erosion. Wilcox et al. ( 2003 ) found that the average annual runoff
on disturbed vegetative slopes was almost double that on undisturbed slopes, while
the average annual erosion on disturbed slopes was more than three times greater
than on undisturbed slopes. McIvor et al. ( 1995 ) and Scanlan et al. ( 1996a , b ) also
found that soil erosion on grazed slope land was much higher than that on
undisturbed slope land, while the aboveground biomass of long-term grazed slopes
was significantly lower than that of undisturbed slopes.
1.4.2 Landscape Pattern and Soil Erosion at Slope Scale
Slope is composed of multiple landscape patches. Runoff has several possible
destinations at the slope scale: being intercepted by plants, being infiltrated into
deep soils, remaining as runoff, and transforming to evapotranspiration; further-
more, the evapotranspiration can have a bearing on the micro-climate at slope scale
by exchanging water with the atmosphere. Factors affecting landscape pattern and
soil erosion are more voluminous at slope scale than at patch scale. (1) Topo-
graphical factors, such as slope gradient, features (direction), and micro-topography
play important roles in soil water movement. Specifically, slope gradient is the most
important factor in affecting the runoff generation, i.e., runoff at low slope gradients
has low kinetic energy, and causes less soil erosion. In addition, the ability of
vegetation to intercept water and nutrients is more significant at low slope gradi-
ents. Slope aspect influences the water-heat conditions of the slope and conse-
quently affects evapotranspiration. Generally, north-facing slopes have weaker