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Pedogenesis–Terrain Links in Zero-Order Watersheds after Chaparral to Grass Vegetation Conversion

^a Dep. of Geosciences, Univ. of the Pacific, Stockton, CA 95211
^b Dep. of Forest Resources, Univ. of Idaho, Moscow, ID 83844
^c USDA-ARS, U.S. Salinity Lab., 450 W. Big Springs Rd., Riverside, CA 92507
^d Dep. of Environmental Science, Univ. of California, Riverside, CA 92521

View larger version (22K): [in a new window]   Fig. 1. Development of surface cover after the 1960 fire in watersheds with native chaparral vegetation and those that underwent the high-density perennial and barley (HDPB) treatment. Canopy surface cover was measured from 1961 through 1964 (Corbett and Green, 1965). Chaparral provided more cover in the years immediately after the fire. The barley from the HDPB treatment did not return after the fourth year. Surface cover data averaged for watersheds examined in this study show that canopy cover for each vegetation type reached 65% (Williamson et al., 2004).

View larger version (52K): [in a new window]   Fig. 2. Probability density diagrams for primary and compound terrain attributes for each watershed. The most consistent difference between chaparral and grass is that grass watersheds have higher densities of concave (negative) curvature. Watersheds for each vegetation type are listed in order of decreasing size (Table 2). In chaparral watersheds, several attributes show a link to watershed size. Topography in grass watersheds is similar regardless of watershed size.

View larger version (66K): [in a new window]   Fig. 3. Depth to weathered rock and soil water content in two zero-order watersheds. These examples are from the Grass 3 and Chaparral 2 watersheds. Both soil characteristics are shown as a 3-m grid, overlain by a topographic map of each watershed; points indicate measurement locations. In the six zero-order watersheds examined, depth to weathered rock generally is thickest at the summit and thins toward the outlet of the watershed. In all watersheds, soil water content reflects depth to weathered rock; however, this relation is strongest in grass watersheds.

View larger version (46K): [in a new window]   Fig. 4. Scatterplots and correlation coefficients between terrain attributes and soil characteristics. For each set of correlation coefficients, values for chaparral are above the line and grass below. *Significant correlation (p 0.05). •Significant difference between chaparral and grass (p 0.01).