Effects of Soil-Surface Morphology on Emergence and Survival of Seedlings in Big Sagebrush Communities

Abstract

Various kinds of soil-surface microsites occur on loess-mantled Aridisols in central and northern Nevada. This study evaluates the potential of trampled and untrampled microsites to influence natural revegetation and either secondary succession or retrogression. Microsites present on different soil surfaces included the litter- and moss-covered Type I surface that occurs under the shrub canopy; the trench-like cracks and pinnacled polygons of the Type II surface that occur adjacent to the Type I surface; and the narrow cracks and smooth polygons with crusted, vesicular structure of the Type III surface that occurs in the interspaces between shrubs. Emergence and survival of Wyoming big sagebrush generally were greatest on the Type I and III surfaces, in the untrampled crack microsite of the Type III surface, and on the heavily trampled polygon microsite of the Type III surface. Emergence and survival of perennial grasses generally were greatest on the untrampled Type I surface, in the untrampled trench microsite of the Type II surface, and on moderately trampled trench and pinnacle microsites of the Type II surface. Emergence of annual and perennial forbs generally was greatest on untrampled trench and crack microsites of the Type II and III soil surfaces. Heavy trampling of trench and crack microsites reduced the emergence of perennial grasses, and both moderate and heavy trampling reduced the emergence of annual and perennial forbs. The potential for secondary succession would appear to be greatest where Types I and II surfaces and associated microsites predominate on a site and when trampling is moderate or absent. The potential for retrogression would appear to be greatest where the Type III surface and associated microsites predominate and when trampling is heavy.