ECOLOGICAL SITES OF THE WALNUT GULCH EXPERIMENTAL WATERSHED

摘要

Soil and water conservation efforts on rangelands require a marriage of hydrologic and range management concepts. One important range management concept is that of an ecological site, which is defined by its ability to produce a plant community consisting of certain kinds, amounts, and proportions of vegetation. Multiple soil series can produce the same plant community, and so are associated with a single ecological site. One can create maps of ecological sites using SSURGO soils maps by assigning map units, each consisting of a number of soil series, to the ecological site of the dominant soil series in each map unit. Such maps are too coarse for ranch management. However, these maps might be the only way to apply currently documented range management knowledge in hydrologic models, at least until ecological sites are more widely mapped. The Natural Resources Conservation Service (NRCS) provides written descriptions of ecological sites, including a state and transition model and some information applicable to hydrologic models. We examine the utility of ecological sites for hydrologic research in the context of the Walnut Gulch Experimental Watershed (WGEW), a 150 km2 research watershed in southeastern Arizona. We illustrate the distribution of ecological sites across the watershed; describe a state and transition model and its management implications for one ecological site, Loamy Upland; list the common ecological sites on Walnut Gulch and present hydrologic information about ecological sites contained in NRCS site descriptions; and explain how to access ecological site information for other locations based on the SSURGO database.