Ecological Sites of the Walnut Gulch Experimental Watershed

Authors: Heilman, Philip - Phil; Stone, Jeffry; ROBINETT, D. - Retired Non ARS Employee

Submitted to: American Water Resources Association Summer Specialty Conference
Publication Type: Proceedings
Publication Acceptance Date: 3/1/2010
Publication Date: 3/29/2010
Citation: Heilman, P., Stone, J.J., Robinett, D. 2010. Ecological Sites of the Walnut Gulch Experimental Watershed. Proceedings of AWRA 2010 Spring Specialty Conference Geographic Information Systems (GIS) and Water Resources VI March 29-31, 2010 Orlando, Florida.

Interpretive Summary: Rangeland managers manage vegetation. Thus, they need a conceptual framework that defines potential vegetation communities, describes how management can shift from one vegetation community to another, and documents the expected benefits provided by the various potential vegetation communities. The most widely used conceptual unit in the range discipline is the “ecological site”. The NRCS defines an ecological site to be “a distinctive kind of land with specific physical characteristics that differs from other kinds of land in its ability to produce a distinctive kind and amount of vegetation.” Hydrologic objectives of importance on rangeland include reducing on-site runoff and erosion and off-site sedimentation, as well as the maintaining riparian ecological communities and avoiding flooding and associated expensive infrastructure investments. In rapidly urbanizing watersheds, communities will attempt to maintain natural flow regimes through a combination of designed landscape features in developed areas and vegetation management elsewhere, particularly on publicly owned land. Hydrologists will increasingly be asked to quantify the hydrologic effect of potential management options as part of integrated efforts to achieve objectives at the watershed scale. We illustrate the utility of using ecological sites for water resources management on rangelands with examples from the Walnut Gulch Experimental Watershed and explain how to access ecological site information for other locations based on the SSURGO database.

Technical Abstract: 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; list the common ecological sites on Walnut Gulch and present hydrologic information about ecological sites contained in NRCS site descriptions; describe a state and transition model and its hydrologic implications for one ecological site, Loamy Upland; and explain how to access ecological site information for other locations based on the SSURGO database.