Application of the Rangeland Hydrology and Erosion Model to Ecological Site Descriptions and Management

Authors: Williams, Christopher - Jason; Pierson Jr, Frederick; SPAETH, KENNETH - Natural Resources Conservation Service (NRCS, USDA); Nearing, Mark; Weltz, Mark; AL-HAMDAN, OSAMA - Texas A&M University; Hernandez, Mariano

Submitted to: International Rangeland Congress
Publication Type: Proceedings
Publication Acceptance Date: 1/5/2016
Publication Date: 7/18/2016
Citation: Williams, C.J., Pierson Jr, F.B., Spaeth, K.E., Nearing, M.A., Weltz, M.A., Al-Hamdan, O.Z., Hernandez Narvaez, M.N. 2016. Application of the Rangeland Hydrology and Erosion Model to Ecological Site Descriptions and Management. International Rangeland Congress. In: Proceedings of the X International Rangeland Congress, July 18-22, 2016, Saskatoon, Saskatchewan, Canada.

Interpretive Summary:

Technical Abstract: The utility of Ecological Site Descriptions (ESDs) and State-and-Transition Models (STMs) concepts in guiding rangeland management hinges on their ability to accurately describe and predict community dynamics and the associated consequences. For many rangeland ecosystems, plant community dynamics are directly influenced by key ecohydrologic feedbacks. For example, vegetation and ground cover facilitate infiltration and soil stability, and soil water recharge and nutrients further enhance vegetation productivity. In contrast, bare ground promotes runoff and erosion that further reduce soil water availability, remove critical soil nutrients, and limit vegetation productivity. Vegetation dynamics for rangeland communities are commonly well understood, but quantitative data associated with stabilizing ecohydrologic feedbacks and thresholds are often limited in ESDs and STMs. This paper demonstrates utility of the Rangeland Hydrology and Erosion Model (RHEM) for predicting hydrologic and erosion responses to plant community dynamics and for enhancement of ESDs in guiding management decisions. We applied the RHEM tool (Version 2.3) to a site dominated by dense cover of sagebrush-steppe vegetation under reference conditions, but that may transition to a woodland following encroachment by juniper conifers. Following juniper encroachment, competition for limited soil water produces a landscape with isolated juniper and shrubs and extensive bare ground. Sagebrush-steppe is also subject to invasion by a fire-prone grass, cheatgrass. Frequent fire following cheatgrass invasions facilitates a cheatgrass monoculture. The magnitude to which community transitions from a sagebrush-steppe to a juniper woodland or a cheatgrass monoculture affects runoff and erosion varies across the diverse domain in which sagebrush-steppe vegetation occurs. We used the RHEM tool, populated with characteristic vegetation cover, soil properties, and topography for the selected site, to assess hydrologic and erosion responses to potential management practices, including “do nothing” approaches. RHEM predicted runoff and sediment yield reveal the influence of vegetation and ground cover on hydrologic and erosion processes. RHEM predicted runoff was generally low for 2-25 yr return-interval runoff events on well-vegetated sagebrush-steppe, cheatgrass, and the post-tree-removal sagebrush-steppe communities. In contrast, runoff from bare woodland and burned conditions generated moderate to high levels of runoff and erosion for the 10-100 yr events. Results suggest the woodland community and immediate post-fire conditions are susceptible to high levels of runoff and erosion, even for high likelihood events (i.e., 10 yr event). The high levels of erosion for the burned condition demonstrate the risk of amplified long-term soil loss associated with frequent re-burning (every 5 to 10 yr) of cheatgrass monocultures. Cutting appears to be a viable option to reduce runoff and erosion with favorable vegetation re-establishment. Although burning amplifies runoff and erosion from woodlands, tree removal by burning may reduce long-term soil loss with favorable sagebrush-steppe re-establishment. Our results demonstrate application of RHEM in assessing runoff and erosion responses in ESDs. For sites with important ecohydrologic feedbacks, RHEM results can be combined in ESDs with plant community dynamics to quantify associated ecohydrologic ramifications and guide management. The example here is limited, but the approach can easily be expanded for complex management scenarios.