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Title: Structural and functional connectivity as a driver of hillslope erosion following disturbance

item Williams, Christopher - Jason
item Pierson Jr, Frederick
item ROBICHAUD, PETER - Us Forest Service (FS)
item AL-HAMDAN, OSAMA - University Of Idaho
item BOLL, JAN - University Of Idaho
item STRAND, EVA - University Of Idaho

Submitted to: International Journal of Wildland Fire
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/9/2015
Publication Date: 7/7/2015
Citation: Williams, C.J., Pierson Jr, F.B., Robichaud, P.R., Al-Hamdan, O.Z., Boll, J., Strand, E.K. 2015. Structural and functional connectivity as a driver of hillslope erosion following disturbance. International Journal of Wildland Fire. doi: 10.1071/WF14114.

Interpretive Summary: High levels of runoff and soil erosion are a major concern in the management of degraded and burned rangelands. In particularly, flood events on these landscapes pose hazards to values-at-risk, such as resources, property, and human life. This study used rainfall simulation and hydrologic modeling techniques to evaluate runoff and erosion behavior across various spatial scales at two degraded and burned woodlands sites in the Great Basin, USA. High rates of runoff and sediment measured at fine spatial scales (< 1 m) were sources for runoff and erosion over larger spatial scales. The connectivity of runoff and erosion processes and sources of available sediment were the primary drivers of high levels of runoff and erosion over the hillslope scale for burned and degraded conditions. The results highlight the importance in considering runoff and erosion process connectivity in the forecasting and mitigation of hydrologic and erosion responses to disturbances, particularly for burned landscapes in close proximity to values-at-risk. Furthermore, the results are informative to the development of hydrologic prediction tools through increased understanding and quantification of runoff and erosion processes occurring across spatial scales on burned and degraded rangelands.

Technical Abstract: Hydrologic response to rainfall input on fragmented or burnt hillslopes is strongly influenced by the ensuing connectivity of runoff and erosion processes. Yet, cross-scale process connectivity is seldom evaluated in field studies due scale limitations in experimental design. This study quantified surface susceptibility and hydrologic response across point- to hillslope-scales at two degraded unburnt and burnt woodland sites using rainfall simulation and hydrologic modeling. High runoff (31-47 mm) and erosion (154-1893 g m-2) at the patch-scale (13 m2) were associated with accumulation of fine-scale (0.5 m2) splash-sheet runoff and sediment sources and formation of concentrated flow through contiguous bare zones (64-85% bare ground). Burning increased the continuity of runoff and sediment availability and yield. Cumulative runoff was consistent across plot-scales while erosion increased with increasing plot area due to enhanced sediment detachment and transport. Predicted hillslope-scale runoff and erosion reflected measured patch-scale trends and the connectivity of processes and sediment availability. The cross-scale experiments and simulations indicate the magnitude of hillslope response is governed by rainfall input and the connectivity of surface susceptibility, sediment availability, and runoff and erosion processes. The results demonstrate the importance in considering cross-scale structural and process connectivity when forecasting hydrologic and erosion responses to disturbances.