Hydrology, erosion, and soil interrelationships after rangeland wildfire

Authors: SPAETH, KENNETH - NRCS; Pierson Jr, Frederick; Moffet, Corey

Submitted to: Proceedings of the National Conference on Grazing Lands
Publication Type: Abstract Only
Publication Acceptance Date: 12/13/2006
Publication Date: 12/13/2006
Citation: Spaeth, K.E., Pierson, F.B., and Moffet, C.A. 2006. Hydrology, erosion, and soil interrelationships after rangeland wildfire. In: Proceedings of the 3rd National Conference on Grazing Lands, December 13-16, 2006, St. Louis, Missouri.

Interpretive Summary:

Technical Abstract: Wildfire is a major ecological process and management issue on rangelands throughout the western United States. Fire suppression and land management activities over the past century have disrupted natural fire cycles which can result in more intense and sometimes catastrophic events. Managers are now challenged with dealing with high probabilities of catastrophic fires and rehabilitation or using proactive management alternatives like prescribed fire to return ecosystems to their natural fire regimes. Fire can reduce infiltration, subsurface water recharge and increase runoff and erosion causing reduced site productivity and impairing water quality. After fire, water repellency is typically found on the soil surface or a few centimeters below and is also common on unburned rangelands and dry soils conditions. However, the causal agents of water repellency are different for burned and unburned conditions. Rainfall simulation studies were conducted for 3 consecutive years immediately following a catastrophic wildfire in Denio, Nevada in 1999. Study sites were located on burned and unburned mountain big sagebrush (Artemisia tridentata ssp. vaseyana) sites (35-40% slope). Indirect gradient analysis was used to evaluate and summarize pertinent relationships between vegetation, soil, topographic features, infiltration, runoff, sediment production, and microsite distinction (shrub coppice and interspace) on burned and unburned areas. In the multivariate context, higher infiltration trends were associated with the burned treatment compared to the unburned treatment. Water repellency on the burned sites was apparent at the soil surface; however, it appears that repellency was also a significant factor on the unburned area. Water repellency in the unburned treatment was likely caused by assorted litter buildup (up to 11,605 kg/ha) in >80 year stands (sagebrush duff and grass in the shrub coppice areas and grass litter in the interspace). Fire impacts on infiltration were localized primarily on coppice microsites directly under shrubs characterized by high surface litter accumulations. Burned coppice microsites exhibited the greatest water repellency and highest interrill erosion rates compared to unburned coppices. The influence of soil water repellency on infiltration decreased with time and was generally insignificant after two growing seasons following fire. The presence of certain grasses, forbs and shrubs were correlated with infiltration, runoff, and sediment loss on burned and unburned sites. On the unburned sites, water repellency and higher runoff was correlated with Sandberg bluegrass (Poa secunda) and western aster (Symphyotrichum ascendens). Greater infiltration capacity was correlated with increasing cover of Idaho fescue (Festuca idahoensis) and mountain big sagebrush.