Hydrology, erosion, plant, and soil relationships after rangeland wildfire

Authors: SPAETH, KENNETH - NRCS; Pierson Jr, Frederick; ROBICHAUD, PETER - US FOREST SERVICE; Moffet, Corey

Submitted to: Wildland Shrub Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/10/2004
Publication Date: 7/1/2007
Citation: Spaeth, K.E., Pierson, F.B., Robichaud, P.R., and Moffet, C.A. 2007. Hydrology, erosion, and soil interrelationships after rangeland wildfire. In: Sosebee, R.E., Wester, D.B., Britton, C.M., McArthur, E.D., Kitchen, S.G, comp. Proceedings: Shrubland dynamics-fire and water, August 10-12, 2004, Lubbock, TX. Proceedings RMRS-P-47, U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fort Collins. p. 62-68.

Interpretive Summary: Wildfire is an important ecological process and management issue on western rangelands. Fire suppression activities in the past century have increased the number and severity of wildfires, resulting in increased soil erosion and decreased water quality. Many infiltration studies on rangeland have shown that litter and vegetation cover protect the soil and enhance infiltration. 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 burned conditions. The objective of this study was to determine if relationships exist between vegetation, soil, and topographic features, and hydrologic variables such infiltration, runoff, and sediment production on burned and unburned areas. The first ordination (strategy 1) used 4 infiltration parameters and the results were unexpected: In the multivariate context, higher infiltration was associated with the burned treatment compared to the unburned treatment. Higher values for cumulative runoff, water repellency, total grass cover, and litter were found on the unburned plots. 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). The second ordination (strategy 2) involved the same 4 infiltration parameters, but included plots only from the burned treatment. More runoff and sediment was associated with the burn shrub coppice plots; in contrast, higher infiltration capacity in the burned interspace. The 3rd ordination (strategy 3) was based on plant canopy cover by species. Discrete taxa of native 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, bluebunch wheatgrass, and western aster. Greater infiltration capacity was correlated with increasing cover of Idaho fescue and mountain big sagebrush. Future analysis will evaluate conditions after the first years growing season and beyond.

Technical Abstract: Wildfire is an important ecological process and management issue on western rangelands. Fire suppression activities in the past century have increased the number and severity of wildfires, resulting in increased soil erosion and decreased water quality. Many infiltration studies on rangeland have shown that litter and vegetation cover protect the soil and enhance infiltration. 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 burned conditions. Rainfall simulation studies were conducted for 3 consecutive years immediately following a catastrophic wildfire in Denio, Nevada in 1999. The objective of this study was to use indirect gradient analysis on the 1999 data 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. The first ordination (strategy 1) used 4 infiltration parameters and the results were unexpected: In the multivariate context, higher infiltration was associated with the burned treatment compared to the unburned treatment. Higher values for cumulative runoff, water repellency, total grass cover, and litter were found on the unburned plots. 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). The second ordination (strategy 2) involved the same 4 infiltration parameters, but included plots only from the burned treatment. More runoff and sediment was associated with the burn shrub coppice plots; in contrast, higher infiltration capacity in the burned interspace. The 3rd ordination (strategy 3) was based on plant canopy cover by species. Discrete taxa of native 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), bluebunch wheatgrass (Pseudoroegneria spicata), and western aster (Symphyotrichum ascendens). Greater infiltration capacity was correlated with increasing cover of Idaho fescue (Festuca idahoensis) and mountain big sagebrush. Future analysis will evaluate conditions after the first years growing season and beyond.