Johnson, D.W., R.F. Walker, M. McNulty, B.M. Rau, W.W. Miller and B.G. Johnson. The Long-Term Effects of Wildfire and Post-Fire Vegetation on Sierra Nevada Forest Soils. Submitted to Forests April 2012.
Johnson, B.G., D.W. Johnson, W.W. Miller and D.I. Board. 2012. The Effects of Ash Influx on Burned and Unburned Soil Water Extractable Nutrients Using a Mechanical Vacuum Extractor. Soil Science 177 (5): 338-344.
Johnson, B.G., D.W. Johnson, W.W. Miller, E.M. Carroll-Moore and D.I. Board. 2011. The Effects of Slash Pile Burning on Soil and Water Macronutrients. Soil Science 176 (8): 413-425.
Johnson, B.G., D.W. Johnson, J.C. Chambers and R.R. Blank. 2011. Fire Effects on the Mobilization and Uptake of Nitrogen by Cheatgrass (Bromus tectorum
L.). Plant Soil 341: 437-445.
Johnson, B.G. "Fire Effects on Soil and Water Quality in the Sierra Nevada Mountains and Great Basin Ecosystems: Emphasis on Nitrogen." MS Thesis. University of Nevada, Reno, 2010. Print.
The Effects of Slash Pile Burning on Soil and Water Macronutrients
When slash piles are used for fire and ecosystem management, concerns arise over the effects of prolonged, severe burning on soil fertility and water quality. This study examines soil macronutrient, runoff, and soil solution responses to intense burning under slash piles in two locations (Upland and Meadow) in Little Valley, located in the eastern Sierra Nevada Mountains of Nevada. Our data indicates that slash pile burning has significant effects on soil chemistry and water quality, particularly for N and P
Slash piles in Upland and Meadow sites were instrumented post-burn with ceramic cup lysimeters, runoff collectors, and resin stakes (PRSTM probes) along transects from pile centers to unburned areas. Ash and soil samples also were collected. The pH and concentrations of most nutrients in the soil were highest in the centers of the piles. Larger piles had decreased levels of total carbon and total nitrogen in the pile centers which is indicative of high burn temperatures and volatilization while smaller piles did not display this trend. There also were differences between Meadow and non-Meadow systems including higher soil NO3- and lower SO42- amounts in the Meadow areas. Soil solution data indicated that peak concentrations exceeded EPA water quality standards for both NO2--N and NO3--N at all three sites and were 2.5 to 3 times the standards in two sites. Runoff solution peak concentrations also exceeded the standards but only in the Meadow site.
A laboratory study was performed to test the effects of burning on soil solutions. Soils from beneath slash piles that had been burned as well as soils from unburned areas were amended with varying amounts of ash to create ratios of ash:soil ranging from pure ash to pure soil. Amended soils were then repeatedly extracted with deionized water. Results showed that a large quantity of nutrients, particularly potassium and NO3--N, were released from the ash into soil extractant. In most cases, nutrients from ash dominated the observed effects, but in the case of NH4+, burned soil was the main source (Figure 2). Calcium, Mg2+ and PO43--P showed signs of being more responsive to soil chemical processes (displacement of native soil ions, dissolution, adsorption and precipitation) than to the ash influx. Snowpack Manipulation Simulating Climate Changes in the Sierras
Changes in climate, particularly warming trends, are predicted to have a significant effect on snowfall. Areas at mid to high latitudes with low precipitation and soil with low water storage capacity, like the arid West, are forecasted to be the most severely impacted. Snowpack manipulations in Little Valley, NV have provided the opportunity to examine the effects of changing water availability on soil moisture, temperature and decomposition. This study is ongoing within the valley but preliminary results indicate that soil moisture was affected by snow removal and addition for at least two years after the manipulation (Figure 3) while soil temperature was only affected during the experimental period and litter decomposition was not significantly altered. This project is funded by the Whittell Forest Fellowship.
Figure 1: Soil total C (TC), total N (TN), total mineral N (TMN), pH, sulfate, Bray-P, calcium and potassium concentrations (A-H, respectively) at the 0-10 cm depth in the Newly Burned (NB) Upland site. Values are mean ± S.E. Lower-case letters indicate significant differences among position by collection combinations and are derived from Tukey post-hoc tests.
Figure 2: Mean and S.E. of cumulative NO3--N and NH4+-N for the three extracts in the upland (A and B) and meadow (C and D). Lower-case letters represent significant differences in total extractable NO3--N and NH4+-N among different soil type*ash treatment interactions.
Figure 3: Average soil moisture for the snow addition ("+Snow"), snow removal ("-Snow") and control ("Interspace") plots one winter after the snow manipulation occurred (year two effects).