Special Issue "Long-Term Effects of Fire on Forest Soils"

Guest Editor
Prof. Dr. Dale W. Johnson
Natural Resources and Environmental Science, University of Nevada, Reno, Fleischmann Agriculture Bldg., Ms 370, Reno, NV 89557, USA
Website: http://www.ag.unr.edu/dwj/
E-Mail: dwj@cabnr.unr.edu
Phone: +1 775 784 4511
Fax: +1 775 784 4789
Interests: biogeochemical cycling in natural systems; effects of regional and global phenomena (atmospheric pollution, increased carbon dioxide and climate change) and localized influences (such as harvesting, fire, fertilization) on biochemical cycling, primarily in forest ecosystems; soil-soil solution chemical interactions; factors affecting organic carbon accumulation and loss in soils; nitrogen, sulfur, phosphorus transformations in soils

Dear Colleagues,

There have been many studies and some excellent reviews of the effects of fire on soils. In most cases, these papers and reviews have focused on the immediate effects of fire on soil chemical, biological, and physical properties, and in general these effects are very pronounced. As is the case with many ecosystem perturbations, however, information on longer term effects is more sparse, mostly because few studies are funded for a sufficient length of time to investigate such changes.

Longer term effects of a wildfire could be a result of the immediate and direct effects of burning and the associated carbon and nitrogen losses, ash incorporation, or the indirect effects of charcoal and post-fire vegetation (especially nitrogen-fixing vegetation) along with the lingering effects of burning and ash that occurred immediately after the fire. Longer term effects of repeated prescribed fires could have all of the above as well as the cumulative effects of immediate soil responses. This special issue of Forests will address the longer-term effects of fire from both an observational and theoretical perspective.

Prof. Dr. Dale W. Johnson
Guest Editor

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• prescribed fire
• wild fire
• soil
• chemistry
• biology
• vegetation
• charcoal

Title: Long-Term Effects of Fire and Post-Fire Vegetation on Soils of Differing Parent Material in the Sierra Nevada Mountains, Nevada and California
Authors: D. W. Johnson *, R. F. Walker, W. W. Miller and M. McNulty
Affiliation: Natural Resources and Environmental Science, University of Nevada, Reno, NV 89557, USA; E-Mail: dwj@cabnr.unr.edu; Tel.: +1-775-784-4511
Abstract: This paper compares the results of post-fire (30 to 45 years) analyses of soils and vegetation in two sites in the Sierra Nevada Mountains: Little Valley, Nevada and Sagehen, California. Soils at the Little Valley site are dominated by Entisols and Inceptisols derived from decomposed granite, and soils from the Sagehen site are dominated by Alfisols derived from andesite. The Little Valley fire occurred in 1981 and the site was sampled in 1997–2001; the Sagehen site was burned in the Donner Ridge fire of 1961 and sampled in 2006-2011. In both cases, burned and adjacent forested sites were sampled for vegetation biomass vegetation nutrient content, O horizon mass and nutrient content, and soil nutrient concentrations and contents. In the Little Valley site, the results of which were previously published  (Johnson et al., 2005), soils in the previously burned site were enriched in total C, total N, Ca, and Mg compared to the nearby forested site dominated by Pinus jeffreyi. We attributed the C and N enrichment in the burned site to the presence of Ceanothus velutinus, a nitrogen-fixing shrub which dominated the site at the time of re-sampling. The very large enrichment in Ca and Mg in the shrub site was far greater than could be accounted for by ash inputs from burned vegetation and is presumed to be due to rapid recycling from deeper soil horizons (>60 cm) in the shrub site. In the Sagehen site (the data from which has not been previously published), the previously burned area has an understory also dominated by Ceanothus velutinus with a scattered overstory dominated by Pinus jeffreyi and the  nearby forested site is dominated by mature Pinus jeffreyi with considerable Ceanothus prostratus , a nitrogen-fixing ground cover. In this case, soils in the previously burned site have slightly higher contents of C and N, similar contents of Ca, K, and Mg. On the other hand, extractable P in soils at the Sagehen site, which were 2 to 10 times greater than in the Little Valley site, were significantly lower in the burned than in the forested site. We attribute the difference in extractable P to immobilization by post-fire shrubs, as has been observed in Alnus rubra stands in the northwestern US. Comparing these results to those from a recent wildfire, we conclude that the long-term effects of fire are more strongly influenced by post-fire vegetation than by the fire itself, and that soil parent material is a major factor affecting the nature of these responses.

Title: Soil Total and Charcoal Carbon from Mountain Shrublands to Subalpine Forests in the Colorado Front Range
Authors: C. W. Licata and R. L. Sanford
Affiliation: Department of Biological Sciences, University of Denver, 2190 E. Iliff Ave., Denver, CO 80208-9010, USA; E-Mail: pioneer.licata@gmail.com
Abstract: Temperate conifer forests and mountain shrublands in the Rocky Mountain Front Range, Colorado are fire-adapted ecosystems where wildland fires leave a legacy in the form of char and charcoal. Long-term, persistent soil charcoal carbon pools result from the combined effects of repeated wildland fires, aboveground biomass characteristics and soil transfer mechanisms. However, only a few studies have measured these pools in the dominant vegetation types of this region at a watershed scale. We quantified charcoal C in the upper 10 cm mineral soil with a thermochemical digest method which retains only the most recalcitrant C forms for mid-slope positions with east facing aspects and discovered that charcoal C pools do not follow a linear pattern of increasing amounts with elevation gain. A significant statistical effect of vegetation type on soil charcoal C pools along this ecological gradient suggests fire-derived charcoal C forms and accumulates via unique conditions such as fire regime. There is a bimodal pattern of initial charcoal C gain with elevation between mountain shrublands and the lower montane forest types prior to a mid-elevation decline in upper montane lodgepole pine forests before increasing again in the subalpine forests. Charcoal C amounts did not cause a significant increase or decrease in total SOC pools in these vegetation types in contrast with findings for other temperate ecosystems. Both the range of total soil charcoal C and ratios of charcoal C to total SOC are comparable to but lower than other regional estimates. This study yielded one of the largest collections of soil samples analyzed for charcoal C in the United States. Future modeling and field-based efforts are called for after revealing a landscape-pattern of SOC and charcoal C pools across these vegetation types.

Title: Long and Short-Term Effects of Fire on Soil Charcoal of a Conifer Forest in Southwest Oregon
Authors: Melissa R.A. Pingree ¹, Peter S. Homann ¹, Brett Morrissette ² and Robyn Darbyshire ³
Affiliations: ¹ Huxley College of the Environment, Western Washington University, 516 High St., Bellingham, WA 98225, USA; E-Mail: Peter.Homann@wwu.edu (P.S.H.)
² Department of Forest Ecosystems and Society, Oregon State University, Corvallis, OR 97331, USA
³ Wallowa-Whitman National Forest, Baker City, OR 97814, USA
Abstract: In 2002, the Biscuit Wildfire burned previously established, replicated conifer unthinned and thinned experimental units of the Long-Term Ecosystem Productivity (LTEP) experiment, Southwest Oregon. Charcoal C in pre and postfire O horizon and mineral soil was quantified by physical separation and a peroxide-acid digestion method. Changes in charcoal C did not differ among unthinned wildfire, thinned wildfire, and thinned prescribed fire treatments, but the burned treatments differed from unburned. O horizon charcoal C increased by a factor of ten to 200 kg C ha⁻¹ as a result of fire, and the charcoal that formed averaged 3% of the surface woody fuels consumed. In contrast, charcoal C averaged 2000 kg ha⁻¹ in 0−3-cm mineral soil and decreased 20% as a result of fire. Charcoal C in 3−15-cm mineral soil was stable at 5300 kg C ha⁻¹. Long-term soil C sequestration in the Siskiyou LTEP soils is greatly influenced by the contribution of charcoal C, which makes up 20% of mineral soil organic C. The effect of recent fire on the O horizon demonstrates significant short-term fire effects and the dynamic nature of the O horizon. This research reiterates the importance of fire to soil C in a southwestern Oregon coniferous forest ecosystem.