Thinning and prescribed fire are common management tools used to eliminate thick fuel loads that could otherwise facilitate and encourage a more severe catastrophic wildfire. The objective of this study was to quantify the lasting effects of prescribed fire on forest floor and soil nutrients approximately 9 yr after a burn occurred near Truckee, CA. The study site includes a prescribed fire following various harvest and understory removal treatments: whole‐tree thinning, cut‐to‐length thinning, and no thinning. Data were collected before, immediately after, and 9 yr later following a prescribed burn. All forest floor and soil samples were analyzed for nutrients (O horizon: total N; mineral soil: total N, total C, mineral N). Fuel reductions were evident 9 yr after the fire in the burned plots. No significant changes in total C or total N in surface (0–20‐cm) mineral soils occurred during the 9‐yr period. Mineral N concentrations in surface soils were greater in unburned than in burned cut‐to‐length thinning treatments after 9 yr. These differences were attributed to N inputs from decomposing slash and to the reduction in the biomass of N 2 fixers by burning.

The effects of thinning followed by residue mastication (THIN), prescribed fire (BURN), and thinning plus residue mastication plus burning (T+B) on nutrient budgets and resin-based (plant root simulator [PRS] probe) measurements of soil nutrient availability in a mixed-conifer forest were measured. Because of site differences, removals of carbon (C) and nutrients by harvesting were greater in the T+B than in the THIN (Mg) treatment. Harvesting caused greater exports of C, phosphorus, potassium (K), calcium (Ca), and magnesium than burning, harvesting and burning caused approximately equal exports of nitrogen (N), and burning caused greater exports of sulfur than harvesting. Burning caused greater volatilization losses of C and N from the T+B than from the BURN treatment because the addition of chips from mastication in the T+B treatment caused greater combustion of the native forest floor. The most significant effect of the chips on soil nutrients was the addition of K to the forest floor pools, which was also reflected in resin-based measurements of soil nutrients. Burning caused increases in soil NO−3−N, mineral N, Ca2+, and SO2−4 as measured by PRS probes, which persisted for 2 years after the burn. The more intense burning in the T+B treatment also caused elevated orthophosphate levels 2 years after the burn. Burning effects on K+ and Mg2+ were not significant. Overall, the most ecologically significant effect of treatment was the export of N from the combination of harvesting and burning in the T+B treatment, which totaled 932 kg ha−1 and 13

The effects of rock content on nutrient concentrations and contents (kgha−1) in a skeletal soil derived from andesite were investigated. Rock content to a 60cm depth ranged from 8 to 69% among 20 quantitative soil pits within a 10ha area. On average, rocks contained 9% of total soil C, 19% of total soil N, 3% of total ecosystem C, and 12% of total ecosystem N. Percent rock content also appeared to cause increases in organic matter concentrations: rock content was significantly, positively correlated with total C and total N concentrations in the fine earth (>2mm) fraction. Soil C was organic; no carbonates were present. Percent rock content was also significantly, positively correlated with fine earth C:N ratio, suggesting that organic matter in rockier soils was in an earlier stage of decomposition at any given depth. Other consistent correlations with rock content included Bray P (positive) and exchangeable Mg2+ (negative). The decrease in fine earth mass with increasing percent rock content offsets the increase in C concentration such that there was no correlation between percent rock content and either fine earth or total soil (fine earth plus rock) C content (kgha−1). Percent rock content was significantly negatively correlated with total N, Bray P, inorganic N, exchangeable K+, Ca2+, and Mg2+ contents, however. The results of this study show that high rock content can affect soil C and nutrient pools not only because of the contributions of the rocks themselves, but also because high rock content appears to cause higher concentrations in the fine earth fraction.

Re-examination of data distributions from several forested sites in the eastern Sierra Nevada Mountains shows consistent, positive outliers and skew for NH 4 + , NO 3 − , and mineral N in resin lysimeters and resin capsules, indicating that most values were low but hotspots of high N flux were present in most cases. Exact causes of these N flux hotspots is not known, but could include water flux hotspots (e.g., preferential flowpaths), microbial hotspots, and possibly the entry of N-enriched O horizon interflow. Soil and resin stake (PRS probe) data from one site (North Lake Tahoe) also showed consistent, positive outliers and skew for NH 4 + , NO 3 − , and mineral N, suggesting the presence of microbially produced hotspots. Bicarbonate-P data from soils and ortho -P data from PRS probes also showed highly positive skew and extreme outliers, but Bray (HCl/NH 4 F-extractable) P in soils did not. Other measured nutrients (extractable Mg 2+ , K + , SO 4 2− , and Ca 2+ ) also showed positive skew and outliers, but less so than NH 4 + , NO 3 − , and mineral N. Calcium stood out among measured nutrients as the most abundant nutrient with the least outliers and the lowest (sometimes negative) skew. The differences in distributions of NH 4 + , NO 3 − , and mineral N and those of Ca 2+ may reflect relative abundance: the most abundant ion, Ca 2+ , shows little evidence of hotspots whereas the much less abundant ions, NH 4 + , NO 3 − consistently show evidence of hotspots. We hypothesize that the differing distributions of N and Ca reflect the relative biological competition for these nutrients and that positively-skewed distributions and hotspots will be characteristic of any other nutrient when it is in limited supply relative to biological demand.

The presence of nitrogen (N) fixing vegetation can have significant deleterious effects on water quality and also soil leaching. This study investigates the effects of snowbrush ( Ceanothus velutinus Dougl.), a common post‐disturbance N fixer in the western United States, on water quality and soil leaching. We compared mineral N concentrations in soil solution, runoff, O horizon leachates and resin lysimeters in adjacent snowbrush and Jeffrey pine ( Pinus jeffreyii Grev. & Balf) stands in one site in the eastern Sierra Nevada Mountains in Nevada. Soil solutions from snowbrush had slightly but not significantly greater NO 3 − concentrations than those from Jeffrey pine. Leaching rates of NO 3 − and NH 4 + measured by resin lysimeters were lower in snowbrush than in Jeffrey pine, and leaching rates in mineral soil (15 cm) were not significantly different. Nitrate and NH 4 + concentrations in runoff were greater in the snowbrush than Jeffrey pine, and ancillary field column studies confirmed that snowbrush litter was the primary source of this elevated mineral N. Cutting, followed by mastication and herbicide treatments had no effect on mineral N leaching in a snowbrush stand growing on a recently burned (1994) site in the eastern Sierra Nevada Mountains of California. We conclude from this and previous studies that snowbrush, unlike some other post‐disturbance N‐fixing species, has minimal and inconsistent effects on water quality in the eastern Sierra Nevada Mountains. Copyright © 2009 John Wiley & Sons, Ltd.

Fire suppression in Sierran ecosystems creates a substantial wildfire hazard and may exacerbate nutrient inputs into Lake Tahoe by allowing the buildup of O horizon material, which serves as a source for high N and P concentrations in runoff water. The purpose of this study was to evaluate the effects of biomass reduction using cut-to-length mechanical harvest followed by chipping and controlled burning on surface runoff volume and water quality. Based on previous findings regarding N and P leaching flux and soil solution concentrations, we hypothesized that controlled burning and/or mechanical harvest with residue chipping does not increase inorganic N, P, and S concentrations in overland flow. Runoff, snowmelt, and rainfall were collected, volume measurements were taken, and samples were analyzed for NO(3)-N, NH(4)-N, PO(4)-P, and SO(4). Runoff volume, season, and year were identified as important parameters influencing overland flow nutrient concentrations and loads. Higher nutrient concentrations were commonly associated with summer rather than winter runoff, but the opposite was true for nutrient loads due to the higher runoff volumes. Treatment (unharvested, harvested, unburned, burned) effect was a strong predictor for discharge loads of NO(3)-N and SO(4) but was a weak predictor for PO(4)-P. Discharge loads of NO(3)-N and SO(4) were greater for the unburned harvested and the burned unharvested treatments than for the unburned, unharvested control sites or the burned and harvested combined treatment. Although mechanical harvest and/or controlled burning had a small initial impact on increased nutrient loading, the effects were minimal compared with background levels. Hence, these management practices may have the potential to improve forest health without the danger of large-magnitude nutrient mobilization and degradation of runoff water quality found with wildfire.