Watkins W. Miller

PRESCRIBED FIRE EFFECTS ON FOREST FLOOR AND SOIL NUTRIENTS IN A SIERRA NEVADA FOREST

The objectives of this study were to quantify the effects of prescribed fire on forest floor C and nutrient content, soil chemical properties, and soil leaching in a Jeffrey pine (Pinus jeffreyi [Grev. and Balf.]) forest in the eastern Sierra Nevada Mountains of California. The study included a prescribed fire and three timber harvest treatments: whole-tree (WT) thinning, cut-to-length (CTL) thinning, and no harvest (CONT). Prescribed fire resulted in significant decreases in forest floor C (−8 to −23 mg ha−1, or 39% to 61% decrease), N (−114 to −252 kg ha−1, or −31% to 51% decrease), S (0 to −15 kg ha−1, or 0% to 48% decrease), and K (−3 to −45 kg ha−1, or 12% to 51% decrease) contents but no significant change in Ca or Mg contents. In each case, the decreases were greatest in the CTL treatment, where slash accumulation before burning was greatest. Burning caused statistically significant effects on soil total nitrogen, C:N ratio, pH, water-extractable ortho-P, and water-extractable SO42− in some cases, but these effects were generally small, inconsistent among harvest treatments and horizons, and in the case of ortho-P much less than the temporal variation in both burned and unburned plots. There were no statistically significant effects of burning on total C, Bray-extractable P, bicarbonate-extractable P, and exchangeable Ca2+, K+, or Mg2+. Burning had no significant effect on soil solution pH, ortho-P, SO42−, NO3−, or NH4+ as measured by ceramic cup lysimeters and no effect on the cumulative leaching of ortho-P, NO3−, or NH4+ as measured by resin lysimeters. Burning had no effect on needle weight or nutrient contents as measured by the vector analysis. We conclude that prescribed fire had minimal effects on soils or water quality at this site, and that the most ecologically significant effect was the loss of N from the forest floor.

Fire Effects on Carbon and Nitrogen Budgets in Forests

Estimates of C and N loss by gasification during a wildfire in a Jeffrey pine (Pinus Jeffreyii [Grev. and Balf.]) forest in Little Valley, Nevada are compared to potential losses in more mesic forests in the Integrated Forest Study (IFS). In Little Valley, the fire consumed the forest floor, foliage, and an unknown amount of soil organic matter, but little standing large woody material. on an ecosystem level, the fire consumed approximately equal percentages of C and N (12 and 9%, respectively), but a considerably greater proportion of aboveground N (71%) than C (21%). Salvage logging was the major factor in loss, and C lost from the site will not be replenished until forest vegetation is established and succeeds the current shrub vegetation. N2 fixation by Ceanothus velutinus [Dougl.l in the post-fire shrub vegetation appears to have more than made up for N lost by gasification in the fire over the first 16 yr, and may result in long-term increases in C stocks once forest vegetation takes over the site. N loss from the fire equaled > 1,000 years of atmospheric N deposition and > 10,000 years of N leaching at current rates. Calculations of C and N losses from theoretical wildfires in the IFS sites show similar patterns to those in Little Valley. Calculated losses of N in most of the IFS sites would equal many centuries of leaching. Conceptual models of biogeochemical cycling in forests need to include episodic events such as fire.

Nutrient fluxes in a snow-dominated, semi-arid forest: Spatial and temporal patterns

We tested five hypotheses regarding the potential effects of precipitation change on spatial and temporal patterns of water flux, ion flux, and ion concentration in a semiarid, snowmelt-dominated forest in Little Valley, Nevada. Variations in data collected from 1995 to 1999 were used to examine the potential effects of snowpack amount and duration on ion concentrations and fluxes. Soil solution NO3−, NH4+, and ortho-phosphate concentrations and fluxes were uniformly low, and the variations in concentration bore no relationship to snowmelt water flux inputs of these ions. Weathering and cation exchange largely controlled the concentrations and fluxes of base cations from soils in these systems; however, soil solution base cation concentrations were affected by cation concentrations during snowmelt episodes. Soil solution Cl− and SO42− concentrations closely followed the patterns in snowmelt water, suggesting minimal buffering of either ion by soils. In contrast to other studies, the highest concentration and the majority of ion flux from the snowpack in Little Valley occurred in the later phases of snowmelt. Possible reasons for this include sublimation of the snowpack and dry deposition of organic matter during the later stages of snowmelt. Our comparison of interannual and spatial patterns revealed that variation in ion concentration rather than water flux is the most important driver of variation in ion flux. Thus, it is not safe to assume that changes in total precipitation amount will cause concomitant changes in ion inputs to this system.

Thinning and Prescribed Fire Effects on Forest Floor Fuels in the East Side Sierra Nevada Pine Type

Abstract Forest thinning accomplished with cut-to-length and whole-tree harvesting systems combined with prescribed underburning were assessed for their impacts on downed and dead fuel loading of all timelag categories in eastern Sierra Nevada Jeffrey pine (Pinus jeffreyi Grev. & Balf.). Cut-to-length harvesting resulted in an approximate doubling of total fuel loads with the greatest increases occurring in the 100-hr and 1000-hr categories, while changes associated with whole tree harvesting were marginal to the extent that overall posttreatment loading differed little between whole-tree and unfhinned treatments. Following the thinning operations, 1 + 10-hr and total fuel accumulations in the cut-to-lengfh treatment and 1000-hr fuels in the whole-tree treatment were positively correlated with harvested basal area and harvested foliage, branch, bole, and total tree biomass in simple regression models. Subsequent consumption during underburning eliminated 1 + 10-hr and 100-hr fuel additions from cut-to-lengfh harvesting along with a portion of the natural loading in these categories but was much less effective in reducing the 1000-hr fuels generated by this harvesting. Consumption of 1 + 10-hr, 100-hr, and total fuels in all thinning treatments was positively correlated with the amounts present within each category before underburning. Results reported here provide insight into fuel load modifications resulting from field practices that are being increasingly integrated into comprehensive management efforts to improve forest health and fire resilience in the western United States.

The combined effects of thinning and prescribed fire on carbon and nutrient budgets in a Jeffrey pine forest

Abstract• Both burning and harvesting cause carbon and nutrient removals from forest ecosystems, but few studies have addressed the combination of these effects. For a Pinus jeffreyii forest in the Sierra Nevada Mountains of California, we posed the question: what are the relative impacts of thinning and subsequent burning on carbon and nutrient removals?• The thinning methods included whole-tree thinning (WT, where all aboveground biomass was removed) cut to length (CTL, where branches and foliage were left on site in a slash mat on top of skid trails) and no harvest (CONT). Total C and nutrient exports with thinning and burning were greater in the WT and CTL than in the CONT treatments. Total C and N removals were approximately equal for the WT and CTL treatments, although harvesting dominated exports in the WT treatment and burning dominated exports in the CTL treatment. Total removals of P, K, Ca, Mg and S were greatest in the WT treatments, where harvesting dominated removals.• Comparisons of nutrient removals with ecosystem capital and calculations of potential replenishment by atmospheric deposition suggested that N is the nutrient likely to be most depleted by harvesting and burning treatments.Résumé• L’un et l’autre, le brûlage et les récoltes, causent un enlèvement important de carbone et de nutriments dans les écosystèmes forestiers, mais peu de travaux se sont attelés à l’étude de la combinaison de ces effets. Pour une forêt de Pinus jeffreyii nous posons la question suivante : quels sont les impacts relatifs d’une éclaircie et d’un brûlage ultérieur sur l’enlèvement du carbone et des nutriments, dans les Montagnes de la Sierra Nevada en Californie?• Les méthodes d’éclaircie comprennent : éclaircie totale des arbres (WT, toute la biomasse au-dessus du sol est enlevée), coupe à la dimension désirée (CTL, branches et feuillage ont été laissés sur site en andains) et pas de récolte (CONT). L’exportation totale de carbone et de nutriments avec éclaircie et brûlage dans les traitements WT et CTL a été plus importante que dans le traitement CONT. Les sommes totales de carbone et d’azote enlevées ont été approximativement les mêmes pour les traitements WT et CTL, bien que la récolte est été prédominante dans les exportations pour le traitement WT et que le brûlage soit prédominant dans les exportations pour le traitement CTL. Le total des enlèvements de P, K, Ca, Mg et S dans le traitement WT a été le plus grand dans les traitements WT où la récolte était plus importante que l’enlèvement.• La comparaison des nutriments enlevés par rapport au capital de l’écosystème et le calculs de réapprovisionnement par des apports atmosphériques suggère que l’azote (N) est le nutriment probablement le plus épuisé par les traitements de récolte et de brûlage.

Hydrologic Response of a Central Nevada Pinyon-Juniper Woodland to Prescribed Fire

Abstract This study was conducted to determine the effect of prescribed fire on surface hydrology in Great Basin pinyon-juniper (Pinus monophylla Torr. & Frém.—Juniperus osteosperma Torr.) woodlands. Infiltration rates were measured using a single ring infiltrometer over an elevation gradient (2 103, 2 225, and 2 347 m) at 3 microsites (tree canopy, shrub canopy, and interspace) and 2 tree cover types (intermediate and high) in August 2001, before a spring prescribed burn conducted in May 2002, and then following the prescribed burn in August 2002. Infiltration experiments were used to calculate saturated hydraulic conductivity (K[θs]) rates, and water drop penetration times were determined to evaluate the development of water-repellent soils. Infiltration rates before the burn were greater at the low elevation than at the mid and high-elevation study sites because of differences in measured soil texture. Before burning, the infiltration and saturated hydraulic conductivity (K[θs]) rates measured on interspace and shrub canopy microsites were less than on tree canopy microsites at the midelevation study site (2 225 m). Following burning, the intermediate tree cover tree canopy microsites had greater infiltration rates than interspace microsites; all other microsites were similar to each other. No significant differences in K(θs) rates existed among the microsites after burning. However, on the higher elevation study site before the burn, the interspace microsites had final infiltration rates less than the tree canopy microsites, and burning caused no deviation from this trend. Saturated hydraulic conductivity rates at the high elevation did not differ by microsite before the burn, but after burning interspace microsites had K(θs) rates less than tree canopy microsites. Burning increased water repellency of surface soils (0–3 cm) for all cover types. Spring burning in Pinyon-juniper woodlands may produce a hydrologic response depending on surface soil texture and vegetation cover.

FOREST HEALTH IMPACTS OF BARK BEETLES, DWARF MISTLETOE, AND BLISTER RUST IN A LAKE TAHOE BASIN MIXED CONIFER STAND

Abstract Interactions between forest health variables and mensurational characteristics in an uneven-aged eastern Sierra Nevada mixed conifer stand were examined. The stand was located in the Lake Tahoe Basin on a site featuring a coarsely textured granitic soil and numerous rock outcrops. Its composition was dominated by California white fir (Abies concolor var. lowiana [Gord.] Lemm.), with Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and sugar pine (Pinus lambertiana Dougl.) less prominent and incense-cedar (Libocedrus decurrens Torr.) and mountain alder (Alnus tenuifolia Nutt.) the most minor constituents. The majority of saplings and seedlings were white fir. The stand exhibited no evidence that its development had been influenced by fire and, overall, it consisted of numerous small trees accruing little radial growth. Nearly one-quarter of all standing stems pole size or larger were dead, with mortality concentrated in white fir. Forest-floor fuel accumulations were excessive, and coarse debris was especially prominent. A fir engraver beetle (Scolytus ventralis LeConte) epidemic in white fir contrasted against apparent endemic population levels of the Jeffrey pine (Dendroctonus jeffreyi Hopkins) and red turpentine (Dendroctonus valens LeConte) beetles in Jeffrey pine and of the mountain pine beetle (Dendroctonus ponderosae Hopkins) in sugar pine. The severity of fir engraver attack on white fir was weakly related to overall tree size and to the proportion of composition consisting of this host species, while in Jeffrey pine and sugar pine, bark beetle attacks were strongly correlated with the individual proportions of these 2 hosts. Across all species, basal area explained a substantial proportion of the variation in overall attack severity. We found light infestations of true fir dwarf mistletoe (Arceuthobium abietinum Engelm. ex Munz f. sp. concoloris) in white fir and western dwarf mistletoe (Arceuthobium campylopodum Engelm.) in Jeffrey pine, plus an early stage of infection by the white pine blister rust (Cronartium ribicola J.C. Fischer) in sugar pine. Collectively, this case study characterized and quantified many of the conditions, symptoms, and causative agents inherent in a decadent mixed conifer stand in the eastern Sierra Nevada.

Effects of mechanical harvest plus chipping and prescribed fire on Sierran runoff water quality.

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.

Effects of Mechanized Thinning and Prescription Fire on Stand Structure, Live Crown, and Mortality in Jeffrey Pine

ABSTRACT Forest thinning, using cut-to-length and whole-tree harvesting systems with subsequent underburning were assessed for their influence on stand structure, health, and fire resilience in uneven-aged Jeffrey pine (Pinus jeffreyi Grev. & Balf). Stand attributes, derived from measuring trees ≥ 10.2 cm diameter at breast height (DBH), were collected from permanent plots. Trees were divided into three size classes that generally corresponded to dominant/codominant, intermediate, and suppressed crown classes. Comparisons of post- to pre-burning mortality revealed significant thinning and fire main treatment effects as well as significant interaction between these two treatments in the two larger size classes. Mortality increased by 250% in the intermediate crown class within the burned stand portion of the whole-tree treatment, whereas among dominant/codominant trees mortality rose by 160% in the burned cut-to-length treatment combination. Pre- to post-burning shifts in live crown, expressed as a percentage of total tree height, were significantly influenced by both thinning and fire main treatments in the two larger size classes, while the interaction of these treatments was also significant among the largest trees. Within both of these size classes, decreases in live crown percentage were greatest in the burned portion of the unthinned treatment, where intermediate crown class trees lost over 20% of their crowns, while reductions in dominant/codominant trees averaged nearly 25%. The second highest losses for both size classes occurred within the burned cut-to-length treatment. In the smallest trees, mortality rose sharply and live crown decreased substantially after burning in both thinning treatments and in the unthinned control. Within the two larger size classes, preburn live crown size was negatively correlated with changes in crown size subsequent to underburning while DBH was negatively correlated with postburning changes in mortality, but only in intermediate crown class trees. These results present land managers with outcomes of differing management practices presently being evaluated for their potential to enhance forest health and reduce wildfire risk in the Sierra Nevada and similar dry forest regions.

The Effects of Slash Pile Burning on Soil and Water Macronutrients

Significant effects of slash pile burning on soil chemistry and water quality were observed in forested sites in the eastern Sierra Nevada Mountains of Nevada. Slash piles in upland and meadow sites were instrumented postburn with ceramic cup lysimeters, runoff collectors, and resin stakes (Plant Root Simulator™ probes) along transects from pile centers to unburned areas. Ash and soil samples also were collected along these transects. The pH and concentrations of most nutrients in the soil were highest in the centers of the piles. Larger piles had lower levels of total carbon and total nitrogen in the pile centers (indicative of high burn temperatures and volatilization) compared with smaller piles. 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 US Environmental Protection Agency 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.