Tahoe Basin Research Articles

60 k.y. record of extension across the western boundary of the Basin and Range province: Estimate of slip rates from offset shoreline terraces and a catastrophic slide beneath Lake Tahoe

Deformation across three major fault strands within the Lake Tahoe basin has been mapped by using a novel combination of high-resolution seismic chirp, airborne laser- and acoustic-multibeam-derived bathymetry, and deep- and shallow-water sediment cores. Submerged erosional terraces of late Pleistocene age (19.2 6 1.8 ka) record vertical de- formation across fault strands that ranges between 10 and 15 m; offset of 10 m is observed across the southern part of the West Tahoe fault. Avalanche deposits from the catastrophic McKinney Bay slide (ca. 60 ka) are offset across the Stateline fault by at least 21-25 m. The submerged shoreline terraces and debris avalanche provide marker beds with which to constrain the extensional history of the region for the past 60 k.y. This history is then used to assess the future seismic hazard of the region. Data on deformation across these two important marker beds, combined with chronological control from 14 C and optically stimulated luminescence measurements, yield an estimate of extension across the Lake Tahoe basin that is 0.4-0.5 mm/yr. On the basis of these measurements, there exists the potential for a large, seiche wave-generating M7 earthquake every ;3 k.y. Late Pleisto- cene and Holocene vertical deformation rates within the Tahoe basin are characteristic of Basin and Range faulting and place the Tahoe basin within the western limits of the extensional Basin and Range province.

Decomposition of macrophytes and dynamics of enzyme activities in subalpine marshes in Lake Tahoe basin, U.S.A.

To reveal the environmental and substrate quality effects on decomposition process and enzyme activities, litterbag experiments containing Nuphar and Carex leaves, Nuphar rhizome, and Ranunculus shoot, were carried in five-subalpine marshes in Lake Tahoe basin, USA. Alkaline phosphatase, β-glucosidase, and β-xylosidase activities were determined by a fluorogenic method using methyumbelliferyl substrates. Carex leaves, Nuphar rhizome and leaves, and Ranunculus shoots lost, respectively, 33, 67, 82 and 93% of original dry weight over 268 days. Decay rates were different among substrates but not among marshes. Nitrogen and carbon contents increased during the first 58 days and subsequently remained stable. Phosphorus content was stable during the experimental period except for a decrease in the first 16 days in Nuphar shoots. Enzyme activities in decomposing Carex and Nuphar leaves in four marshes were not significantly affected by environmental conditions. β-glucosidase and β-xylosidase activities in decomposing Carex leaves increased with time, but in other plant tissue these enzyme activities remained stable during experimental period. Enzyme activities were significantly different among decomposing substrates. Alkaline phosphatase activity was highest in Nuphar leaves (ca. 1286 µ-mole h−1 g DW −1) but lower and similar in other plant tissues (ca. 100 and 10 µ-mole h −1 g DW −1, respectively). This study showed differences in decay rates and enzyme activities rely on substrate and not the environment conditions of the study area. Decomposition rates in the early stage of decomposition were related to cumulative enzyme activities.

No Sparks Fly: Policy Participants Agree on Thinning Trees in the Lake Tahoe Basin

Abstract This article reports an analysis of mail-in questionnaires of policy participants in the Lake Tahoe Basin. The results show all stakeholder affiliations are concerned about the severity of fire risk relative to other important issue areas in the Basin, support thinning trees to reduce fire risk, and are skeptical that thinning trees will have adverse effects on scenic resources in the Basin. Support for thinning tress is strong among stakeholders with pro-development beliefs and with advanced degrees but is minimally influenced by owning property in the Basin.

Evaluation of deterrent techniques and dogs to alter behavior of “nuisance” black bears

The general public often prefers nonlethality when dealing with problem black bears (Ursus americanus). We evaluated the efficacy of nonlethal deterrent techniques on 62 bears in the Lake Tahoe Basin of the Sierra Nevada range. We contrasted animals randomly assigned to a control (no treatment) group (n = 21), an experimental (treatment) group (n = 21), or a treatment + dog group (n = 20). Experimental bears were peppersprayed, shot with 12-gauge rubber buckshot and a rubber slug, and exposed to cracker shells. Bears in the treatment + dog group were chased by hounds in addition to the combination of other deterrents. We tested and modeled the effectiveness of deterrents and dogs using a survival analysis with Cox proportional hazards and ANOVA. Relative success was evaluated by the latency of time (days) between treatment and return to the urban patch (RUP). Predictor variables in the saturated model included age, weight, season, sex, distance moved, and treatment. Only treatment remained in the most parsimonious model. However, mean number of days until RUP did not vary among the 3 treatment levels (ANOVA, P = 0.55). In all but 5 of 62 cases, bears eventually returned to the urban patch in which they were captured; 33 of 62 bears (53%) returned within 1 month and 70% (n = 44) of all bears returned in ≤40 days. We conclude that in the Lake Tahoe Basin the most common nonlethal deterrents, used by agencies responsible for black bear management, are not very effective at altering bear behavior over periods of time >1 month.

IDENTIFYING FOREST REFERENCE CONDITIONS ON EARLY CUT-OVER LANDS, LAKE TAHOE BASIN, USA

Pre-Euro-American settlement forest structure and fire regimes for Jeffrey pine-white fir, red fir-western white pine, and lodgepole pine forests in the Lake Tahoe Basin (California and Nevada, USA) were identified using stand structural analysis and fire scars based on measurements of stumps of trees that were cut in the 19th century. Com- parisons of the presettlement reference with contemporary conditions were then used to determine how and why contemporary conditions deviate from presettlement conditions and to guide ecological restoration. Contemporary forests varied in different ways compared to the presettlement reference. Contemporary Jeffrey pine-white fir forests have more and smaller trees, more basal area, less structural variability, and trees with a more clumped spatial distribution than preset- tlement forests. The mean presettlement fire-return interval for Jeffrey pine-white fir forests was 11.4 yr, and most ( .90%) fires burned in the dormant season; no fire was recorded in the study area after 1871. Similar differences were identified in the structural characteristics of contemporary and presettlement red fir-western white pine and lodgepole pine forests. However, 19th-century logging changed the composition of red fir-western white pine forests, and these forests now have more lodgepole pine than red fir or western white pine. Comparison of contemporary forests with the presettlement reference suggests that resto- ration treatments in Jeffrey pine-white fir forests should include: (1) density and basal- area reduction, primarily of smaller diameter trees; (2) reintroduction of frequent fire as a key regulating disturbance process; and (3) increasing structural heterogeneity by shifting clumped tree distributions to a more random pattern. Restoration treatments in red fir- western white pine forests should include: (1) a shift in species composition by a density and basal-area reduction of lodgepole pine; and (2) increasing structural heterogeneity by shifting tree distributions to a more random pattern. In lodgepole pine forests the restoration emphasis should be: (1) a density and basal-area reduction of small-diameter trees; and (2) an increase in structural heterogeneity that shifts tree spatial patterns from clumped to a more random distribution. Reintroduction of fire as a regulating process into high-elevation red fir-western white pine and lodgepole pine forests can be viewed as a longer-term restoration goal. The method for quantifying presettlement reference conditions from stumps complements, or is an alternative to, methods based on dendroecology or repeat photog-

Simulated rainfall evaluation of revegetation/mulch erosion control in the Lake Tahoe Basin—1: method assessment

AbstractRevegetation of road cuts and fills is intended to stabilize those drastically disturbed areas so that sediment is not transported to adjacent waterways. Sediment has resulted in water quality degradation, an extremely critical issue in the Lake Tahoe Basin. Many revegetation efforts in this semiarid, subalpine environment have resulted in low levels of plant cover, thus failing to meet project goals. Further, no adequate physical method of assessing project effectiveness has been developed, relative to runoff or sediment movement. This paper describes the use of a portable rainfall simulator (RS) to conduct a preliminary assessment of the effectiveness of a variety of erosion‐control treatments and treatment effects on hydrologic parameters and erosion. The particular goal of this paper is to determine whether the RS method can measure revegetation treatment effects on infiltration and erosion. The RS‐plot studies were used to determine slope, cover (mulch and vegetation) and surface roughness effects on infiltration, runoff and erosion rates at several roadcuts across the basin. A rainfall rate of ≈60 mm h−1, approximating the 100‐yr, 15‐min design storm, was applied over replicated 0·64 m2 plots in each treatment type and over bare‐soil plots for comparison. Simulated rainfall had a mean drop size of ≈2·1 mm and approximately 70% of ‘natural’ kinetic energy. Measured parameters included time to runoff, infiltration, runoff/infiltration rate, sediment discharge rate and average sediment concentration as well as analysis of total Kjeldahl nitrogen (TKN) and dissolved phosphorus (TDP) from filtered (0·45 μm) runoff samples. Runoff rates, sediment concentrations and yields were greater from volcanic soils as compared to that from granitic soils for nearly all cover conditions. For example, bare soil sediment yields from volcanic soils ranged from 2–12 as compared to 0·3–3 g m−2 mm−1 for granitic soils. Pine‐needle mulch cover treatments substantially reduced sediment yields from all plots. Plot microtopography or roughness and cross‐slope had no effect on sediment concentrations in runoff or sediment yield. RS measurements showed discernible differences in runoff, infiltration, and sediment yields between treatments. Runoff nutrient concentrations were not distinguishable from that in the rainwater used. Copyright © 2004 John Wiley & Sons, Ltd.

Transtensional deformation in the Lake Tahoe region, California and Nevada, USA

Dextral transtensional deformation is occurring along the Sierra Nevada–Great Basin boundary zone (SNGBBZ) at the eastern edge of the Sierra Nevada microplate. In the Lake Tahoe region of the SNGBBZ, transtension is partitioned spatially and temporally into domains of north–south striking normal faults and transitional domains with conjugate strike-slip faults. The normal fault domains, which have had large Holocene earthquakes but account only for background seismicity in the historic period, primarily accommodate east–west extension, while the transitional domains, which have had moderate Holocene and historic earthquakes and are currently seismically active, primarily record north–south shortening. Through partitioned slip, the upper crust in this region undergoes overall constrictional strain. Major fault zones within the Lake Tahoe basin include two normal fault zones: the northwest-trending Tahoe–Sierra frontal fault zone (TSFFZ) and the north-trending West Tahoe–Dollar Point fault zone. Most faults in these zones show eastside down displacements. Both of these fault zones show evidence of Holocene earthquakes but are relatively quiet seismically through the historic record. The northeast-trending North Tahoe–Incline Village fault zone is a major normal to sinistral-oblique fault zone. This fault zone shows evidence for large Holocene earthquakes and based on the historic record is seismically active at the microearthquake level. The zone forms the boundary between the Lake Tahoe normal fault domain to the south and the Truckee transition zone to the north. Several lines of evidence, including both geology and historic seismicity, indicate that the seismically active Truckee and Gardnerville transition zones, north and southeast of Lake Tahoe basin, respectively, are undergoing north–south shortening. In addition, the central Carson Range, a major north-trending range block between two large normal fault zones, shows internal fault patterns that suggest the range is undergoing north–south shortening in addition to east–west extension. A model capable of explaining the spatial and temporal partitioning of slip suggests that seismic behavior in the region alternates between two modes, one mode characterized by an east–west minimum principal stress and a north–south maximum principal stress as at present. In this mode, seismicity and small-scale faulting reflecting north–south shortening concentrate in mechanically weak transition zones with primarily strike-slip faulting in relatively small-magnitude events, and domains with major normal faults are relatively quiet. A second mode occurs after sufficient north–south shortening reduces the north–south S hmax in magnitude until it is less than S v, at which point S v becomes the maximum principal stress. This second mode is then characterized by large earthquakes on major normal faults in the large normal fault domains, which dominate the overall moment release in the region, producing significant east–west extension.

Characteristics of Snowmelt Runoff from Highways in the Tahoe Basin and Treatment Investigations for Improving Runoff Quality

To reduce the current trend of decreasing water clarity of Lake Tahoe, the California Regional Water Control Board's Lahontan Region imposed numeric discharge limits for five pollutants (total nitrogen, total phosphorus, total iron, turbidity, and oil and grease) for both surface water and infiltration discharges in the Tahoe basin. To assess its compliance with these discharge limits, the California Department of Transportation (Caltrans) monitored six representative sites for snowmelt and other storm water runoff from summer 2000 through spring 2003. In addition, Caltrans has investigated several existing double-barrel sand traps for their effectiveness in removing pollutants and complying with the Tahoe basin discharge limits. The results obtained to date indicate that ( a) concentrations of pollutants found in the snowmelt runoff are higher than the specified storm water discharge limits; ( b) double-barrel sand traps were capable of capturing sand and sediment, but the capture was not complete; ( c) particles that range from 100 to 2,000 μm represented the highest proportion, but no correlation was found between particles and chemical concentrations; and ( d) sand traps did provide modest improvement in runoff quality, but this improvement was insufficient to meet Tahoe basin discharge limits, and hence additional treatment was found to be needed to bring the effluent water quality into compliance.

Gasoline-Related Organics in Lake Tahoe Before and After Prohibition of Carbureted Two-Stroke Engines

ABSTRACT On June 1, 1999, carbureted two-stroke engines were banned on waters within the Lake Tahoe Basin of California and Nevada. The main gasoline components MTBE (methyl tert-butyl ether) and BTEX (benzene, toluene, ethylbenzene, and xylenes) were present at detectable concentrations in all samples taken from Lake Tahoe during 1997–98 prior to the ban. Samples taken from 1999 through 2001 after the ban contained between 10 and 60 percent of the pre-ban concentrations of these compounds, with MTBE exhibiting the most dramatic change (a 90 percent decrease). MTBE and BTEX concentrations in water samples from Lake Tahoe and Lower Echo Lake were related to the amount of boat use at the sampling sites. Polycyclic aromatic hydrocarbon (PAH) compounds are produced by high-temperature pyrolytic reactions. They were sampled using semipermeable membrane sampling devices in Lake Tahoe and nearby Donner Lake, where carbureted two-stroke engines are legal. PAHs were detected in all samples taken from Lake Tahoe and Donner Lake. The number of PAH compounds and their concentrations are related to boat use. The highest concentrations of PAH were detected in samples from two heavily used boating areas, Tahoe Keys Marina and Donner Lake boat ramp. Other sources of PAH, such as atmospheric deposition, wood smoke, tributary streams, and automobile exhaust do not contribute large amounts of PAH to Lake Tahoe. Similar numbers of PAH compounds and concentrations were found in Lake Tahoe before and after the ban of carbureted two-stroke engines.

Evaluation of Water Quality Projects in the Lake Tahoe Basin

Lake Tahoe is a large sub alpine lake located in the Sierra Nevada Range in the states of California and Nevada. The Lake Tahoe watershed is relatively small (800 km(20) and is made up of soils with a very low nutrient content and when combined with the Lake's enormous volume (156 km(3)) produces water of unparalleled clarity. However, urbanization around the Lake during the past 50 yr has greatly increased nutrient flux into the Lake resulting in increased algae production and rapidly declining water clarity. Lake transition from nitrogen limiting to phosphorous limiting during the last 30 yr suggests the onset of cultural eutrophication of Lake Tahoe. Protecting Lake Tahoe's water quality has become a major public concern and much time, effort, and money has been, and will be, spent on this undertaking. The effectiveness of remedial actions is the subject of some debate. Local regulatory agencies have mandated implementation of best management practices (BMPs) to mitigate the effects of development, sometimes at great additional expense for developers and homeowners who question their effectiveness. Conclusive studies on the BMP effectiveness are also expensive and can be difficult to accomplish such that very few such studies have been completed. However, several project evaluations have been completed and more are underway. Such study usually demonstrates support of the project's effectiveness in decreasing nutrient flux to Lake Tahoe. Here, we review the existing state of knowledge of nutrient loading to the Lake and to highlight the need for further evaluative investigations of BMPs in order to improve their performance in present and future regulatory actions.

Prescribed fire, soils, and stream water chemistry in a watershed in the Lake Tahoe Basin, California

Before Euro-American settlement fire was a common process in the forests of the Lake Tahoe Basin. The combination of drought, fire suppression, and past harvesting has produced ecosystems that are susceptible to high-severity wildfires. Consequently, a program of prescribed fire has been recommended but there is incomplete understanding of the ecological effects of fuels treatments, especially with regard to how treatments will affect the flow of nutrients to Lake Tahoe. Nitrogen and phosphorus are the most important nutrients affecting algal growth, and thus lake clarity. Existing data demonstrate a long-term shift from a co-limitation by both nitrogen and phosphorus to phosphorus limitation. Two high-consumption, moderate-intensity prescribed fires were conducted to determine their effects on soil and stream water chemistry. Stream water calcium concentrations increased in burned watersheds whereas soluble reactive phosphorus concentrations were not significantly different. Prescribed fires released calcium and raised soil pH and this may have resulted in the incorporation of phosphorus into insoluble forms. Stream monitoring data indicates water quality effects last for ~3 months. Prescribed fires did not significantly increase the amount of soluble reactive phosphorus in stream waters. However, additional research is needed to determine if prescribed fire increases erosion or movement of particulate P, particularly in areas with steep slopes.

Historical Food Web Structure and Restoration of Native Aquatic Communities in the Lake Tahoe (California–Nevada) Basin

Plans for the restoration of aquatic ecosystems are increasingly focusing on the restoration and rehabilitation of self-sustaining native fish communities. Such efforts have not traditionally adopted an ecosystem-based perspective, which considers species as embedded within a broader food web context. In this study, we quantify food web changes in Lake Tahoe (California-Nevada) over the last century based on stable isotope analysis of museum-archived, preserved fish specimens collected during 4 historical periods and under present conditions. We also examine the contemporary food web of nearby Cascade Lake, which is free from most exotic species and contains a species assemblage resembling that of Lake Tahoe prior to historical species introductions. During the last century, the freshwater shrimp Mysis relicta and lake trout (Salvelinus namaycush) have been introduced and established in Lake Tahoe, and the native top predator, Lahontan cutthroat trout (Oncorhynchus clarki henshawi; hereafter LCT), has been extirpated. Isotope analysis indicates that lake trout now occupy a trophic niche similar to that of historical LCT. Fish production has shifted from benthic to pelagic, corresponding with the eutrophication of Lake Tahoe during recent decades. The current Cascade Lake food web resembles that of the historical Lake Tahoe food web. Our isotope-based food web reconstructions reveal long-term food web changes in Lake Tahoe and can serve as the basis for setting historically relevant restoration targets. Unfortunately, the presence of nonnative species, particularly Mysis and lake trout, have dramatically altered the pelagic food web structure; as such, they are barriers to native fish community restoration. Fish community restoration efforts should focus on adjacent ecosystems, such as Cascade Lake, which have a high likelihood of success because they have not been heavily affected by nonnative introductions.

USING BLACK BEARS TO TEST IDEAL-FREE DISTRIBUTION MODELS EXPERIMENTALLY

Models on the distribution of animals are invaluable in understanding how individuals and, ultimately, populations respond to ecological processes. Rarely, have they been applied to conservation issues at a landscape level. We capitalized on the distribution of a previously unavailable novel food resource, found at the juxtaposition of urban and wildland areas, to test the generality of ideal-free distribution (IFD) models using a mammalian carnivore, the black bear (Ursus americanus). The primary question we addressed was whether an increase in the prevalence of individuals in a geographical region reflects a population increase or a landscape level redistribution. Combining spatial and temporal data sets with empirically obtained information spanning 12‐15 years, we contrasted demographic, lifehistory, and reproductive parameters between individuals at urban‐wildland interface (experimental) and wildland (control) areas at the interface of the Sierra Nevada Range and Great Basin Desert in western North America. Bears were expected to respond to natural versus artificially clumped resources according to an IFD model. Evidence only partially supported this idea because individuals in urban areas had densities 3 times the historical values from the same area, sex ratios were 4.25 times more skewed toward males, bears had 30% larger body mass, home ranges were reduced by 90% for males and 70% for females, and bears entered dens significantly later than wildland conspecifics. However, females in urban-interface areas gave birth to 3 times the number of cubs, although only half as many dispersed successfully relative to wildland females. Further, urban-interface females had a higher proportion (0.57) of potential reproductive years, in which they had young, compared with wildland females (0.29). We present evidence suggesting that bears in Nevada and in the Lake Tahoe basin conform primarily to an ideal-despotic distribution model. Our findings on population reallocation, rather than demographic increase, reemphasize how knowledge about correlates of individual performance and distribution over time helps to understand the extent to which humans change ecosystems, whether their actions are intentional or not.

Detecting and discriminating impervious cover with high-resolution IKONOS data using principal component analysis and morphological operators

The objective of this study was to directly detect impervious cover using new high-resolution IKONOS imagery in South Lake Tahoe, California, USA. The research presented was a pilot analysis to assess the ability of satellite imagery to derive accurate estimates of impervious cover, critical for assessing impacts to water quality, wildlife, and fish habitat. A combination of image processing methods based on principal component analysis and spatial morphological operators was developed for a 25 km2 urban area in the Lake Tahoe Basin. The methodology produced very accurate identification of both commercial and residential impervious cover in an area dominated by dense conifer canopy. Sub-canopy and sub-shadow surfaces were not only detectable, but also discernible with respect to the underlying substrate. An overall accuracy of 92.94% was obtained, with an even higher user accuracy of 95.83% based on 170 ground truth points. Impervious cover is a difficult feature to delineate accurately and efficiently using direct methods. For this application, spatial resolution proved a better operator than spectral resolution. Results from this analysis will be used to better understand the impacts of urban development on the ecology of the Lake Tahoe Basin.

Aircraft measurements of nitrogen and phosphorus in and around the Lake Tahoe Basin: implications for possible sources of atmospheric pollutants to Lake Tahoe.

Atmospheric deposition of nitrogen (N) and phosphorus (P) into Lake Tahoe appears to have been a major factor responsible for the shifting of the lake's nutrient response from N-limited to P-limited. To characterize atmospheric N and P in and around the Lake Tahoe Basin during summer, samples were collected using an instrumented aircraft flown over three locations: the Sierra Nevada foothills east of Sacramento ("low-Sierra"), further east and higher in the Sierra ("mid-Sierra"), and in the Tahoe Basin. Measurements were also made within the smoke plume downwind of an intense forest fire just outside the Tahoe Basin. Samples were collected using a denuder-filter pack sampling system (DFP) and analyzed for gaseous and water-soluble particle components including HNO3/ NO3-, NH3 /NH4+, organic N (ON), total N, SRP (soluble reactive phosphate) and total P. The average total gaseous and particulate N concentrations (+/- 1sigma) measured over the low- and mid-Sierra were 660 (+/- 270) and 630 (+/- 350) nmol N/m3-air, respectively. Total airborne N concentrations in the Tahoe samples were one-half to one-fifth of these values. The forest fire plume had the highest concentration of atmospheric N (860 nmol N/m3-air) and a greater contribution of organic N (ON) to the total N compared to nonsmoky conditions. Airborne P was rarely observed over the low- and mid-Sierra but was present at low concentrations over Lake Tahoe, with average +/- 1sigma) concentrations of 2.3 +/- 2.9 and 2.8 +/- 0.8 nmol P/m3-air under typical clear air and slightly smoky air conditions, respectively. Phosphorus in the forestfire plume was present at concentrations approximately 10 times greater than over the Tahoe Basin. P in these samples included both fine and coarse particulate phosphate as well as unidentified, possibly organic, gaseous P species. Overall, our results suggest that out-of-basin emissions could be significant sources of nitrogen to Lake Tahoe during the summer and that forest fires could be important sources of both N and P.

Dwarf Mistletoe-Host Interactions in Mixed-Conifer Forests in the Sierra Nevada

ABSTRACT We determined the spatial pattern of dwarf mistletoe (Arceuthobium spp.) associated with two different conifer hosts, white fir (Abies concolor) and Jeffrey pine (Pinus jeffreyi), in forests around the Lake Tahoe Basin and at the Teakettle Experimental Forest, both located in the Sierra Nevada. We also examined a number of host variables and bark beetle incidence to determine how these factors might be involved in the Arceuthobium-conifer interaction. There was no significant relationship between dwarf mistletoe-infected trees and associated bark beetles. We found the highest incidence of dwarf mistletoe on Jeffrey pine in Lake Tahoe (87%), followed by dwarf mistletoe on white fir in Lake Tahoe (30%), with the lowest incidence on white fir at Teakettle (27%). Dwarf mistletoe incidence on white fir in our Lake Tahoe grid was not correlated to density but the dwarf mistletoe rating (DMR) was positively correlated to host size. At the Teakettle Forest, dwarf mistletoe incidence on white fir was not correlated with host density but the DMR was correlated with host size. Dwarf mistletoe incidence and DMR on Jeffrey pine were correlated with host density. Individuals, of both conifer species, in all diameter size classes were susceptible to dwarf mistletoe, with the lowest infection rate in the seedling-10-cm-diameter class. Arceuthobium on white fir in Lake Tahoe showed spatial dependence to a range of 20 m. However, Arceuthobium on Jeffrey pine in Lake Tahoe and on white fir at Teakettle showed no clear pattern of spatial structuring. The degree of infection and stand history appear to be important in the spatial dynamics of Arceuthobium spp.

The use of inferential models for estimating nitric acid vapor deposition to semi-arid coniferous forests

Urban areas emit significant amounts of pollutants that impact forest ecosystems. One of the most important of these is nitric acid vapor (HNO 3), a nitrogen-containing gas that deposits efficiently to forest canopies. Since measuring HNO 3 fluxes directly is often impractical and costly in remote forest locales, inferential techniques are most often used to estimate HNO 3 flux. Given the highly efficient deposition of HNO 3, many of these inferential models assume that leaf surfaces are a ‘perfect sink’ for HNO 3 (i.e., that resistance to HNO 3 deposition is negligibly small or zero). This study tests the ‘perfect sink’ assumption in an open gas exchange system by exposing Abies magnifica, Abies concolor, and Pinus jeffreyi seedlings to concentrations of 1–13 ppb at 4–20% relative humidity. We find that, at these humidities and concentrations, cuticles are not perfect sinks for HNO 3, with cuticular resistance values ranging from 20 to 184 s m −1. In addition, our results indicate that accumulating HNO 3 on leaf cuticles at these concentrations leads to higher cuticular resistance over 8–12 h exposure periods. Based on this laboratory data, we then parameterized cuticular resistance using a single-layer inferential model for semi-arid forests in the Lake Tahoe Basin. Modeled fluxes using this modification were 33% lower during well-mixed daytime conditions than the fluxes from an identical model run using the perfect sink assumption. Since HNO 3 can often account for more than half of atmospheric deposition, we conclude that inferential models that assume foliage to be perfect HNO 3 sinks are inaccurate, especially in semi-arid forests where significant amounts of HNO 3 can accumulate on leaf surfaces during dry periods.

Present and past old‐growth forests of the Lake Tahoe Basin, Sierra Nevada, US

Abstract. We described 38 relictual old‐growth stands – with data on the mortality, regeneration, floristic richness, fuel load and disease incidence in our study area in the Tahoe Basin of California and Nevada. The stands are within the lower and upper montane zones (1900–2400 m a.s.l.) and they are rare, occupying < 2% of the land in the Basin's watershed. Correlation matrices and ANOVAs of forest types and conifer species with environmental gradients revealed significant relationships with elevation, distance east of the Sierran crest, slope aspect, annual precipitation, date of complete snow melt, litter depth and degree of soil profile development. Pathogens, parasites and wood‐boring insects were present on 23% of living trees; 16% of all trees were dead. We compared these stands to a reconstruction of pre‐contact Basin forests and to ecologically analogous old‐growth forests of Baja California that have never experienced fire suppression management. Currently, overstorey trees (> 180 yr old) in the Basin stands have ca. 33% cover, 54 m2.ha‐1 basal area and 107 individuals.ha‐1, values very similar to reconstructions of pre‐contact Basin forests and to modern Baja California forests. Understorey trees (60–180 yr old), however, are several times more dense than historic levels and species composition is strongly dominated by A. concolor, regardless of the overstorey composition. The ratio of Pinus: Abies has increased – and the age structure of extant stands predicts that it will continue to increase – from approximately 1:1 in pre‐contact time to 1:7 within the next century. Disease incidence and mortality in Baja forests were lower. Although we quantitatively defined current Basin old‐growth forests – in terms of stand structure – we realize that our definition will differ from that of both past and future old‐growth forests unless management protocols are changed.

Present and past old-growth forests of the Lake Tahoe Basin, Sierra Nevada, US

Abstract We described 38 relictual old-growth stands – with data on the mortality, regeneration, floristic richness, fuel load and disease incidence in our study area in the Tahoe Basin of California and Nevada. The stands are within the lower and upper montane zones (1900–2400 m a.s.l.) and they are rare, occupying 180 yr old) in the...

Comparison of K Factors Using Two Different Nomographs on Surface Soils in the Lake Tahoe Basin, California-Nevada

Soil Survey HorizonsVolume 43, Issue 2 p. 53-57 Article Comparison of K Factors Using Two Different Nomographs on Surface Soils in the Lake Tahoe Basin, California-Nevada John H. Rogers, John H. Rogers Consulting Soil Scientist 2607 Catalina Drive, Davis, CA, 95616Search for more papers by this authorGrant M. Kennedy, Grant M. Kennedy Consulting Soil Scientist 1316 La Sierra Drive, Sacramento, CA, 95864Search for more papers by this authorSidney W. Davis, Corresponding Author Sidney W. Davis Consulting Earth Scientists davis@innercite.com P.O. Box 734, Georgetown, CA, 95634Search for more papers by this author John H. Rogers, John H. Rogers Consulting Soil Scientist 2607 Catalina Drive, Davis, CA, 95616Search for more papers by this authorGrant M. Kennedy, Grant M. Kennedy Consulting Soil Scientist 1316 La Sierra Drive, Sacramento, CA, 95864Search for more papers by this authorSidney W. Davis, Corresponding Author Sidney W. Davis Consulting Earth Scientists davis@innercite.com P.O. Box 734, Georgetown, CA, 95634Search for more papers by this author First published: 04 August 2015 https://doi.org/10.2136/sh2002.2.0053Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume43, Issue2Summer 2002Pages 53-57 RelatedInformation