Lake Tahoe Basin Research Articles

Fire Injury Severity in an Eastern Sierra Nevada Mixed Conifer Stand: Variability and Influencing Factors

Variability of postfire injury and stand and individual tree factors that affected survival responses of eastern Sierra Nevada conifers to wildfire were examined. Prefire measurements served as a basis of comparison for postfire conditions in a mixed conifer stand located in the eastern portion of the Lake Tahoe Basin and provided insight into predisposing influences on survival. Species composition consisted primarily of Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and California white fir (Abies concolor var. lowiana [Gord.] Lemm.) along with a minor component of sugar pine (Pinus lambertiana Dougl.). Postfire survival was higher in Jeffrey pine than white fir but was highest overall in sugar pine. Catastrophic crown loss occurred less frequently in Jeffrey pine than in the fir but was least common in sugar pine. Survival generally increased with tree size, but this relationship did not extend to the largest trees in the stand. Among an array of regression models used to evaluate selected variables for their predictive capacity regarding postfire survival, prefire stand density was found to negatively influence that of Jeffrey and sugar pine, and survival of Jeffrey pine and white fir was negatively correlated with bole char. These results provide natural resource managers guidance in the selection of viable trees for retention during the salvage harvesting operations that often follow wildfire events.

Ecology of whitebark pine populations in relation to white pine blister rust infection in subalpine forests of the Lake Tahoe Basin, USA: Implications for restoration

For over a century, white pine blister rust (WPBR), caused by the introduced fungal pathogen, Cronartium ribicola J.C. Fisch., has affected white pine (Subgenus Strobus) individuals, populations, and associated forest communities in North America. We surveyed eight populations of whitebark pine (Pinus albicaulis Engelm.) across a range of environmental conditions in subalpine forests of the Lake Tahoe Basin, California and Nevada, to determine how WPBR is influencing host fecundity (i.e., female cone production and recruitment), survival, and current population trends. In this region and throughout its range whitebark pine is an important component of subalpine ecosystems. In high-elevation forests of the Lake Tahoe Basin, the primary negative effect of this rust pathogen on whitebark pine is infection and mortality of cone-bearing branches.Mean incidence of WPBR among whitebark pine populations was 35% and ranged from 1% to 65%. Given the high disease incidence, relationships were found between WPBR infection and reproductive output. Percent of individuals infected per population (R2=0.78), average number of WPBR-infected branches per population (R2=0.71), and severity of stem girdling (R2=0.76) were all negatively related with cone production. A positive relationship was found between disease severity (i.e., extent of stem girdling) and available water capacity and a negative relationship was found between disease severity and%sand content. Environmental conditions, including soil properties, may affect pathogen growth and potentially influence the rate at which green infected trees lose the ability to produce female cones. Demographic trends for 7 of 8 whitebark pine populations were stable, with estimates of geometric growth rate (λ)⩾1.0. Population stability is a function of adequate population sizes, mixed-size structure, high survivorship, and moderate fecundity. Results show that WPBR is adversely affecting fecundity but having little effect on survivorship. Restoration strategies are designed to facilitate whitebark pine recruitment and deploy genetically diverse seedling material and potentially WPBR-resistant phenotypes. Our study highlights a need for long-term demographic data and monitoring of WPBR-infection to better understand population consequences and host responses in the future.

Small-scale best management practices to protect lake water quality

Lake Tahoe, on the border of Nevada and California in the Sierra Nevada, is the world’s 11th deepest lake and is one of the clearest high altitude lakes in the world. Since Secchi disk monitoring began in the late 1960s, average water transparency has decreased from over 30 m to about 20 m. Efforts to reduce the decline in the water clarity of Lake Tahoe have been ongoing; since the early 1970s. One unique method to reduce nonpoint source pollution of the lake is the Best Management Practice (BMP) Retrofi t program of the Tahoe Regional Planning Agency (TRPA). This bi-state agency requires all developed properties in the Lake Tahoe Basin to implement water quality BMPs. The TRPA has worked with local Conservation Districts, the USDA Natural Resources Conservation Service and University of Nevada Cooperative Extension to develop small-scale erosion control and runoff infi ltration practices. Homeowners and small business owners can install these BMPs to reduce the amount of nutrient and fi ne sediment-bearing runoff fl owing into street and highway storm drains from private properties. In turn, city and state road departments can design facilities sized only for the runoff from the public right-of-way. This saves city and state governments millions of dollars in infrastructure costs. Special techniques have been developed to capture runoff from rooftops and driveways, convey it to an infi ltration system, and let it soak into the soil. Bare soil areas must be planted and/or covered with mulch to prevent erosion. Bare areas on slopes over 50% must be treated with structures as well as vegetation. Building and landscape contractors are trained annually in proper BMP installation, and the textbook, How to Install Residential Scale Best Management Practices (BMPs) in the Lake Tahoe Basin, has been translated into Spanish. Lake monitoring since 2000 shows positive results.

Variation in tree mortality and regeneration affect forest carbon recovery following fuel treatments and wildfire in the Lake Tahoe Basin, California, USA

BackgroundForest fuel treatments have been proposed as tools to stabilize carbon stocks in fire-prone forests in the Western U.S.A. Although fuel treatments such as thinning and burning are known to immediately reduce forest carbon stocks, there are suggestions that these losses may be paid back over the long-term if treatments sufficiently reduce future wildfire severity, or prevent deforestation. Although fire severity and post-fire tree regeneration have been indicated as important influences on long-term carbon dynamics, it remains unclear how natural variability in these processes might affect the ability of fuel treatments to protect forest carbon resources. We surveyed a wildfire where fuel treatments were put in place before fire and estimated the short-term impact of treatment and wildfire on aboveground carbon stocks at our study site. We then used a common vegetation growth simulator in conjunction with sensitivity analysis techniques to assess how predicted timescales of carbon recovery after fire are sensitive to variation in rates of fire-related tree mortality, and post-fire tree regeneration.ResultsWe found that fuel reduction treatments were successful at ameliorating fire severity at our study site by removing an estimated 36% of aboveground biomass. Treated and untreated stands stored similar amounts of carbon three years after wildfire, but differences in fire severity were such that untreated stands maintained only 7% of aboveground carbon as live trees, versus 51% in treated stands. Over the long-term, our simulations suggest that treated stands in our study area will recover baseline carbon storage 10–35 years more quickly than untreated stands. Our sensitivity analysis found that rates of fire-related tree mortality strongly influence estimates of post-fire carbon recovery. Rates of regeneration were less influential on recovery timing, except when fire severity was high.ConclusionsOur ability to predict the response of forest carbon resources to anthropogenic and natural disturbances requires models that incorporate uncertainty in processes important to long-term forest carbon dynamics. To the extent that fuel treatments are able to ameliorate tree mortality rates or prevent deforestation resulting from wildfire, our results suggest that treatments may be a viable strategy to stabilize existing forest carbon stocks.

Fine particulate matter and visibility in the Lake Tahoe Basin: Chemical characterization, trends, and source apportionment

Speciated PM2.5 (particulate matter with an aerodynamic diameter ≤2.5 μm) data has been collected for about 20 yr (1990–present) at a rural location in the Lake Tahoe Basin (Bliss State Park) and about 15 yr (1989–2004) at an urban site in South Lake Tahoe. The Bliss State Park site is representative of the Desolation Wilderness, a Class I air quality area with visibility protection under the Clean Air Act. Carbonaceous aerosol dominated reconstructed fine mass at both sites, with 58% at Bliss State Park (BLIS) and 68% at South Lake Tahoe (SOLA). Fine mass at SOLA is 2.5 times that at BLIS, mainly due to enhanced organic and elemental carbon (OC and EC). SOLA experiences a winter peak in PM2.5 mainly due to OC and EC from residential wood combustion, whereas BLIS experiences a summer peak in PM2.5 mainly due to OC and EC from wildfires. Carbonaceous aerosol dominates visibility impairment, causing about ½ the reconstructed aerosol light extinction at BLIS and 70% at SOLA. Trend analysis (1990–2009) showed statistically significant decreases in aerosol extinction at BLIS on 20% best and 60% middle visibility days and statistically insignificant upward trends on 20% worst days. SOLA (1990–2003) showed statistically significant decreases in aerosol extinction for all day categories, driven by decreasing OC and EC. From the regional haze rule baseline period of 2000–2004 until 2005–2009, BLIS saw 20% best days improving and 20% worst days getting worse due to increased wildfire effects. Receptor modeling was performed using positive matrix factorization (PMF) and chemical mass balance (CMB). It confirmed that (1) biomass burning dominanted PM2.5 sources at both sites with increasing importance over time; (2) low combustion efficiency burning accounts for most of the biomass burning contribution; (3) road dust and traffic contributions were much higher at SOLA than at BLIS; and (4) industrial combustion and salting were minor sources. Implications: Visibility on the 20% worst visibility days decreased at Bliss State Park, which represents the Desolation and Mokelumne Wilderness Class I areas. This decrease in visibility, contrary to Regional Haze Rule requirements, was mainly due to increased wildfire activity. Increased sulfate-caused light extinction on worst visibility days may be due to long-range transport from Asia. These factors may make it difficult to achieve reasonable progress toward the national visibility goal. Methods need to be developed to account for the effect of wildfires and intercontinental transport when evaluating progress toward the national goal. Supplemental Materials: Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of the Air & Waste Management Association for details of the receptor modeling, including the average and signal-to-noise ratio (SNR) of PM2.5 mass and chemical concentrations for the 3 PMF modeling groups, PMF factor profiles, and sensitivity test results for the EV-CMP modeling.

Airborne LiDAR analysis and geochronology of faulted glacial moraines in the Tahoe-Sierra frontal fault zone reveal substantial seismic hazards in the Lake Tahoe region, California-Nevada, USA

We integrated high-resolution bare-earth airborne light detection and ranging (LiDAR) imagery with field observations and modern geochronology to characterize the Tahoe-Sierra frontal fault zone, which forms the neotectonic boundary between the Sierra Nevada and the Basin and Range Province west of Lake Tahoe. The LiDAR imagery clearly delineates active normal faults that have displaced late Pleistocene glacial moraines and Holocene alluvium along 30 km of linear, right-stepping range front of the Tahoe-Sierra frontal fault zone. Herein, we illustrate and describe the tectonic geomorphology of faulted lateral moraines. We have developed new, three-dimensional modeling techniques that utilize the high-resolution LiDAR data to determine tectonic displacements of moraine crests and alluvium. The statistically robust displacement models combined with new ages of the displaced Tioga (20.8 ± 1.4 ka) and Tahoe (69.2 ± 4.8 ka; 73.2 ± 8.7 ka) moraines are used to estimate the minimum vertical separation rate at 17 sites along the Tahoe-Sierra frontal fault zone. Near the northern end of the study area, the minimum vertical separation rate is 1.5 ± 0.4 mm/yr, which represents a two- to threefold increase in estimates of seismic moment for the Lake Tahoe basin. From this study, we conclude that potential earthquake moment magnitudes (M w ) range from 6.3 ± 0.25 to 6.9 ± 0.25. A close spatial association of landslides and active faults suggests that landslides have been seismically triggered. Our study underscores that the Tahoe-Sierra frontal fault zone poses substantial seismic and landslide hazards.

Short-term changes in-stream macroinvertebrate communities following a severe fire in the Lake Tahoe basin, California

Large and severe wildfires can dramatically alter terrestrial and aquatic ecosystems. We documented changes in benthic macroinvertebrate communities and physical habitat at two sites along Angora Creek, CA, USA for 2 years following a severe fire. Although post-fire years had low precipitation, canopy cover and bank stability declined dramatically following the wildfire (canopy cover: 88% pre-fire, 22% post-fire; stable bank: 93% pre-fire, 11% post-fire). Substrate also changed substantially, with fine sediment 8× more abundant post-fire and cobble 7× less abundant post-fire. We found no consistent changes in taxonomic richness or diversity following the fire, but post-fire densities and percentage of sensitive taxa were significantly reduced. We observed large reductions in relative abundances of shredder and scraper taxa, while collector-gatherer abundances increased. Community composition shifted away from pre-fire configurations, and continued to diverge in the second year following the fire. Scores from a regionally derived index of biotic integrity (IBI) were variable but overall much lower in post-fire samples and did not show recovery after 2 years. Overall, our study demonstrated substantial post-fire effects to aquatic ecosystems even in the absence of large flooding or scouring events, and showed that these effects can be transmitted downstream into unburned reaches.

Analysis of the effectiveness of control measures to mitigate road dust emissions in a regional network

The effectiveness of control measures to reduce road dust emissions is analyzed using a year’s data of road dust emissions collected with a mobile sampling platform and a survey of road maintenance practices in the Lake Tahoe Basin of Nevada and California US. Attributes such as sweeping practices, anti-icing, shoulder improvement, pavement condition, trackout, and abrasive material from road segments were analyzed with a feature subset selection algorithm. Street sweeping was found to be an effective means of controlling dust emissions from roads. Road dust from dirty tertiary roads served as a continuous source of suspendable material for adjacent high-speed roads in the winter time. To be most effective, emission control strategies require that not only primary roads, but all roads be swept after snow storms to recover applied abrasive material.

Linking Global Climate Models to an Integrated Hydrologic Model: Using an Individual Station Downscaling Approach

Abstract:This paper implements an individual station‐based downscaled approach based on a quantil–quantile bias correction mapping to further downscale regional gridded simulated output into individual station locations. We describe and propose a framework to optimize the usefulness of this downscaling approach over small watersheds in mountain regions, where downscale gridded data (∼10km) is still too coarse for use in sub‐regional hydrologic simulation studies. Two regional downscaled data sets were downscaled to individual station locations: the Desert Research Institute‐Regional Climate Model based on the Weather Research and Forecasting model (DRI‐RCM; 12 km resolution); and the US Bureau of Reclamation Bias‐Corrected Spatial Disaggregation (BCSD; 12 km resolution). We applied the station‐based downscaled data in the integrated hydrologic model, GSFLOW, as adapted to the Incline Creek watersheds in the northeastern Lake Tahoe basin. Hydrologic model results showed that the proposed downscaled approach provides reasonable downscaled climate data that can be used to evaluate sub‐regional scale hydrologic processes.

Foes to Friends: Changing Contexts and Changing Intergroup Perceptions

To advance the study of comparative public policy there must be stronger methodological and theoretical descriptions and explanations of the development of policies and the actors, events, and contexts surrounding their development. Using the social construction and advocacy coalition frameworks, this study compares intergroup perceptions in adversarial and collaborative contexts in the Lake Tahoe Basin, United States. The results suggest one of the benefits of collaborative compared to adversarial contexts is improved intergroup perceptions. However, years may be needed for improved intergroup perceptions to take effect, and these effects may indicate the continuation of relative group positions.

Water quality response to the Angora Fire, Lake Tahoe, California

The Angora Fire (summer of 2007) was the largest and most severe wildfire in recent history within the Lake Tahoe basin of the Sierra Nevada. To determine the watershed response and to assess the potential for downstream impacts of nutrient and sediment delivery to Lake Tahoe, we monitored the post-fire hydrology and stream water chemistry for 2 years at four locations along the length of Angora Creek, a perennial stream draining the burned watershed. When compared with unburned streams, the hydrology of Angora Creek indicated an earlier and faster melting of the spring snowpack. Peak stream water concentrations of total N (TN) and ammonium occurred within the burned area, whereas peak concentrations of nitrate (NO3 −), total P, soluble reactive P, total suspended solids, turbidity, electrical conductivity (EC), and dissolved organic C occurred below the burned area. In comparison to pre-fire data, TN, NO3 −, TP, total dissolved P, EC, and turbidity increased following the fire, particularly in the wetter second year. Yields for subwatershed areas suggest that the burned urban subwatershed was the largest source of nutrients and sediments, whereas the wet meadow subwatershed downstream of the burned area retained materials. Erosion control efforts, below-average annual precipitation and the timing of its arrival (absence of summer and fall rainstorms), and the existence of a wet meadow below the burned watershed likely reduced the negative impacts that would have been expected from such a severe wildfire.

Duration and severity of Medieval drought in the Lake Tahoe Basin

Droughts in the western U.S. in the past 200 years are small compared to several megadroughts that occurred during Medieval times. We reconstruct duration and magnitude of extreme droughts in the northern Sierra Nevada from hydroclimatic conditions in Fallen Leaf Lake, California. Stands of submerged trees rooted in situ below the lake surface were imaged with sidescan sonar and radiocarbon analysis yields an age estimate of ∼1250 AD. Tree-ring records and submerged paleoshoreline geomorphology suggest a Medieval low-stand of Fallen Leaf Lake lasted more than 220 years. Over eighty more trees were found lying on the lake floor at various elevations above the paleoshoreline. Water-balance calculations suggest annual precipitation was less than 60% normal from late 10th century to early 13th century AD. Hence, the lake’s shoreline dropped 40–60 m below its modern elevation. Stands of pre-Medieval trees in this lake and in Lake Tahoe suggest the region experienced severe drought at least every 650–1150 years during the mid- and late-Holocene. These observations quantify paleo-precipitation and recurrence of prolonged drought in the northern Sierra Nevada.

Fuel Bed Alterations by Thinning, Chipping, and Prescription Fire in a Sierra Nevada Mixed Conifer Stand

Thinning using cut-to-length harvesting coupled with on-site slash chipping and redistribution and followed by prescribed underburning were assessed for their impacts on downed and dead fuels in an eastern Sierra Nevada mixed conifer stand. California white fir (Abies concolor var. lowiana [Gord.] Lemm.) dominated stand composition and was targeted in the thinning operation while Jeffrey pine (Pinus jeffreyi Grev. & Balf.), sugar pine (Pinus lambertiana Dougl.), incense-cedar (Libocedrus decurrens Torr.), and California red fir (Abies magnifica A. Murr.) were less prevalent. Thinning increased total fuel loading 6% and bed depth 14% but the chipping operation confined the additions to the 1+10-hr and 100-hr timelag categories. Subsequent underburning consumed the fuels produced by the mechanical treatments plus a substantial portion of the preexisting load, and the resulting reduction in total loading was almost twice that combusted in the absence of the thinning and chipping operations. Among an array of regression models used to evaluate assorted variables for their predictive capacity regarding downed and dead fuels, positive correlations between both 1+10-hr and total fuels prior to treatment and pretreatment basal area were prominent. Results reported here quantify fuel load modifications from management practices that are being increasingly utilized to enhance stand health and fire resilience in the Lake Tahoe Basin and surrounding forests.

Population biology of sugar pine ( Pinus lambertiana Dougl.) with reference to historical disturbances in the Lake Tahoe Basin: Implications for restoration

Historical logging, fire suppression, and an invasive pathogen, Cronartium ribicola, the cause of white pine blister rust (WPBR), are assumed to have dramatically affected sugar pine ( Pinus lambertiana) populations in the Lake Tahoe Basin. We examined population- and genetic-level consequences of these disturbances within 10 sugar pine populations by assessing current population structure and trends for 1129 individuals, genetic diversity for 250 individuals, and frequency of WPBR-resistance for 102 families. Logging had occurred in 9 of 10 sites and fire suppression was evident in all stands. High density of white fir ( Abies concolor) is often an indicator of fire suppression and we found a negative relationship between sugar pine survivorship and white fir basal area ( r 2 = 0.31). C. ribicola was present in 90% of stands (incidence range: 0–48%) and we found a significant relationship between mean host survivorship and disease incidence ( r 2 = 0.46). We estimated population growth rates ( λ) from size-based transition matrices. For six of 10 sugar pine populations λ was ⩾1.0, indicating that these populations appear to be stable; for four populations, λ was <1.0, indicating populations that may be in decline. A population specific drift parameter, c i , which is a measure of genetic differentiation in allele frequencies relative to an ancestral population, ranged from 0.009 to 0.048. Higher values of c i indicate greater genetic drift, possibly due to a bottleneck caused by historical logging, other agents of mortality or much older events affecting population sizes. Effects of drift are known to be greater in small populations and we found a negative relationship between sugar pine density and c i ( r 2 = 0.36). Allele frequency of the Cr1 gene, responsible for WPBR-resistance in sugar pine, averaged 0.068 for all populations sampled; no WPBR infection was found in one population in which the Cr1 frequency was 0.112. Historical disturbances and their interactions have likely influenced the population biology of sugar pine in the Tahoe Basin; for some populations this has meant reduced population size, higher genetic drift, and poor survival of small- and intermediate-sized individuals. Possible management strategies include restoring population numbers, deploying WPBR-resistance, treating stands to promote natural sugar pine regeneration, and enhancing genetic diversity.

Restoring Forest Raptors: Influence of Human Disturbance and Forest Condition on Northern Goshawks

The Northern Goshawk (Accipiter gentilis) occurs throughout the Holarctic region in wooded environments. Changes in food supply and breeding habitat, along with human encroachment into otherwise suitable habitat, have negatively impacted the goshawk in some regions. Thus, conservation of the species requires coordinated planning to restore and manage both habitat and human activities in goshawk territories. Using our work in the Sierra Nevada (Lake Tahoe Basin) as a case study, we investigated why territories were abandoned and identified actions needed to reverse conditions negatively impacting goshawks that should lead to more successful goshawk conservation worldwide. We summarized all nesting records available on the goshawk in the Basin, quantified human activity levels within and near frequently and infrequently occupied territories, and described the forest structure and species composition of territories and related these parameters to goshawk territory occupancy. As we hypothesized, reproductive success was higher within frequently occupied territories. Human activity was twice as high within infrequently as compared to frequently occupied territories. There was a greater extent of all types of roads and trails within the infrequently occupied territories. Our findings, along with results from Europe, suggest that goshawk protection has been insufficient in some regions and actions that will reduce anthropogenic disturbance should be initiated, including reducing and re‐routing human activity, and reducing the extent of roads and trails within territories. We provide guidance on how to prioritize territories for restoration.

Inferring deposition velocities from changes in aerosol size distributions downwind of a roadway

Abstract Deposition velocities for particulate matter (PM) from road traffic in the Lake Tahoe basin were estimated with a mass-balance model and measurements using four size-specific PM profilers and meteorological instruments located at 15 m upwind and 5, 30 and 100 m downwind of major highway in the Lake Tahoe basin. Coarse PM (2.5–10 μm) concentration decreased exponentially with downwind distance from the highway. With tall aspen trees barrier, at 30 m and 100 m downwind, the PM10 mass concentrations decreased respectively to 51% and 11% from the observed concentrations at 5 m. Particles with diameters between 0.3 and 0.5 μm show almost a homogeneous distribution across the road indicating the smallest particles are unrelated to a road source. Calculated deposition velocities generally increased with particle size and ranged from 15 μm diameter, which is consistent with the Stokes settling velocities, implying the Stokes settling velocities may represent a reliable lower bound on the deposition rate. The wind speed and direction play important roles in determining the deposition velocities of road traffic induced particles. Higher PM concentrations were observed when strong onshore winds dominated during the daytime coupled with high traffic counts. Between late afternoon and early morning, offshore winds blew traffic induced PM towards the Lake, where they could deposit and impact the water clarity.

Role of Snow in Runoff Processes in a Subalpine Hillslope: Field Study in the Ward Creek Watershed, Lake Tahoe, California, during 2000 and 2001 Water Years

Field study is an essential component of hydrologic science because all hydrological studies must be conducted by such observation-based knowledge of real watersheds. Hillslope runoff processes have been intensively investigated, but the flow process at the boundary between the snowpack and ground surface has not been well documented. A field site at the northwest sector of the Ward Creek watershed, Lake Tahoe Basin, was built for observations of overland flow, subsurface stormflow, and channel flow, simultaneously with atmospheric measurements to examine the hydrology at a snow-covered hillslope. Also, the groundwater table under the snowpack was monitored by shallow wells at the hillslope. All field-measured atmospheric data were synthesized with an energy-balance snow model, and the snowmelt rate and energy balance were computed. The results of the analyses indicate that most of the snowmelt water infiltrated into the topsoil layers and that saturated subsurface flow was the largest contributor to the ...

A Synthesis of Sierran Forest Biomass Management Studies and Potential Effects on Water Quality

The Lake Tahoe basin, located along the California and Nevada border between the Carson and Sierra Nevada mountain ranges, represents a complex forested ecosystem consisting of numerous sub-watersheds and tributaries that discharge directly to Lake Tahoe. This synthesis focuses on historical and current nutrient pools and the effects of biomass management in watersheds of the basin relative to their potential impacts on nutrient (N, P) related discharge water quality. An accumulating forest floor as a result of fire suppression has resulted in the build-up of large nutrient pools that now provide a “natural” source of long term nutrient availability to surface waters. As a consequence, stand and forest floor replacing wildfire may cause a large magnitude nutrient mobilization impact on runoff water quality. Hence, mechanical harvest and controlled burning have become popular management strategies. The most ecologically significant long-term effects of controlled fire appear to be the loss of C and N from the forest floor. Although the application of controlled fire may have some initial impact on overland/litter interflow nutrient loading, controlled burning in conjunction with mechanical harvest has the potential to improve runoff water quality by reducing N and P discharge and improving the overall health of forest ecosystems without the danger of a high intensity wildfire.

Habitat Use by Saw‐Whet Owls in the Sierra Nevada

Abstract:Northern saw‐whet owls (Aegolius acadicus) are secondary cavity‐nesters and their dependence on snags has potential repercussions on forest management practices. Descriptive studies exist regarding habitat characteristics around saw‐whet nest and roost areas, yet few studies have examined associations within larger areas or relative to snag characteristics (e.g., density). We conducted owl broadcast surveys and snag sampling during the spring and summer of 2006 and 2007 in the Lake Tahoe Basin of the central Sierra Nevada; we measured additional habitat variables from Geographic Information System layers. We modeled detection and occupancy probabilities for saw‐whets using sampling and site covariates at survey sites. In addition, we used stepwise logistic regression to compare habitat characteristics at owl use sites and nonuse sites at 2 spatial scales. Detection probability was low in 2006 and decreased throughout the survey period; detection probability was slightly higher in 2007 and unaffected by day of survey. Probability of occupancy was affected by elevation and dominant tree species in 2007. Similarly, stepwise logistic regression indicated saw‐whet occurrence was negatively correlated with the percentage of area dominated by white fir (Abies concolor) at both the macrohabitat (approx. 260 ha) and microhabitat (approx. 20 ha) scales and was positively correlated with the percentage of area containing open canopy at the microhabitat scale. We did not find correlations between saw‐whet occurrence and snag characteristics. Current restoration projects in areas of the Sierra Nevada aim to decrease relative abundance of white fir and the number of snags in forest stands. We recommend continued monitoring of saw‐whets to understand potential effects of these restoration activities. Our estimates of saw‐whet occupancy and detection probabilities can be used by forest managers to determine necessary survey effort for reliable results when developing monitoring protocols.

Long-term impact of de-icing salts on tree health in the Lake Tahoe Basin: Environmental influences and interactions with insects and diseases

Lake Tahoe, on the boundary of California and Nevada, is world renown for its natural beauty and is also a popular location for winter-sporting activities. De-icing compounds, such as sodium chloride (NaCl), are used to maintain safe winter driving conditions. Sodium chloride, however, can damage roadside vegetation and affect surface and ground water quality. Our objectives were to: investigate the relationship among salt damage to trees and other damage (from insects, diseases, and other biotic and abiotic factors), examine the effects of vegetation characteristics and environmental factors on salt damage to trees, and to quantify the long-term impacts of de-icing salts on roadside conifers in the Tahoe Basin. From 2006 to 2008, 442 square plots (0.1 ha) were established and surveyed throughout the Lake Tahoe Basin, including 176 control plots > 300 m from roads, and 137 plots originally established in 1990 that were used for long-term trends. Both incidence and severity of salt damage, diseases, insect pests, and other abiotic damage were recorded on all trees within plots (more than 10,000 trees). Soil and vegetation samples were collected from a subset of plots and analyzed for salt content. At least 15% of roadside trees were damaged by salt every year. Very large year-to-year variation in the incidence of salt damage was observed, but the severity of salt damage has decreased since 1990. A clear roadside effect on roadside conifers existed because symptoms of salt damage were only observed on trees in roadside plots and never in control plots, and foliage from trees in roadside plots had more sodium and chloride content than those in control plots for both salt symptomatic and asymptomatic foliage. Incidence of salt damage decreased with increasing distance from roads, was more frequent on rocky soils, and increased with downhill slope steepness and tree density. Pines ( Pinus spp.) were more frequently and severely damaged by salt than firs ( Abies spp.). Trees were more likely to be damaged by something other than salt, and the relationship among salt damage and other damages was antagonistic rather than synergistic. The results from this study have important implications for the ecology and management of conifer forests in relation to salinity and road maintenance.