Lassen National Forest Research Articles

If a tree falls in a forest: implications of forest structure persistence for the Pacific marten (Martes caurina)

AbstractA global decline in large trees, largely driven by anthropogenic influences, has potentially dire consequences for cavity‐dependent wildlife. For several species of conservation concern in western North America, including Pacific martens (Martes caurina), fishers (Pekania pennanti), and spotted owls (Strix occidentalis), large live and dead trees (snags) with cavities are forest structural elements that are requisite to fulfilling life history requirements. More than a century may be necessary for trees to develop cavities of a suitable size for use by martens, fishers, and owls, yet the relative amount of time that such trees persist as usable prior to senescence is largely unknown, despite the implications for how forests are managed as habitat for these wildlife species. To address this uncertainty, in 2016, we re‐located 44 live trees and snags identified as marten rest structures between 2009 and 2012 in the Lassen National Forest, California. Upon re‐location, we assessed structure persistence by determining whether structures had changed type (e.g., a live tree that died and transitioned to a snag) or usability (any structure that was degraded to a point where it was no longer usable by a marten). After 5–7 yr, 25% (n = 11) of marten rest structures changed type and 16% (n = 7) appeared to be unusable—a stark contrast compared to a similar study investigating persistence of fisher rest structures, which documented one‐third of the change in structure type and no change in usability over roughly twice the return interval (8–12 yr). Our results emphasize the vast disparity between the lengthy period required for trees to become suitable for marten use and the potentially short period for which they may remain usable. We suggest that forest managers consider the importance of these fine‐scale forest structural elements when developing broad‐scale strategies to reduce fire risk and improve resilience in western North American forests.

How big is enough? Vegetation structure impacts effective fuel treatment width and forest resiliency

AbstractFuel treatments are designed with multiple management goals, including improving suppression capacity and restoring the historical structure of dry forests. Fuelbreaks are a class of fuel treatment that remove fuels within a wide strip of land, with an overarching objective to reduce fire behavior and provide safe access for suppression. In an empirical analysis of shaded fuelbreaks that burned during the 2014 Bald Fire (15,950 ha on the Lassen National Forest, California, USA), we found that overall fire severity was reduced in the treated areas relative to untreated. A non‐linear mixed effects model estimates that the reduction was detected more than 400 m into the treated area, greater than the standard width of the prescribed fuelbreak. Both pre‐ and post‐fire species composition differed between treated and untreated forest, with few living stems remaining in the measured untreated areas. In the post‐fire treated area, we documented a mixed conifer forest dominated by larger diameter Pinus, implying that the fuelbreak did result in a more resilient post‐fire structure and composition. These results indicate that fuelbreak design may need to be wider than generally prescribed and that even during extreme fire conditions fuel treatments can result in resilient forest structures.

Do repeated wildfires promote restoration of oak woodlands in mixed-conifer landscapes?

Oak woodlands are dependent on frequent fire to maintain the low stem density and diverse understories that typify these ecosystems. Without this recurrent disturbance, fire-sensitive conifer competitors encroach on oaks, reducing their vigor, and diminishing habitat quality. In fire-excluded oak woodlands, stand-replacing wildfire can trigger shifts in canopy dominance from seed-generated conifers to oaks, which are capable of vigorous sprouting following topkill. We examined the occurrence and sprouting dynamics of California black oak (Quercus kelloggii Newb.) following repeated wildfires in the Lassen National Forest, California. We found that following reburn, changes in oak relative stand dominance, as well as oak sprout basal area and height, were each positively related to fire severity (P < 0.0001 for each analysis). While conifer regeneration suffered complete mortality at moderate and high reburn severities, 97% of topkilled oaks resprouted from surviving rootstocks, reinforcing oak dominance. Black oak resprouts that originated following topkill in the first wildfire were frequently topkilled in the second fire, including at lower burn severities survived by advance conifer regeneration. The results of this study indicate that while as individuals, black oaks are resilient to recurring wildfire, restoration of historic woodland structure and function is an unlikely outcome of these repeated disturbances. Management of post-wildfire regenerating oak stands in this region will require supplemental fuel reduction treatments, including prescribed burning.

Logistic quantile regression provides improved estimates for bounded avian counts: A case study of California Spotted Owl fledgling production

Counts of avian fledglings, nestlings, or clutch size that are bounded below by zero and above by some small integer form a discrete random variable distribution that is not approximated well by conventional parametric count distributions such as the Poisson or negative binomial. We developed a logistic quantile regression model to provide estimates of the empirical conditional distribution of a bounded discrete random variable. The logistic quantile regression model requires that counts are randomly jittered to a continuous random variable, logit transformed to bound them between specified lower and upper values, then estimated in conventional linear quantile regression, repeating the 3 steps and averaging estimates. Back-transformation to the original discrete scale relies on the fact that quantiles are equivariant to monotonic transformations. We demonstrate this statistical procedure by modeling 20 years of California Spotted Owl fledgling production (0−3 per territory) on the Lassen National Forest, California, USA, as related to climate, demographic, and landscape habitat characteristics at territories. Spotted Owl fledgling counts increased nonlinearly with decreasing precipitation in the early nesting period, in the winter prior to nesting, and in the prior growing season; with increasing minimum temperatures in the early nesting period; with adult compared to subadult parents; when there was no fledgling production in the prior year; and when percentage of the landscape surrounding nesting sites (202 ha) with trees ≥25 m height increased. Changes in production were primarily driven by changes in the proportion of territories with 2 or 3 fledglings. Average variances of the discrete cumulative distributions of the estimated fledgling counts indicated that temporal changes in climate and parent age class explained 18% of the annual variance in owl fledgling production, which was 34% of the total variance. Prior fledgling production explained as much of the variance in the fledgling counts as climate, parent age class, and landscape habitat predictors. Our logistic quantile regression model can be used for any discrete response variables with fixed upper and lower bounds.

Response of understory vegetation to salvage logging following a high‐severity wildfire

AbstractTimber is frequently salvage‐logged following high‐severity stand‐replacing wildfire, but the practice is controversial. One concern is that compound disturbances could result in more deleterious impacts than either disturbance individually, with mechanical operations having the potential to set back recovering native species and increase invasion by non‐native species. Following the 2002 Cone Fire on the Lassen National Forest, three replicates of five salvage treatments were applied to 15 units formerly dominated by ponderosa pine, covering a range of disturbance intensities from unsalvaged to 100% salvaged. Understory species richness and cover data were collected every two years between 2006 and 2012. Richness of both native and non‐native species did not differ among salvage treatments, but both showed strong changes over time. While cover of forbs and graminoids did not differ with salvage treatment, cover of shrubs was significantly reduced at the higher salvage intensities. The three main shrub species are all stimulated to germinate by fire, potentially leaving seedlings vulnerable to any mechanical disturbance occurring immediately postgermination. Many other native perennial species emerge from rhizomes or other deeply buried underground structures and appear to be less affected by salvage harvest. Over time, the plant community in all salvage treatments shifted from dominance by shrubs and forbs to shrubs and grasses. Most of the grasses were native, except Bromus tectorum (cheatgrass), which was found in 4% of measurement quadrats in 2006 and 52% in 2012. Our results indicated that understory vegetation change 4–10 years post‐high‐severity wildfire appeared to be influenced more strongly by factors other than salvage logging.

Retained satellite information influences performance of GPS devices in a forested ecosystem

ABSTRACTGlobal Positioning System (GPS) units used in animal telemetry often suffer from nonrandom data loss and location error. GPS units use stored satellite information to estimate locations, including almanac and ephemeris data reflecting satellite positions at weekly and at &lt;4‐hr temporal scales, respectively. Using the smallest GPS collars (45–51 g) available for mammals, we evaluate how satellite information and environmental conditions affected GPS performance in 27 mobile trials, and field reliability during 56 deployments on Pacific marten (Martes caurina). We conducted trials in Lassen National Forest, California, USA, during March 2011–January 2012. We programmed GPS units to retain or remove satellite data (i.e., continuous or cold‐start mode) before attempting a location (fix), thereby mimicking differing fix intervals. In continuous mode, fix success was 2.2× higher, was not influenced by environmental obstructions, and improved after a location with ≥4 satellites (3 ‐D). In cold‐start mode, fix success was negatively correlated with vegetation cover. Location error was lower for 3‐D fixes. Censoring cold‐start fixes with only 3 satellites (2‐D) and 2‐D locations prior to the first 3‐D fix in continuous mode decreased location error by 91% and 55%, ensuring &lt;50 m accuracy. The significance of previous fix success and reduced battery expenditure underscores the benefits of ephemeris data and short fix intervals. Only 66% of 56 units functioned upon delivery for field deployment. Once tested and deployed, 28% malfunctioned. This study demonstrates that GPS tests should use the same fix schedules as field deployments, and GPS data quality in dense cover improves with short fix intervals. Miniature GPS units are a promising tool, but the study design should be carefully considered. © 2015 The Wildlife Society.

Ketamine and midazolam anesthesia in Pacific martens (Martes caurina).

Abstract The use of midazolam as a tranquilizer for anesthesia in mustelids in conjunction with the cyclohexamine ketamine is not well documented. Because midazolam is fast acting, inexpensive, and quickly metabolized, it may serve as a good alternative to other more commonly used tranquilizers. We trapped and anesthetized 27 Pacific martens (Martes caurina) in Lassen National Forest (northern California, US) August 2010-April 2013. We assessed anesthesia with ketamine at 18 and 25mg/kg combined with 0.2mg/kg of midazolam by comparing mean times of induction, return to consciousness, and recovery, plus physiologic parameters. No reversal was used for the midazolam portion of the anesthetic. Mean (±SD) induction for both ketamine dosages was 1.7±0.5 and 1.8±1.0min, respectively. Return to consciousness mean times were 8.0min longer (P<0.001) for martens receiving a 25mg/kg ketamine dosage. Mean recoveries were 15.1min longer (P<0.003) for the 25mg/kg ketamine dosage. Physiologic parameter means were similar for both ketamine dosages with no statistically significant differences. Body temperatures and heart and respiratory rates were generally stable, but percentage of oxygen saturation and end tidal carbon dioxide values were below those seen in previous mustelid studies. The combination of ketamine, at both dosages, and midazolam provided reliable field anesthesia for Pacific martens, and supplemental oxygen is recommended as needed.

Avian Response to Mechanical Aspen Restoration in Sierra Nevada Coniferous Forest

Using mechanical treatments to mimic natural disturbances is becoming a standard management and restoration approach. In the Sierra Nevada, as throughout much of western North America, much of aspen habitat is in poor health. Because of the high ecological value of healthy aspen, and its limited extent on the landscape, restoration to reverse the decline and improve stand health has become a management priority in the region. To evaluate the ecological effects of mechanically removing competing conifers to restore aspen in the Sierra Nevada, we compared vegetation characteristics and bird abundance in treated and untreated aspen stands on the Lassen National Forest before and up to 13 years after mechanical conifer removal. Treatments reduced total canopy cover and increased herbaceous cover and the number of aspen stems, while shrub and overstory aspen covers were unchanged. Of 10 aspen focal bird species, 7 increased in abundance following treatment relative to controls, including all species associated with early seral aspen habitat and cavity nesting species; none declined. In contrast, of the six conifer focal species, the four associated with denser conifer habitat declined as a result of the treatments. The two species associated with conifer edges and understory cover increased. Our results demonstrate mechanical conifer removal treatments can provide ecologically meaningful changes in habitat for the avian community and are an effective tool for restoring ecological values of degraded aspen habitat for birds in the Sierra Nevada.

Aquatic Ecosystem Response to Timber Harvesting for the Purpose of Restoring Aspen

The removal of conifers through commercial timber harvesting has been successful in restoring aspen, however many aspen stands are located near streams, and there are concerns about potential aquatic ecosystem impairment. We examined the effects of management-scale conifer removal from aspen stands located adjacent to streams on water quality, solar radiation, canopy cover, temperature, aquatic macroinvertebrates, and soil moisture. This 8-year study (2003–2010) involved two projects located in Lassen National Forest. The Pine-Bogard Project consisted of three treatments adjacent to Pine and Bogard Creeks: (i) Phase 1 in January 2004, (ii) Phase 2 in August 2005, and (iii) Phase 3 in January 2008. The Bailey Project consisted of one treatment adjacent to Bailey Creek in September 2006. Treatments involved whole tree removal using track-laying harvesters and rubber tire skidders. More than 80% of all samples analyzed for NO3-N, NH4-N, and PO4-P at Pine, Bogard, and Bailey Creeks were below the detection limit, with the exception of naturally elevated PO4-P in Bogard Creek. All nutrient concentrations (NO3-N, NH4-N, PO4-P, K, and SO4-S) showed little variation within streams and across years. Turbidity and TSS exhibited annual variation, but there was no significant increase in the difference between upstream and downstream turbidity and TSS levels. There was a significant decrease in stream canopy cover and increase in the potential fraction of solar radiation reaching the streams in response to the Pine-Bogard Phase 3 and Bailey treatments; however, there was no corresponding increase in stream temperatures. Macroinvertebrate metrics indicated healthy aquatic ecosystem conditions throughout the course of the study. Lastly, the removal of vegetation significantly increased soil moisture in treated stands relative to untreated stands. These results indicate that, with careful planning and implementation of site-specific best management practices, conifer removal to restore aspen stands can be conducted without degrading aquatic ecosystems.

Post-fire regeneration across a fire severity gradient in the southern Cascades

Large scale, high-severity fires are increasing in the western United States. Despite this trend, there have been few studies investigating post-fire tree regeneration. We established a study in the footprint of the 2000 Storrie Fire, a 23,000ha wildfire that occurred in northern California, USA. We used a stratified sampling design to quantify post-fire vegetation dynamics across four levels of burn severity and three forest types on the Lassen National Forest nine and ten years following fire. Within each sampled stand, we recorded tree seedlings, forest overstory, shrub cover, and abiotic factors hypothesized to influence growth and establishment.Median conifer seedling densities varied substantially by burn severity: 1918 seedlings ha−1 in the Unchanged units; 4838 seedlings ha−1 in the Low-severity units; 6484 seedlings ha−1 in the Medium-severity units; and 710 seedlings ha−1 in the High-severity units. Increased burn severity was associated with greater shrub coverage: shrub cover in High-severity burns was more than three times those of lower burn severities. We calculated Shannon’s Species Diversity (H′) and Pielou’s Evenness (EH) indices to examine woody shrub and tree diversity. Abies spp. were by far the most abundant regenerating conifer species, which may be a concern for land managers; shrub cover after High-severity burns was dominated by Ceanothus spp. Although fir regeneration was prolific, the Storrie Fire generated diverse vegetative responses, potentially aiding in the reintroduction of the diverse landscape mosaic homogenized by a century of landscape-scale fire exclusion.

LETHALPROCYRNEAINFECTION IN A BLACK-BACKED WOODPECKER (PICOIDES ARCTICUS) FROM CALIFORNIA

The black-backed woodpecker (Picoides arcticus) is a species of management concern in California. As part of a study of black-backed woodpecker home range size and foraging ecology, nine birds in Lassen National Forest (Shasta and Lassen Counties, California) were radio-tracked during the 2011 breeding season. One of the marked birds was found dead after being tracked for a 10-wk period in which it successfully nested. A postmortem examination of the dead bird revealed that it was emaciated and autolyzed, with the presumptive cause being numerous spiruroid nematodes of the genus Procyrnea in the gizzard. This first observation of Procyrnea nematodes in a black-backed woodpecker is notable because the Procyrnea infection was considered lethal and because Procyrnea has been implicated in substantial die-offs in other bird species, including woodpeckers.

Cattle Selection for Aspen and Meadow Vegetation: Implications for Restoration

There is concern over the decline of aspen and the lack of successful regeneration due to excessive browsing of aspen suckers by cattle and other wild and domestic ungulates. We conducted a 2-yr study on Lassen National Forest, California, to aid development of cattle grazing strategies to enhance aspen regeneration. We evaluated seasonal biomass, nutritional quality, and utilization by cattle of aspen suckers, aspen herbaceous understory vegetation, and meadow herbaceous vegetation within six aspen–meadow complexes. Aspen suckers had greater nutritional quality compared to aspen understory and meadow vegetation regardless of season or year. Nutritional quality declined with season in all three vegetation types. Early-growing season foraging by cattle focused on meadow and aspen understory vegetation. Mid-growing season decreases in meadow and aspen understory nutritional quality coincided with a marked increase in utilization of aspen suckers. By late-growing season, utilization on aspen suckers was significantly greater than aspen understory or meadow vegetation. Managers can use early-growing season grazing to reduce aspen consumption by cattle, set stocking rates so that adequate herbaceous vegetation is available throughout the growing season, provide nutritional supplements to reduce demand for nutritious aspen suckers, construct protective fencing, and implement grazing systems that insure years with mid- and late-growing season rest from heavy browsing. Existe la preocupación por la disminucion del alamo y la falta de resultados en la regeneracion debido al excesivo ramoneo de las yemas de los alamos por el ganado y otro ungulados silvestres y domesticos. Realizamos un estudio de dos años en el Bosque Nacional Lassen en California en EUA para ayudar a desarrollar estrategias de pastoreo del ganado que estimulen la regeneracion del alamo. Evaluamos la biomasa estacional, calidad nutricional y utilización por el ganado de las yemas del aspen, la vegetación herbacea debajo del alamo y la vegetación herbacea de pradera dentro de seis complejos de alamo-pradera. Las yemas del alamo tuvieron la mas alta calidad nutricional comparada con la vegetación debajo del alamo y la vegetación de pradera independientemente, de la temporada del año. La calidad nutricional disminuyo con la temporada en los tres tipos de vegetación. Al inicio de la temporada de crecimiento el ganado se inclino por la vegetacion debajo del alamo. A mitad de la temporada de crecimiento disminuyo la calidad nutricional de la pradera y la vegetacion de abajo del alamo coincidiendo, con un marcado incremento en la utilizacion de las yemas de alamo. Al final de la temporada de crecimiento la utilizacion de las yemas de alamo fue significativamente mayor que la de la pradera y de abajo del alamo. Los administradores pueden implementar pastoreo al inicio de la temporada de crecimiento para reducir el consumo de alamo por el ganado, establecer la carga animal previendo la disponibilidad adeucada de vegetacion herbacea a través de la temporada de crecimiento, usar suplemento nutricional para reducir la demanda de la nutritiva yema de alamo, construir cercos de proteccion e implementar sistemas de pastoreo que aseguren años con descansos de ramoneo intenso a mediados y finales de la temporada de crecimiento.

Population Dynamics of Spotted Owls in the Sierra Nevada, California

Abstract The California spotted owl (Strix occidentalis occidentalis) is the only spotted owl subspecies not listed as threatened or endangered under the United States Endangered Species Act despite petitions to list it as threatened. We conducted a meta-analysis of population data for 4 populations in the southern Cascades and Sierra Nevada, California, USA, from 1990 to 2005 to assist a listing evaluation by the United States Fish and Wildlife Service. Our study areas (from N to S) were on the Lassen National Forest (LAS), Eldorado National Forest (ELD), Sierra National Forest (SIE), and Sequoia and Kings Canyon National Parks (SKC). These study areas represented a broad spectrum of habitat and management conditions in these mountain ranges. We estimated apparent survival probability, reproductive output, and rate of population change for spotted owls on individual study areas and for all study areas combined (meta-analysis) using model selection or model-averaging based on maximum-likelihood estimation...

Does Raking Basal Duff Affect Tree Growth Rates or Mortality?

Abstract Mortality and reduced growth rates due to raking accumulated basal duff were evaluated for old, large-diameter ponderosa and Jeffrey pine trees on the Lassen National Forest, California. No fire treatments were included to isolate the effect of raking from fire. Trees were monitored annually for 5 years after the raking treatment for mortality and then cored to measure basal area increment. Results showed that raking basal duff and litter to mineral soil from the bole out to 60 cm had no effect on basal area increment or mortality for 5 years posttreatment. Results are pertinent to managers who question whether raking basal duff will decrease tree vigor or increase tree mortality of large and old ponderosa and Jeffrey pine trees in northern California.

Effect of Simulated Browsing on Aspen Regeneration: Implications for Restoration

Abstract Aspen (Populus tremuloides Michx.) is a disturbance-dependent, fire-resilient, shade-intolerant, clonal species that is in decline throughout western North America. The objective of this study was to examine the effects of intensity and season of browsing on annual height growth of aspen suckers. The goal was to aid development of livestock grazing strategies to restore stands in decline due to excessive livestock browsing. We implemented 33 combinations of intensity and season of browse on aspen suckers in three aspen stands on Eagle Lake Range District, Lassen National Forest, California, USA, during 2003 and 2004. Greatest growth was on suckers with no terminal leader browse and ≤ 25% of biomass removed from branches. Lowest growth occurred when 90% of terminal leader length and 50% of branch biomass was removed. Growth was most negatively affected by browse on terminal leader. Growth was lowest for suckers browsed midseason only and suckers browsed both early and midseason. Occurrence of coni...

Detection and quantification of Leptographium wageneri, the cause of black-stain root disease, from bark beetles (Coleoptera: Scolytidae) in Northern California using regular and real-time PCR

Black-stain root disease is a threat to conifer forests in western North America. The disease is caused by the ophiostomatoid fungus Leptographium wageneri (W.B. Kendr.) M.J. Wingf., which is associated with a number of bark beetle (Coleoptera: Scolytidae) and weevil species (Coleoptera: Curculionidae). We developed a polymerase chain reaction test to identify and quantify fungal DNA directly from insects. Leptographium wageneri DNA was detected on 142 of 384 bark beetle samples (37%) collected in Lassen National Forest, in northeastern California, during the years 2001 and 2002. Hylastes macer (LeConte) was the bark beetle species from which Leptographium DNA was amplified most regularly (2001: 63.4%, 2002: 75.0% of samples). Lower insect–fungus association rates were found for Hylurgops porosus (LeConte), Hylurgops subcostulatus (Mannerheim), Hylastes gracilis (LeConte), Hylastes longicollis (Swaine), Dendroctonus valens (LeConte), and Ips pini (Say). The spore load per beetle ranged from 0 to over 1 × 105 spores, with only a few beetles carrying more than 1 × 103 spores. The technique permits the processing of a large number of samples synchronously, as required for epidemiological studies, to study infection rates in bark beetle populations and to identify potential insect vectors.

Removal of Encroaching Conifers to Regenerate Degraded Aspen Stands in the Sierra Nevada

Abstract Aspen is considered a keystone species, and aspen communities are critical for maintaining biodiversity in western landscapes. Inventories of aspen stand health across the Eagle Lake Ranger District (ELRD), Lassen National Forest, California, U.S.A., indicate that 77% of stands are in decline and at risk of loss as defined by almost complete loss of mature aspen with little or no regeneration. This decline is due to competition from conifers establishing within aspen stands as a result of modification of natural fire regimes coupled with excessive browsing by livestock. Restoration treatments were implemented in four aspen stands in 1999 using mechanical equipment to remove competing conifers to enhance the growth environment for aspen. Recruitment and establishment of aspen stems were measured in treated stands (removal of competing conifers) and non‐treated stands (control) immediately prior to treatment and 2 and 4 years post‐treatment. There was a significant increase in total aspen stem density and in two of three aspen regeneration size classes for treated stands compared to controls. Pre‐treatment total aspen density was positively associated with total aspen density and density in all size classes of aspen (p &lt; 0.001). The results demonstrate that mechanical removal of conifers is an effective treatment for restoring aspen.

Spatial and temporal variation of fire regimes in a mixed conifer forest landscape, Southern Cascades, California, USA

AimIn this study, we evaluated the fire‐forest mosaic of a mixed conifer forest landscape by testing the hypothesis that pre‐fire suppression fire regime parameters vary with species composition (tree species), and environment (i.e. slope aspect, slope position, elevation).LocationOur study was conducted in the 1587 ha Cub Creek Research Natural Area (CCRNA), Lassen National Forest, CA, USA.MethodsWe quantified the return interval, seasonal occurrence, size, rotation period, and severity of fires using dendroecology.ResultsSlope aspect, potential soil moisture, forest composition, and fire regime parameters in our study area co‐vary. Median composite and point fire return intervals (FRI) were longest on higher, cooler, more mesic, north‐facing (NF) slopes covered with white fir (Abies concolor), Douglas fir (Pseudotsuga menziesii)–white fir, and red fir (A. magnifica)–white fir forests, shortest on the dry, south‐facing (SF) slopes covered with ponderosa pine (Pinus ponderosa)–white fir forests and intermediate on west‐facing slopes dominated by white fir–sugar pine (P. lambertiana)–incense cedar (Libocedrus decurrens) forests. The spatial pattern for length of fire rotation (FR) was the same as that for FRI. Fires in CCRNA mixed conifer forests occurred mainly (90%) in the dormant season. Size of burns in CCRNA mixed conifer forests were generally small (mean=106 ha), however, during certain drought years widespread fires burned across fuel breaks and spread throughout the watershed. Fire severity was mainly high on upper slopes, low on lower slopes and moderate and low severity on middle slopes. Patterns of fire severity also varied with slope aspect. Fire frequency decreased dramatically in CCRNA after 1905.ConclusionsIn CCRNA, fire regime parameters [e.g. FRI, fire extent, FR, fire severity] varied widely with species composition, slope aspect and slope position. There was also temporal variation in fire extent with the most widespread fires occurring during drought years. The important contributions of topography and climate to variation in the fire regime indicates that exogenous factors play a key role in shaping the fire‐forest structure mosaic and that the fire‐forest structure mosaic is more variable, less predictable and less stable than previously thought. Finally, some characteristics of the fire regime (i.e. fire severity, season of burn) in CCRNA are different than those described for other mixed conifer forests and this suggests that there are geographical differences in mixed conifer fire regimes along the Pacific slope.

Abundances of Small Mammals in Fir Forests in Northeastern California

We compared abundances of seven species of forest rodents among three types of fir ( Abies concolor and A. magnifica ) forest: unlogged old-growth, unlogged mature, and shelter-wood-logged old-growth. Small mammals were livetrapped during summers 1991 and 1992 in four grids within each type of forest; grids were located in the Lassen National Forest in northeastern California. Shelterwood-logged forests had been logged 6–7 years previously. Differences in capture rates between unlogged, old-growth and shelterwood-logged, old-growth forests suggest that logging led to significant increases in populations of golden-mantled ground squirrels ( Spermophilus lateralis ), yellow pine chipmunks ( Tamias amoenus ), and lodgepole chipmunks ( Tamias speciosus ) but may have led to reduced populations of western red-backed voles ( Clethrionomys californicus ). Capture rates of Douglas' squirrels ( Tamiasciurus douglasii ), Allen's chipmunks ( Tamias senex ), and deer mice ( Peromyscus maniculatus ) did not differ significantly between unlogged and shelterwood-logged forests. Capture rate of T. douglasii was significantly greater in mature forests than in old-growth forests in 1992, but we did not detect significant differences between old-growth and mature forests for the other six species. These results illustrate how opening of the canopy and disturbance of the forest floor can lead to significant changes in patterns of abundance of forest rodents.

Truffle production in old-growth and mature fir stands in northeastern California

Few studies have examined fruiting patterns of hypogeous fungi, and relationships between sporocarp production of hypogeous fungi and forest habitat components such as organic soil depth and amounts of decayed wood are poorly understood. We sampled sporocarps of hypogeous fungi (truffles) in four old-growth (>200 years) and four paired, mature (ca 100 years) fir ( Abies spp.) stands during four sample periods in 1993 and three sample periods in 1994 in the Lassen National Forest in northeastern California. Truffles were collected from 4-m 2 circular plots systematically located at 36 grid points per stand during each sample period. Habitat characteristics were measured in 50.3-m 2 circles centered at each grid point in 1993. We found a total of 46 truffle species in 30.4% of the 2016 total plots, and the total standing dry weight of truffles was equivalent to 2.43 kg ha −1. Total frequency and biomass of truffles and number of truffle species did not differ significantly between stand types in 1993 or 1994, but species composition did. We found no significant associations between measures of total truffle abundance and measures of habitat structure and composition at the 0.25-ha grid scale or at the 50.3-m 2 habitat plot scale. At the scale of the 4-m 2 truffle plot, plots with decayed wood were more likely to have truffles than plots without decayed wood during the final sample period of each year, but the association was significant only in 1993. Mean organic soil depth was greater in plots with truffles than plots without truffles in each sample period in both years, but ranked values were only marginally significant in one sample period. Goodness-of-fit tests to the Poisson distribution indicated that individual truffles had clumped distributions, but we could not reject the null hypothesis of random distribution of truffle collections. Our results indicate that total truffle production had recovered from stand-replacement wildfire in the mature stands, and that total truffle abundance was not strongly associated with habitat characteristics within the range of habitat variation exhibited in these stands. Individual species, however, were associated with old-growth stands and others with mature stands.