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Sierra Nevada (sierra + nevada)
Selected AbstractsSpatial Tests of the Pesticide Drift, Habitat Destruction, UV-B, and Climate-Change Hypotheses for California Amphibian DeclinesCONSERVATION BIOLOGY, Issue 6 2002Carlos Davidson In California, the transport and deposition of pesticides from the agriculturally intensive Central Valley to the adjacent Sierra Nevada is well documented, and pesticides have been found in the bodies of Sierra frogs. Pesticides are therefore a plausible cause of declines, but to date no direct links have been found between pesticides and actual amphibian population declines. Using a geographic information system, we constructed maps of the spatial pattern of declines for eight declining California amphibian taxa, and compared the observed patterns of decline to those predicted by hypotheses of wind-borne pesticides, habitat destruction, ultraviolet radiation, and climate change. In four species, we found a strong positive association between declines and the amount of upwind agricultural land use, suggesting that wind-borne pesticides may be an important factor in declines. For two other species, declines were strongly associated with local urban and agricultural land use, consistent with the habitat-destruction hypothesis. The patterns of decline were not consistent with either the ultraviolet radiation or climate-change hypotheses for any of the species we examined. Resumen: Por mucho tiempo se ha sugerido que los pesticidas transportados por el viento son una causa de la declinación de anfibios en áreas sin destrucción de hábitat evidente. En California, el transporte y depósito de pesticidas provenientes del Valle Central, donde se practica la agricultura intensiva, hacia la Sierra Nevada adyacente está bien documentado y se han encontrado pesticidas en el cuerpo de ranas de la Sierra. Por lo tanto, los pesticidas son una causa verosímil de las declinaciones, pero a la fecha no se han encontrado relaciones directas entre los pesticidas y la declinación de anfibios. Construimos mapas de sistemas de información geográfica del patrón espacial de las declinaciones de ocho taxones de anfibios de California, y comparamos los patrones de declinación observados con los esperados por las hipótesis de pesticidas transportados por el viento, la destrucción del hábitat, la radiación ultravioleta y el cambio climático. En cuatro especies, encontramos una fuerte asociación positiva entre las declinaciones y la cantidad de tierras de uso agrícola en dirección contraria a los vientos, lo que sugiere que los pesticidas transportados por el viento pueden ser un factor importante en las declinaciones. Para otras dos especies, las declinaciones se asociaron contundentemente con el uso del suelo urbano y agrícola, lo cual es consistente con la hipótesis de la destrucción del hábitat. Los patrones de declinación no fueron consistentes con la hipótesis de la radiación ultravioleta ni la de cambio climático para ninguna de las especies examinadas. [source] Range size, taxon age and hotspots of neoendemism in the California floraDIVERSITY AND DISTRIBUTIONS, Issue 3 2010Nathan J. B. Kraft Abstract Aim, Sustaining biological diversity requires the protection of the ecological, evolutionary and landscape-level processes that generate it. Here, we identify areas of high neoendemism in a global diversity hotspot, the California flora, using range size data and molecular-based estimates of taxon age. Location, California, USA. Methods, We compiled distribution and range size data for all plant taxa endemic to California and internal transcribed spacer (ITS)-based age estimates for 337 putative neoendemics (15% of the endemic flora). This information was combined to identify areas in the state with high proportions of young and restricted-range taxa. We overlaid the distribution of neoendemic hotspots on maps of currently protected lands and also explored correlations between our diversity measures and climate. Results, The central coast of California, the Sierra Nevada and the San Bernardino Range contained endemics with the most restricted distributions on average, while areas in the Desert and Great Basin provinces found within the state were composed of the youngest neoendemics on average. Diversity measures that took age and range size into account shifted the estimate of highest endemic diversity in the state towards the Desert and Great Basin regions relative to simple counts of endemic species richness. Our diversity measures were poorly correlated with climate and topographic heterogeneity. Main conclusions, Substantial portions of California with high levels of plant neoendemism fall outside of protected lands, indicating that additional action will be needed to preserve the geographic areas apparently associated with high rates of plant diversification. The neoendemic flora of the deserts appears particularly young in our analyses, which may reflect the relatively recent origin of desert environments within the state. [source] Limited phylogeographic structure in the flightless ground beetle, Calathus ruficollis, in southern CaliforniaDIVERSITY AND DISTRIBUTIONS, Issue 5 2007Stylianos Chatzimanolis ABSTRACT The California Floristic Province is home to more than 8000 species of beetles, yet their geographical patterns of supra- and infraspecific diversity remain largely unexplored. In this paper, we investigate the phylogeography and population demographics of a flightless ground beetle, Calathus ruficollis (Coleoptera: Carabidae), in southern California. We sampled 136 specimens from 25 localities divided into 10 populations using a fragment of the mitochondrial cytochrome oxidase I gene. We tested several hypotheses, including the association of geography with particular clades and populations, the degree of differentiation among regions, and the expansion of populations. Parsimony and Bayesian phylogenetic analyses along with nested clade analysis and amova indicate a deep split between the southern Sierra Nevada population and populations south and west. This split corresponds closely to the split between subspecies C. ruficollis ignicollis (southern Sierra Nevada) and C. ruficollis ruficollis. Populations otherwise exhibit limited geographical structure, though Fst values indicate some local differentiation. Mismatch distributions and Fu's Fs indicate range expansion of several populations, suggesting that some structure may have been obscured by recent exchange. The population of C. ruficollis on Santa Cruz Island, which might have been expected to be isolated, shares several haplotypes with mainland populations, appearing to represent multiple colonizations. [source] Effects of wet meadow riparian vegetation on streambank erosion.EARTH SURFACE PROCESSES AND LANDFORMS, Issue 7 2002Abstract We measured the effect of wet meadow vegetation on the bank strength and failure mechanics of a meandering montane meadow stream, the South Fork of the Kern River at Monache Meadow, in California's Sierra Nevada. Streambanks colonized by ,wet' graminoid meadow vegetation were on average five times stronger than those colonized by ,dry' xeric meadow and scrub vegetation. Our measurements show that strength is correlated with vegetation density indicators, including stem counts, standing biomass per unit area, and the ratio of root mass to soil mass. Rushes appear better than sedges at stabilizing coarse bar surfaces, while sedges are far more effective at stabilizing actively eroding cut banks. Wet meadow floodplain vegetation creates a composite cut bank configuration (a cohesive layer overlying cohesionless materials) that erodes via cantilever failure. Field measurements and a geotechnical model of cantilever stability show that by increasing bank strength, wet meadow vegetation increases the thickness, width, and cohesiveness of a bank cantilever, which, in turn, increases the amount of time required to undermine, detach, and remove bank failure blocks. At Monache Meadow, it takes approximately four years to produce and remove a 1 m wide wet meadow bank block. Wet meadow vegetation limits bank migration rates by increasing bank strength, altering bank failure modes, and reducing bank failure frequency. Copyright © 2002 John Wiley & Sons, Ltd. [source] Topographic controls on spatial patterns of conifer transpiration and net primary productivity under climate warming in mountain ecosystemsECOHYDROLOGY, Issue 4 2009C. Tague Abstract The response of forests to a warmer climate depends upon the direct impacts of temperature on forest ecophysiology and indirect effects related to a range of biogeophysical processes. In alpine regions, reduced snow accumulation and earlier melt of seasonal snowpacks are expected hydrologic consequences of warming. For forests, this leads to earlier soil moisture recharge, and may increase summer drought stress. At the same time, increased air temperature alters plant net primary productivity. Most models of climate change impacts focus either on hydrologic behaviour or ecosystem structure or function. In this study we address the interactions between them. We use a coupled model of eco-hydrologic processes to estimate changes in evapotranspiration and vegetation productivity under temperature warming scenarios. Results from Yosemite National Park, in the California Sierra Nevada, suggest that for most snow-dominated elevations, the shift in the timing of recharge is likely to lead to declines in productivity and vegetation water use, even with increased water-use efficiency associated with elevated atmospheric CO2 concentrations. The strength of this effect, however, depends upon interactions between several factors that vary substantially across elevation gradients, including the initial timing of melt relative to the summer growing season, vegetation growth, and the extent to which initial vegetation is water-limited or temperature-limited. These climate-driven changes in vegetation water use also have important implications for summer streamflow. Results from this analysis provide a framework that can be used to develop strategic measurement campaigns and to extrapolate from local measurements of vegetation responses to watershed scale patterns. Copyright © 2009 John Wiley & Sons, Ltd. [source] Spring temperatures in the Sagehen Basin, Sierra Nevada, CA: implications for heat flow and groundwater circulationGEOFLUIDS (ELECTRONIC), Issue 3 2009MARIA BRUMM Abstract Heat flow in the Sierra Nevada, CA, is low despite its young geologic age. We investigate the possibility that advective heat transport by groundwater flow leads to an underestimate of heat flow in the Sierras based purely on borehole measurements. Using temperature and discharge measurements at springs in Sagehen Basin, we find that groundwater removes the equivalent of approximately 20,40 mW m,2 of geothermal heat from the basin. This is comparable with other heat flow measurements in the region and indicates that, in this basin, at least, groundwater does transport a significant amount of geothermal heat within the basin. Additionally, we use estimates of the mean residence time of water discharged at the springs along with hourly temperature records in springs to provide constraints on groundwater flow depths within the basin. An analytical model based on these constraints indicates that the heat removed by groundwater may represent 20% to >90% of the total heat flow in the basin. Without better constraints on the regional hydrogeology and the depth of circulation, we cannot determine whether the heat discharged at the springs represents a change in the mode of heat transfer, i.e. from conduction to advection at shallow depths (<100 m) or whether this is a component of heat transfer that should be added to measured conductive values. If the latter is true, and Sagehen Basin is representative of the Sierras, basal heat flow in the Sierra Nevada may be higher than previously thought. [source] Talus Instability in a Recent Deglaciation Area and Its Relationship to Buried Ice and Snow Cover Evolution (Picacho Del Veleta, Sierra Nevada, Spain)GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 2 2003Antonio Gómez The southernmost glacier in Europe formed during the Little Ice Age at the foot of the north wall of Picacho del Veleta (3 398 m) in Sierra Nevada, in the southeast region of the Iberian Peninsula (lat. 37,03,N, long. 3,22,W). The glacier gradually retreated during the last century, leaving a large talus slope at the base of the wall. The unconsolidated material covering the ice masses acted as a thermal insulator. Recent bottom temperature of snow (BTS) analyses and drillings indicate that the ice still exists within the talus. Evidence from field observations made during the period 1995,2001, revealed that large mass movements occurred during the driest summers (1998 and especially, 1999 and 2000) when the talus was snow free. These conditions suggest a direct relationship between talus stability and thermal insulation from the snow cover in areas where buried ice or decaying marginal permafrost exists. [source] Temporal and spatial variability of cation and silica export in an alpine watershed, Emerald Lake, CaliforniaHYDROLOGICAL PROCESSES, Issue 10 2004T. Meixner Abstract A reaction set of possible mineral weathering reactions is proposed to explain observed cation and silica export for the Emerald Lake watershed, a small Sierra Nevada, California catchment. The reaction set was calculated through a stoichiometric mole-balance method, using a multiyear record of stream flow and snowpack chemical analyses and site-specific mineral compositions. Reaction-set calculations were intended to explore how the processes controlling stream cation and silica export depend on differing bedrock mineralogy across the catchment as snowmelt and runoff patterns change over the year. Different regions within the watershed can be differentiated by lake inflow subdrainages, each exhibiting different stream-flow chemistry and calculated weathering stoichiometry, indicating that different silica and cation generation processes are dominant in wet steep portions of the catchment. Short-term differences in stream concentrations were assumed to reflect ion exchange equilibria and rapid biological processes, whereas long-term persistent stream concentration differences in different areas of the catchment were assumed to reflect spatial variability in mineral weathering stoichiometry. Mineralogical analyses of rock samples from the watershed provided site-specific chemical compositions of major mineral species for reaction calculations. Reaction sets were evaluated by linear regression of calculated versus observed differences between snowmelt and stream-flow chemistry and by a combined measure. Initially, single weathering reactions were balanced and evaluated to determine the reactions that best explained observed stream chemical export. Next, reactions were combined, using mineral compositions from different rock types to estimate the dependence of ion fluxes on lithology. The seasonal variability of major solute calculated fluxes is low, approximately one order of magnitude, relative to the observed three orders of magnitude variability in basin discharge. Reaction sets using basin-averaged lithology and Aplite lithologies gave superior explanations of stream chemical composition. Copyright © 2004 John Wiley & Sons, Ltd. [source] Contrasting phylogeographies inferred for the two alpine sister species Cardamine resedifolia and C. alpina (Brassicaceae)JOURNAL OF BIOGEOGRAPHY, Issue 1 2009Judita Lihová Abstract Aim, We use Cardamine alpina and C. resedifolia as models to address the detailed history of disjunctions in the European alpine system. These species grow on siliceous bedrock: C. alpina in the Alps and Pyrenees, and C. resedifolia in several mountain ranges from the Sierra Nevada to the Balkans. We explore differentiation among their disjunct populations as well as within the contiguous Alpine and Pyrenean ranges, and compare the phylogeographical histories of these diploid sister species. We also include samples of the closely related, arctic diploid C. bellidifolia in order to explore its origin and post-glacial establishment. Location, European alpine system, Norway and Iceland. Methods, We employed amplified fragment length polymorphisms (AFLPs). AFLP data were analysed using principal coordinates analysis, neighbour joining and Bayesian clustering, and measures of diversity and differentiation were computed. Results, For the snow-bed species C. alpina (27 populations, 203 plants) we resolved two strongly divergent lineages, corresponding to the Alps and the Pyrenees. Although multiple glacial refugia were invoked in the Pyrenees, we inferred only a single one in the Maritime Alps , from which rapid post-glacial colonization of the entire Alps occurred, accompanied by a strong founder effect. For C. resedifolia (33 populations, 247 plants), which has a broader ecological amplitude and a wider distribution, the genetic structuring was rather weak and did not correspond to the main geographical disjunctions. This species consists of two widespread and largely sympatric main genetic groups (one of them subdivided into four geographically more restricted groups), and frequent secondary contacts exist between them. Main conclusions, The conspicuously different histories of these two sister species are likely to be associated with their different ecologies. The more abundant habitats available for C. resedifolia may have increased the probability of its gradual migration during colder periods and also of successful establishment after long-distance dispersal, whereas C. alpina has been restricted by its dependence on snow-beds. Surprisingly, the arctic C. bellidifolia formed a very divergent lineage with little variation, contradicting a scenario of recent, post-glacial migration from the Alps or Pyrenees. [source] Historical and contemporary distributions of carnivores in forests of the Sierra Nevada, California, USAJOURNAL OF BIOGEOGRAPHY, Issue 8 2005William J. Zielinski Abstract Aim, Mammalian carnivores are considered particularly sensitive indicators of environmental change. Information on the distribution of carnivores from the early 1900s provides a unique opportunity to evaluate changes in their distributions over a 75-year period during which the influence of human uses of forest resources in California greatly increased. We present information on the distributions of forest carnivores in the context of two of the most significant changes in the Sierra Nevada during this period: the expansion of human settlement and the reduction in mature forests by timber harvest. Methods, We compare the historical and contemporary distributions of 10 taxa of mesocarnivores in the conifer forests of the Sierra Nevada and southern Cascade Range by contrasting the distribution of museum and fur harvest records from the early 1900s with the distribution of detections from baited track-plate and camera surveys conducted from 1996 to 2002. A total of 344 sample units (6 track plates and 1 camera each) were distributed systematically across c. 3,000,000 ha area over a 7-year period. Results, Two species, the wolverine (Gulo gulo) and the red fox (Vulpes vulpes), present in the historical record for our survey area, were not detected during the contemporary surveys. The distributions of 3 species (fisher [Martespennanti], American marten [M. americana], and Virginia opossum [Didelphisvirginiana]) have substantially changed since the early 1900s. The distributions of fishers and martens, mature-forest specialists, appeared to have decreased in the northern Sierra Nevada and southern Cascade region. A reputed gap in the current distribution of fishers was confirmed. We report for the first time evidence that the distribution of martens has become fragmented in the southern Cascades and northern Sierra Nevada. The opossum, an introduced marsupial, expanded its distribution in the Sierra Nevada significantly since it was introduced to the south-central coast region of California in the 1930s. There did not appear to be any changes in the distributions of the species that were considered habitat generalists: gray fox (Urocyon cinereoargenteus), striped skunk (Mephitis mephitis), western spotted skunk (Spilogale gracilis), or black bear (Ursus americanus). Detections of raccoons (Procyon lotor) and badgers (Taxidea taxus) were too rare to evaluate. Contemporary surveys indicated that weasels (M. frenata and M. erminea) were distributed throughout the study area, but historical data were not available for comparison. Main conclusions, Two species, the wolverine and Sierra Nevada red fox, were not detected in contemporary surveys and may be extirpated or in extremely low densities in the regions sampled. The distributions of the mature forest specialists (marten and fisher) appear to have changed more than the distributions of the forest generalists. This is most likely due to a combination of loss of mature forest habitat, residential development and the latent effects of commercial trapping. Biological characteristics of individual species, in combination with the effect of human activities, appear to have combined to affect the current distributions of carnivores in the Sierra Nevada. Periodic resampling of the distributions of carnivores in California, via remote detection methods, is an efficient means for monitoring the status of their populations. [source] The accuracy of matrix population model projections for coniferous trees in the Sierra Nevada, CaliforniaJOURNAL OF ECOLOGY, Issue 4 2005PHILLIP J. VAN MANTGEM Summary 1We assess the use of simple, size-based matrix population models for projecting population trends for six coniferous tree species in the Sierra Nevada, California. We used demographic data from 16 673 trees in 15 permanent plots to create 17 separate time-invariant, density-independent population projection models, and determined differences between trends projected from initial surveys with a 5-year interval and observed data during two subsequent 5-year time steps. 2We detected departures from the assumptions of the matrix modelling approach in terms of strong growth autocorrelations. We also found evidence of observation errors for measurements of tree growth and, to a more limited degree, recruitment. Loglinear analysis provided evidence of significant temporal variation in demographic rates for only two of the 17 populations. 3Total population sizes were strongly predicted by model projections, although population dynamics were dominated by carryover from the previous 5-year time step (i.e. there were few cases of recruitment or death). Fractional changes to overall population sizes were less well predicted. Compared with a null model and a simple demographic model lacking size structure, matrix model projections were better able to predict total population sizes, although the differences were not statistically significant. Matrix model projections were also able to predict short-term rates of survival, growth and recruitment. Mortality frequencies were not well predicted. 4Our results suggest that simple size-structured models can accurately project future short-term changes for some tree populations. However, not all populations were well predicted and these simple models would probably become more inaccurate over longer projection intervals. The predictive ability of these models would also be limited by disturbance or other events that destabilize demographic rates. [source] Inclusion trail patterns in porphyroblasts from the Foothills Terrane, California: a record of orogenesis or local strain heterogeneity?JOURNAL OF METAMORPHIC GEOLOGY, Issue 4 2001S. R. Paterson Abstract A major problem with the current use of porphyroblast,matrix microstructural relationships to infer orogenic histories, such as multiple orthogonal orogenic events, is that other evidence for these events is typically lacking. For example, a comparison of regional relationships and local structures formed in and adjacent to porphyroblasts present in contact aureoles in the Foothills Terrane, Sierra Nevada, California, shows that: (1) except in shear zones, contact aureoles and local zones along lithological contacts, the Foothills Terrane has a single regional cleavage, although locally formed by multiple processes; (2) the regional cleavage and locally developed porphyroblast inclusion trails have variable orientations, and neither dataset supports the formation of dominantly subhorizontal and subvertical cleavages in this orogen; (3) structural and metamorphic heterogeneities occur at all scales and can markedly affect inclusion trail patterns in porphyroblasts; (4) complex porphyroblast growth features and internal inclusion trail patterns can form in porphyroblasts that grow during short time intervals in contact aureoles, indicating that local complexity in porphyroblasts does not imply regional complex ty. Because of these conclusions, multiple datasets, rather than data acquired only from porphyroblasts, should be considered when attempting to understand the evolution of orogens. Furthermore, using microstructural information preserved only in porphyroblasts to infer orogenic processes and plate motions is generally unjustified. [source] Contrasting Lumped and Distributed Hydrology Models for Estimating Climate Change Impacts on California Watersheds,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2010Edwin P. Maurer Maurer, Edwin P., Levi D. Brekke, and Tom Pruitt, 2010. Contrasting Lumped and Distributed Hydrology Models for Estimating Climate Change Impacts on California Watersheds. Journal of the American Water Resources Association (JAWRA) 46(5):1024,1035. DOI: 10.1111/j.1752-1688.2010.00473.x Abstract:, We compare the projected changes to streamflows for three Sierra Nevada rivers using statistically downscaled output from 22 global climate projections. The downscaled meteorological data are used to drive two hydrology models: the Sacramento Soil Moisture Accounting model and the variable infiltration capacity model. These two models differ in their spatial resolution, computational time step, and degree and objective of calibration, thus producing significantly different simulations of current and future streamflow. However, the projected percentage changes in monthly streamflows through mid-21st Century generally did not differ, with the exceptions of streamflow during low flow months, and extreme low flows. These findings suggest that for physically based hydrology models applied to snow-dominated basins in Mediterranean climate regimes like the Sierra Nevada, California, model formulation, resolution, and calibration are secondary factors for estimating projected changes in extreme flows (seasonal or daily). For low flows, hydrology model selection and calibration can be significant factors in assessing impacts of projected climate change. [source] AN ORGANIZED SIGNAL IN SNOWMELT RUNOFF OVER THE WESTERN UNITED STATES,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 2 2000D. H. Peterson ABSTRACT: Daily-to-weekly discharge during the snowmelt season is highly correlated among river basins in the upper elevations of the central and southern Sierra Nevada (Carson, Walker, Tuolumne, Merced, San Joaquin, Kings, and Kern Rivers). In many cases, the upper Sierra Nevada watershed operates in a single mode (with varying catchment amplitudes). In some years, with appropriate lags, this mode extends to distant mountains. A reason for this coherence is the broad scale nature of synoptic features in atmospheric circulation, which provide anomalous insolation and temperature forcing that span a large region, sometimes the entire western U.S. These correlations may fall off dramatically, however, in dry years when the snowpack is spatially patchy. [source] Facilitation of tree saplings by nurse plants: Microhabitat amelioration or protection against herbivores?JOURNAL OF VEGETATION SCIENCE, Issue 2 2008Lorena Gómez-Aparicio Abstract Question: Positive interactions are predicted to be common in communities developing under high physical stress or high herbivory pressure due to neighbour amelioration of limiting physical and consumer stresses, respectively. However, when both stress sources meet in the same community, the relative importance of the two facilitation mechanisms is poorly understood. We ask: What is the relative importance of abiotic vs. biotic mechanisms of facilitation of tree saplings by shrubs in Mediterranean mountain forests? Location: Sierra Nevada, SE Spain (1800,1850 m a.s.l.) Methods: Saplings of four tree taxa (Acer opalus ssp. grana-tense, Quercus ilex, Pinus nigra ssp. salzmanii and P. sylvestris var. nevadensis) were planted following a 2 × 2 factorial design: two levels of herbivory (control and ungulate exclusion) and two microhabitats (under shrubs and in open areas). Sapling survival and growth were monitored for five years. Results: Shrubs had positive effects on sapling survival both in control and ungulate excluded plots. This effect was species-specific, with shrubs increasing the survival of Acer opalus and Quercus ilex three and twofold, respectively, but having a minor effect on the Pinus species. Herbivory damage was also species-specific, being much higher for Acer opalus than for any other species. Shrubs did not protect saplings of any species against ungulates. Thus, all Acer saplings (the most damaged species) suffered herbivory outside the exclosures, which largely reduced sapling height. Conclusions: Protection from abiotic stress (summer drought and winter frost) was much more relevant than protection from biotic stress (herbivory). However, we propose that the final balance between the two mechanisms can be expected to vary strongly between sites, depending on the relative magnitude of the different sources of stress and the intrinsic traits (e.g. palatability) of the species interacting. [source] Fire disturbance and forest structure in old-growth mixed conifer forests in the northern Sierra Nevada, CaliforniaJOURNAL OF VEGETATION SCIENCE, Issue 6 2007R. Matthew Beaty Abstract Question: This study evaluates how fire regimes influence stand structure and dynamics in old-growth mixed conifer forests across a range of environmental settings. Location: A 2000-ha area of mixed conifer forest on the west shore of Lake Tahoe in the northern Sierra Nevada, California. Methods: We quantified the age, size, and spatial structure of trees in 12 mixed conifer stands distributed across major topographic gradients. Fire history was reconstructed in each stand using fire scar dendrochronology. The influence of fire on stand structure was assessed by comparing the fire history with the age, size, and spatial structure of trees in a stand. Results: There was significant variation in species composition among stands, but not in the size, age and spatial patterning of trees. Stands had multiple size and age classes with clusters of similar aged trees occurring at scales of 113 - 254 m2. The frequency and severity of fires was also similar, and stands burned with low to moderate severity in the dormant season on average every 9,17 years. Most fires were not synchronized among stands except in very dry years. No fires have burned since ca. 1880. Conclusions: Fire and forest structure interact to perpetuate similar stand characteristics across a range of environmental settings. Fire occurrence is controlled primarily by spatial variation in fuel mosaics (e.g. patterns of abundance, fuel moisture, forest structure), but regional drought synchronizes fire in some years. Fire exclusion over the last 120 years has caused compositional and structural shifts in these mixed conifer forests. [source] Present and past old-growth forests of the Lake Tahoe Basin, Sierra Nevada, USJOURNAL OF VEGETATION SCIENCE, Issue 4 2002M. Barbour Hickman (1993) for vascular plants; Furniss & Carolin (1977) for bark beetles; Hansen & Lewis (1997) for pathogens 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. [source] Food habits of the wildcat (Felis silvestris) in a peculiar habitat: the Mediterranean high mountainJOURNAL OF ZOOLOGY, Issue 1 2003M. Moleón The feeding spectrum of the wildcat Felis silvestris Schreber, 1777 was studied in two sites with different ecological characteristics, both situated in the same Mediterranean environment in the high mountain of the Sierra Nevada National Park, south-east Spain, where the rabbit Oryctolagus cuniculus is absent. Scat analysis (n=101 faeces; n=402 prey items) showed that the diet is based on rodents, fundamentally wood mouse Apodemus sylvaticus, Mediterranean pine vole Microtus duodecimcostatus and south-western water vole Arvicola sapidus. Results showed strong differences between the two sites (,2=74.04, d.f.=5, P<0.001), that is a predominance of voles in the mesic Chico river, whereas mice are predominant in the xeric Tejos ravine. Red-legged partridge Alectoris rufa and carrion also played an important role, especially in biomass terms. The overall diet differed essentially from that of the Mediterranean region, which surrounds the study area, since in these areas rabbits constitute the primary prey. However, the diet of the mountain wildcats is similar to that in the Eurosiberian floral region, despite its distance from the Sierra Nevada. In conclusion, the Iberian wildcat seems to behave as a facultative specialist, since it prefers rabbits whenever they are available, but rodents constitute most of its diet if rabbits are scarce or absent. [source] Phylogeography of Douglas-fir based on mitochondrial and chloroplast DNA sequences: testing hypotheses from the fossil recordMOLECULAR ECOLOGY, Issue 9 2010PAUL F. GUGGER Abstract The integration of fossil and molecular data can provide a synthetic understanding of the ecological and evolutionary history of an organism. We analysed range-wide maternally inherited mitochondrial DNA and paternally inherited chloroplast DNA sequence data with coalescent simulations and traditional population genetic methods to test hypotheses of population divergence generated from the fossil record of Douglas-fir (Pseudotsuga menziesii), an ecologically and economically important western North American conifer. Specifically, we tested (i) the hypothesis that the Pliocene orogeny of the Cascades and Sierra Nevada caused the divergence of coastal and Rocky Mountain Douglas-fir varieties; and (ii) the hypothesis that multiple glacial refugia existed on the coast and in the Rocky Mountains. We found that Douglas-fir varieties diverged about 2.11 Ma (4.37 Ma,755 ka), which could be consistent with a Pliocene divergence. Rocky Mountain Douglas-fir probably resided in three or more glacial refugia. More variable molecular markers would be required to detect the two coastal refugia suggested in the fossil record. Comparison of mitochondrial DNA and chloroplast DNA variation revealed that gene flow via pollen linked populations isolated from seed exchange. Postglacial colonization of Canada from coastal and Rocky Mountain refugia near the ice margin at the Last Glacial Maximum produced a wide hybrid zone among varieties that formed almost exclusively by pollen exchange and chloroplast DNA introgression, not seed exchange. Postglacial migration rates were 50,165 m/year, insufficient to track projected 21st century warming in some regions. Although fossil and genetic data largely agree, each provides unique insights. [source] An AFLP clock for the absolute dating of shallow-time evolutionary history based on the intraspecific divergence of southwestern European alpine plant speciesMOLECULAR ECOLOGY, Issue 4 2009MATTHIAS KROPF Abstract The dating of recent events in the history of organisms needs divergence rates based on molecular fingerprint markers. Here, we used amplified fragment length polymorphisms (AFLPs) of three distantly related alpine plant species co-occurring in the Spanish Sierra Nevada, the Pyrenees and the southwestern Alps/Massif Central to establish divergence rates. Within each of these species (Gentiana alpina, Kernera saxatilis and Silene rupestris), we found that the degree of AFLP divergence (DN72) between mountain phylogroups was significantly correlated with their time of divergence (as inferred from palaeoclimatic/palynological data), indicating constant AFLP divergence rates. As these rates did not differ significantly among species, a regression analysis based on the pooled data was utilized to generate a general AFLP rate. The application of this latter rate to AFLP data from other herbaceous plant species (Minuartia biflora: Schönswetter et al. 2006; Nigella degenii: Comes et al. 2008) resulted in a plausible timing of the recolonization of the Svalbard Islands and the separation of populations from the Alps and Scandinavia (Minuartia), and of island population separation in the Aegean Archipelago (Nigella). Furthermore, the AFLP mutation rate obtained in our study is of the same magnitude as AFLP mutation rates published previously. The temporal limits of our AFLP rate, which is based on intraspecific vicariance events at shallow (i.e. late glacial/Early Holocene) time scales, remains to be tested. [source] Extreme population subdivision throughout a continuous range: phylogeography of Batrachoseps attenuatus (Caudata: Plethodontidae) in western North AmericaMOLECULAR ECOLOGY, Issue 20 2007IÑIGO MARTÍNEZ, SOLANO Abstract Low-vagility species with deep evolutionary histories are key to our understanding of the biogeographical history of geologically complex areas, such as the west coast of North America. We present a detailed study of the phylogeography of the salamander Batrachoseps attenuatus (Caudata: Plethodontidae) using sequences of the mitochondrial gene cob from 178 individuals sampled from throughout the species' range. Sequences of three other mitochondrial genes (16S, cox1, nad4) and a nuclear gene (RAG-1) were used to investigate the deeper evolutionary history of the species. We found high levels of genetic diversity and deep divergences within a mostly continuous distribution, with five genetically well-differentiated and geographically structured mitochondrial DNA clades. Significant association between geographical and genetic distances within these clades suggests demographic stability, whereas Fu's FS tests suggest demographic expansions in three of them. Mantel tests identify two biogeographical barriers, the San Andreas Fault and the Sacramento,San Joaquin Delta, as important in the diversification of lineages. The timing of the main splitting events between intraspecific lineages was estimated by applying relaxed molecular clock methods combining several mutation rates and a fossil calibration. The earliest splitting events are old (Pliocene/Miocene), with more recent (Pleistocene) subdivisions in some clades. Disjunct populations distributed along the western foothills of the Sierra Nevada colonized this area relatively recently from a single refugium east of San Francisco Bay. The combination of fine-scale, comprehensive sampling with phylogenetic, historical demographic and hypothesis-based tests allowed delineation of a complex biogeographical scenario with general implications for the study of codistributed taxa. [source] Phylogeography of the mountain chickadee (Poecile gambeli): diversification, introgression, and expansion in response to Quaternary climate changeMOLECULAR ECOLOGY, Issue 5 2007GARTH M. SPELLMAN Abstract Since the late 1990s, molecular techniques have fuelled debate about the role of Pleistocene glacial cycles in structuring contemporary avian diversity in North America. The debate is still heated; however, there is widespread agreement that the Pleistocene glacial cycles forced the repeated contraction, fragmentation, and expansion of the North American biota. These demographic processes should leave genetic ,footprints' in modern descendants, suggesting that detailed population genetic studies of contemporary species provide the key to elucidating the impact of the late Quaternary (late Pleistocene,Holocene). We present an analysis of mitochondrial DNA (mtDNA) variation in the mountain chickadee (Poecile gambeli) in an attempt to examine the genetic evidence of the impact of the late Quaternary glacial cycles. Phylogenetic analyses reveal two strongly supported clades of P. gambeli: an Eastern Clade (Rocky Mountains and Great Basin) and a Western Clade (Sierra Nevada and Cascades). Post-glacial introgression is apparent between these two clades in the Mono Lake region of Central California. Within the Eastern Clade there is evidence of isolation-by-distance in the Rocky Mountain populations, and of limited gene flow into and around the Great Basin. Coalescent analysis of genetic variation in the Western Clade indicates that northern (Sierra Nevada/Cascades) and southern (Transverse/Peninsular Ranges) populations have been isolated and evolving independently for nearly 60 000 years. [source] Radial growth responses to gap creation in large, old Sequoiadendron giganteumAPPLIED VEGETATION SCIENCE, Issue 4 2010Robert A. York Abstract Questions: Do large, old Sequoiadondron giganteum trees respond to the creation of adjacent canopy gaps? Do other co-occurring tree species and younger S. giganteum adjacent to gaps also respond? What are the likely factors affecting growth responses? Location: Mixed-conifer forests of the southern Sierra Nevada, California, USA. Methods: We measured the growth response of large, old S. giganteum trees (mean DBH=164 cm; ages estimated >1000 yr) to gap creation by coring trees and comparing growth after gap creation to growth before gap creation. We also measured young Abies concolor, Pinus lambertiana, and young S. giganteum. Gap-adjacent trees were compared with non-adjacent reference trees. Tree rings were analysed for carbon isotope discrimination and for longer-term growth trend correlations with climate. Results: Following gap creation gap-adjacent old S. giganteum grew more than reference trees. Abies concolor trees also exhibited a growth response to gap creation. No response was detected for young S. giganteum or P. lambertiana, although detection power was lower for these groups. There was no difference in carbon isotope discrimination response to gap creation between gap-adjacent and reference trees for old S. giganteum and radial growth was positively correlated with winter precipitation, but not growing season temperature. Conclusion: It is unclear what caused the growth release in old S. giganteum trees, although liberation of below-ground resources following removal of competing vegetation appears to be a significant contributor. Sequoiadondron giganteum, the third-longest lived and the largest of all species, remains sensitive to local environmental changes even after canopy emergence. Management activities that reduce vegetation surrounding individual specimen trees can be expected to result in increased vigor of even these very old and large trees. [source] Understory vegetation response to mechanical mastication and other fuels treatments in a ponderosa pine forestAPPLIED VEGETATION SCIENCE, Issue 2 2010Jeffrey M. Kane Abstract Questions: What influence does mechanical mastication and other fuel treatments have on: (1) canopy and forest floor response variables that influence understory plant development; (2) initial understory vegetation cover, diversity, and composition; and (3) shrub and non-native species density in a second-growth ponderosa pine forest. Location: Challenge Experimental Forest, northern Sierra Nevada, California, USA. Methods: We compared the effects of mastication only, mastication with supplemental treatments (tilling and prescribed fire), hand removal, and a control on initial understory vegetation response using a randomized complete block experimental design. Each block (n=4) contained all five treatments and understory vegetation was surveyed within 0.04-ha plots for each treatment. Results: While mastication alone and hand removal dramatically reduced the midstory vegetation, these treatments had little effect on understory richness compared with control. Prescribed fire after mastication increased native species richness by 150% (+6.0 species m2) compared with control. However, this also increased non-native species richness (+0.8 species m2) and shrub seedling density (+24.7 stems m2). Mastication followed by tilling resulted in increased non-native forb density (+0.7 stems m2). Conclusions: Mechanical mastication and hand removal treatments aided in reducing midstory fuels but did not increase understory plant diversity. The subsequent treatment of prescribed burning not only further reduced fire hazard, but also exposed mineral soil, which likely promoted native plant diversity. Some potential drawbacks to this treatment include an increase of non-native species and stimulation of shrub seed germination, which could alter ecosystem functions and compromise fire hazard reduction in the long-term. [source] Summary of the Sierra Rotors Project wave and rotor eventsATMOSPHERIC SCIENCE LETTERS, Issue 4 2008Vanda Grubi Abstract This study summarizes wave and rotor events observed during the Sierra Rotors Project (SRP). This summary is on the basis of numerical model simulations of SRP events. The events are classified according to the lee-side maxima of vertical and horizontal velocities. Generally, the above classification agrees with the classification on the basis of the obstacle-perpendicular ridge-top winds. The updraft maxima are found to preferentially lie within the leading-edge updraft of a lee wave in the immediate lee and near the crest height of the Sierra Nevada. Simulated waves and lower turbulence zones are illustrated with the wave and rotor structures in two of the strongest SRP events. Copyright © 2008 Royal Meteorological Society [source] Rickettsiae in ticks from wild ungulates of Sierra Nevada and Doñana national parks (Spain)CLINICAL MICROBIOLOGY AND INFECTION, Issue 2009F. J. Márquez No abstract is available for this article. [source] | |||||||||||||||||||