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Trophic cascades are extensively documented in nature, but they are also known to vary widely in strength and frequency across ecosystems. Therefore, much effort has gone into understanding which ecological factors generate variation in cascade strength. To identify which factors covary with the strength of cascades in streams, we performed a concurrent experiment across 17 streams throughout the Sierra Nevada Mountains. We eliminated top consumers from experimental substrates using electrical exclusions and compared the strength of indirect effects of consumers on the biomass of primary producers relative to control patches. In each stream we 1) classified the dominant invertebrate herbivores according to life-history traits that influence their susceptibility to predators, 2) determined the abundance and diversity of algae and herbivores, and 3) measured production-to-biomass ratios (P:B) of the stream biofilm. This allowed us to assess three common predictions about factors thought to influence the strength of trophic cascades: cascade strength 1) is weaker in systems dominated by herbivores with greater ability to evade or defend against predators, 2) is stronger in systems characterized by low species diversity, and 3) increases with increasing producer P:B. When averaged across all streams, the indirect effect of predators increased the biomass of periphyton by a mean 60%. However, impacts of predators on algae varied widely, ranging from effects that exacerbated algal loss to herbivores, to strong cascades that increased algal biomass by 4.35 times. Cascade strength was not related to herbivore traits or species diversity, but decreased significantly with increasing algal diversity and biofilm P:B in a stream. Partial regression analyses suggested that the relationship between cascade strength and algal diversity was spurious, and that the only significant covariate after statistically controlling for cross-correlations was algal P:B. Our study contributes to the ongoing debate about why trophic cascade strength varies in nature and is useful because it eliminates factors that have no potential to explain variation in cascades within these stream ecosystems. [ABSTRACT FROM AUTHOR]

We studied home range and habitat selection of radio-marked adult California spotted owls (Strix occidentalis occidentalis) randomly selected from among the breeding population of owls in the central Sierra Nevada, California from June to October 2006. The most parsimonious home-range estimate for our data was 555 ha (SE = 100 ha). Home-range size was positively correlated with the number of vegetation patches in the home range (habitat heterogeneity). We used resource selection ratios to examine selection of vegetation types by owls within our study area. Owl home ranges contained a high proportion of mature conifer forest, relative to its availability, although the confidence interval for this estimate overlapped one. We also used resource selection functions (RSF) to examine owl foraging habitat selection. Relative probability of selection of foraging habitat was correlated with vegetation classes, patch size, and their interaction. Owls showed highest selection rates for large patches (>10 ha) of pole-sized coniferous forest. Our results suggested that spotted owls in the central Sierra Nevada used habitat that contained a high proportion of mature conifer forest at the home-range scale, but at a finer scale (foraging site selection) owls used other vegetation classes interspersed among mature forest patches, consistent with our hypothesis that spotted owls may use other forest types besides old growth and mature forests when foraging. Our study provides an unbiased estimate of habitat use by spotted owls in the central Sierra Nevada. Our results suggest that forest managers continue to protect remaining mature and old-growth forests in the central Sierra Nevada because owl home ranges contain high proportions of these habitats. However, our results also showed that owls used younger stands as foraging habitat so that landscape heterogeneity, with respect to cover types, may be an important consideration for management but we did not attempt to relate our findings to fitness of owls. Thus management for some level of landscape heterogeneity for the benefit of owls should proceed with caution or under an adaptive management framework. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

1. Non-native trout have been stocked in streams and lakes worldwide largely without knowledge of the consequences for native ecosystems. Although trout have been introduced widely throughout the Sierra Nevada of California, U.S.A., fishless streams and their communities of native invertebrates persist in some high elevation areas, providing an opportunity to study the effects of trout introductions on natural fishless stream communities. 2. We compared algal biomass and cover, organic matter levels and invertebrate assemblages in 21 natural fishless headwater streams with 21 paired nearby streams containing stocked trout in Yosemite National Park. 3. Although environmental conditions and particulate organic matter levels did not differ between the fishless and trout streams, algal biomass (as chlorophyll a concentration) and macroalgal cover were, on average, approximately two times and five times higher, respectively, in streams containing trout. 4. There were no differences in the overall densities of invertebrates in fishless versus paired trout streams; however, invertebrate richness (after rarefaction), evenness, and Simpson and Shannon diversities were 10–20% higher in fishless than in trout streams. 5. The densities of invertebrates belonging to the scraper-algivore and predator functional feeding guilds were higher, and those for the collector-gatherer guild lower, in fishless than trout streams, but there was considerable variation in the effects of trout on specific taxa within functional feeding groups. 6. We found that the densities of 10 of 50 common native invertebrate taxa (found in more than half of the stream pairs) were reduced in trout compared to fishless streams. A similar number of rarer taxa also were absent or less abundant in the presence of trout. Many of the taxa that declined with trout were conspicuous forms (by size and behaviour) whose native habitats are primarily high elevation montane streams above the original range of trout. 7. Only a few taxa increased in the presence of trout, possibly benefiting from reductions in their competitors and predators by trout predation. 8. These field studies provide catchment-scale evidence showing the selective influence of introduced trout on stream invertebrate and algal communities. Removal of trout from targeted headwater streams may promote the recovery of native taxa, community structure and trophic organisation. [ABSTRACT FROM AUTHOR]

Question: How does habitat degradation affect recruitment limitation and its components (seed limitation versus establishment limitation) of woody plant communities in a Mediterranean landscape? Location: 1600-1900 m a.s.l. in the Sierra Nevada National Park, southern Spain. The landscape is a mosaic composed of native forest and two degraded landscape units: reforestation stands and shrubland. Methods: We evaluated fruit production, seed rain, seedling emergence and seedling survival in two consecutive years with contrasting rainfall patterns. Seed and seedling data were used to calculate values of seed and establishment limitation. Results: In general, the woody community was both severely seed- and establishment-limited. Species were less seed-limited in the landscape units with higher adult density (i.e. shrub species in shrubland, Pinus spp. in reforestation stands). In contrast, degradation did not exacerbate establishment limitation, which was severe in all landscape units. This general pattern was modulated by the biogeographical distribution, dispersal type, and life form of the species. Boreo-alpine species were more limited in establishment than species with a typical Mediterranean distribution. Zoochorous species were less seed-limited in the landscape units preferred by dispersers (i.e. native forest). Tree species were more establishment-limited than shrub species, irrespective of the landscape unit. Seed limitation, and especially establishment limitation, varied among years, with establishment being almost nil in the very dry year. Conclusion: In the case of Mediterranean landscapes, when degradation from human impact involves a reduction in the adult abundance of the woody plant community (trees and shrubs), seed limitation increases, although establishment limitation is generally high in all landscape units, especially for boreo-alpine species. Conservation and restoration strategies should take into account our results showing that tree species were unable to recruit in an extremely dry year, because more aridity is expected under a climatic change scenario in Mediterranean ecosystems. [ABSTRACT FROM AUTHOR]

Biogeographical patterns within the California Floristic Province have been greatly affected by geological and climatic events. Here, we investigate the phylogeography of foxtail pine ( Pinus balfouriana) in an effort to date its range disjunction using molecular data and to further our understanding of phylogeographical patterns for plants within the California Floristic Province. The distribution of foxtail pine is characterized by a 500-km disjunction separating populations located in the Klamath Mountains from those in the southern Sierra Nevada. Previous authors suggested that this disjunction occurred approximately 4000–8000 years ago during the Holocene Xerotherm when western North America became warmer and drier. Those dates, however, are inconsistent with the morphological differences that separate regional populations into formally recognized subspecies. Using the coalescent-based isolation with migration model and DNA sequence data from the chloroplast, mitochondrial, and nuclear genomes, we evaluate several hypotheses addressing the timing of this range disjunction and its effects on subsequent patterns of gene flow. Results from all three genomes are largely consistent with Middle to Early Pleistocene divergence dates. Those dates correspond to the Sherwin glaciation, which was the largest Pleistocene glacial episode in the Sierra Nevada. Gene flow, moreover, was only documented using data from the chloroplast genome, suggesting that low levels of long-distance pollen dispersal ( Nem<0.5) have occurred since this divergence event. These results are extended to a discussion of the biogeographical development of subalpine forests in California. [ABSTRACT FROM AUTHOR]

• Our primary goal was to determine whether detection of Rhizopogon internal transcribed spacer (ITS) groups is affected by the pine species used in seedling bioassays. Our secondary goal was to investigate composition of Rhizopogon spore banks in the Eastern Sierra Nevada of California, a previously unsampled region. • We used seedlings of Pinus contorta, Pinus jeffreyi, Pinus lambertiana, and Pinus muricata as bioassay plants and identified the Rhizopogon retrieved by internal transcribed spacer (ITS) sequence analysis. • We found that each of the pine species retrieved all of the abundant Rhizopogon ITS groups, but there were significant differences among pines in the richness of Rhizopogon ITS groups recovered. Pinus muricata recovered all ITS groups found in this study and was significantly better than P. lambertiana. Rhizopogon communities from the five sampled sites contained six to eight ITS groups per site, with two unique sequence groups and a higher abundance of the Rhizopogon ellenae and Rhizopogon arctostaphyli groups than at previously sampled sites. • These results show high cross-receptivity between Rhizopogon and pine species, and regional patterns in spore bank composition. [ABSTRACT FROM AUTHOR]

Aim The physiological requirements and tolerances of a species partially determine both its habitat preferences within a community and its broader geographic range. Therefore, we predicted that local ecology should be correlated with geographic distribution. We tested for a correlation between local ecology and range size, and we attempted to account for this correlation by the climate of the range. Location Bishop Creek Watershed, on the eastern side of the Sierra Nevada, California. Methods We recorded all plant species growing in each of 263 plots in the montane to alpine zones of the watershed. The local habitat preferences of 282 species were described in terms of wetness, elevation, soil, and amount of shade. The size and centre of the geographic range for each species were determined from regional floras. Results Wetness preference within the watershed was significantly correlated with range size. Specifically, plants of wet sites had larger ranges that extend to the north, whereas plants of dry sites tended to have smaller ranges centred to the east. The correlation between local wetness preference and range size was entirely explained by the location of the range centre of the species. Main conclusions A possible reason for the large ranges of mesophilic plants in our study area is that mesic habitats are continuous throughout the western Cordillera, while dry alpine habitats are isolated by valleys to the east. The correspondence between local ecology and geographic distributions implies evolutionary stasis in the niches of these plant species. [ABSTRACT FROM AUTHOR]

We developed equations which describe relationships between the relative abundance of diatom assemblages in the surface sediments of twenty-seven Sierra Nevada lakes and the present pH and acid neutralizing capacity in these lakes. 2. These equations were employed to reconstruct pH and acid neutralizing capacity at twenty-four depth intervals in a 20 cm long sediment core from Emerald Lake, a dilute, high elevation lake, located in Sequoia National Park, California, U.S.A. 3. The diatom-inferred pH and acid neutralizing capacity values indicated that neither pH nor acid neutralizing capacity exhibited significant trends since about A.D, 1825. We conclude from our diatom analysis that Emerald Lake has not been affected by acidic deposition. [ABSTRACT FROM AUTHOR]

The Oligocene and Miocene Valley Springs Formation is one element in the middle to late Cenozoic alluvial fill of the Central Valley of California and represents a large fluvial depositional system that extended westward from sediment-filled palaeovalleys in the high Sierra Nevada to a piedmont alluvial plain under the present Central Valley. The Valley Springs Formation consists largely of tuffaceous mudrock, tuffaceous sandstone, polymict conglomerate and rhyodacitic tuff. The most prominent lithofacies in the formation is yellowish grey or greyish yellow, tuffaceous mudstone and claystone characterized by crude, commonly wavy layering or bedding, an irregular fracture, and common clay-lined partings, fissures, and small branching tubules. Petrographic and X-ray diffraction analysys of the composition, texture, fabric, mineralogy and organic content of an 8 m thick section of the tuffaceous mudrock lithofacies have provided evidence for an origin quite different from the earlier interpretations of this lithofacies as altered tuffs. Numerous rounded mudstone or claystone clasts in a detrital mud matrix, together with abundant freshwater microfossils (megaspores, chrysophyte cysts, diatoms and sponge spicules), indicates that the lithofacies is a mostly epiclastic sedimentary deposit. Root traces, fissuring, orientated clay skins lining pores and secondary surfaces, and mineralogical data are evidence of periodic exposure and desiccation The tuffaceous mudrock lithofacies of the Valley Springs Formation, interpreted in the context of the middle to lower regions of a piedmont alluvial system, most probably represents a complex of ephemeral lake and marsh environments on a low gradient alluvial plain. The referred abundance of shallow lakes, ponds and marshes implies a climate that was wetter than the semi-and climate of the region today. [ABSTRACT FROM AUTHOR]

The article discusses the research proposal which aims to conserve Dodecatheon jeffreyi against D. jeffreyanum (Primulaceae). The genera is believed to be widely scattered in the mountainous regions of Sierra Nevada and other places in the North America. In conjuntion with what precedes, these species are claimed to have been cultivated in the horticultural literature in most mountainous areas in the area mentioned.