Orbicular and comb layer textures in igneous environments are evidence of an unusual heating and cooling regime in small pockets at the edges of crystallizing magmas. Changes in the composition of a magma spark rapid changes in temperature, which cause the temporary suppression of normal crystal nucleation. As the superheated or supercooled magma returns to equilibrium temperature, crystallization occurs exclusively on pre-existing nucleation surfaces (floating xenoliths or wall rocks), creating orbicular and comb layering textures. Orbs and comb layers collected from two localities in the central Sierra Nevada Batholith were analyzed to determine 1) how they formed and 2) what their formation history reveals about the emplacement histories of their respective host plutons. Geochemical analysis including XRF, U-Pb dating and Sr-Nd and O isotope analysis was used to constrain the characteristics of the orbicular magma. Cathodoluminescence as well as macro and microscale petrography was used to determine the specific growth history of the orbs and comb layers. This study shows that orbs and comb layers from both localities formed due to superheating caused by the influx of water into the orbicular melt. Subsequent cooling was caused by mixing–induced depolymerization and fluid enrichment (Big Meadows Creek) or emplacement into a cooler host rock (Deer Creek). Both locations studied are 2–3 Ma younger than their host plutons, indicating that the processes which form orb and comb layers may cause late melting and magma remobilization in larger plutons.

Meadows in the Sierra Nevada Mountains are an important ecological resource that have degraded in quality and distribution due to several environmental and anthropogenic stressors. The encroachment of conifers beyond forest meadow ecotones is largely responsible for the decline of meadow habitat throughout the past century. Currently, there is little research that quantifies the hydrologic response to removal of conifers encroaching meadows in terms of implicating successful meadow restoration. This study has implemented a before after control intervention (BACI) study design to determine the hydrologic response associated with the removal of conifers from a historic meadow encroached by conifers. The primary goals of this research were to: (1) establish a method to evaluate the weekly water balance of an encroached meadow before and after conifer removal (restoration) (2) characterize the hydrology of an encroached meadow and a nearby control meadow prior to restoration (3) assess the effectiveness of electrical resistivity tomography in improving the spatial interpretation of subsurface hydrology on our study site. A water budget approach was developed to quantify the hydrology of a control and study meadow (Marian Meadow) before and after restoration. In order to determine weekly changes in groundwater depth, 14 Odyssey water level capacitance instruments were installed to a 1.5 meter depth in PVC wells. In order to quantify changes in soil moisture storage, 14 soil moisture probes were installed to a ~1 ft (30 cm) depth. Both sets of instruments were installed using a spatially balanced random sampling approach. Electrical resistivity tomography was conducted on both meadows on three separate dates during: September 9-10 2013, May 5 2014 and September 6-7 2014. A method to quantify runoff from a stream that drains Marian Meadow (Marian Creek) was also established. The Priestley Taylor model was used to estimate daily evapotranspiration from both meadows. Electrical resistivity tomography improved the spatial interpretation of groundwater recharge and facilitated the use of a recession curve analysis to model groundwater recharge when the water table receded beyond instrument detection depths. Electrical resistivity also demonstrated a change in hydrologic characteristics across a forest –meadow ecotone. Analysis of the pre-removal hydrologic characteristics from September 2013 to December 2014 indicates that Marian Meadow may be a favorable candidate for restoration (in terms of hydrology). On Marian Meadow, volumetric soil moisture was higher than the Control Meadow from May-November 2014. Sufficient soil moisture in the summer months is thought to be critical to the maintenance of endemic meadow flora. The water table depth on Marian Meadow and the Control Meadow was similar throughout the analysis period, but Marian Meadow had a shallower water table during the summer months. The Control Meadow had near surface groundwater during short periods from February-April 2014 and December 2014. If conifer removal from Marian Meadow causes an increase in seasonal volumetric soil moisture and a decrease in seasonal groundwater depth, an augmented version of the stable hydrologic system already present on Marian Meadow may result in hydrologic conditions more favorable to meadow restoration.

The Sierra Nevada snowpack is vital to the water supply of California, the world’s sixth largest economy. Though tree ring and instrumental records show the dramatic influence of environmental change on California’s hydroclimate over the last millennium, few proxy archives assess winter precipitation variability farther back in time. Here, we use diatoms from a ~3,200 yr. old sediment core to reconstruct the paleolimnology of June Lake, a hydrologically closed glacial lake in the eastern Sierra Nevada. We test the hypothesis that limnologic and climatic changes control diatom assemblages at June Lake. Fossil diatom assemblages from June Lake sediments chiefly consist of the planktic genera Stephanodiscus and Lindavia; their relative abundances in sediments are controlled by lake response to changes in the length of the winter season. We establish a Lindavia:Stephanodiscus index to infer winter length; our results indicate three periods where winter seasons are longer than average: ~3.2-2.9 ka, ~2.2-1.7 ka, and ~0.6 ka-0.05 ka. Over the last ~100 yrs., June Lake has experienced stronger water column stratification and an expansion of the available benthic diatom habitat, indicating significantly warmer winters and lower lake levels. It is possible that this change is the result of anthropogenic climate warming.

O presente trabalho explora eventos de articulação entre coletivos indígenas da Serra Nevada de Santa Marta, localizada ao norte da Colômbia, e o estado, entendo-os como mundos com planos ontológicos e sistemas epistemológicos diferentes que coexistem e se reorganizam em cada um dos eventos, respondendo a hegemonias específicas em contextos particulares. A lei de Sé, ou lei da origem, estabelece uma política de alteridade que permite a existência de multiplicidades e diferenças que não se reduzem a princípios determinados, pois se trata de domínios móveis de conhecimento e pensamento que constroem pessoas, corpos e o território a partir de conexões parciais, potencialmente perigosas se não forem mediadas por lideranças espirituais (os mamos) para que aconteçam em harmonia e acordo entre os seres (Yuluka). As entidades múltiplas são subordinadas e ignoradas nos espaços de tomada de decisões sob o território, a partir de sistemas de conhecimento e políticas que entendem a natureza como cenário externo e objetivo, e a cultura como marcador da diferença que essencializa, isola e nega conflitos históricos e políticos, em um marco em que tanto natureza e cultura são potencialmente mercantilizáveis. Neste contexto, as práticas de patrimônio são uma estratégia do estado para regular a mercantilização da diferença, enquanto que os indígenas as apropriam como estratégia para defender a vitalidade do seu território, entendido como tecido de relações entre seres diversos. No entanto, a subordinação não implica a captura, pois as multiplicidades continuam coexistindo no movimento contínuo entre resistência e novos ou renovados mecanismos de captura. / Este trabajo explora eventos de articulación entre los colectivos indígenas de la Sierra Nevada de Santa Marta, ubicada al norte de Colombia, y el estado, entendiendo que se trata de mundos con planos ontológicos y sistemas epistemológicos diferentes, que coexisten y se reorganizan en cada uno de esos eventos respondiendo a hegemonías específicas, en contextos históricos particulares. La ley de Sé, o ley de origen establece una política de la alteridad, que permite la existencia de multiplicidades y diferencias, que no se reducen a principios predeterminados sino que se trata de dominios móviles de conocimiento y pensamiento que construyen personas, cuerpos y territorio a partir de conexiones parciales, que potencialmente pueden ser peligrosas si no son mediadas por los mamos para que se den en armonía y acuerdo entre los seres (yuluka). Estas existencias múltiples, son subordinadas e ignoradas en los espacios de toma de decisiones sobre el territorio, a partir de sistemas de conocimiento y políticas que entienden la naturaleza como un escenario externo y objetivo, y la cultura como marcador de diferencia que esencializa, aísla y niega conflictos históricos y políticos, en un marco en el que tanto naturaleza y cultura son potencialmente mercadeables. En este contexto, las prácticas de patrimonio son una estrategia del estado para regular la mercantilización de la diferencia, mientras que los indígenas la apropian como estrategia para defender la vitalidad de su territorio, entendido como tejido de relaciones entre seres diversos. Sin embargo la subordinación no implica la captura, pues las multiplicidades siguen coexistiendo, en el movimiento continuo entre resistencia y nuevos o renovados mecanismos de captura.

O presente trabalho explora eventos de articulação entre coletivos indígenas da Serra Nevada de Santa Marta, localizada ao norte da Colômbia, e o estado, entendo-os como mundos com planos ontológicos e sistemas epistemológicos diferentes que coexistem e se reorganizam em cada um dos eventos, respondendo a hegemonias específicas em contextos particulares. A lei de Sé, ou lei da origem, estabelece uma política de alteridade que permite a existência de multiplicidades e diferenças que não se reduzem a princípios determinados, pois se trata de domínios móveis de conhecimento e pensamento que constroem pessoas, corpos e o território a partir de conexões parciais, potencialmente perigosas se não forem mediadas por lideranças espirituais (os mamos) para que aconteçam em harmonia e acordo entre os seres (Yuluka). As entidades múltiplas são subordinadas e ignoradas nos espaços de tomada de decisões sob o território, a partir de sistemas de conhecimento e políticas que entendem a natureza como cenário externo e objetivo, e a cultura como marcador da diferença que essencializa, isola e nega conflitos históricos e políticos, em um marco em que tanto natureza e cultura são potencialmente mercantilizáveis. Neste contexto, as práticas de patrimônio são uma estratégia do estado para regular a mercantilização da diferença, enquanto que os indígenas as apropriam como estratégia para defender a vitalidade do seu território, entendido como tecido de relações entre seres diversos. No entanto, a subordinação não implica a captura, pois as multiplicidades continuam coexistindo no movimento contínuo entre resistência e novos ou renovados mecanismos de captura. / Este trabajo explora eventos de articulación entre los colectivos indígenas de la Sierra Nevada de Santa Marta, ubicada al norte de Colombia, y el estado, entendiendo que se trata de mundos con planos ontológicos y sistemas epistemológicos diferentes, que coexisten y se reorganizan en cada uno de esos eventos respondiendo a hegemonías específicas, en contextos históricos particulares. La ley de Sé, o ley de origen establece una política de la alteridad, que permite la existencia de multiplicidades y diferencias, que no se reducen a principios predeterminados sino que se trata de dominios móviles de conocimiento y pensamiento que construyen personas, cuerpos y territorio a partir de conexiones parciales, que potencialmente pueden ser peligrosas si no son mediadas por los mamos para que se den en armonía y acuerdo entre los seres (yuluka). Estas existencias múltiples, son subordinadas e ignoradas en los espacios de toma de decisiones sobre el territorio, a partir de sistemas de conocimiento y políticas que entienden la naturaleza como un escenario externo y objetivo, y la cultura como marcador de diferencia que esencializa, aísla y niega conflictos históricos y políticos, en un marco en el que tanto naturaleza y cultura son potencialmente mercadeables. En este contexto, las prácticas de patrimonio son una estrategia del estado para regular la mercantilización de la diferencia, mientras que los indígenas la apropian como estrategia para defender la vitalidad de su territorio, entendido como tejido de relaciones entre seres diversos. Sin embargo la subordinación no implica la captura, pues las multiplicidades siguen coexistiendo, en el movimiento continuo entre resistencia y nuevos o renovados mecanismos de captura.

O presente trabalho explora eventos de articulação entre coletivos indígenas da Serra Nevada de Santa Marta, localizada ao norte da Colômbia, e o estado, entendo-os como mundos com planos ontológicos e sistemas epistemológicos diferentes que coexistem e se reorganizam em cada um dos eventos, respondendo a hegemonias específicas em contextos particulares. A lei de Sé, ou lei da origem, estabelece uma política de alteridade que permite a existência de multiplicidades e diferenças que não se reduzem a princípios determinados, pois se trata de domínios móveis de conhecimento e pensamento que constroem pessoas, corpos e o território a partir de conexões parciais, potencialmente perigosas se não forem mediadas por lideranças espirituais (os mamos) para que aconteçam em harmonia e acordo entre os seres (Yuluka). As entidades múltiplas são subordinadas e ignoradas nos espaços de tomada de decisões sob o território, a partir de sistemas de conhecimento e políticas que entendem a natureza como cenário externo e objetivo, e a cultura como marcador da diferença que essencializa, isola e nega conflitos históricos e políticos, em um marco em que tanto natureza e cultura são potencialmente mercantilizáveis. Neste contexto, as práticas de patrimônio são uma estratégia do estado para regular a mercantilização da diferença, enquanto que os indígenas as apropriam como estratégia para defender a vitalidade do seu território, entendido como tecido de relações entre seres diversos. No entanto, a subordinação não implica a captura, pois as multiplicidades continuam coexistindo no movimento contínuo entre resistência e novos ou renovados mecanismos de captura. / Este trabajo explora eventos de articulación entre los colectivos indígenas de la Sierra Nevada de Santa Marta, ubicada al norte de Colombia, y el estado, entendiendo que se trata de mundos con planos ontológicos y sistemas epistemológicos diferentes, que coexisten y se reorganizan en cada uno de esos eventos respondiendo a hegemonías específicas, en contextos históricos particulares. La ley de Sé, o ley de origen establece una política de la alteridad, que permite la existencia de multiplicidades y diferencias, que no se reducen a principios predeterminados sino que se trata de dominios móviles de conocimiento y pensamiento que construyen personas, cuerpos y territorio a partir de conexiones parciales, que potencialmente pueden ser peligrosas si no son mediadas por los mamos para que se den en armonía y acuerdo entre los seres (yuluka). Estas existencias múltiples, son subordinadas e ignoradas en los espacios de toma de decisiones sobre el territorio, a partir de sistemas de conocimiento y políticas que entienden la naturaleza como un escenario externo y objetivo, y la cultura como marcador de diferencia que esencializa, aísla y niega conflictos históricos y políticos, en un marco en el que tanto naturaleza y cultura son potencialmente mercadeables. En este contexto, las prácticas de patrimonio son una estrategia del estado para regular la mercantilización de la diferencia, mientras que los indígenas la apropian como estrategia para defender la vitalidad de su territorio, entendido como tejido de relaciones entre seres diversos. Sin embargo la subordinación no implica la captura, pues las multiplicidades siguen coexistiendo, en el movimiento continuo entre resistencia y nuevos o renovados mecanismos de captura.

No description available.

In California's northern Sierra Nevada mountains, the fire-dependent processes of forest ecosystems have been interrupted and altered by human land use and fire suppression. U.S. Forest Service policy directs land managers to plan for a future that includes multiple use and the restoration of resilient ecosystems. Planning decisions are to be informed by an analysis of the range of variability of ecological processes at multiple scales. Current climate trends in the northern Sierra are of increasing temperatures, increased precipitation, and earlier snowmelt, as well as changes to the frequency and duration of drought. These climate changes have and continue to influence fire frequency, extent, and severity. For this thesis, project partners and I adapted the Rocky Mountain Landscape Simulator (RMLands), a spatially explicit, stochastic, landscape disturbance and succession model, for use in the Sierra Nevada. RMLands was used to simulate wildfires and vegetation dynamics on a portion of the Tahoe National Forest in California, first under historical climate settings and then under alternative climate trajectories based on the Representative Concentration Pathway RCP8.5 projections. I then quantified the historical and the future ranges of variability in the disturbance regime, seral stage distribution, and patch configuration, and compared these to the current landscape. My results suggest more frequent and extensive high severity fire, as well as higher canopy closure, than most other studies of mixed conifer Sierran forests. However, the results typically agree qualitatively with other research, and some differences may be due to differences in study design. Under warmer and drier future climate scenarios, the total area burned, and the proportion burned at high severity, increased. Due to fire's effects on vegetation, the current landscape departs from either historical or future conditions by several statistical measures. Based on these findings, I recommend that managers implement aggressive restoration efforts, utilize mitigation measures where the consequences of changing fire regimes are socially unacceptable, and carefully balance the needs of different ecosystems and of the resident communities. My study can be used to inform goals and specific strategies in restoration planning and help project planners think about impacts at the landscape scale.

abstract: Geochronology and thermochronology are valuable tools for investigating the synergy between the deformational and erosional processes that shape mountainous terrains. Though numerous techniques have been developed to probe the rate and timing of events within these settings, the research presented here explores how scientists can use fewer samples to produce richer data products with broader contextual importance. The beginning of this compilation focuses on establishing laboratory techniques to facilitate this goal. I developed a novel laser ablation ‘double dating’ (LADD) technique that rapidly yields paired U/Pb and (U-Th)/He dates for the accessory minerals zircon, titanite, and apatite. The technique obviates the need for geometric corrections typically applied during (U-Th)/He data reduction, enables the analysis of a broader spectrum of detrital crystals, and provides the opportunity for additional mapping and isotopic analyses that are traditionally challenging to procure and/or fraught with assumptions. Despite the technique’s promise, I also found it essential to weigh several considerations of relevance when attempting to date young (≤ Miocene) accessory minerals with low concentrations of U + Th. Consequently, I discuss the impact that such variables have on the magnitude of analytical imprecision and the data’s flexibility for geologic interpretation. Beyond the lab, I collected a suite of bedrock and detrital samples from small catchments draining the southeastern Sierra Nevada mountains of California. Using the techniques described above as well as conventional methods for (U-Th)/He zircon dating, I compared the utility of both bedrock and detrital approaches for extrapolating local exhumation histories. I additionally tested the ability to employ detrital datasets to extrapolate cooling histories that span from mineral crystallization to rock exhumation through the upper crust. Employing principal mode dates from a combination of zircon and apatite LADD dates and detrital hornblende 40Ar/39Ar dates, I was able to derive thermal models that demonstrate the existence of significant variability in the cooling histories of various intrusive units along the eastern Sierra Nevada. While these results only scratch the surface of what’s possible within the realm of detrital-based research, this contribution demonstrates the utility of expanding the temporal and spatial scope of traditional detrital methodologies. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2019

An increasing amount of evidence suggests that as temperatures increase, montane animals are moving upward in elevation (IPCC 2007, Parmesan and Yohe 2003). As suitable habitats rise in elevation and then disappear altogether, these animals could be pushed to extinction. The American pika, Ochotona princeps, is a montane mammal that lives in western North America, usually at elevations above 1500 m (Smith and Weston 1990). Recent evidence suggests that pika population numbers are dropping in response to rising temperatures (Beever et al. 2010). The pika is a small herbivorous lagomorph, a relative of hares and rabbits. Its habitat is tightly restricted to talus slopes (rockfields) and the surrounding vegetation (Grayson 2005). Pikas have a high tolerance for cold temperatures, and do not hibernate during the long montane winter. However, they have very little tolerance for even mildly warm temperatures, and have been found to die when confined above ground at 25.5˚ C (Smith 1974b). To better understand pika persistence, we resurveyed 17 historic pika sites in the Lassen Peak region of northern California in August and September, 2009. Six of the historic sites were abandoned, as well as an additional 11 of 17 new sites surveyed. At each site we collected habitat information, and analyzed the data for factors that were correlated with site occupancy. We also installed 38 iButton thermal dataloggers in abandoned and occupied pika use sites, to determine if temperature affects occupancy. The dataloggers remained in pika sites for 14 months and recorded temperature every 1.5 hours. Abandoned pika sites had higher average temperatures and more days below 0˚ C. They also had greater shrub cover, less forb and graminoid cover, and a greater percentage of litter substrate. These findings suggest that the current warming trend may be having a negative impact on pikas in the Lassen Peak Region. As temperatures rise, pikas may be declining due to unsuitable temperatures and altered vegetative communities. In addition to the Lassen surveys, I investigated pika behavior in different temperature regimes in the Sierra Nevada. If pikas are able to adapt to climate change, it is possible that populations of pikas in different temperature regimes may exhibit behavioral plasticity, or have evolved genetic differences, such that these populations have different daily activity schedules. To determine if there is a difference in pika behavior at different elevations I observed pikas in one low and one high elevation site within the Bishop Creek drainage system in the Sierra Nevada. I conducted behavioral observations of pikas in four time blocks throughout the day in August and September, 2010. I recorded specific behaviors, such as foraging and haying (vegetation collecting), and compared these activities between low and high elevation pikas at different times of day. In August, pikas in the low elevation site exhibited a different activity profile than those in the high elevation site. Low elevation pikas were significantly more crepuscular (most active at dawn and dusk) during this month. I also observed more foraging behavior in the high elevation than the low elevation site, in both August and September. Reduced activity at higher temperatures may have negative impacts on pikas as temperatures increase. Low elevation pikas may be stressed due to reduced time spent foraging and haypile (overwinter vegetation cache) gathering. However, if pikas were able to switch their activity schedules to a more nocturnal schedule, they could escape higher daytime temperatures. To detect the possibility of nocturnal behavior in low elevation pikas, I set up four infra-red remote cameras in the low elevation site. I had variable success in capturing pika behavior with the cameras, and detected no evidence of nocturnal behavior. More research on the possibility of nocturnal behavior in pikas would be worthwhile, in part to determine what chance, if any, pikas have of adapting to rising global temperatures.