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• 1. [Article] Bridging environmental physiology and community ecology : temperature effects at the community level

  Most climate change predictions focus on the response of individual species to changing local conditions and ignore species interactions, largely due to the lack of a sound theoretical foundation for how ...

  Citation × Citation Citation Abstract Copy Title: Bridging environmental physiology and community ecology : temperature effects at the community level Author: Iles, Alison C. Most climate change predictions focus on the response of individual species to changing local conditions and ignore species interactions, largely due to the lack of a sound theoretical foundation for how interactions are expected to change with climate and how to incorporate them into climate change models. Much of the variability in species interaction strengths may be governed by fundamental constraints on physiological rates, possibly providing a framework for including species interactions into climate change models. Metabolic rates, ingestion rates and many other physiological rates are relatively predictable from body size and body temperature due to constraints imposed by the physical and chemical laws that govern fluid dynamics and the kinetics of biochemical reaction times. My dissertation assesses the usefulness of this framework by exploring the community-level consequences of physiological constraints. In Chapter 2, I incorporated temperature and body size scaling into the biological rate parameters of a series of realistically structured trophic network models. The relative magnitude of the temperature scaling parameters affecting consumer energetic costs (metabolic rates) and energetic gains (ingestion rates) determined how consumer energetic efficiency changed with temperature. I systematically changed consumer energetic efficiency and examined the sensitivity of network stability and species persistence to various temperatures. I found that a species' probability of extinction depended primarily on the effects of organismal physiology (body size and energetic efficiency with respect to temperature) and secondarily on the effects of local food web structure (trophic level and consumer generality). This suggests that physiology is highly influential on the structure and dynamics of ecological communities. If consumer energetic efficiency declined as temperature increased, that is, species did best at lower temperatures, then the simulated networks had greater stability at lower temperatures. The opposite scenario resulted in greater stability at higher temperatures. Thus, much of the community-level response depends on what species energetic efficiencies at the organismal-level really are, which formed the research question for Chapter 3: How does consumer energetic efficiency change with temperature? Existing evidence is scarce but suggestive of decreasing consumer energetic efficiency with increasing temperature. I tested this hypothesis on seven rocky intertidal invertebrate species by measuring the relative temperature scaling of their metabolic and ingestion rates as well as consumer interaction strength under lab conditions. Energetic efficiencies of these rocky intertidal invertebrates declined and species interaction strengths tended to increase with temperature. Thus, in the rocky intertidal, the mechanistic effect of temperature would be to lower community stability at higher temperatures. Chapter 4 tests if the mechanistic effects of temperature on ingestion rates and species interaction strengths seen in the lab are apparent under field conditions. Bruce Menge and I related bio-mimetic estimates of body temperatures to estimates of per capita mussel ingestion rates and species interaction strengths by the ochre sea star Pisaster ochraceus, a keystone predator of the rocky intertidal. We found a strong, positive effect of body temperature on both per capita ingestion rates and interaction strengths. However, the effects of season and the unique way in which P. ochraceus regulates body temperatures were also apparent, leaving room for adaptation and acclimation to partially compensate for the mechanistic constraint of body temperature. Community structure of the rocky intertidal is associated with environmental forcing due to upwelling, which delivers cold, nutrient rich water to the nearshore environment. As upwelling is driven by large-scale atmospheric pressure gradients, climate change has the potential to affect a wide range of significant ecological processes through changes in water temperature. In Chapter 5, my coauthors and I identified long-term trends in the phenology of upwelling events that are consistent with climate change predictions: upwelling events are becoming stronger and longer. As expected, longer upwelling events were related to lower average water temperatures in the rocky intertidal. Furthermore, recruitment rates of barnacles and mussels were associated with the phenology of upwelling events. Thus climate change is altering the mode and the tempo of environmental forcing in nearshore ecosystems, with ramifications for community structure and function. Ongoing, long-term changes in environmental forcing in rocky intertidal ecosystems provide an opportunity to understand how temperature shapes community structure and the ramifications of climate change. My dissertation research demonstrates that the effect of temperature on organismal performance is an important force structuring ecological communities and has potential as a tractable framework for predicting the community level effects of climate change. Title: Bridging environmental physiology and community ecology : temperature effects at the community level Author: Iles, Alison C. Most climate change predictions focus on the response of individual species to changing local conditions and ignore species interactions, largely due to the lack of a sound theoretical foundation for how interactions are expected to change with climate and how to incorporate them into climate change models. Much of the variability in species interaction strengths may be governed by fundamental constraints on physiological rates, possibly providing a framework for including species interactions into climate change models. Metabolic rates, ingestion rates and many other physiological rates are relatively predictable from body size and body temperature due to constraints imposed by the physical and chemical laws that govern fluid dynamics and the kinetics of biochemical reaction times. My dissertation assesses the usefulness of this framework by exploring the community-level consequences of physiological constraints. In Chapter 2, I incorporated temperature and body size scaling into the biological rate parameters of a series of realistically structured trophic network models. The relative magnitude of the temperature scaling parameters affecting consumer energetic costs (metabolic rates) and energetic gains (ingestion rates) determined how consumer energetic efficiency changed with temperature. I systematically changed consumer energetic efficiency and examined the sensitivity of network stability and species persistence to various temperatures. I found that a species' probability of extinction depended primarily on the effects of organismal physiology (body size and energetic efficiency with respect to temperature) and secondarily on the effects of local food web structure (trophic level and consumer generality). This suggests that physiology is highly influential on the structure and dynamics of ecological communities. If consumer energetic efficiency declined as temperature increased, that is, species did best at lower temperatures, then the simulated networks had greater stability at lower temperatures. The opposite scenario resulted in greater stability at higher temperatures. Thus, much of the community-level response depends on what species energetic efficiencies at the organismal-level really are, which formed the research question for Chapter 3: How does consumer energetic efficiency change with temperature? Existing evidence is scarce but suggestive of decreasing consumer energetic efficiency with increasing temperature. I tested this hypothesis on seven rocky intertidal invertebrate species by measuring the relative temperature scaling of their metabolic and ingestion rates as well as consumer interaction strength under lab conditions. Energetic efficiencies of these rocky intertidal invertebrates declined and species interaction strengths tended to increase with temperature. Thus, in the rocky intertidal, the mechanistic effect of temperature would be to lower community stability at higher temperatures. Chapter 4 tests if the mechanistic effects of temperature on ingestion rates and species interaction strengths seen in the lab are apparent under field conditions. Bruce Menge and I related bio-mimetic estimates of body temperatures to estimates of per capita mussel ingestion rates and species interaction strengths by the ochre sea star Pisaster ochraceus, a keystone predator of the rocky intertidal. We found a strong, positive effect of body temperature on both per capita ingestion rates and interaction strengths. However, the effects of season and the unique way in which P. ochraceus regulates body temperatures were also apparent, leaving room for adaptation and acclimation to partially compensate for the mechanistic constraint of body temperature. Community structure of the rocky intertidal is associated with environmental forcing due to upwelling, which delivers cold, nutrient rich water to the nearshore environment. As upwelling is driven by large-scale atmospheric pressure gradients, climate change has the potential to affect a wide range of significant ecological processes through changes in water temperature. In Chapter 5, my coauthors and I identified long-term trends in the phenology of upwelling events that are consistent with climate change predictions: upwelling events are becoming stronger and longer. As expected, longer upwelling events were related to lower average water temperatures in the rocky intertidal. Furthermore, recruitment rates of barnacles and mussels were associated with the phenology of upwelling events. Thus climate change is altering the mode and the tempo of environmental forcing in nearshore ecosystems, with ramifications for community structure and function. Ongoing, long-term changes in environmental forcing in rocky intertidal ecosystems provide an opportunity to understand how temperature shapes community structure and the ramifications of climate change. My dissertation research demonstrates that the effect of temperature on organismal performance is an important force structuring ecological communities and has potential as a tractable framework for predicting the community level effects of climate change. Close

• 2. [Article] Soil organic carbon response to six years of warming : assessing the impacts of altered diurnal temperature range

  There is a growing consensus that anthropogenic warming will impact soil organic matter (SOM). Globally, soil contains 2-3 times more carbon (C) than plants, and like plants, temperature induced change ...

  Citation × Citation Citation Abstract Copy Title: Soil organic carbon response to six years of warming : assessing the impacts of altered diurnal temperature range Author: Murphey, Virginia L. W. There is a growing consensus that anthropogenic warming will impact soil organic matter (SOM). Globally, soil contains 2-3 times more carbon (C) than plants, and like plants, temperature induced change of SOM could have significant climate repercussions. Although, the majority of warming experiments have increased day and night temperatures equally, there is evidence of greater increase in global minimum temperatures compared to midday maxima, resulting in an altered mean diurnal temperature range (DTR). Here, intact grassland mesocosms (Terracosm facility, Corvallis OR) were used to assess soil organic C (SOC) changes resulting from altered DTR over a six year period. We assessed the response of SOC to a mean temperature increase of 3.5°C with three temperature treatments: symmetric (SYM) warming of +3.5°C, asymmetric (ASYM) warming of +5°C/ +2°C at minimum and maximum daily temperature, respectively, and control treatments that were kept at ambient (AMB) temperatures. After six years of warming SOC was surprisingly unaltered by increased temperature and was more strongly influenced by plant dynamics than expected. The strongest temperature response was from soil respiration (reported as In-situ cumulative soil C mineralization) with at least 33% higher cumulative C mineralization in warming treatments. In agreement with the soil respiration response, light fraction C (<1.8g/cm³) was depleted in warming treatments (8-10% less C than AMB) at shallow depths. However, laboratory cumulative soil C mineralization, a measure of most easily degraded SOC, had a lack of response to temperature, and actually had trends for greater C in warming treatments. This response was further validated by increased soil water dissolved organic C (DOC) concentration in warming treatments. An increase in these measures suggested that plants were more influential than temperature for highly labile SOC. Aggregates, an important part of SOC allocation and sequestration, had a differential response to SYM and ASYM treatments but this was likely more directly caused by root dynamics than temperature treatment. Due to varying responses of SOC indicators, C budgets were used to assess total ecosystem C balance. We found that under AMB conditions soil was an atmospheric C sink and under both SYM and ASYM conditions soil was an atmospheric C source, with ASYM having a higher source potential than SYM. Overall, SOC responded to both temperature increase via soil respiration and differentially to temperature treatments based on plant response. We expect that a reduced diurnal temperature range could affect soil C differently than mean temperature increase, if plant differences are sustained. Title: Soil organic carbon response to six years of warming : assessing the impacts of altered diurnal temperature range Author: Murphey, Virginia L. W. There is a growing consensus that anthropogenic warming will impact soil organic matter (SOM). Globally, soil contains 2-3 times more carbon (C) than plants, and like plants, temperature induced change of SOM could have significant climate repercussions. Although, the majority of warming experiments have increased day and night temperatures equally, there is evidence of greater increase in global minimum temperatures compared to midday maxima, resulting in an altered mean diurnal temperature range (DTR). Here, intact grassland mesocosms (Terracosm facility, Corvallis OR) were used to assess soil organic C (SOC) changes resulting from altered DTR over a six year period. We assessed the response of SOC to a mean temperature increase of 3.5°C with three temperature treatments: symmetric (SYM) warming of +3.5°C, asymmetric (ASYM) warming of +5°C/ +2°C at minimum and maximum daily temperature, respectively, and control treatments that were kept at ambient (AMB) temperatures. After six years of warming SOC was surprisingly unaltered by increased temperature and was more strongly influenced by plant dynamics than expected. The strongest temperature response was from soil respiration (reported as In-situ cumulative soil C mineralization) with at least 33% higher cumulative C mineralization in warming treatments. In agreement with the soil respiration response, light fraction C (<1.8g/cm³) was depleted in warming treatments (8-10% less C than AMB) at shallow depths. However, laboratory cumulative soil C mineralization, a measure of most easily degraded SOC, had a lack of response to temperature, and actually had trends for greater C in warming treatments. This response was further validated by increased soil water dissolved organic C (DOC) concentration in warming treatments. An increase in these measures suggested that plants were more influential than temperature for highly labile SOC. Aggregates, an important part of SOC allocation and sequestration, had a differential response to SYM and ASYM treatments but this was likely more directly caused by root dynamics than temperature treatment. Due to varying responses of SOC indicators, C budgets were used to assess total ecosystem C balance. We found that under AMB conditions soil was an atmospheric C sink and under both SYM and ASYM conditions soil was an atmospheric C source, with ASYM having a higher source potential than SYM. Overall, SOC responded to both temperature increase via soil respiration and differentially to temperature treatments based on plant response. We expect that a reduced diurnal temperature range could affect soil C differently than mean temperature increase, if plant differences are sustained. Close

• 3. [Article] Utilizing Humidity and Temperature Data to Advance Monitoring and Prediction of Meteorological Drought

  The fraction of land area over the Continental United States experiencing extreme hot and dry conditions has been increasing over the past several decades, consistent with expectation from anthropogenic ...

  Citation × Citation Citation Abstract Copy Title: Utilizing Humidity and Temperature Data to Advance Monitoring and Prediction of Meteorological Drought Author: Behrangi, Ali, Loikith, Paul C., Fetzer, Eric J., Nguyen, Hai M., Granger, Stephanie L. Year: 2015 The fraction of land area over the Continental United States experiencing extreme hot and dry conditions has been increasing over the past several decades, consistent with expectation from anthropogenic climate change. A clear concurrent change in precipitation, however, has not been confirmed. Vapor pressure deficit (VPD), combining temperature and humidity, is utilized here as an indicator of the background atmospheric conditions associated with meteorological drought. Furthermore, atmospheric conditions associated with warm season drought events are assessed by partitioning associated VPD anomalies into the temperature and humidity components. This approach suggests that the concurrence of anomalously high temperature and low humidity was an important driver of the rapid development and evolution of the exceptionally severe 2011 Texas and the 2012 Great Plains droughts. By classification of a decade of extreme drought events and tracking them back in time, it was found that near surface atmospheric temperature and humidity add essential information to the commonly used precipitation-based drought indicators and can advance efforts to determine the timing of drought onset and its severity. Title: Utilizing Humidity and Temperature Data to Advance Monitoring and Prediction of Meteorological Drought Author: Behrangi, Ali, Loikith, Paul C., Fetzer, Eric J., Nguyen, Hai M., Granger, Stephanie L. Year: 2015 The fraction of land area over the Continental United States experiencing extreme hot and dry conditions has been increasing over the past several decades, consistent with expectation from anthropogenic climate change. A clear concurrent change in precipitation, however, has not been confirmed. Vapor pressure deficit (VPD), combining temperature and humidity, is utilized here as an indicator of the background atmospheric conditions associated with meteorological drought. Furthermore, atmospheric conditions associated with warm season drought events are assessed by partitioning associated VPD anomalies into the temperature and humidity components. This approach suggests that the concurrence of anomalously high temperature and low humidity was an important driver of the rapid development and evolution of the exceptionally severe 2011 Texas and the 2012 Great Plains droughts. By classification of a decade of extreme drought events and tracking them back in time, it was found that near surface atmospheric temperature and humidity add essential information to the commonly used precipitation-based drought indicators and can advance efforts to determine the timing of drought onset and its severity. Close

• 4. [Article] An Analysis of the Impact of Global Warming on Hurricane Activity in the United States

  This paper discusses the influence of global warming on ocean temperatures, and explains how vertical wind shear affects hurricane formation. It explores the scientific arguments against linking global ...

  Citation × Citation Citation Abstract Copy Title: An Analysis of the Impact of Global Warming on Hurricane Activity in the United States Author: Senzer, Jesse Year: 2012 This paper discusses the influence of global warming on ocean temperatures, and explains how vertical wind shear affects hurricane formation. It explores the scientific arguments against linking global warming to increased hurricanes, that ocean warming increases vertical wind shear in the main development region for Atlantic hurricanes, and that current/recent American hurricane trends fall within the realm of natural, multidecadal oscillations. Arguments supporting the link between global warming and hurricanes are addressed with climate modeling that links sea surface temperature (SST) increase to anthropogenic causes. It discusses SST’s influencing hurricane activity globally, if not locally to the U.S., and points to the need for consensus and action. Title: An Analysis of the Impact of Global Warming on Hurricane Activity in the United States Author: Senzer, Jesse Year: 2012 This paper discusses the influence of global warming on ocean temperatures, and explains how vertical wind shear affects hurricane formation. It explores the scientific arguments against linking global warming to increased hurricanes, that ocean warming increases vertical wind shear in the main development region for Atlantic hurricanes, and that current/recent American hurricane trends fall within the realm of natural, multidecadal oscillations. Arguments supporting the link between global warming and hurricanes are addressed with climate modeling that links sea surface temperature (SST) increase to anthropogenic causes. It discusses SST’s influencing hurricane activity globally, if not locally to the U.S., and points to the need for consensus and action. Close

• 5. [Article] Analyzing large paleoclimate datasets : implications for past and future climate change

  This dissertation presents the results of statistical analyses of large climate datasets from two time intervals – the 20th century instrumental record and the proxy record of the last deglaciation – in ...

  Citation × Citation Citation Abstract Copy Title: Analyzing large paleoclimate datasets : implications for past and future climate change Author: Shakun, Jeremy D., 1981- This dissertation presents the results of statistical analyses of large climate datasets from two time intervals – the 20th century instrumental record and the proxy record of the last deglaciation – in order to understand the forcings and mechanisms of past climate variability. A longstanding question in climate dynamics concerns the origin of Pacific decadal variability (PDV). This issue is addressed by calculating the Southern Hemisphere equivalent of the Pacific Decadal Oscillation (PDO) index from Pacific sea surface temperature (SST) anomalies over the 20th century, which is found to be similar to its Northern Hemisphere counterpart. The Northern and Southern PDO indices both exhibit pronounced seasonality in autocorrelation with interannual persistence of winter SST anomalies despite their absence during the intervening summer, suggesting a role for reemergence. These two indices can be reasonably well reproduced using a first-order autoregressive model forced by the El Niño-Southern Oscillation, suggesting that Pacific decadal variability on both sides of the equator may largely be a reddened response to tropical forcing. Over 100 high-resolution proxy climate time series spanning parts or all of the Last Glacial Maximum (LGM) to Holocene interval are analyzed to characterize spatiotemporal patterns of glacial-interglacial climate change. Peak glacial and interglacial conditions occurred statistically synchronously between the Northern (22.1 ± 4.3 ka and 8.0 ± 3.2 ka) and Southern (22.3 ± 3.6 ka and 7.4 ± 3.7 ka) Hemispheres, suggesting that the hemispheres were synchronized by greenhouse gases, local insolation, and/or ocean circulation. Global cooling during the LGM was likely ≥4.9°C, but only ~0.6°C during the Younger Dryas. Younger Dryas climate anomalies exhibit a general hemispheric seesaw pattern with the largest negative anomalies in the high northern latitudes, mixed sign anomalies in the low latitudes, and modest positive anomalies in the high southern latitudes, consistent with an ocean circulation driver of this event. Empirical Orthogonal Function analysis of 71 records from 19-11 ka indicates that 72% of deglacial climate variability can be explained by two modes. The first mode (61% of the variance) shows a globally near-uniform signal and its associated principal component is strongly correlated with ice-core records of atmospheric CO₂. The second mode (11% of the variance) displays a more variable spatial pattern and its principal component parallels variations in Atlantic Meridional Overturning Circulation (AMOC) strength. Averaging 77 calibrated proxy temperature records over the last deglaciation indicates that global mean temperature was highly correlated and varied nearly in phase with the rise in CO₂, which differs from ice-core studies suggesting Antarctic temperature led CO₂. This result thus suggests a primary role for CO₂ in driving deglacial warming and the global deglaciation. Northern and Southern Hemisphere mean temperature time series both bear the imprint of CO₂ forcing, but differ largely in response to the millennial-scale seesawing of heat between the hemispheres related to AMOC variability. An analysis of deglacial temperature variability by latitude indicates that deglacial warming began near-synchronously throughout the Southern Hemisphere and tropics at ~19 ka and was coeval with abrupt cooling in the northern extratropics. These worldwide temperature changes may have been driven by a collapse of the AMOC related to the 19-kyr meltwater pulse. As this meltwater event has been tied to initial melting of Northern Hemisphere ice sheets in response to boreal summer insolation forcing, a classic Milankovitch trigger is implicated for the last deglaciation. Title: Analyzing large paleoclimate datasets : implications for past and future climate change Author: Shakun, Jeremy D., 1981- This dissertation presents the results of statistical analyses of large climate datasets from two time intervals – the 20th century instrumental record and the proxy record of the last deglaciation – in order to understand the forcings and mechanisms of past climate variability. A longstanding question in climate dynamics concerns the origin of Pacific decadal variability (PDV). This issue is addressed by calculating the Southern Hemisphere equivalent of the Pacific Decadal Oscillation (PDO) index from Pacific sea surface temperature (SST) anomalies over the 20th century, which is found to be similar to its Northern Hemisphere counterpart. The Northern and Southern PDO indices both exhibit pronounced seasonality in autocorrelation with interannual persistence of winter SST anomalies despite their absence during the intervening summer, suggesting a role for reemergence. These two indices can be reasonably well reproduced using a first-order autoregressive model forced by the El Niño-Southern Oscillation, suggesting that Pacific decadal variability on both sides of the equator may largely be a reddened response to tropical forcing. Over 100 high-resolution proxy climate time series spanning parts or all of the Last Glacial Maximum (LGM) to Holocene interval are analyzed to characterize spatiotemporal patterns of glacial-interglacial climate change. Peak glacial and interglacial conditions occurred statistically synchronously between the Northern (22.1 ± 4.3 ka and 8.0 ± 3.2 ka) and Southern (22.3 ± 3.6 ka and 7.4 ± 3.7 ka) Hemispheres, suggesting that the hemispheres were synchronized by greenhouse gases, local insolation, and/or ocean circulation. Global cooling during the LGM was likely ≥4.9°C, but only ~0.6°C during the Younger Dryas. Younger Dryas climate anomalies exhibit a general hemispheric seesaw pattern with the largest negative anomalies in the high northern latitudes, mixed sign anomalies in the low latitudes, and modest positive anomalies in the high southern latitudes, consistent with an ocean circulation driver of this event. Empirical Orthogonal Function analysis of 71 records from 19-11 ka indicates that 72% of deglacial climate variability can be explained by two modes. The first mode (61% of the variance) shows a globally near-uniform signal and its associated principal component is strongly correlated with ice-core records of atmospheric CO₂. The second mode (11% of the variance) displays a more variable spatial pattern and its principal component parallels variations in Atlantic Meridional Overturning Circulation (AMOC) strength. Averaging 77 calibrated proxy temperature records over the last deglaciation indicates that global mean temperature was highly correlated and varied nearly in phase with the rise in CO₂, which differs from ice-core studies suggesting Antarctic temperature led CO₂. This result thus suggests a primary role for CO₂ in driving deglacial warming and the global deglaciation. Northern and Southern Hemisphere mean temperature time series both bear the imprint of CO₂ forcing, but differ largely in response to the millennial-scale seesawing of heat between the hemispheres related to AMOC variability. An analysis of deglacial temperature variability by latitude indicates that deglacial warming began near-synchronously throughout the Southern Hemisphere and tropics at ~19 ka and was coeval with abrupt cooling in the northern extratropics. These worldwide temperature changes may have been driven by a collapse of the AMOC related to the 19-kyr meltwater pulse. As this meltwater event has been tied to initial melting of Northern Hemisphere ice sheets in response to boreal summer insolation forcing, a classic Milankovitch trigger is implicated for the last deglaciation. Close

• 6. [Article] Carbon Dynamics in the Future Forest: the Importance of Long-Term Successional Legacy and Climate–Fire Interactions

  Understanding how climate change may influence forest carbon (C) budgets requires knowledge of forest growth relationships with regional climate, long-term forest succession, and past and future disturbances, ...

  Citation × Citation Citation Abstract Copy Title: Carbon Dynamics in the Future Forest: the Importance of Long-Term Successional Legacy and Climate–Fire Interactions Author: Loudermilk, E. Louise, Scheller, Robert M., Weisberg, Peter J., Yang, Jian, Dilts, Thomas E., Karam, Sarah L., Skinner, Carl Year: 2013 Understanding how climate change may influence forest carbon (C) budgets requires knowledge of forest growth relationships with regional climate, long-term forest succession, and past and future disturbances, such as wildfires and timber harvesting events. We used a landscape-scale model of forest succession, wildfire, and C dynamics (LANDIS-II) to evaluate the effects of a changing climate (A2 and B1 IPCC emissions; Geophysical Fluid Dynamics Laboratory General Circulation Models) on total forest C, tree species composition, and wildfire dynamics in the Lake Tahoe Basin, California, and Nevada. The independent effects of temperature and precipitation were assessed within and among climate models. Results highlight the importance of modeling forest succession and stand development processes at the landscape scale for understanding the C cycle. Due primarily to landscape legacy effects of historic logging of the Comstock Era in the late 1880s, C sequestration may continue throughout the current century, and the forest will remain a C sink (Net Ecosystem Carbon Balance > 0), regardless of climate regime. Climate change caused increases in temperatures limited simulated C sequestration potential because of augmented fire activity and reduced establishment ability of subalpine and upper montane trees. Higher temperatures influenced forest response more than reduced precipitation. As the forest reached its potential steady state, the forest could become C neutral or a C source, and climate change could accelerate this transition. The future of forest ecosystem C cycling in many forested systems worldwide may depend more on major disturbances and landscape legacies related to land use than on projected climate change alone. Title: Carbon Dynamics in the Future Forest: the Importance of Long-Term Successional Legacy and Climate–Fire Interactions Author: Loudermilk, E. Louise, Scheller, Robert M., Weisberg, Peter J., Yang, Jian, Dilts, Thomas E., Karam, Sarah L., Skinner, Carl Year: 2013 Understanding how climate change may influence forest carbon (C) budgets requires knowledge of forest growth relationships with regional climate, long-term forest succession, and past and future disturbances, such as wildfires and timber harvesting events. We used a landscape-scale model of forest succession, wildfire, and C dynamics (LANDIS-II) to evaluate the effects of a changing climate (A2 and B1 IPCC emissions; Geophysical Fluid Dynamics Laboratory General Circulation Models) on total forest C, tree species composition, and wildfire dynamics in the Lake Tahoe Basin, California, and Nevada. The independent effects of temperature and precipitation were assessed within and among climate models. Results highlight the importance of modeling forest succession and stand development processes at the landscape scale for understanding the C cycle. Due primarily to landscape legacy effects of historic logging of the Comstock Era in the late 1880s, C sequestration may continue throughout the current century, and the forest will remain a C sink (Net Ecosystem Carbon Balance > 0), regardless of climate regime. Climate change caused increases in temperatures limited simulated C sequestration potential because of augmented fire activity and reduced establishment ability of subalpine and upper montane trees. Higher temperatures influenced forest response more than reduced precipitation. As the forest reached its potential steady state, the forest could become C neutral or a C source, and climate change could accelerate this transition. The future of forest ecosystem C cycling in many forested systems worldwide may depend more on major disturbances and landscape legacies related to land use than on projected climate change alone. Close

• 7. [Article] Environmental variability and system heterogeneity in terrestrial biogeochemical models

  Ecosystems are highly heterogeneous systems subjected to important levels of environmental variability; however, it is common in terrestrial biogeochemical models to assume homogeneous properties of the ...

  Citation × Citation Citation Abstract Copy Title: Environmental variability and system heterogeneity in terrestrial biogeochemical models Author: Sierra, Carlos Alberto Ecosystems are highly heterogeneous systems subjected to important levels of environmental variability; however, it is common in terrestrial biogeochemical models to assume homogeneous properties of the elements of the system or constant environmental conditions. For some processes, heterogeneity in these models is treated very simplistically, but there is not much information about the advantages of including more complex representations in these models. By environmental variability I refer to the continuous changes of abiotic drivers in ecosystems, mainly climatic conditions. System heterogeneity is treated here as the diversity of elements that compose an ecosystem and respond differently to biotic and abiotic drivers. In this dissertation I performed a theoretical analysis to evaluate the consequences of ignoring heterogeneity and variability on the representation of carbon and nitrogen cycling in terrestrial biogeochemical models. For this purpose I used tools from probability theory and simulation models to test the hypothesis that ignoring heterogeneity and variability excludes a variety of system properties and behaviors that cannot be obtained with simpler models. Explicit treatments of climatic variability showed that changes in temperature variance alone can modify the amounts of respiration and carbon storage in ecosystems. Additionally, changes in temperature variance can modify predictions solely based on changes in temperature averages. This behavior is strongly dependent on the degree and nature of nonlinearity in ecosystems. Effects of system heterogeneity on carbon and nitrogen cycling are also strongly influenced by nonlinearities. Extrapolations of average system behavior are only valid when the system is linear and the elements of the system are distributed homogeneously or symmetrically around an average value. In all other cases, the nonlinearity of the system and the distribution of its elements produce complex behaviors that are impossible to predict with simple models. Title: Environmental variability and system heterogeneity in terrestrial biogeochemical models Author: Sierra, Carlos Alberto Ecosystems are highly heterogeneous systems subjected to important levels of environmental variability; however, it is common in terrestrial biogeochemical models to assume homogeneous properties of the elements of the system or constant environmental conditions. For some processes, heterogeneity in these models is treated very simplistically, but there is not much information about the advantages of including more complex representations in these models. By environmental variability I refer to the continuous changes of abiotic drivers in ecosystems, mainly climatic conditions. System heterogeneity is treated here as the diversity of elements that compose an ecosystem and respond differently to biotic and abiotic drivers. In this dissertation I performed a theoretical analysis to evaluate the consequences of ignoring heterogeneity and variability on the representation of carbon and nitrogen cycling in terrestrial biogeochemical models. For this purpose I used tools from probability theory and simulation models to test the hypothesis that ignoring heterogeneity and variability excludes a variety of system properties and behaviors that cannot be obtained with simpler models. Explicit treatments of climatic variability showed that changes in temperature variance alone can modify the amounts of respiration and carbon storage in ecosystems. Additionally, changes in temperature variance can modify predictions solely based on changes in temperature averages. This behavior is strongly dependent on the degree and nature of nonlinearity in ecosystems. Effects of system heterogeneity on carbon and nitrogen cycling are also strongly influenced by nonlinearities. Extrapolations of average system behavior are only valid when the system is linear and the elements of the system are distributed homogeneously or symmetrically around an average value. In all other cases, the nonlinearity of the system and the distribution of its elements produce complex behaviors that are impossible to predict with simple models. Close

• 8. [Article] Climate Change Preparedness of Oregon Municipal Water Providers in Snow-Transient Basins

  8 p.

  Citation × Citation Citation Abstract Copy Title: Climate Change Preparedness of Oregon Municipal Water Providers in Snow-Transient Basins Author: Climate Leadership Initiative, Bartleson, Becca, Doppelt, Bob Year: 2008, 2007 8 p. Title: Climate Change Preparedness of Oregon Municipal Water Providers in Snow-Transient Basins Author: Climate Leadership Initiative, Bartleson, Becca, Doppelt, Bob Year: 2008, 2007 8 p. Close

• 9. [Article] Assessing Mechanisms of Climate Change Impact on the Upland Forest Water Balance of the Willamette River Basin, Oregon

  Projected changes in air temperature, precipitation, and vapor pressure for the Willamette River Basin (Oregon, USA) over the next century will have significant impacts on the river basin water balance, ...

  Citation × Citation Citation Abstract Copy Title: Assessing Mechanisms of Climate Change Impact on the Upland Forest Water Balance of the Willamette River Basin, Oregon Author: Turner, David P., Conklin, David R., Vache, Kellie B., Schwartz, Cynthia, Nolin, Anne, Chang, Heejun, Watson, Eric, Bolte, John P. Year: 2016 Projected changes in air temperature, precipitation, and vapor pressure for the Willamette River Basin (Oregon, USA) over the next century will have significant impacts on the river basin water balance, notably on the amount of evapotranspiration (ET). Mechanisms of impact on ET will be both direct and indirect, but there is limited understanding of their absolute and relative magnitudes. Here, we developed a spatially explicit, daily time-step, modeling infrastructure to simulate the basin-wide water balance that accounts for meteorological influences, as well as effects mediated by changing vegetation cover type, leaf area, and ecophysiology. Three CMIP5 climate scenarios (Lowclim, Reference, and HighClim) were run for the 2010–2100 period. Besides warmer temperatures, the climate scenarios were characterized by wetter winters and increasing vapor pressure deficits. In the mid-range Reference scenario, our landscape simulation model (Envision) projected a continuation of forest cover on the uplands but a threefold increase in area burned per year. A decline (12–30%) in basin-wide mean leaf area index (LAI) in forests was projected in all scenarios. The lower LAIs drove a corresponding decline in ET. In a sensitivity test, the effect of increasing CO2 on stomatal conductance induced a further substantial decrease (11–18%) in basin-wide mean ET. The net effect of decreases in ET and increases in winter precipitation was an increase in annual streamflow. These results support the inclusion of changes in land cover, land use, LAI, and ecophysiology in efforts to anticipate impacts of climate change on basin-scale water balances. Title: Assessing Mechanisms of Climate Change Impact on the Upland Forest Water Balance of the Willamette River Basin, Oregon Author: Turner, David P., Conklin, David R., Vache, Kellie B., Schwartz, Cynthia, Nolin, Anne, Chang, Heejun, Watson, Eric, Bolte, John P. Year: 2016 Projected changes in air temperature, precipitation, and vapor pressure for the Willamette River Basin (Oregon, USA) over the next century will have significant impacts on the river basin water balance, notably on the amount of evapotranspiration (ET). Mechanisms of impact on ET will be both direct and indirect, but there is limited understanding of their absolute and relative magnitudes. Here, we developed a spatially explicit, daily time-step, modeling infrastructure to simulate the basin-wide water balance that accounts for meteorological influences, as well as effects mediated by changing vegetation cover type, leaf area, and ecophysiology. Three CMIP5 climate scenarios (Lowclim, Reference, and HighClim) were run for the 2010–2100 period. Besides warmer temperatures, the climate scenarios were characterized by wetter winters and increasing vapor pressure deficits. In the mid-range Reference scenario, our landscape simulation model (Envision) projected a continuation of forest cover on the uplands but a threefold increase in area burned per year. A decline (12–30%) in basin-wide mean leaf area index (LAI) in forests was projected in all scenarios. The lower LAIs drove a corresponding decline in ET. In a sensitivity test, the effect of increasing CO2 on stomatal conductance induced a further substantial decrease (11–18%) in basin-wide mean ET. The net effect of decreases in ET and increases in winter precipitation was an increase in annual streamflow. These results support the inclusion of changes in land cover, land use, LAI, and ecophysiology in efforts to anticipate impacts of climate change on basin-scale water balances. Close

• 10. [Article] Climate Master Handbook: A Step-by-Step Guide to Help People Curb Their Household Climate Impact

  53 p. : ill. (some col.)

  Citation × Citation Citation Abstract Copy Title: Climate Master Handbook: A Step-by-Step Guide to Help People Curb Their Household Climate Impact Author: Climate Leadership Initiative Year: 2010, 2009 53 p. : ill. (some col.) Title: Climate Master Handbook: A Step-by-Step Guide to Help People Curb Their Household Climate Impact Author: Climate Leadership Initiative Year: 2010, 2009 53 p. : ill. (some col.) Close