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Book Synopsis Forests under pressure: The need for interdisciplinary approaches to address forest vulnerability to tree mortality in response to drought by : Angelo Rita
Download or read book Forests under pressure: The need for interdisciplinary approaches to address forest vulnerability to tree mortality in response to drought written by Angelo Rita and published by Frontiers Media SA. This book was released on 2023-03-14 with total page 131 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Multiscale Approach to Assess Forest Vulnerability by : Giovanna Battipaglia
Download or read book Multiscale Approach to Assess Forest Vulnerability written by Giovanna Battipaglia and published by Frontiers Media SA. This book was released on 2020-07-14 with total page 240 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Trees are among the longest-living organisms. They are sensitive to extreme climatic events and document the effects of environmental changes in form of structural modifications of their tissues. These modifications represent an integrated signal of complex biological responses enforced by the environment. For example, temporal change in stem increment integrates multiple information of tree performance, and wood anatomical traits may be altered by climatic extremes or environmental stress. Recent developments in preparative tools and computational image analysis enable to quantify changes in wood anatomical features, like vessel density or vessel size. Thus, impacts on their functioning can be related to climatic forcing factors. Similarly, new developments in monitoring (cambial) phenology and mechanistic modelling are enlightening the interrelationships between environmental factors, wood formation and tree performance and mortality. Quantitative wood anatomy is a reliable indicator of drought occurrence during the growing season, and therefore has been studied intensively in recent years. The variability in wood anatomy not only alters the biological and hydraulic functioning of a tree, but may also influence the technological properties of wood, with substantial impacts in forestry. On a larger scale, alterations of sapwood and phloem area and their ratios to other functional traits provide measures to detect changes in a tree’s life functions, and increasing risk of drought-induced mortality with possible impacts on hydrological processes and species composition of plant communities. Genetic variability within and across populations is assumed to be crucial for species survival in an unpredictable future world. The magnitude of genetic variation and heritability of adaptive traits might define the ability to adapt to climate change. Is there a relation between genetic variability and resilience to climate change? Is it possible to link genetic expression and climate change to obtain deeper knowledge of functional genetics? To derive precise estimates of genetic determinism it is important to define adaptive traits in wood properties and on a whole-tree scale. Understanding the mechanisms ruling these processes is fundamental to assess the impact of extreme climate events on forest ecosystems, and to provide realistic scenarios of tree responses to changing climates. Wood is also a major carbon sink with a long-term residence, impacting the global carbon cycle. How well do we understand the link between wood growth dynamics, wood carbon allocation and the global carbon cycle? Papers contribution to this Research Topic will cover a wide range of ecosystems. However, special relevance will be given to Mediterranean-type areas. These involve coastal regions of four continents, making Mediterranean-type ecosystems extremely interesting for investigating the potential impacts of global change on growth and for studying responses of woody plants under extreme environmental conditions. For example, the ongoing trend towards warmer temperatures and reduced precipitation can increase the susceptibility to fire and pests. The EU-funded COST Action STREeSS (Studying Tree Responses to extreme Events: a SynthesiS) addresses such crucial tree biological and forest ecological issues by providing a collection of important methodological and scientific insights, about the current state of knowledge, and by opinions for future research needs.
Book Synopsis Studying Tree Responses to Extreme Events by : Achim Bräuning
Download or read book Studying Tree Responses to Extreme Events written by Achim Bräuning and published by Frontiers Media SA. This book was released on 2017-06-05 with total page 468 pages. Available in PDF, EPUB and Kindle. Book excerpt: Trees are among the longest-living organisms. They are sensitive to extreme climatic events and document the effects of environmental changes in form of structural modifications of their tissues. These modifications represent an integrated signal of complex biological responses enforced by the environment. For example, temporal change in stem increment integrates multiple information of tree performance, and wood anatomical traits may be altered by climatic extremes or environmental stress. Recent developments in preparative tools and computational image analysis enable to quantify changes in wood anatomical features, like vessel density or vessel size. Thus, impacts on their functioning can be related to climatic forcing factors. Similarly, new developments in monitoring (cambial) phenology and mechanistic modelling are enlightening the interrelationships between environmental factors, wood formation and tree performance and mortality. Quantitative wood anatomy is a reliable indicator of drought occurrence during the growing season, and therefore has been studied intensively in recent years. The variability in wood anatomy not only alters the biological and hydraulic functioning of a tree, but may also influence the technological properties of wood, with substantial impacts in forestry. On a larger scale, alterations of sapwood and phloem area and their ratios to other functional traits provide measures to detect changes in a tree’s life functions, and increasing risk of drought-induced mortality with possible impacts on hydrological processes and species composition of plant communities. Genetic variability within and across populations is assumed to be crucial for species survival in an unpredictable future world. The magnitude of genetic variation and heritability of adaptive traits might define the ability to adapt to climate change. Is there a relation between genetic variability and resilience to climate change? Is it possible to link genetic expression and climate change to obtain deeper knowledge of functional genetics? To derive precise estimates of genetic determinism it is important to define adaptive traits in wood properties and on a whole-tree scale. Understanding the mechanisms ruling these processes is fundamental to assess the impact of extreme climate events on forest ecosystems, and to provide realistic scenarios of tree responses to changing climates. Wood is also a major carbon sink with a long-term residence, impacting the global carbon cycle. How well do we understand the link between wood growth dynamics, wood carbon allocation and the global carbon cycle? Papers contribution to this Research Topic will cover a wide range of ecosystems. However, special relevance will be given to Mediterranean-type areas. These involve coastal regions of four continents, making Mediterranean-type ecosystems extremely interesting for investigating the potential impacts of global change on growth and for studying responses of woody plants under extreme environmental conditions. For example, the ongoing trend towards warmer temperatures and reduced precipitation can increase the susceptibility to fire and pests. The EU-funded COST Action STREeSS (Studying Tree Responses to extreme Events: a SynthesiS) addresses such crucial tree biological and forest ecological issues by providing a collection of important methodological and scientific insights, about the current state of knowledge, and by opinions for future research needs.
Climate change is expected to drive shifts in forest species distribution to track ideal climatic conditions. The relative capacity for a tree species to persist under climatic stress is dependent on life history traits, such as growth, survival, and reproduction. Trees that produce large amounts of seed may be better able to colonize newly suitable habitats, while those that survive stress at current locations may persist longer than nearby competitors. These traits each represent distinct resource sinks, however. What remains unknown is how physiological modification in response to drought influences both survival and reproductive capacity. I analyzed growth, tree ring anatomy, and reproductive capacity in Pinus ponderosa and P. jeffreyi in the Sierra Nevada mountains of California, where the unprecedented 2012-2016 drought led to large-scale forest mortality. I found that trees that died during drought unexpectedly exhibited anatomical traits thought to confer drought tolerance, such as thicker walls in water-conducting xylem cells. Under drought, trees close stomata (pores in their leaf surface involved in gas exchange) to limit water loss, but at the expense of carbon (C) uptake. This leads to a theoretical expectation of C depletion in drought-stressed trees, particularly during prolonged (i.e., multi-year) drought. While direct evidence of this "C-starvation" has not been recorded in nature, my results point to a potential mechanism of the impact of C depletion on mortality. The sampled trees also experienced a high level of bark beetle (Dendroctonus spp.) attack, which is typically defended against in trees via the production of C-rich resin and other chemical defenses. Drought appears to have weakened sampled trees, and excessive allocation of available resources to drought defense may have depleted reserves necessary for fending off beetle attack. To quantify potential tradeoffs between drought defense and reproduction, I developed a novel technique to measure total lignin (a C-expensive material involved in xylem cell wall thickening) in tree rings, and found that trees that died had higher lignin content than living trees. To further explore these patterns, I modeled likelihood of tree mortality as a function of tree ring width (growth), xylem anatomy, competition, and climate. I first compared multiple commonly used drought metrics with ring widths from>800 trees from across the Sierra Nevada and found that drought metric choice influences interpretation of drought impacts. I then showed that trees that grew not only thicker-walled xylem cells, but also more variable growth rings and variable cells between years were more likely to die. Trees that grew the same amount each year, or grew rings with relatively constant xylem cell diameters and wall thicknesses, were more likely to survive drought, counter to hypothesized tradeoffs between growth and reproduction during drought. Finally, cone counts of measured trees show that ring width (growth) was the primary determinant of reproductive capacity, with trees that grew more producing more cones. These results demonstrate that tree response to drought is a function of variation in xylem anatomy and ring width, with the mechanism of mortality being associated with C depletion. Trees that are less responsive to climate and maintain fairly constant growth appear to be most likely to survive prolonged drought, and trees that grow large rings (with low variance between years) are more likely to reproduce. These results improve our understanding of whole-forest response to future climate change by demonstrating the importance of both cellular scale (xylem anatomy) and forest-scale (drought metrics and competition) variation in influencing drought-induced forest mortality
Book Synopsis From the Cell to the Stand by : Jeffrey Lauder
Download or read book From the Cell to the Stand written by Jeffrey Lauder and published by . This book was released on 2020 with total page 334 pages. Available in PDF, EPUB and Kindle. Book excerpt: Climate change is expected to drive shifts in forest species distribution to track ideal climatic conditions. The relative capacity for a tree species to persist under climatic stress is dependent on life history traits, such as growth, survival, and reproduction. Trees that produce large amounts of seed may be better able to colonize newly suitable habitats, while those that survive stress at current locations may persist longer than nearby competitors. These traits each represent distinct resource sinks, however. What remains unknown is how physiological modification in response to drought influences both survival and reproductive capacity. I analyzed growth, tree ring anatomy, and reproductive capacity in Pinus ponderosa and P. jeffreyi in the Sierra Nevada mountains of California, where the unprecedented 2012-2016 drought led to large-scale forest mortality. I found that trees that died during drought unexpectedly exhibited anatomical traits thought to confer drought tolerance, such as thicker walls in water-conducting xylem cells. Under drought, trees close stomata (pores in their leaf surface involved in gas exchange) to limit water loss, but at the expense of carbon (C) uptake. This leads to a theoretical expectation of C depletion in drought-stressed trees, particularly during prolonged (i.e., multi-year) drought. While direct evidence of this "C-starvation" has not been recorded in nature, my results point to a potential mechanism of the impact of C depletion on mortality. The sampled trees also experienced a high level of bark beetle (Dendroctonus spp.) attack, which is typically defended against in trees via the production of C-rich resin and other chemical defenses. Drought appears to have weakened sampled trees, and excessive allocation of available resources to drought defense may have depleted reserves necessary for fending off beetle attack. To quantify potential tradeoffs between drought defense and reproduction, I developed a novel technique to measure total lignin (a C-expensive material involved in xylem cell wall thickening) in tree rings, and found that trees that died had higher lignin content than living trees. To further explore these patterns, I modeled likelihood of tree mortality as a function of tree ring width (growth), xylem anatomy, competition, and climate. I first compared multiple commonly used drought metrics with ring widths from>800 trees from across the Sierra Nevada and found that drought metric choice influences interpretation of drought impacts. I then showed that trees that grew not only thicker-walled xylem cells, but also more variable growth rings and variable cells between years were more likely to die. Trees that grew the same amount each year, or grew rings with relatively constant xylem cell diameters and wall thicknesses, were more likely to survive drought, counter to hypothesized tradeoffs between growth and reproduction during drought. Finally, cone counts of measured trees show that ring width (growth) was the primary determinant of reproductive capacity, with trees that grew more producing more cones. These results demonstrate that tree response to drought is a function of variation in xylem anatomy and ring width, with the mechanism of mortality being associated with C depletion. Trees that are less responsive to climate and maintain fairly constant growth appear to be most likely to survive prolonged drought, and trees that grow large rings (with low variance between years) are more likely to reproduce. These results improve our understanding of whole-forest response to future climate change by demonstrating the importance of both cellular scale (xylem anatomy) and forest-scale (drought metrics and competition) variation in influencing drought-induced forest mortality
Understanding ecosystem structure and function requires familiarity with the techniques, knowledge and concepts of the three disciplines of plant physiology, remote sensing and modelling. This is the first textbook to provide the fundamentals of these three domains in a single volume. It then applies cross-disciplinary insights to multiple case studies in vegetation and landscape science. A key feature of these case studies is an examination of relationships among climate, vegetation structure and vegetation function, to address fundamental research questions. This book is for advanced students and researchers who need to understand and apply knowledge from the disciplines of plant physiology, remote sensing and modelling. It allows readers to integrate and synthesise knowledge to produce a holistic understanding of the structure, function and behaviour of forests, woodlands and grasslands.
Book Synopsis Vegetation Dynamics by : Derek Eamus
Download or read book Vegetation Dynamics written by Derek Eamus and published by Cambridge University Press. This book was released on 2016-03-31 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Understanding ecosystem structure and function requires familiarity with the techniques, knowledge and concepts of the three disciplines of plant physiology, remote sensing and modelling. This is the first textbook to provide the fundamentals of these three domains in a single volume. It then applies cross-disciplinary insights to multiple case studies in vegetation and landscape science. A key feature of these case studies is an examination of relationships among climate, vegetation structure and vegetation function, to address fundamental research questions. This book is for advanced students and researchers who need to understand and apply knowledge from the disciplines of plant physiology, remote sensing and modelling. It allows readers to integrate and synthesise knowledge to produce a holistic understanding of the structure, function and behaviour of forests, woodlands and grasslands.
"... The idea to produce this book originated from discussions in the IUFRO-WFSE Steering Committee (SC) meetings in Vienna (2011) and Helsinki (2012). The SC concluded that, despite the considerable attention devoted to advancing sustainable forest management (SFM), increased understanding of the aspects that foster or hinder progress towards SFM is needed. The sustainable management of natural resources, especially forests, is of vital importance to global, regional, and national efforts to achieve sustainable development and should play a key role in efforts to mitigate and adapt to climate change and further low-carbon development. The goal of this book, therefore, is to increase the understanding of the conditions and combinations of conditions that foster or hinder progress towards SFM and forest-related sustainable development. The book focuses on these conditions at the local level and also includes processes and influences originating at broader national and global scales. The book is divided into four parts: Part I introduces the rationale, overall structure, and analytical framework of the book; Part II consists of 27 local- and regionallevel case studies from different parts of the world; Part III presents a synthesis of the case studies and the main findings derived from an analysis across the cases; Part IV is forward-looking and discusses several of the issues and findings from Parts II and III in the context of future outlooks and scenarios. We hope that this publication provides invaluable insights that may help advance SFM and forest-related livelihoods in different parts of the world."--Preface.
Book Synopsis Forests Under Pressure by : Pia Katila
Download or read book Forests Under Pressure written by Pia Katila and published by . This book was released on 2014 with total page 561 pages. Available in PDF, EPUB and Kindle. Book excerpt: "... The idea to produce this book originated from discussions in the IUFRO-WFSE Steering Committee (SC) meetings in Vienna (2011) and Helsinki (2012). The SC concluded that, despite the considerable attention devoted to advancing sustainable forest management (SFM), increased understanding of the aspects that foster or hinder progress towards SFM is needed. The sustainable management of natural resources, especially forests, is of vital importance to global, regional, and national efforts to achieve sustainable development and should play a key role in efforts to mitigate and adapt to climate change and further low-carbon development. The goal of this book, therefore, is to increase the understanding of the conditions and combinations of conditions that foster or hinder progress towards SFM and forest-related sustainable development. The book focuses on these conditions at the local level and also includes processes and influences originating at broader national and global scales. The book is divided into four parts: Part I introduces the rationale, overall structure, and analytical framework of the book; Part II consists of 27 local- and regionallevel case studies from different parts of the world; Part III presents a synthesis of the case studies and the main findings derived from an analysis across the cases; Part IV is forward-looking and discusses several of the issues and findings from Parts II and III in the context of future outlooks and scenarios. We hope that this publication provides invaluable insights that may help advance SFM and forest-related livelihoods in different parts of the world."--Preface.
Maintaining the resilience of ecological systems in an era of global change is a priority for management and conservation. In California, forests are currently threatened by a suite of disturbances that include altered fire regimes, legacy effects from timber harvesting, a warming and drying climate, chronic air pollution, and uncharacteristically severe attacks by insects and pathogens. Managing to preserve the characteristic structure and function of California forests under novel disturbance regimes requires a clear understanding of these forests' historical conditions as well as an understanding of the drivers of change in these forests. A major challenge of managing for resilience is the lack of quantifiable metrics to assess changes in a system's resilience over time. This dissertation uses a multi-timescale approach that quantifies changes in the structure and composition of California mixed-conifer forests since European settlement and suggests a framework for measuring and monitoring forest resilience. This work can be used to guide conservation and restoration activities with the goal of maintaining the characteristic structure and function of forests under changing disturbance regimes. In Chapter 1, I explore the demographic responses that have led to a reordering of species dominance in Sierra Nevada mixed-conifer forests. California mixed-conifer forests have been subjected to a century of fire suppression, resulting in a shift in the structure and composition of these forests over time. Historically, a high-frequency, low-severity fire regime maintained structurally heterogeneous forests where dominance was shared among several conifer species. With the removal of fire from this system, forest density increased, as did the prevalence of shade-tolerant fir species at the expense of pines. Previous work suggests that species-specific differences in demography have contributed to a shift away from a heterogeneous, resilient forest to a monodominant forest that is more susceptible to catastrophic loss from fire, drought, or invasive pests or pathogens. However, these conclusions are typically derived from extrapolations from short-term data. I use a 57-year inventory record from an old-growth mixedconifer stand in the Plumas National Forest, CA, where fires have been excluded since the early 20th century. Using a Bayesian hierarchical modeling approach, I measure species-specific rates of mortality, recruitment, and growth over this 57-year period. I also correlated climate trends with demographic data to determine whether climate may be a driver of shifts in species composition. I found that basal area, density, and aboveground carbon have increased linearly over the 57-year period in spite of increasing temperatures, which I expected might have negatively affected growth. The recruitment and growth rates of Pseudotsuga menziesii (Douglas-fir) and Abies concolor (white fir) were significantly higher than the community-level means, while the recruitment and growth rates of Pinus lambertiana (sugar pine) and Pinus ponderosa (ponderosa pine) were significantly lower than the community-level means. Mortality rates were similar among species. These results indicate that differences in species-specific growth and recruitment rates are the main drivers of a shift towards a low-diversity forest system and may potentially lead to the loss of pines from mixed-conifer forests. These results also quantify the strong effect that fire has on the regulation of forest biomass and density in this system. In Chapter 2, I address the need for accurate understandings of historical forest conditions to be used as guides when implementing management and restoration plans. Because historical Sierra- Nevada mixed conifer forests were considered to be resilient to disturbance due to their heterogeneous structure and function, historical conditions are often considered to be the target state for restoration. However, multiple methods for estimating historical forest conditions are available and these methods sometimes give conflicting results regarding the density of forests prior to European settlement. The General Land Office (GLO) surveys of the late 19th and early 20th centuries provide data on forest structure across a broad geographic range of the western US. Distance-based plotless density estimators (PDE) have been used previously to estimate density from the GLO data but this approach is limited due to errors that arise when trees are not randomly distributed. Recently, an area-based method was developed in order overcome this limitation of distance-based PDEs. The area-based method relies on estimating the speciesspecific Voronoi area of individual trees based on regression equations derived in contemporary stands. This method predicts historical densities that are 2-5 times higher than previous estimates, and the method has not been independently vetted. I applied three distance-based PDEs (Cottam, Pollard, and Morisita) and two area-based PDEs (Delincé and mean harmonic Voronoi density (MHVD)) in six mixed-conifer and pine-dominated stands in California, US and Baja California Norte, Mexico. These stands ranged in density from 784-159 trees ha-1. I found that the least biased estimate of tree density in every stand was obtained with the Morisita estimator and the most biased was obtained with the MHVD estimator. Estimates of tree density derived from the MHVD estimator were 1-4 times larger than the true densities. While the concept of area-based estimators is theoretically sound, as demonstrated by the accuracy of the Delincé estimates, the Delincé approach cannot be used with GLO data and the extension of the approach to the MHVD estimator is flawed. The inaccuracy of the MHVD method was attributed to two causes: (1) the use of a crown scaling factor that does not correct for the number of trees sampled and (2) the persistent underestimate of the true VA due to a weak relationship between tree size and VA. The results of this study suggest that estimates of historical conditions derived from applying the MHVD method to GLO data are likely to overestimate density and that tree size is not an accurate predictor of tree area in these open-canopy forests. I suggest caution in using density estimates derived from the MHVD method to inform restoration and management in Sierra Nevada mixed-conifer forests, and recommend the Morisita estimator as the least biased of the distance-based estimators. In Chapter 3, I address the concept of resilience as it relates to forest ecology and management and outline a framework that can be used to determine quantifiable metrics of resilience. Resilience is an aggregate property of ecological systems that maintains the structure, function, and composition of the system when faced with a disturbance. The main challenge inherent in using resilience to inform management and conservation is the multitude of definitions and concepts that have been developed to describe the resilience of ecological systems. The framework I develop for operationalizing resilience builds on the theoretical concept of resilience but provides explicit metrics for measurement. In this framework, resilience is composed of two properties: resistance to disturbance and recovery from disturbance. I outline four dimensions of resistance and recovery that can be used to measure and monitor resilience, including heterogeneity, complexity, quality, and reserves. I dispense with the concept of strictly-defined alternate stable states and instead focus resilience goals on target states, which are determined by ecological, economic, recreational, or aesthetic considerations. I also conduct a literature review of papers which measure forest resilience to assess measurements and analyses that can be used to quantify the four dimensions of resilience in the context of resistance and recovery. The results of this review indicate that studies of resilience can effectively make use of simple methods for quantification and analysis and that the most compelling studies address both components of resilience (resistance to and recovery from disturbance) and multiple dimensions of resilience. I then apply metrics to quantify the dimensions of resilience in three case study systems: the Sierra Nevada mixed-conifer forest of California, the eastern hemlock forest of the northeastern US, and the northern hardwood forest of the northeastern US. I found that this resilience framework is limited by the fact that no single, absolute measure of resilience can be derived. However, the framework is useful for defining baseline resilience measures and establishing protocols for measuring relative changes in forest resilience over time.
Book Synopsis Forest Resilience Measured by : Carrie Levine Levine
Download or read book Forest Resilience Measured written by Carrie Levine Levine and published by . This book was released on 2017 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt: Maintaining the resilience of ecological systems in an era of global change is a priority for management and conservation. In California, forests are currently threatened by a suite of disturbances that include altered fire regimes, legacy effects from timber harvesting, a warming and drying climate, chronic air pollution, and uncharacteristically severe attacks by insects and pathogens. Managing to preserve the characteristic structure and function of California forests under novel disturbance regimes requires a clear understanding of these forests' historical conditions as well as an understanding of the drivers of change in these forests. A major challenge of managing for resilience is the lack of quantifiable metrics to assess changes in a system's resilience over time. This dissertation uses a multi-timescale approach that quantifies changes in the structure and composition of California mixed-conifer forests since European settlement and suggests a framework for measuring and monitoring forest resilience. This work can be used to guide conservation and restoration activities with the goal of maintaining the characteristic structure and function of forests under changing disturbance regimes. In Chapter 1, I explore the demographic responses that have led to a reordering of species dominance in Sierra Nevada mixed-conifer forests. California mixed-conifer forests have been subjected to a century of fire suppression, resulting in a shift in the structure and composition of these forests over time. Historically, a high-frequency, low-severity fire regime maintained structurally heterogeneous forests where dominance was shared among several conifer species. With the removal of fire from this system, forest density increased, as did the prevalence of shade-tolerant fir species at the expense of pines. Previous work suggests that species-specific differences in demography have contributed to a shift away from a heterogeneous, resilient forest to a monodominant forest that is more susceptible to catastrophic loss from fire, drought, or invasive pests or pathogens. However, these conclusions are typically derived from extrapolations from short-term data. I use a 57-year inventory record from an old-growth mixedconifer stand in the Plumas National Forest, CA, where fires have been excluded since the early 20th century. Using a Bayesian hierarchical modeling approach, I measure species-specific rates of mortality, recruitment, and growth over this 57-year period. I also correlated climate trends with demographic data to determine whether climate may be a driver of shifts in species composition. I found that basal area, density, and aboveground carbon have increased linearly over the 57-year period in spite of increasing temperatures, which I expected might have negatively affected growth. The recruitment and growth rates of Pseudotsuga menziesii (Douglas-fir) and Abies concolor (white fir) were significantly higher than the community-level means, while the recruitment and growth rates of Pinus lambertiana (sugar pine) and Pinus ponderosa (ponderosa pine) were significantly lower than the community-level means. Mortality rates were similar among species. These results indicate that differences in species-specific growth and recruitment rates are the main drivers of a shift towards a low-diversity forest system and may potentially lead to the loss of pines from mixed-conifer forests. These results also quantify the strong effect that fire has on the regulation of forest biomass and density in this system. In Chapter 2, I address the need for accurate understandings of historical forest conditions to be used as guides when implementing management and restoration plans. Because historical Sierra- Nevada mixed conifer forests were considered to be resilient to disturbance due to their heterogeneous structure and function, historical conditions are often considered to be the target state for restoration. However, multiple methods for estimating historical forest conditions are available and these methods sometimes give conflicting results regarding the density of forests prior to European settlement. The General Land Office (GLO) surveys of the late 19th and early 20th centuries provide data on forest structure across a broad geographic range of the western US. Distance-based plotless density estimators (PDE) have been used previously to estimate density from the GLO data but this approach is limited due to errors that arise when trees are not randomly distributed. Recently, an area-based method was developed in order overcome this limitation of distance-based PDEs. The area-based method relies on estimating the speciesspecific Voronoi area of individual trees based on regression equations derived in contemporary stands. This method predicts historical densities that are 2-5 times higher than previous estimates, and the method has not been independently vetted. I applied three distance-based PDEs (Cottam, Pollard, and Morisita) and two area-based PDEs (Delincé and mean harmonic Voronoi density (MHVD)) in six mixed-conifer and pine-dominated stands in California, US and Baja California Norte, Mexico. These stands ranged in density from 784-159 trees ha-1. I found that the least biased estimate of tree density in every stand was obtained with the Morisita estimator and the most biased was obtained with the MHVD estimator. Estimates of tree density derived from the MHVD estimator were 1-4 times larger than the true densities. While the concept of area-based estimators is theoretically sound, as demonstrated by the accuracy of the Delincé estimates, the Delincé approach cannot be used with GLO data and the extension of the approach to the MHVD estimator is flawed. The inaccuracy of the MHVD method was attributed to two causes: (1) the use of a crown scaling factor that does not correct for the number of trees sampled and (2) the persistent underestimate of the true VA due to a weak relationship between tree size and VA. The results of this study suggest that estimates of historical conditions derived from applying the MHVD method to GLO data are likely to overestimate density and that tree size is not an accurate predictor of tree area in these open-canopy forests. I suggest caution in using density estimates derived from the MHVD method to inform restoration and management in Sierra Nevada mixed-conifer forests, and recommend the Morisita estimator as the least biased of the distance-based estimators. In Chapter 3, I address the concept of resilience as it relates to forest ecology and management and outline a framework that can be used to determine quantifiable metrics of resilience. Resilience is an aggregate property of ecological systems that maintains the structure, function, and composition of the system when faced with a disturbance. The main challenge inherent in using resilience to inform management and conservation is the multitude of definitions and concepts that have been developed to describe the resilience of ecological systems. The framework I develop for operationalizing resilience builds on the theoretical concept of resilience but provides explicit metrics for measurement. In this framework, resilience is composed of two properties: resistance to disturbance and recovery from disturbance. I outline four dimensions of resistance and recovery that can be used to measure and monitor resilience, including heterogeneity, complexity, quality, and reserves. I dispense with the concept of strictly-defined alternate stable states and instead focus resilience goals on target states, which are determined by ecological, economic, recreational, or aesthetic considerations. I also conduct a literature review of papers which measure forest resilience to assess measurements and analyses that can be used to quantify the four dimensions of resilience in the context of resistance and recovery. The results of this review indicate that studies of resilience can effectively make use of simple methods for quantification and analysis and that the most compelling studies address both components of resilience (resistance to and recovery from disturbance) and multiple dimensions of resilience. I then apply metrics to quantify the dimensions of resilience in three case study systems: the Sierra Nevada mixed-conifer forest of California, the eastern hemlock forest of the northeastern US, and the northern hardwood forest of the northeastern US. I found that this resilience framework is limited by the fact that no single, absolute measure of resilience can be derived. However, the framework is useful for defining baseline resilience measures and establishing protocols for measuring relative changes in forest resilience over time.
Abstract: In summer 2018, Central Europe was hit by an extreme drought event that widely impacted ecosystems and markedly increased tree mortality in forest ecosystems across the continent. As climate models predict an increase in frequency and severity of such events, there is an urgent need to adapt forests in order to maintain the diverse benefits they provide. Soil processes play an essential role in this context and are key for a plethora of terrestrial ecosystem functions, but they are strongly dependent on water availability. Here, we investigated how tree species richness (TSR), composition, and identity in a 13-year-old temperate tree diversity experiment influenced selected ecosystem functions (as important representatives of different ecosystem processes) during the 2018 summer drought. We focused on the stability of soil microbial biomass and standard litter decomposition, as well as tree species-specific mortality rates. Contrary to our expectations, TSR did not generally increase the resistance of soil functions or decrease tree mortality rates. However, the resistance of these functions was determined by tree species identity and community composition. For the resistance of both soil functions (microbial biomass and litter decomposition), we found that TSR effects depended on the presence of certain tree species. Moreover, we found that the performance of a specific tree species in monoculture, Norway spruce, was a poor predictor of its response to drought in tree species mixtures. Taken together, the results of our study demonstrate that the species composition of tree stands determines tree mortality and the resistance of soil functions under drought. This indicates that enhancing multiple ecosystem functions under environmental disturbance requires maintaining diverse forests
Book Synopsis Tree Community Composition Stabilizes Ecosystem Functions in Response to Drought by : Felix Gottschall
Download or read book Tree Community Composition Stabilizes Ecosystem Functions in Response to Drought written by Felix Gottschall and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Abstract: In summer 2018, Central Europe was hit by an extreme drought event that widely impacted ecosystems and markedly increased tree mortality in forest ecosystems across the continent. As climate models predict an increase in frequency and severity of such events, there is an urgent need to adapt forests in order to maintain the diverse benefits they provide. Soil processes play an essential role in this context and are key for a plethora of terrestrial ecosystem functions, but they are strongly dependent on water availability. Here, we investigated how tree species richness (TSR), composition, and identity in a 13-year-old temperate tree diversity experiment influenced selected ecosystem functions (as important representatives of different ecosystem processes) during the 2018 summer drought. We focused on the stability of soil microbial biomass and standard litter decomposition, as well as tree species-specific mortality rates. Contrary to our expectations, TSR did not generally increase the resistance of soil functions or decrease tree mortality rates. However, the resistance of these functions was determined by tree species identity and community composition. For the resistance of both soil functions (microbial biomass and litter decomposition), we found that TSR effects depended on the presence of certain tree species. Moreover, we found that the performance of a specific tree species in monoculture, Norway spruce, was a poor predictor of its response to drought in tree species mixtures. Taken together, the results of our study demonstrate that the species composition of tree stands determines tree mortality and the resistance of soil functions under drought. This indicates that enhancing multiple ecosystem functions under environmental disturbance requires maintaining diverse forests
This dissertation aims to quantify the sensitivity and adaptive capacity of forest tree species to climate change in Canada and North America, with applications of guiding sustainable forest management through case studies focusing on Alberta. The general idea is that management interventions should focus on ecosystems, species or populations that are most likely to experience stress or mortality, or alternatively to focus on new forest management opportunities associated with warming climate conditions at high latitudes. The research addresses several specific problems at different spatial scales. The research starts at the broadest scale, for North America, with a remote-sensing based vulnerability assessment of forest ecosystems to historical droughts. One of the most striking findings was a very high spatial diversity of vegetation response to historical climate variability. Broad continental patterns of vegetation response are readily apparent and conform to expectations, with southern interior ecosystems being limited by water availability and boreal populations limited by short growing seasons. However, within these broad geographic trends in growth response, finer scale (and often contradictory) response patterns emerge. For example, across the western boreal forest local patches show populations restricted in growth by warm summer temperatures and drought. Next, a species-specific analysis investigates the adaptive capacity of an important boreal forest tree species, white spruce, using dendrochronological analysis. Results showed evidence for population differentiation in resistance and recovery parameters, but provenances conformed to approximately the same growth rates under drought conditions and had similar resilience metrics. The lack of populations with better growth rates under drought conditions is contrary to expectations for a wide-ranging species with distinct regional climate and we provide a counter example for drought tolerance traits, where assisted migration prescriptions may be ineffective to mitigate climate change impacts. An analysis of population response in the context of climatic conditions across Canada supports the view that northeastern Canada will provide a refugium for white spruce under climate change, while the species is sensitive to growth reductions under climate change in the western boreal. In a case study for Alberta, a comprehensive series of genetic test plantations was analyzed to determine the optimal climate niche of selected planting stock. The results suggest that seed transfers can improve growth in some cases. However, the climate change vector does not always align with geographic gradients, which makes finding well adapted seed sources difficult or impossible. This issue may partially be addressed by relying on additional silvicultural adaptation options to address climate change. The case study provides a methodological template of how jurisdictions can determine feasibility as well as magnitude and direction of assisted migration prescriptions to adapt their reforestation programs to new planting environments. When assisted migration is used to address climate change, tree seedlings may have to be moved to substantially colder environments in anticipation of climate warming over their life span. To assess the risk associated with moving planting stock north or to higher elevation, a climatic assessment of frost risk associated with assisted migration was performed. The results indicate that late spring and early fall frost risks do not change significantly for transfers toward the north. In contrast, moving planting stock toward higher elevation generally leads to a substantial increase in exposure to unseasonal frosts. In conclusion, transfers toward the north are preferable to transfers up in elevation in reforestation for the most important commercial tree species in western Canada that were evaluated in this study. Lastly, the research explores how results may be translated to management prescriptions through an on-line seed selection tool for forest managers to identify the overall best planting stock for a reforestation site, synthesizing multiple criteria including vulnerability, adaptive capacity and growth of species and genotypes.
Book Synopsis Forest Tree Population Response to Climate Variability and Climate Change by : Zihaohan Sang
Download or read book Forest Tree Population Response to Climate Variability and Climate Change written by Zihaohan Sang and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation aims to quantify the sensitivity and adaptive capacity of forest tree species to climate change in Canada and North America, with applications of guiding sustainable forest management through case studies focusing on Alberta. The general idea is that management interventions should focus on ecosystems, species or populations that are most likely to experience stress or mortality, or alternatively to focus on new forest management opportunities associated with warming climate conditions at high latitudes. The research addresses several specific problems at different spatial scales. The research starts at the broadest scale, for North America, with a remote-sensing based vulnerability assessment of forest ecosystems to historical droughts. One of the most striking findings was a very high spatial diversity of vegetation response to historical climate variability. Broad continental patterns of vegetation response are readily apparent and conform to expectations, with southern interior ecosystems being limited by water availability and boreal populations limited by short growing seasons. However, within these broad geographic trends in growth response, finer scale (and often contradictory) response patterns emerge. For example, across the western boreal forest local patches show populations restricted in growth by warm summer temperatures and drought. Next, a species-specific analysis investigates the adaptive capacity of an important boreal forest tree species, white spruce, using dendrochronological analysis. Results showed evidence for population differentiation in resistance and recovery parameters, but provenances conformed to approximately the same growth rates under drought conditions and had similar resilience metrics. The lack of populations with better growth rates under drought conditions is contrary to expectations for a wide-ranging species with distinct regional climate and we provide a counter example for drought tolerance traits, where assisted migration prescriptions may be ineffective to mitigate climate change impacts. An analysis of population response in the context of climatic conditions across Canada supports the view that northeastern Canada will provide a refugium for white spruce under climate change, while the species is sensitive to growth reductions under climate change in the western boreal. In a case study for Alberta, a comprehensive series of genetic test plantations was analyzed to determine the optimal climate niche of selected planting stock. The results suggest that seed transfers can improve growth in some cases. However, the climate change vector does not always align with geographic gradients, which makes finding well adapted seed sources difficult or impossible. This issue may partially be addressed by relying on additional silvicultural adaptation options to address climate change. The case study provides a methodological template of how jurisdictions can determine feasibility as well as magnitude and direction of assisted migration prescriptions to adapt their reforestation programs to new planting environments. When assisted migration is used to address climate change, tree seedlings may have to be moved to substantially colder environments in anticipation of climate warming over their life span. To assess the risk associated with moving planting stock north or to higher elevation, a climatic assessment of frost risk associated with assisted migration was performed. The results indicate that late spring and early fall frost risks do not change significantly for transfers toward the north. In contrast, moving planting stock toward higher elevation generally leads to a substantial increase in exposure to unseasonal frosts. In conclusion, transfers toward the north are preferable to transfers up in elevation in reforestation for the most important commercial tree species in western Canada that were evaluated in this study. Lastly, the research explores how results may be translated to management prescriptions through an on-line seed selection tool for forest managers to identify the overall best planting stock for a reforestation site, synthesizing multiple criteria including vulnerability, adaptive capacity and growth of species and genotypes.
Earth’s atmosphere is unequivocally warming due to CO2 and other greenhouse gas (GHG) emissions from human activities and this is having widespread impacts on forest ecosystems that provide important services to human societies. Forest ecosystems help regulate atmospheric CO2 concentrations by sequestering carbon in tree biomass and soils, which is a valuable ecosystem service that is sensitive to climate change and forest management. Rising air temperatures contributed to increased aridity and drought during recent decades among forests in the western United States and projections suggest that many parts of this region could become hotter and drier over the coming century barring significant reductions in GHG emissions. Managing regional forests and GHG emissions in a warming world requires better understanding of how forest carbon cycling is influenced by climate, including climate-mediated disturbance (e.g., fires). The objectives of this dissertation were to assess (1) forest response to water availability and (2) tree mortality from disturbance during recent decades in the western US. Forest response to water availability was assessed, in part, by quantifying changes in forest productivity and live biomass across sites that varied widely in average water availability. Bioclimatic relationships were developed using (1) field measurements from 12 sites in the eastern Cascade Mountains, (2) inventory and ancillary plot measurements from 1,953 sites in Washington, Oregon, and California (WAORCA), and (3) remote sensing measurements spanning 18 Mha of mature forest in the western US. In each case, forest productivity and live biomass increased markedly across sites as average water availability increased. For instance, median forest productivity increased from 2.2 to 5.6 Mg C ha−1 yr−1 between the driest and wettest 5% of sites in WAORCA, while live biomass increased from 26 to 281 Mg C ha−1. These bioclimatic relationships illustrate that forests are widely sensitive to changes in water availability, suggesting that continued warming and drying could reduce carbon sequestration over the coming century in parts of the region. Tree mortality from fires, bark beetles, and timber harvest was quantified from 2003-2012 across the region using remote sensing, federal harvest statistics, and ancillary information. Tree mortality was quantified in terms of carbon storage in aboveground biomass killed by disturbance. Regional tree mortality from these disturbances together averaged 45.8±16.0 Tg C yr−1 (±95% confidence interval), with harvest, beetles, and fires accounting for 50%, 32%, and 18% of mortality, respectively. Tree mortality from timber harvest was concentrated in the high-biomass forests of the Washington and Oregon. Tree mortality from bark beetles occurred largely in Colorado, Wyoming, and Montana, where tree defenses were suppressed by drought and beetle populations bolstered by rising winter temperatures. Tree mortality from fires was highest in California, Idaho, and Montana, which also experienced very dry conditions during this decade. Tree biomass killed by disturbance will gradually decompose and emit CO2 to the atmosphere over decades to centuries, where it will act as a GHG. This analysis illustrates both opportunities and challenges to managing GHG emissions from forest ecosystems in the region. Swift and significant reductions in GHG emissions are needed to curtail adverse impacts of climate change on forest ecosystems and human societies.
Book Synopsis Forest Response to Water Forest Response to Water Availability and Disturbance in the Western United States by : Logan T. Berner
Download or read book Forest Response to Water Forest Response to Water Availability and Disturbance in the Western United States written by Logan T. Berner and published by . This book was released on 2017 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: Earth’s atmosphere is unequivocally warming due to CO2 and other greenhouse gas (GHG) emissions from human activities and this is having widespread impacts on forest ecosystems that provide important services to human societies. Forest ecosystems help regulate atmospheric CO2 concentrations by sequestering carbon in tree biomass and soils, which is a valuable ecosystem service that is sensitive to climate change and forest management. Rising air temperatures contributed to increased aridity and drought during recent decades among forests in the western United States and projections suggest that many parts of this region could become hotter and drier over the coming century barring significant reductions in GHG emissions. Managing regional forests and GHG emissions in a warming world requires better understanding of how forest carbon cycling is influenced by climate, including climate-mediated disturbance (e.g., fires). The objectives of this dissertation were to assess (1) forest response to water availability and (2) tree mortality from disturbance during recent decades in the western US. Forest response to water availability was assessed, in part, by quantifying changes in forest productivity and live biomass across sites that varied widely in average water availability. Bioclimatic relationships were developed using (1) field measurements from 12 sites in the eastern Cascade Mountains, (2) inventory and ancillary plot measurements from 1,953 sites in Washington, Oregon, and California (WAORCA), and (3) remote sensing measurements spanning 18 Mha of mature forest in the western US. In each case, forest productivity and live biomass increased markedly across sites as average water availability increased. For instance, median forest productivity increased from 2.2 to 5.6 Mg C ha−1 yr−1 between the driest and wettest 5% of sites in WAORCA, while live biomass increased from 26 to 281 Mg C ha−1. These bioclimatic relationships illustrate that forests are widely sensitive to changes in water availability, suggesting that continued warming and drying could reduce carbon sequestration over the coming century in parts of the region. Tree mortality from fires, bark beetles, and timber harvest was quantified from 2003-2012 across the region using remote sensing, federal harvest statistics, and ancillary information. Tree mortality was quantified in terms of carbon storage in aboveground biomass killed by disturbance. Regional tree mortality from these disturbances together averaged 45.8±16.0 Tg C yr−1 (±95% confidence interval), with harvest, beetles, and fires accounting for 50%, 32%, and 18% of mortality, respectively. Tree mortality from timber harvest was concentrated in the high-biomass forests of the Washington and Oregon. Tree mortality from bark beetles occurred largely in Colorado, Wyoming, and Montana, where tree defenses were suppressed by drought and beetle populations bolstered by rising winter temperatures. Tree mortality from fires was highest in California, Idaho, and Montana, which also experienced very dry conditions during this decade. Tree biomass killed by disturbance will gradually decompose and emit CO2 to the atmosphere over decades to centuries, where it will act as a GHG. This analysis illustrates both opportunities and challenges to managing GHG emissions from forest ecosystems in the region. Swift and significant reductions in GHG emissions are needed to curtail adverse impacts of climate change on forest ecosystems and human societies.
