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Author: Alison Kelly Macalady
Publisher:
ISBN:
Category : Global warming
Languages : en
Pages : 212
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Book Description
Forests play an important role in the earth system, regulating climate, maintaining biodiversity, and provisioning human communities with water, food and fuel. Interactions between climate and forest dynamics are not well constrained, and high uncertainty characterizes projections of global warming impacts on forests and associated ecosystem services. Recently observed tree mortality and forest die-off forewarn an acceleration of forest change with rising temperature and increased drought. However, the processes leading to tree death during drought are poorly understood, limiting our ability to anticipate future forest dynamics. The objective of this dissertation was to improve understanding of drought-associated tree mortality through literature synthesis and tree-ring studies on trees that survived and died during droughts in the southwestern USA. Specifically, this dissertation 1) documented global tree mortality patterns and identified emerging trends and research gaps; 2) quantified relationships between growth, climate, competition and mortality of piñon pine during droughts in New Mexico; 3) investigated tree defense anatomy as a potentially key element in piñon avoidance of death; and, 4) characterized the climate sensitivity of piñon resin ducts in order to gain insight into potential trends in tree defenses with climate variability and change. There has been an increase in studies reporting tree mortality linked to drought, heat, and the associated activity of insects and pathogens. Cases span the forested continents and occurred in water, light and temperature-limited forests. We hypothesized that increased tree mortality may be an emerging global phenomenon related to rising temperatures and drought (Appendix A). Recent radial growth was 53% higher on average in piñon that survived versus died during two episodes of drought-associated mortality, and statistical models of mortality risk based on average growth, growth variability, and abrupt growth changes correctly classified the status of ~70% of trees. Climate responses and competitive interactions partly explained growth differences between dying and surviving trees, with muted response to wet/cool conditions and enhanced sensitivity to competition from congeners linked to growth patterns associated with death. Discrimination and validation of models of mortality risk varied widely across sites and drought events, indicating shifting growth-mortality relationships and differences in mortality processes across space and time (Appendix B). Pre-formed defense anatomy is strongly associated with piñon survivorship over a range of sites and stand conditions. Models of mortality risk that account for both growth and resin duct attributes had≈1019 more support than models that contained only growth. The greatest improvement in classification was among trees from the 2000s drought, suggesting an enhanced role for tree defense allocation and/or bark beetle activity during recent warm versus historic cool drought. Accounting for defense characteristics and growth-defense allocation is likely to be important for improving representation of drought-associated mortality (Appendix C). Piñon resin duct chronologies contain climate responses that are coherent and distinct from those of radial growth. Growth responds positively and strongly to previous fall and current winter precipitation, and negatively to late spring and early summer temperature. A relatively equal positive resin duct response to winter precipitation and positive response to mid-to-late summer drought suggests that changes in climate will affect tree defense anatomy in complex ways, with the outcome determined by seasonal changes in precipitation and temperature (Appendix D).
Author: Alison Kelly Macalady
Publisher:
ISBN:
Category : Global warming
Languages : en
Pages : 212
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Book Description
Forests play an important role in the earth system, regulating climate, maintaining biodiversity, and provisioning human communities with water, food and fuel. Interactions between climate and forest dynamics are not well constrained, and high uncertainty characterizes projections of global warming impacts on forests and associated ecosystem services. Recently observed tree mortality and forest die-off forewarn an acceleration of forest change with rising temperature and increased drought. However, the processes leading to tree death during drought are poorly understood, limiting our ability to anticipate future forest dynamics. The objective of this dissertation was to improve understanding of drought-associated tree mortality through literature synthesis and tree-ring studies on trees that survived and died during droughts in the southwestern USA. Specifically, this dissertation 1) documented global tree mortality patterns and identified emerging trends and research gaps; 2) quantified relationships between growth, climate, competition and mortality of piñon pine during droughts in New Mexico; 3) investigated tree defense anatomy as a potentially key element in piñon avoidance of death; and, 4) characterized the climate sensitivity of piñon resin ducts in order to gain insight into potential trends in tree defenses with climate variability and change. There has been an increase in studies reporting tree mortality linked to drought, heat, and the associated activity of insects and pathogens. Cases span the forested continents and occurred in water, light and temperature-limited forests. We hypothesized that increased tree mortality may be an emerging global phenomenon related to rising temperatures and drought (Appendix A). Recent radial growth was 53% higher on average in piñon that survived versus died during two episodes of drought-associated mortality, and statistical models of mortality risk based on average growth, growth variability, and abrupt growth changes correctly classified the status of ~70% of trees. Climate responses and competitive interactions partly explained growth differences between dying and surviving trees, with muted response to wet/cool conditions and enhanced sensitivity to competition from congeners linked to growth patterns associated with death. Discrimination and validation of models of mortality risk varied widely across sites and drought events, indicating shifting growth-mortality relationships and differences in mortality processes across space and time (Appendix B). Pre-formed defense anatomy is strongly associated with piñon survivorship over a range of sites and stand conditions. Models of mortality risk that account for both growth and resin duct attributes had≈1019 more support than models that contained only growth. The greatest improvement in classification was among trees from the 2000s drought, suggesting an enhanced role for tree defense allocation and/or bark beetle activity during recent warm versus historic cool drought. Accounting for defense characteristics and growth-defense allocation is likely to be important for improving representation of drought-associated mortality (Appendix C). Piñon resin duct chronologies contain climate responses that are coherent and distinct from those of radial growth. Growth responds positively and strongly to previous fall and current winter precipitation, and negatively to late spring and early summer temperature. A relatively equal positive resin duct response to winter precipitation and positive response to mid-to-late summer drought suggests that changes in climate will affect tree defense anatomy in complex ways, with the outcome determined by seasonal changes in precipitation and temperature (Appendix D).
Author:
Publisher:
ISBN:
Category : Forest declines
Languages : en
Pages : 0
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Book Description
Climate change is projected to bring more frequent and prolonged droughts, causing widespread forest die-off. Identifying tree mortality over large spatial extents in response to the most recent California drought will help forest managers and conservationists understand where there may be a greater likelihood of future die-offs. In order to find more at-risk areas, this study evaluated how interacting site-specific topographic, climate, substrate, and stand characteristics mediated tree mortality in the Central Sierra Nevada during the 2012-2016 drought. The author used lidar and hyperspectral imagery provided by the National Ecological Observatory Network to identify individual dead trees using the Random Forest classification method and created a Random Forest Regression model to assess site-specific environmental variables that had a greater influence on tree mortality. The results show that the most influential variables were tree height, density, and elevation. Results also found higher mortality rates in pines and oaks, meaning further widespread die-off of these trees could reduce forest productivity, increase fire hazard risk, and drive a shift in community composition over the long-term. This study provides a finer resolution mapping of tree mortality over the research area than was reported by the USFS Aerial Detection Survey. Due to the confounding evidence regarding the relative influence of environmental factors on tree mortality during droughts, these results provide robust information to help maintain these changing forests in a climate-informed manner. Because this study is site-specific, more research is needed to assess how environmental factors mediate drought-induced mortality in other regions also projected to have more intense droughts as a result of climate change.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 5
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Sudden and widespread forest die-back and die-off (e.g., Huang & Anderegg, 2012) and increased mortality rates (e.g., Peng et al., 2011) in many forest ecosystems across the globe have been linked to drought and elevated temperatures (Allen et al., 2010, Fig. 1). Furthermore, these observations have caused a focus on the physiological mechanisms of drought-induced tree mortality (e.g. McDowell et al., 2008) and many studies, both observational and manipulative, have been carried out to explain tree death during drought from a physiological perspective.
Author: Angelo Rita
Publisher: Frontiers Media SA
ISBN: 2832510914
Category : Science
Languages : en
Pages : 131
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Book Description
Author: Samuel W. Flake
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 218
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Book Description
Widespread dieoff of trees associated with severe drought is a recent global phenomenon of increasing conservation and management concern. Tree dieoff is likely to produce dramatic and widespread alterations to plant community composition and successional dynamics, with associated changes in nutrient cycling, hydrology, and wildlife habitat. In order to predict and manage the effects of future widespread drought, there is a need for greater understanding of both the causes of drought-associated tree mortality as well as the subsequent effects of mortality on tree regeneration and understory dynamics. In this study, we investigated the effects of climate, stand structure, and insect herbivores on tree mortality and canopy dieback of semi-arid pinyon-juniper woodlands, as well as the implications of woodland overstory mortality on the abundance of juvenile trees and the distribution of understory plants. In 2015 we resampled 102 plots in a permanent plot network established in 2005 spanning pinyon-juniper woodlands in eleven mountain ranges in central Nevada, encompassing strong gradients of topography, elevation, soil conditions, and aridity. Using individually-tagged trees, we measured tree survival and changes to canopy greenness. In order to assess the effects of neighborhood tree density on changes in tree canopy health, we recorded high-precision GPS locations for each tree and calculated the basal area of neighboring trees and the distance to the nearest neighbor. We measured tree regeneration in two size classes: seedlings (20 cm tall) and sapling (20cm tall). We also measured understory cover by species in 1-m2 quadrats. We noted the microhabitat of tree juveniles and quadrats in order to assess the importance of fine-scale microhabitat heterogeneity to understory dynamics. This study is the first to document widespread dieoff and canopy decline in Great Basin pinyon-juniper woodlands in response to recent severe drought. We found mortality was most strongly predicted by high growing-season vapor pressure deficit and low winter precipitation (Forest Drought Stress Index), while canopy decline was most closely associated with cumulative climatic water deficit. Trees in sites with deeper soils also experienced greater health declines. Stand structure had a smaller, but significant, effect on tree survival and canopy health, with trees in dense 4-m neighborhoods and those with close neighbors experiencing increased mortality risk and canopy dieback. As predicted, the regeneration of pinyon pine was strongly influenced by changes to the overstory trees. Both seedlings and saplings were positively associated with plot-level dead tree basal area and with fine-scale mortality-associated microhabitats, suggesting that drought mortality may create canopy gaps with increased recruitment. In contrast to microhabitat results, pinyon seedlings were much more abundant in stands with lower levels of canopy dieback and in stands with more live basal area, suggesting that new recruitment may be limited by reduced seed availability. The dynamics of tree regeneration in woodlands will likely depend upon seed availability, resource levels, timescale, and the abundance and spatial arrangement of larger juveniles (advance regeneration) present before the drought. We found little evidence of response to tree mortality for most understory plant functional types. However, Poa secunda and Bromus tectorum were both more abundant than expected in mortality-associated microhabitats. At a plot scale, Bromus tectorum abundance was positively associated with canopy dieback, and has increased in dominance since 2005 in arid sites with high levels of dieback. While some native species may respond positively to resources released by tree mortality, there is a risk of invasion and increasing dominance of cheatgrass under future droughts, underlining the importance of understanding overstory-understory interactions in arid woodlands. This study highlights the need for further research into the effects of within-stand structural heterogeneity on woodland responses to drought. Pinyon-juniper woodlands have a complex, patchy distribution of trees which likely affects the ways in which competition may predispose trees to drought mortality. Overstory mortality creates heterogeneous microhabitats which alter the distribution of juvenile trees as well as understory species, thus spatially structuring the response of these species to drought. Aridity and severe drought are likely to increase in coming decades, and understanding the complex interactions that drive woodland tree mortality and the subsequent understory response is critical to the effective management of resilient woodlands.
Author: Sophia Lemmo
Publisher:
ISBN:
Category : Trees
Languages : en
Pages : 0
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The 2012-2016 California drought was the most severe in the state’s recorded history, contributing to the death of millions of trees. While the effects of this drought on forests are relatively well studied in the central and southern Sierra Nevada, less is known about its effects on the heavily timbered and diverse forests of northern California. Through sampling 54 0.25 ha plots in northern California, this study compared tree mortality and regeneration patterns before, during, and after California’s most recent record-setting drought. This study evaluated 1) the influence of habitat and competitive covariates on mortality and regeneration trends using ridge regression analysis; and 2) tree death and seedling/sapling establishment dates using dendrochronology and Superposed Epoch Analysis to explore the influence of climate on forest demographics. Montane drought-induced tree mortality occurred primarily in trees smaller than 40 cm diameter at breast height (DBH), with no coastal drought-related mortality in trees with DBH greater than 80 cm. The highest rates of overstory mortality across all sites were observed in Abies grandis (51%), Pinus lambertiana (43%), and Pinus monticola (37%). Picea breweriana (6%) and Picea sitchensis (9%) had the lowest average mortality rates. In montane environments, years with high rates of mortality were positively associated with climatic water deficit (CWD; drier than expected conditions) in the 1-2 years preceding and during tree death dates. Pre-drought montane mortality was greater at wet sites than dry sites, and recent montane mortality (~2013-2020) was positively related with canopy openness. In coastal environments, recent tree mortality was positively associated with maximum temperature and topographic position. Regeneration was dominated by advanced regeneration (median age of 32 years) of shade-tolerant species. In montane environments, regeneration dates were significantly associated with lower-than-average CWD the year proceeding. In coastal environments, regeneration was greater at dry sites than wet sites, and was positively associated with stand density and maximum temperature. These data demonstrate that these forests are not actively perpetuating as diversely into the future, especially in montane environments where more mortality is found in white pine species (Pinus lambertiana and P. monticola) and where the regeneration is weighted towards advanced regeneration of shade-tolerant fir species. This work indicates a need to implement targeted management aimed at generating disturbances to foster balanced and responsive regeneration. This management should preferentially retain medium to larger trees, as these size classes seem to be the least vulnerable to mortality. Such management would be promising for supporting the resilience and diversity of northern California landscapes.
Author: Alisha
Publisher:
ISBN: 9783384262271
Category :
Languages : en
Pages : 0
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Author: Markus Riederer
Publisher: John Wiley & Sons
ISBN: 140517157X
Category : Science
Languages : en
Pages : 456
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Book Description
Annual Plant Reviews, Volume 23 A much clearer picture is now emerging of the fine structure of the plant cuticle and its surface, the composition of cuticular waxes and the biosynthetic pathways leading to them. Studies assessing the impact of UV radiation on plant life have emphasized the role of the cuticle and underlying epidermis as optical filters for solar radiation. The field concerned with the diffusive transport of lipophilic organic non-electrolytes across the plant cuticle has reached a state of maturity. A new paradigm has recently been proposed for the diffusion of polar compounds and water across the cuticle. In the context of plant ecophysiology, cuticular transpiration can now be placed in the perspective of whole-leaf water relations. New and unexpected roles have been assigned to the cuticle in plant development and pollen-stigma interactions. Finally, much progress has been made in understanding the cuticle as a specific and extraordinary substrate for the interactions of the plant with microorganisms, fungi and insects. This volume details the major developments of recent years in this important interdisciplinary area. It is directed at researchers and professionals in plant biochemistry, plant physiology, plant ecology, phytopathology and environmental microbiology, in both the academic and industrial sectors.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 15
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Abstract. Using decade-long continuous observations of tree mortality and predawn leaf water potential ([psi]pd) at the Missouri Ozark AmeriFlux (MOFLUX) site, we studied how the mortality of important tree species varied and how such variations may be predicted. Water stress determined inter-annual variations in tree mortality with a time delay of 1 year or more, which was correlated fairly tightly with a number of quantitative predictors formulated based on [psi]pd and precipitation regimes. Predictors based on temperature and vapor pressure deficit anomalies worked reasonably well, particularly for moderate droughts. The exceptional drought of the year 2012 drastically increased the mortality of all species, including drought-tolerant oaks, in the subsequent year. The drought-influenced tree mortality was related to the species position along the spectrum of [psi]pd regulation capacity with those in either ends of the spectrum being associated with elevated risk of death. Regardless of species and drought intensity, the [psi]pd of all species recovered rapidly after sufficiently intense rain events in all droughts. This result, together with a lack of immediate leaf and branch desiccation, suggests an absence of catastrophic hydraulic disconnection in the xylem and that tree death was caused by significant but indirect effects. Species differences in the capacity of regulating [psi]pd and its temporal integral were magnified under moderate drought intensities but diminished towards wet and dry extremes. Severe droughts may overwhelm the capacity of even drought-tolerant species to maintain differential levels of water potential as the soil becomes exhausted of available water in the rooting zone, thus rendering them more susceptible to death if predisposed by other factors such as age.
Author: James M. Vose
Publisher:
ISBN:
Category : Climatic changes
Languages : en
Pages : 302
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Book Description
This assessment provides input to the reauthorized National Integrated Drought Information System (NIDIS) and the National Climate Assessment (NCA), and it establishes the scientific foundation needed to manage for drought resilience and adaptation. Focal areas include drought characterization; drought impacts on forest processes and disturbances such as insect outbreaks and wildfire; and consequences for forest and rangeland values. Drought can be a severe natural disaster with substantial social and economic consequences. Drought becomes most obvious when large-scale changes are observed; however, even moderate drought can have long-lasting impacts on the structure and function of forests and rangelands without these obvious large-scale changes. Large, stand-level impacts of drought are already underway in the West, but all U.S. forests are vulnerable to drought. Drought-associated forest disturbances are expected to increase with climatic change. Management actions can either mitigate or exacerbate the effects of drought. A first principal for increasing resilience and adaptation is to avoid management actions that exacerbate the effects of current or future drought. Options to mitigate drought include altering structural or functional components of vegetation, minimizing drought-mediated disturbance such as wildfire or insect outbreaks, and managing for reliable flow of water.
