No description available.

No description available.

Amazonia contains the largest expanse of tropical forest in the world and is globally significant as a store of carbon, a regulator of climate and an area of high species diversity. The ability of the Amazonian forests to maintain these important ecological functions is however, increasingly under question in light of recent predictions of climate change. There is currently significant uncertainty in model predictions of how Amazonian forests will respond to predicted future climate change. This thesis reports the finding of two field studies, targeted at understanding the responses of two tropical forest carbon fluxes which are poorly simulated in vegetation models, and two modelling studies, which aim to better quantify uncertainty on model predictions of the effects of current and future climate change on the ecological function of Amazonian forests. The responses of forests to varying magnitudes of seasonal changes in climate which occur across Amazonia can give an important insight into the sensitivity of these forests to climate perturbations and changes. Testing the sensitivity of an Amazonian forest in Tambopata, Peru, to seasonal variations in precipitation and temperature, I find that the stem diameter growth of tropical trees is more sensitive to water availability than temperature changes. The vulnerability of trees to reduced soil water varied between tree classes with different functional traits, including wood density, tree height, tree diameter and tree growth rate. Similarly, I find that the respiration flux from tropical dead wood, at a second site in French Guiana, is highly sensitive to variations in water content. I show that these variations in respiration fluxes can be modelled successfully using seasonal variations in soil water content. To date there are few studies which have comprehensively tested vegetation models using ecological data from Amazon forests. Using data assimilation and nine sources of ecological data I estimate the certainty with which we can parameterise a carbon cycle model to represent the effects of a strong dry season on tropical forests. Using this technique I find, that the carbon balance of Amazonian forests can be very sensitive to reductions in water availability, and that these seasonal changes need to be accurately simulated across models to correctly predict annual carbon budgets. The variability in model responses caused by differences in the way processes are structured and parameterised in vegetation models requires better quantification. Using a model inter-comparison I demonstrate that the relative sensitivity of modelled climate-vegetation feedbacks to changes in ambient air temperature and precipitation is highly variable. I find that although the models showed similar directional responses at both the leaf and canopy scale some models showed a greater sensitivity to temperature and others to drought. I therefore demonstrate the need for greater constraint on modelled responses of Amazonian forests to changes in temperature and precipitation. The impact of climate change on Amazonian forests is an important global issue, yet our knowledge is reliant on our ability to understand the uncertainties on our predictions. Using field data to evaluate and to develop model predictions is a valuable way to reduce the uncertainty associated with modelling future change. This thesis presents an investigation of how tropical forests respond to changes in climate and with what certainty we can model these changes in order to predict the response of Amazon forests to predicted future climate change.

<p>Forests change with changes in their environment based on the physiological responses of individual trees. These short-term reactions have cumulative impacts on long-term demographic performance. For a tree in a forest community, success depends on biomass growth to capture above- and belowground resources and reproductive output to establish future generations. Here we examine aspects of how forests respond to changes in moisture and light availability and how these responses are related to tree demography and physiology.</p><p>First we address the long-term pattern of tree decline before death and its connection with drought. Increasing drought stress and chronic morbidity could have pervasive impacts on forest composition in many regions. We use long-term, whole-stand inventory data from southeastern U.S. forests to show that trees exposed to drought experience multiyear declines in growth prior to mortality. Following a severe, multiyear drought, 72% of trees that did not recover their pre-drought growth rates died within 10 years. This pattern was mediated by local moisture availability. As an index of morbidity prior to death, we calculated the difference in cumulative growth after drought relative to surviving conspecifics. The strength of drought-induced morbidity varied among species and was correlated with species drought tolerance. </p><p>Next, we investigate differences among tree species in reproductive output relative to biomass growth with changes in light availability. Previous studies reach conflicting conclusions about the constraints on reproductive allocation relative to growth and how they vary through time, across species, and between environments. We test the hypothesis that canopy exposure to light, a critical resource, limits reproductive allocation by comparing long-term relationships between reproduction and growth for trees from 21 species in forests throughout the southeastern U.S. We found that species had divergent responses to light availability, with shade-intolerant species experiencing an alleviation of trade-offs between growth and reproduction at high light. Shade-tolerant species showed no changes in reproductive output across light environments. </p><p>Given that the above patterns depend on the maintenance of transpiration, we next developed an approach for predicting whole-tree water use from sap flux observations. Accurately scaling these observations to tree- or stand-levels requires accounting for variation in sap flux between wood types and with depth into the tree. We compared different models with sap flux data to test the hypotheses that radial sap flux profiles differ by wood type and tree size. We show that radial variation in sap flux is dependent on wood type but independent of tree size for a range of temperate trees. The best-fitting model predicted out-of-sample sap flux observations and independent estimates of sapwood area with small errors, suggesting robustness in new settings. We outline a method for predicting whole-tree water use with this model and include computer code for simple implementation in other studies. </p><p>Finally, we estimated tree water balances during drought with a statistical time-series analysis. Moisture limitation in forest stands comes predominantly from water use by the trees themselves, a drought-stand feedback. We show that drought impacts on tree fitness and forest composition can be predicted by tracking the moisture reservoir available to each tree in a mass balance. We apply this model to multiple seasonal droughts in a temperate forest with measurements of tree water use to demonstrate how species and size differences modulate moisture availability across landscapes. As trees deplete their soil moisture reservoir during droughts, a transpiration deficit develops, leading to reduced biomass growth and reproductive output.</p><p>This dissertation draws connections between the physiological condition of individual trees and their behavior in crowded, diverse, and continually-changing forest stands. The analyses take advantage of growing data sets on both the physiology and demography of trees as well as novel statistical techniques that allow us to link these observations to realistic quantitative models. The results can be used to scale up tree measurements to entire stands and address questions about the future composition of forests and the land’s balance of water and carbon.</p> / Dissertation

Drought is a complex subject that has varied definitions and perspectives. Although drought has historically been characterized as an environmental problem from both the meteorological and agricultural communities, it is not considered a sociological disaster despite its severe societal impacts. Utilizing the framework developed by Spector and Kitsuse (2011) and Stallings (1995), this research examines the process through which drought is defined as a social problem. An analysis of the data revealed drought was well covered in Africa, India, China, Australia, and New Zealand, yet very little coverage focused on the United States. There were less than 10 articles discussing drought and drought impacts in the United States. The workshops/meetings examined also were lacking in the attention to drought, although their overall theme was focused on hazards and resilience. Six sessions in over 16 years of meetings/workshops focused on the topic of drought, and one session was focused on the condition in Canada. The interviews uncovered five thematic areas demonstrating drought understanding and awareness: Use of outreach to get the message out; agricultures familiarity with drought; the role of drought in media; the variability of what drought is; and water conservation. Drought's claims-makers who are dedicated to providing outreach and education to impacted communities. Drought is often overlooked due to its slow onset and evolving development makes it difficult to determine when to engage in recovery efforts. Drought defined as a social problem also expands theoretical conversations regarding what events or issues should be included within the sociological disaster list of topics.

Master of Science / Department of Animal Sciences and Industry / Barry J. Bradford / Declining ground water supplies are putting significant pressure on the dairy industry in the United States. The water needed for forage production represents the great majority of total water use on most dairy farms, posing a major challenge in the pursuit of improved drought resilience. Teff (Eragrostis tef), a drought-tolerant annual grass (C4 physiology) native to Ethiopia, could prove an attractive alternative to traditional forage crops. While teff grass has potential to fit the needs for forage production in water-stressed regions, very little is currently known about its nutritional characteristics and whether it can support high levels of milk production by dairy cattle. An experiment was conducted to investigate the effects of variety and cutting age on dry matter yield, nutritive values, and digestibility of teff grass. Eighty pots were blocked by location in a greenhouse and randomly assigned to 4 teff varieties (Tiffany, Moxie, Corvallis, and Dessie) and to 5 cutting ages (40, 45, 50, 55, or 60 d after planting [DAP]). Results from this study indicate that, under greenhouse conditions, the first cutting of teff grass should be harvested at 45 to 50 DAP to optimize forage yield, quality, and digestibility in that cutting and in subsequent cuttings. A second experiment was conducted to assess the productivity of lactating dairy cows fed diets with teff hay as the sole forage. Nine multiparous Holstein cows were randomly assigned treatment sequence in a 3 × 3 Latin square design. Diets were either a control, where dietary forage consisted of a combination of corn silage, alfalfa hay, and prairie hay, or 1 of 2 teff diets, where teff hay was the sole forage. The teff diets maintained yields of milk and milk fat while increasing milk protein yield. Together, these two studies suggest that teff-based diets have potential to maintain high levels of milk production while improving the resilience of the dairy industry to future water shortages.

No description available.

Digitized by Kansas Correctional Industries

Ecophysiological traits that vary in response to water stress, and that exhibit significant genotypic variation in Pinus radiata, may reveal a differentiation between genotypes in their ability to respond to and function under water-limitation. Where the genotypic variation of these ecophysiological traits is also genetically correlated with tree growth, they improve the understanding of the genetic variation in growth under water limitation in this species. Ultimately they could be used as selection criteria for improved growth in water-limited environments. The objectives of the thesis were to identify ecophysiological traits in Pinus radiata that responded significantly to water stress; to assess the genotypic variation of those ecophysiological traits in P. radiata; and to determine the genetic correlation between those genetically variable ecophysiological traits and growth. / The thesis assessed the genotypic variation in ecophysiological response to water stress in Pinus radiata, and the genetic correlation between ecophysiological response and growth. These assessments were carried out in seedlings in the glasshouse, in 10 year-old trees in two field trials, and in increment cores of three field trials. / The response of Pinus radiata to water stress was exhibited in a wide range of ecophysiological traits, including growth, respiration, gas exchange, carbon isotope discrimination, chlorophyll fluorescence and osmotic adjustment. Gas exchange and carbon isotope discrimination were not genetically variable in response to water stress, despite significant treatment effects. Some of the other ecophysiological traits, including chlorophyll fluorescence, respiration in growing tissues and osmotic adjustment, did exhibit significant genetic variation under water stress, suggesting some genetic plasticity in P. radiata in response to water stress. However, there were few significant genetic correlations between any of these ecophysiological traits and growth traits, and none of them were demonstrated to be suitable selection criteria for genetic improvement of growth under water stress. / The thesis concludes that genetic variation in ecophysiological response to water stress is limited in P. radiata, and that the growth response to water stress was remarkably homogeneous between genotypes, despite there otherwise being significant genetic variation in growth that was unrelated to water stress. These findings were consistent across several trials and degrees of water stress, in both seedlings and mature trees. They are an important contribution to discussion of the appropriate balance of genetic improvement and silviculture in the optimum management of P. radiata in water-limited environments or under a drying climate, particularly as they are in contrast to results of studies of other Pinus spp such as P. pinaster or P. elliottii x caribaea in growth response to water stress has been shown to be genetically variable.

Bibliography: leaves 134-145. The improvement of drought tolerance of commercial soybean varieties via indirect selection for transpiration efficiency (TE) in breeding programs was investigated. The extent and nature of variation for TE among soybean genotypes were established through glasshouse experiments under well watered conditions, and confirmed in the field under contrasting water stress conditions. The results suggest that increasing TE will be a beneficial strategy to improve soybean grain yield at the crop level, and a protocol developed suited to indirect selection for high TE soybean genotypes under a range of environments. This will have immediate application in the development of soybean varieties specifically adapted to the dryland production areas of the Australian sub-tropics.