Historical forest biomass dynamics modelled with Landsat spectral trajectories

Acknowledgements National Forest Inventory data are available online, provided by Ministerio de Agricultura, Alimentación y Medio Ambiente (España). Landsat images are available online, provided by the USGS.Peer reviewedPostprin

Mobile Water Payment Innovations in Urban Africa

This study assess mobile payment options for water service bills in four urban African contexts. Systems are evaluated to identify differences in adoption levels and motivations and barriers to uptake; how costs are distributed among water service providers, mobile network operators, and customers; and mobile payment applications and designs. Data was collected through interviews with water service providers, mobile network operators and service regulators, as well as a household survey in one of the study regions and the aid of World Bank and national water regulator data. Mobile water payment adoption rates were low, but there was also evidence that key barriers such as limited awareness, lack of physical proof of payment, and high transaction tariffs, could be overcome. Increased mobile water payment is found to result in considerable savings in time and money for consumers, revenue for mobile network operators, and perhaps most importantly, strengthened finances for water service providers to improve their ability to provide sustainable service

Carbon stocks and flows in forest ecosystems based on forest inventory data

Dissertation. University of Helsinki, Department of Forest Ecology. 200

Aboveground woody biomass estimation of green ash trees (Fraxinus pennsylvanica Marsh.) along Colorado's Northern Front Range in response to the invasive emerald ash borer (Agrilus plannipenis Fairmaire)

2018 Summer.Includes bibliographical references.The invasive emerald ash borer (Agrilus planipennis Fairmaire) has killed hundreds of millions of ash trees (Fraxinus spp.) in forests and urban areas across the United States. Green ash (Fraxinus pennsylvanica Marsh.) is the most widely planted street tree in the greater Denver Metro Area, comprising 15% of the urban tree population on a per-stem basis, and up to 33% of the canopy cover in some cities. EAB is currently established in Boulder, Colorado and as the infestation progresses along the Colorado Northern Front Range, municipalities will need to predict and budget for woody debris disposal from EAB-killed trees. Though existing green ash biomass predictive equations exist, most were developed for areas outside the arid West and generally represent only trees in natural forests, with full, healthy crowns. This study aimed to test whether these equations can accurately predict aboveground woody biomass of green ash trees removed as part of emerald ash borer mitigation efforts in urban areas of Colorado's Northern Front Range. Data from 42 destructively sampled ash trees removed from 11 sites as part of emerald ash borer mitigation efforts were used to evaluate the predictive capability of 12 forest-derived and five urban green ash biomass equations. The published urban equations underpredicted total sampled biomass by as much as 38% and overpredicted by as much as 47%. Forest-derived equations underpredicted by as much as 57% and overpredicted up to 52%. A local, published equation developed in the Northern Front Range overpredicted biomass by 47%. This local urban equation was developed using only open-grown trees with full, healthy crowns while the trees sampled for this study exhibited a broad spectrum of crown conditions, better representing trees that will routinely be removed as part of emerald ash borer management strategies. Sampled trees were also used to develop new local green ash biomass equations, more appropriate for use in emerald ash borer management strategies in Colorado's Northern Front Range cities. In addition, the locally-derived average specific gravity value for green ash wood was 0.57, and the locally-derived average moisture content value was 41%. These are 7.5% higher and 24% lower respectively than widely-used published values. The locally-derived values can be used to further improve the accuracy of urban forest mensuration efforts in Colorado's Northern Front Range

Role of tree structure for drought resilience: Insights from a semi-arid ecosystem

Recent increase in forest mortality events worldwide and their relationship with drought episodes highlight the importance of understanding tree resilience to a changing climate. Empirical models of forest mortality have been typically used and were focusing on carbon related variables such as growth to predict tree death. Recent efforts have shifted toward a more mechanistic modeling of mortality. Mechanistic approaches use tree traits and climate as inputs to model processes and represent carbon and water fluxes, all necessary to plant life. The advantage of mechanistic approaches is their ability to account for potential adaptation of trees to climate change, but also to physically explore the causes of vulnerability and resilience to droughts. Mechanistically, the atmospheric demand for moisture at the canopy level is communicated to the tree through stomata, creating a water gradient between the leaves and the roots, and resulting in the ascent of sap via the plant hydraulic structure. Depending on the climate (temperature, atmospheric dryness, light, precipitation), different architectures will perform differently at maintaining the gradient. For example, deep roots can access deep water in dry regions and shallow roots can access rare precipitation events whereas larger leaf area increases the atmospheric demand for moisture. In very harsh conditions such as extreme or lasting droughts, the hydraulic structure might suffer from a steep water gradient. Protection against excessive gradients can be achieved either through an investment in a stronger structure (denser wood) or through a regulation of the pulling force at the top of the canopy (closing leaf stomata). Evolution of structures and physiological strategies have resulted in fitness advantages and partially explain the diversity of species architectures across climates. More importantly, this diversity is at the core of the vulnerability and resilience of each species to increased aridity and frequency of extreme events, and therefore its mortality. This dissertation investigates the resilience to droughts of two co-occuring species in common woodlands of New Mexico, USA. This location is of specific interest because drought conditions (high temperature and/or low precipitation) have become more frequent as a result of global warming and because these ecosystems have suffered extensive mortality in the last decades. The two species, Pinus edulis and Juniper monosperma have very different physiological strategies, which allows for an extra level of vulnerability comprehension. To further test their resilience to extreme drought and possibly future climatic conditions, I studied trees that were subject to a six-year rain-reduction experiment. In the first part we develop a mechanistic model of the tree functioning that includes water and carbon fluxes and is based on their respective supply-demand balances. We use this simplified mechanistic model to study the sensitivity of mortality to hydraulic structure variations and to the physiological strategy of each species. We find that for both species death resulted from an irreversible damage of tissues transporting water. Despite P. edulis’s ability to close stomata to reduce the atmospheric demand, they died first because of their vulnerable tissues. In the second part, I specifically investigate P. edulis’s structural response to drought at the canopy level. By dissecting branch anatomy at an annual resolution, I find that during droughts this species increase relatively more leaf area (water demand) compared to transport area (water supply). I suggest that the structural adjustments that occur at the branch level do not contribute to the protection of the tissues transporting water. In the third part, I analyze the anatomy of these tissues in branches of P. edulis. I find that in response to long-lasting drought the trees built tissues more efficient at transporting water but also more vulnerable to future drought. By contrast, a short-intense drought decreases efficiency without changing vulnerability. I hence show that during lasting drought the anatomical adjustment of branch tissues increase the vulnerability of the piñons. This study shows the importance of considering climate responses of structure and physiology together to compare resilience across species. It also shows that adjustments of hydraulic elements in response to drought tend to decrease hydraulic resilience and could favor a run-away scenario. If the population of Pinus edulis - a dominant species of the Southwest US - were to decline, major shift should be expected in related ecosystems

Ecological-Hydrological Feedback in Forested Wetlands

In forested wetlands, the biotic and abiotic consequences of water level variability is not well understood. The effects of flooding on carbon and water exchanges are important knowledge gaps where progress could benefit management of natural resources and predicting of changes in surface geophysical cycles. Two specific needs are a better understanding of (1) wetland tree responses to hydrologic variations, and (2) the effects of the forest and associated tree stressors on surface energy and water fluxes. Objectives were to determine effects of flooding on evaporation rates and energy dynamics, tree water use and growth responses to river-floodplain connectivity and water level variability, and interactions between tree-level and site-level effects of flooding. Energy-balance measurements in the understory of a permanently flooded swamp showed nearly all energy was partitioned to latent heat, yielding evaporation rates of 0.9-2.0 mm day-1 among months assessed; the seasonal pattern of canopy senescence superimposed upon the pattern of heat storage in the floodwater resulted in highest evaporation rates in October and November, out of phase with above-canopy solar forcing. Evaporation from open water was similar to that from floating vegetation. Tree sapflow measurements in a floodplain forest showed increased transpiration in response to a late season flood pulse at a more flooded site, while, concurrently, transpiration declined at a drier site. The more flood tolerant species (Quercus lyrata) benefited more from flooding than did the less tolerant species (Celtis laevigata), but neither species showed flood stress. To examine radial growth responses to water levels in forested wetlands, a model (VSL-Wet) was developed and calibrated across six baldcypress chronologies. Best model fits were obtained with parameters that suggest permanently flooded trees may benefit from deeper flooding. Last, measurements across differently flooded sites showed that more flooded sites had sparser forests but with higher growth efficiency trees, demonstrating the need to consider tree-level responses separate from stand-level patterns. Consistent with common assumptions, this work shows that abiotic and biotic parameters of forested wetlands, including carbon and water fluxes, are influenced by hydrologic variations; however, consequences of hydrologic influences are not universal across scales

Sparse Predictive Modeling : A Cost-Effective Perspective

Many real life problems encountered in industry, economics or engineering are complex and difficult to model by conventional mathematical methods. Machine learning provides a wide variety of methods and tools for solving such problems by learning mathematical models from data. Methods from the field have found their way to applications such as medical diagnosis, financial forecasting, and web-search engines. The predictions made by a learned model are based on a vector of feature values describing the input to the model. However, predictions do not come for free in real world applications, since the feature values of the input have to be bought, measured or produced before the model can be used. Feature selection is a process of eliminating irrelevant and redundant features from the model. Traditionally, it has been applied for achieving interpretable and more accurate models, while the possibility of lowering prediction costs has received much less attention in the literature. In this thesis we consider novel feature selection techniques for reducing prediction costs. The contributions of this thesis are as follows. First, we propose several cost types characterizing the cost of performing prediction with a trained model. Particularly, we consider costs emerging from multitarget prediction problems as well as a number of cost types arising when the feature extraction process is structured. Second, we develop greedy regularized least-squares methods to maximize the predictive performance of the models under given budget constraints. Empirical evaluations are performed on numerous benchmark data sets as well as on a novel water quality analysis application. The results demonstrate that in settings where the considered cost types apply, the proposed methods lead to substantial cost savings compared to conventional methods

Managing climate risk in water supply systems : materials and tools designed to empower technical professionals to better understand key issues

This manual has been developed as a learning tool to be used with a companion series of practical exercises. They have been developed to provide a hands-on approach to learning key concepts in hydrology and climate science as they relate to climate risk management in water supply systems, as introduced in the text