Browsing by Author "Resler, Lynn M."

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    Analysis of Dryland Forest Phenology using Fused Landsat and MODIS Satellite Imagery
    Walker, Jessica (Virginia Tech, 2012-09-07)
    This dissertation investigated the practicality and expediency of applying remote sensing data fusion products to the analysis of dryland vegetation phenology. The objective of the first study was to verify the quality of the output products of the spatial and temporal adaptive reflectance fusion method (STARFM) over the dryland Arizona study site. Synthetic 30 m resolution images were generated from Landsat-5 Thematic Mapper (TM) data and a range of 500 m Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance datasets and assessed via correlation analysis with temporally coincident Landsat-5 imagery. The accuracy of the results (0.61 < R2 < 0.94) justified subsequent use of STARFM data in this environment, particularly when the imagery were generated from Nadir Bi-directional Reflectance Factor (BRDF)-Adjusted Reflectance (NBAR) MODIS datasets. The primary objective of the second study was to assess whether synthetic Landsat data could contribute meaningful information to the phenological analyses of a range of dryland vegetation classes. Start-of-season (SOS) and date of peak greenness phenology metrics were calculated for each STARFM and MODIS pixel on the basis of enhanced vegetation index (EVI) and normalized difference vegetation index (NDVI) time series over a single growing season. The variability of each metric was calculated for all STARFM pixels within 500 m MODIS extents. Colorado Plateau Pinyon Juniper displayed high amounts of temporal and spatial variability that justified the use of STARFM data, while the benefit to the remaining classes depended on the specific vegetation index and phenology metric. The third study expanded the STARFM time series to five years (2005-2009) to examine the influence of site characteristics and climatic conditions on dryland ponderosa pine (Pinus ponderosa) forest phenological patterns. The results showed that elevation and slope controlled the variability of peak timing across years, with lower elevations and shallower slopes linked to higher levels of variability. During drought conditions, the number of site variables that controlled the timing and variability of vegetation peak increased.
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    An Analysis of Social Vulnerability to Natural Hazards in Nepal Using a Modified Social Vulnerability Index
    Aksha, Sanam K.; Juran, Luke; Resler, Lynn M.; Zhang, Yang (2018-11-16)
    Social vulnerability influences the ability to prepare for, respond to, and recover from disasters. The identification of vulnerable populations and factors that contribute to their vulnerability are crucial for effective disaster risk reduction. Nepal exhibits multihazard risk and has experienced socioeconomic and political upheaval in recent decades, further increasing susceptibility to hazards. However, we still know little regarding social vulnerability in Nepal. Here, we investigate social vulnerability in Nepal by adapting Social Vulnerability Index (SoVI) methods to the Nepali context. Variables such as caste, and populations who cannot speak/understand Nepali were added to reflect the essence of the Nepali context. Using principal component analysis, 39 variables were reduced to seven factors that explained 63.02% of variance in the data. Factor scores were summarized to calculate final SoVI scores. The highest levels of social vulnerability are concentrated in the central and western Mountain, western Hill, and central and eastern Tarai regions of Nepal, while the least vulnerable areas are in the central and eastern Hill regions. These findings, supplemented with smaller-scale analyses, have the potential to assist village officers, policymakers, and emergency managers in the development of more effective and geographically targeted disaster management programs.
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    Assessing and Evaluating Recreational Trails on Public Lands
    Wimpey, Jeremy Felton (Virginia Tech, 2009-07-01)
    This dissertation contains two journal articles; the first article (Chapter 2) evaluates the relative influences of use, managerial and environmental factors on trail width, from a survey of all formal trails in Acadia National Park, Maine, USA. Regression analyses of trail width data focus on increasing our understanding of the relationships among visitor use, environmental and managerial factors and trail width. In particular, regression modeling was used to evaluate the relative importance of factors that influence trail width along hiking trails. ANOVA analyses demonstrate differences in trail width based on trail surface type, and the presence or absence of trail borders. A novel approach of comparing intended widths to actual widths enabled us to look specifically at the avoidable and undesirable impacts associated with having a trail that is wider than intended. Informal trails (visitor created) represent a threat to the natural resources of protected natural areas around the globe. These trails can remove vegetation, displace wildlife, alter hydrology, alter habitat, spread invasive species, and fragment landscapes. The second article (Chapter 3) examines informal and formal trails within Great Falls Park, VA, a sub-unit of the George Washington Memorial Parkway, managed by the U.S. National Park Service. This study sought to answer three specific questions: 1) Are the physical characteristics and topographic alignments of informal trails significantly different from formal trails, 2) Can landscape fragmentation metrics be used to summarize the relative impacts of formal and informal trail networks on a protected natural area?, and 3) What can we learn from examining the spatial distribution of the informal trails within protected natural areas? Statistical comparisons between formal and informal trails in this park indicate that informal trails have less sustainable topographic alignments than their formal counterparts. Spatial summaries of the lineal and areal extent and fragmentation associated with the trail networks by park management zones compare park management goals to the assessed attributes. Hotspot analyses highlight areas of high trail density within the park and findings provide insights regarding potential causes for development of dense informal trail networks.
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    Assessing annual urban change and its impacts on evapotranspiration
    Wan, Heng (Virginia Tech, 2020-06-19)
    Land Use Land Cover Change (LULCC) is a major component of global environmental change, which could result in huge impacts on biodiversity, water yield and quality, climate, soil condition, food security and human welfare. Of all the LULCC types, urbanization is considered to be the most impactful one. Monitoring past and current urbanization processes could provide valuable information for ecosystem services evaluation and policy-making. The National Land Cover Database (NLCD) provides land use land cover data covering the entire United States, and it is widely used as land use land cover data input in numerous environmental models. One major drawback of NLCD is that it is updated every five years, which makes it unsatisfactory for some models requiring land use land cover data with a higher temporal resolution. This dissertation integrated a rich time series of Landsat imagery and NLCD to achieve annual urban change mapping in the Washington D.C. metropolitan area by using time series data change point detection methods. Three different time series change point detection methods were tested and compared to find out the optimal one. One major limitation of using the above time series change point detection method for annual urban mapping is that it relies heavily on NLCD, thus the method is not applicable to near-real time monitoring of urban change. To achieve the near real-time urban change identification, this research applied machine learning-based classification models, including random forest and Artificial Neural Networks (ANN), to automatically detect urban changes by using a rich time series of Landsat imagery as inputs. Urban growth could result in a higher probability of flooding by reducing infiltration and evapotranspiration (ET). ET plays an important role in stormwater mitigation and flood reduction, thus assessing the changes of ET under different urban growth scenarios could yield valuable information for urban planners and policy makers. In this study, spatial-explicit annual ET data at 30-m resolution was generated for Virginia Beach by integrating daily ET data derived from METRIC model and Landsat imagery. Annual ET rates across different major land cover types were compared, and the results indicated that converting forests to urban could result in a huge deduction in ET, thus increasing flood probability. Furthermore, we developed statistical models to explain spatial ET variation using high resolution (1m) land cover data. The results showed that annual ET will increase with the increase of the canopy cover, and it would decrease with the increase of impervious cover and water table depth.
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    Assessing the Impacts of Balsam Woolly Adelgid (Adelges Piceae Ratz.) and Anthropogenic Disturbance on the Stand Structure and Mortality of Fraser Fir (Abies Fraseri (Pursh) Poir.) in the Black Mountains, North Carolina
    McManamay, Rachel Harris (Virginia Tech, 2009-05-06)
    Over the past several decades, naturally occurring populations of Fraser fir (Abies fraseri) in the Black Mountains of North Carolina have been heavily impacted by both direct and indirect anthropogenic disturbances, including logging and logging- associated fires, and high mortality rates due to the introduction of the exotic insect, balsam woolly adelgid (BWA) (Adelges piceae). The decline in Fraser fir is particularly concern because it serves as a foundation species within the spruce-fir forests of the Southern Appalachian Mountains. Our objectives for this research were to 1) use current stand structure to infer whether Fraser fir trees are experiencing a cycle of regeneration-mortality that will lead to eventual decline of the population, 2) determine what role, if any, the site-specific geographic variables of slope, elevation, aspect, and land use history have on stand structure, mortality, and BWA infestation level, and 3) analyze repeat aerial photography to examine broad trends of spruce-fir forest cover change caused by anthropogenic disturbance and the BWA. In order to understand stand structure, mortality, and infestation levels, we conducted detailed field surveys of Fraser fir trees throughout the Black Mountains using 44, fixed-radius circular sampling plots. These plots were placed throughout a series of aspects, elevations, and disturbance types in order to understand geographic variability among these variables. An analysis of 4 repeat aerial photographs and corroborating ground photographs revealed broad spatio-temporal trends of spruce-fir regeneration and mortality from 1954 to 2006. Our results indicate that Fraser fir stands at higher elevations are currently in a state of recovery; whereas stands at lower elevations appear to be more susceptible to BWA-induced mortality. Changes in forest cover area from 1954 to 2006 were influenced greatly by direct and indirect anthropogenic disturbance. Our results call attention to the significant impact that direct and indirect anthropogenic disturbance has had on Fraser fir stand structure, but also provide evidence for the ability of an imperiled ecosystem to recover from high rates of insect caused mortality.
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    Assessing vulnerability and multi-hazard risk in the Nepal Himalaya
    Aksha, Sanam Kumar (Virginia Tech, 2018-11-15)
    Communities around the world are encountering unprecedented rates of change due to population growth, land use change, development, and increased social vulnerability to natural hazards. Understanding how physical processes and human vulnerability to natural hazards interact is a primary objective of researchers, policy makers, and disaster risk reduction practitioners in order to combat increases in natural hazard frequency and intensity. Nepal, a landlocked mountainous country spanning the central Himalayan region, has about 28 million inhabitants in 147,181 square kilometers. Nepal is exposed to a multitude of natural hazards, requiring individuals and communities to interact with and make decisions on risk acceptability on a day-to-day basis. In many cases, Nepal's geographic location, available resources (human, economic, and capital), and limited government capacity coalesce to turn natural hazards into disasters, resulting damaged infrastructure, economic disruptions, and death. This dissertation evaluates the geographic distribution of natural hazard mortality, quantifies social vulnerability to natural hazards, and models multi-hazard risk in the data deficient environment of Nepal. Chapter 1 conceptualizes relevant terms such as natural hazards, disaster, vulnerability, and risk before discussing the challenges associated with multi-hazard risk assessment in Nepal. Chapter 2 evaluates the spatial and temporal distribution of natural hazard mortalities at the village level using a publicly available disaster database. Results reveal that landslides were the deadliest disasters between 1971-2011. Chapter 3 identifies major social factors and processes that contribute to the vulnerability of individuals and communities using census data. Adapting the Social Vulnerability Index (SoVI) method developed for the US context, this chapter investigates the spatial distribution and clustering of various social vulnerabilities across the country. 'Renter and Occupation', 'Poverty and Poor Infrastructure', and 'Favorable Social Conditions' are three major components that influence social vulnerability in Nepal. Results indicate an interesting regional difference: the eastern and central Tarai are more vulnerable than western Tarai, whereas the eastern Hills and Mountains are less vulnerable than western Hills and Mountains. In Chapter 4, a model of risk from multiple natural hazards in the city of Dharan, Nepal, is presented. Freely available geospatial data in combination with socio-economic data collected from local government and secondary sources are used. Multi-hazard risk assessment is data intensive and requires considerable financial and human resources, which are lacking in Nepal. Results show that geospatial modeling techniques can be used to fill the gap and assist local officers and emergency managers in risk management. Cumulatively, this work offers new insights on natural hazards, vulnerability, risk, the use of geospatial technologies, and their inter-relationships. Research findings advance scholarly understandings of multi-hazard risk in general and particularly in the Nepali context. Additionally, this work is valuable to disaster practitioners who seek to implement more effective disaster risk reduction programs and policies.
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    Biophysical and Climate Analysis of the Mountain Pine Beetle (Dendroctonus ponderosae) Infestations in the Crown of the Continent, 1962 to 2014
    Garza, Mario Nicholas (Virginia Tech, 2017-02-22)
    Mountain pine beetles (Dendroctonus ponderosae) are native insects that have decimated millions of hectares of mature pine (Pinaceae) forests in western North America. The purpose of this study is to investigate biophysical and climatic correlates of Mountain Pine Beetle (MPB) insect outbreaks in the Crown of the Continent Ecosystem (CCE) from 1962 to 2014 using Aerial Detection Survey (ADS) and climate data. Specific objectives were: 1) to develop statistical models to determine how selected biophysical correlates (slope, aspect, elevation, and latitude) and 2) to understand how local and global climate variables relate to the extent of the MPB infestations in the CCE, and 3) to contextualize the results of the models with historical climate data. Overall, the major findings of this study are: 1) despite its limitations, the ADS data seems suitable for analysis of beetle damage with respect to climate and topographic factors, on a regional scale, 2) there appears to be a link between local biophysical factors and winter precipitation and TPA within the CCE, and 3) a combination of a negative-phase PDO and La Niña is important in forecasting a decline in MPB spread, during a given year. This study is the first, to our knowledge, to explore spatio-temporal patterns of MPB outbreaks using biophysical factors, and both local and global climate variables, over a fifty-year timespan in the CCE. In the future, additional geospatial analyses may enable a landscape assessment of factors contributing to variability of MPB infestation and damage as this insect continues to spread.
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    Biotic and Abiotic Factors of Picea rubens (Red Spruce) Seedling Regeneration in Disturbed Heathland Barrens of the Central Appalachians
    White, Helen M. (Virginia Tech, 2019-06-20)
    During the late 19th and early 20th centuries, extensive logging reduced the forests of red spruce (Picea rubens) by nearly 99% through portions of West Virginia. In the wake of this disturbance, red spruce has begun regenerating on the ridge and mountaintop areas of Canaan Valley, West Virginia, where heath and grassland communities have both persisted in natural barrens and expanded into formerly forested areas. To understand abiotic and biotic conditions guiding the advance of the red spruce stand, I conducted a broad-scale assessment of thirty-one demographics plots spread across two sites (north Cabin Mountain and Bear Rocks/Dolly Sods), and a more focused assessment of red spruce species associations within thirty-two paired plots at Cabin Mountain. At the 15m x 15m demographics plots, I conducted a count of all P. rubens present, measured specimen height, DBH or diameter at ground level (DGL) for specimens < 1.37m tall, and assessed the relative percent cover of rock, shrub, herbaceous, and tree cover. These data, along with additional abiotic components derived from a DEM, formed the basis of my assessment using a generalized linear mixed model (GLMM) to identify the most significant biophysical variables related to P. rubens count. In the paired plots, I used the relative interactions index (RII) to compare the total cover of each present non-graminoid vascular species and the grouped cover types Rock, Graminoid, Lichen, Litter, and Moss in one 45cm-radius plot with a < 1.37m P. rubens specimen, and one paired 45cm-radius plot in open heath. The significance of differences in total cover were assessed with the Wilcoxon test and Tukey HSD. The GLMM identified percent rock cover and distance from the nearest P. rubens stand to be important correlates of P. rubens count at the demographic plots. Graminoid cover was found to be higher in P. rubens 45cm-radius plots than in paired heath plots, and Vaccinium angustifolium cover was found to be concentrated in 45cm radius plots beyond the first 15cm from the P. rubens stem. These findings reinforce a complex interplay between both the biotic and abiotic characteristics of a microsite and the successful germination and regeneration of a red spruce seedling in the heathland.
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    The Cartographic Representation of Language: Understanding language map construction and visualizing language diversity
    Luebbering, Candice Rae (Virginia Tech, 2011-03-23)
    Language maps provide illustrations of linguistic and cultural diversity and distribution, appearing in outlets ranging from textbooks and news articles to websites and wall maps. They are valuable visual aids that accompany discussions of our cultural climate. Despite the prevalent use of language maps as educational tools, little recent research addresses the difficult task of map construction for this fluid cultural characteristic. The display and analysis capabilities of current geographic information systems (GIS) provide a new opportunity for revisiting and challenging the issues of language mapping. In an effort to renew language mapping research and explore the potential of GIS, this dissertation is composed of three studies that collectively present a progressive work on language mapping. The first study summarizes the language mapping literature, addressing the difficulties and limitations of assigning language to space before describing contemporary language mapping projects as well as future research possibilities with current technology. In an effort to identify common language mapping practices, the second study is a map survey documenting the cartographic characteristics of existing language maps. The survey not only consistently categorizes language map symbology, it also captures unique strategies observed for handling locations with linguistic plurality as well as representing language data uncertainty. A new typology of language map symbology is compiled based on the map survey results. Finally, the third study specifically addresses two gaps in the language mapping literature: the issue of visualizing linguistic diversity and the scarcity of GIS applications in language mapping research. The study uses census data for the Washington, D.C. Metropolitan Statistical Area to explore visualization possibilities for representing the linguistic diversity. After recreating mapping strategies already in use for showing linguistic diversity, the study applies an existing statistic (a linguistic diversity index) as a new mapping variable to generate a new visualization type: a linguistic diversity surface. The overall goal of this dissertation is to provide the impetus for continued language mapping research and contribute to the understanding and creation of language maps in education, research, politics, and other venues.
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    Chagas Disease in the United States: the Emerging Threat and the Role Climate and Awareness Play in Its Spread
    Lambert, Rebecca Click (Virginia Tech, 2007-03-27)
    This study evaluates the roles of temperature variability and disease awareness in the emergence of Chagas disease (American trypanosomiasis). Chagas disease is endemic in Latin America and primarily spreads to humans directly via the triatomine vector. Hosts for most triatomine species are mainly rodents and occasionally dogs. The disease itself is caused by a parasitic protozoan, Trypanosoma cruzi (T. cruzi) which is found in the triatomine's feces and is often spread while the triatomine is consuming a blood meal. T. cruzi from feces enters the body via an abrasion on the skin, the mucous membranes, conjunctivae, or through consumption. To determine the risk of Chagas disease transmission one must define qualities that make the triatomine an effective disease vector as well as investigate the level of disease awareness among physicians and the population within the vector's range. This thesis maps triatomine species within the U.S. that harbor T. cruzi naturally and that exhibit qualities of domesticity. These qualities are defined by whether the species bites humans and dogs as well as reports that the species has been found in the domestic setting. Ranges illustrating temperature thresholds for increased triatomine activity for 2000 and 2030 are also depicted. Additionally, outcomes of a physician survey are presented to gauge the status of Chagas disease awareness in areas at higher risk for disease transmission. Results reveal limited consideration of Chagas disease in physician diagnosis despite the higher risk range which extends through the southern U.S. and is predicted to expand significantly by 2030.
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    Characteristics of Red Spruce (Picea rubens Sarg.) Encroachment at Two Central Appalachian Heathland Study Areas
    White, Helen M.; Resler, Lynn M.; Carroll, David F. (IGI Global, 2021)
    During the late 19th and early 20th centuries, intensive land use nearly eliminated red spruce (Picea rubens Sarg.) throughout portions of West Virginia (WV). Red spruce has been slow to regenerate on mountaintop heathland barrens surrounding Canaan Valley, West Virginia (WV), and little is known about the nature of encroachment. Using field surveys, geospatial data, and statistical modelling, the objectives were to 1) characterize and compare red spruce encroachment at two upland heath study areas in West Virginia (Bear Rocks and Cabin Mountain), 2) characterize percent cover of major ground cover types associated with red spruce regeneration sites in order to elucidate biotic interactions, and 3) model the biophysical correlates of red spruce encroachment using geospatial data and statistical modelling. Red spruce count was similar at both study areas, but there were substantially more seedlings and saplings at Cabin Mountain. Modelling revealed a positive relationship between red spruce count and rock cover and a negative relationship between red spruce and stand distance.
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    Community Structure, Biodiversity, and Ecosystem Services in Treeline Whitebark Pine Communities: Potential Impacts from a Non-Native Pathogen
    Tomback, Diana F.; Resler, Lynn M.; Keane, Robert E.; Pansing, Elizabeth R.; Andrade, Andrew J.; Wagner, Aaron C. (MDPI, 2016-01-19)
    Whitebark pine (Pinus albicaulis) has the largest and most northerly distribution of any white pine (Subgenus Strobus) in North America, encompassing 18° latitude and 21° longitude in western mountains. Within this broad range, however, whitebark pine occurs within a narrow elevational zone, including upper subalpine and treeline forests, and functions generally as an important keystone and foundation species. In the Rocky Mountains, whitebark pine facilitates the development of krummholz conifer communities in the alpine-treeline ecotone (ATE), and thus potentially provides capacity for critical ecosystem services such as snow retention and soil stabilization. The invasive, exotic pathogen Cronartium ribicola, which causes white pine blister rust, now occurs nearly rangewide in whitebark pine communities, to their northern limits. Here, we synthesize data from 10 studies to document geographic variation in structure, conifer species, and understory plants in whitebark pine treeline communities, and examine the potential role of these communities in snow retention and regulating downstream flows. Whitebark pine mortality is predicted to alter treeline community composition, structure, and function. Whitebark pine losses in the ATE may also alter response to climate warming. Efforts to restore whitebark pine have thus far been limited to subalpine communities, particularly through planting seedlings with potential blister rust resistance. We discuss whether restoration strategies might be appropriate for treeline communities.
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    Designing Virtual Pathways for Exploring Glacial Landscapes of Glacier National Park, Montana, USA for Physical Geography Education
    Gielstra, Dianna; Moorman, Lynn; Kelly, Jacquelyn; Schulze, Uwe; Resler, Lynn M.; Cerveny, Niccole V.; Gielstra, Johan; Bryant, Ami; Ramsey, Scott; Butler, David R. (MDPI, 2024-03-05)
    Virtual field trips in physical geography transcend our human limitations regarding distance and accessibility, allowing students to experience exemplars of physical environments. These experiences can be critical for students to connect to the physical world beyond traditional classroom formats of communicating themes and features in physical geography. To maximize the learning potential of these experiences, designers must engage in a translational process to take resources and content from the physical world and migrate it to an online, virtual format. However, these virtual learning experiences need to account for how learners learn; and should draw heavily on the foundations of educational research and field sciences, while highlighting the awe and beauty of the natural landscape itself. Crafting these spatial stories of the natural world with learning elements requires careful and intentional design to maximize the perception of physical features, patterns, and processes at the landscape scale. To help field-trip developers comprehend the workflows used to create perceptible, rich environments that spur students’ learning, we propose a development process (TECCUPD) as a guide to navigate the intersection of education and science, using an example of geodiversity and alpine glacial landscapes found in Glacier National Park, Montana.
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    Detecting and Modeling Landfast Ice in the Alaskan Bering Sea
    Jensen, David Aaron (Virginia Tech, 2020-06-19)
    Seasonal sea ice – ice which freezes in late fall and melts completely the following summer – is a central feature in the ecology, geomorphology, and climatology of the Bering Sea. In this region's coastal zones, sea ice becomes locked into a stationary position against the coastlines to become landfast ice, which influences bioegophysical processes in the region, as well as exchanges of energy and matter among land, ocean, and atmosphere. It provides a platform for human mobility and subsistence activities, habitat for certain marine mammals, regulates terregenous nutrient cycling into ocean environments, and modulates the effect of erosive wind/wave action against coastlines. However, a thorough understanding of how this stationary ice, known as landfast ice, affects biogeophysical processes in the Bering Sea is limited by a lack of data on its areal coverage and seasonal duration. This dissertation establishes a baseline set of observations of landfast ice conditions in the Bering Sea through the creation and analysis of continuous spatial datasets. Chapter 1 focuses on the landfast ice annual cycle in the Eastern Bering Sea, which spans from the western tip of the Seward Peninsula to the southernmost point on the Yukon-Kuskokwim River Deltas. Chapter 1 results in the creation of landfast ice spatial data in these areas ranging from 1996 – 2008. Results show the spatial distribution and seasonal duration of landfast ice vary regionally within our study area, does not generally reach water depths associated with stabilization of the landfast ice cover in other regions of the Arctic, and is shortening in seasonal duration by approximately 9 days. Chapter 2 focuses on the landfast ice annual cycle on St. Lawrence Island, an Alaska Island located in the northern Bering Sea. Chapter 2 results in the creation of landfast ice spatial data in these areas ranging from 1996 – 2019. Results show the spatial distribution of landfast ice to vary regionally on the island, based on the coastlines orientation towards prevailing winds that transport pack ice through the Bering Strait. We also observed a sharp decline in landfast ice cover from 2017-2019, which coincides with record-breaking declines in sea ice coverage for the entire Bearing Sea. We also found coastal morphology and orientation have limited explanatory power when modeling landfast ice widths – the distance between the landfast ice edge and coastline – suggesting the consideration of meteorological variables is needed to improve models. Chapter 3 uses the landfast ice data from Chapter 2 to create an explanatory logistic regression model of landfast ice cover on St. Lawrence Island, using a combination of geographic and meteorological predictor variables. Using these variables, the model was able to predict the location of landfast ice cover with 80-90% accuracy, depending on the region of St. Lawrence Island. The model outputs resulted in very low commission error, with high omission error, which may be improved in future studies with the additional predictor variables. Cumulatively, this dissertation is the most comprehensive analysis of landfast ice cover to date on Alaskan Bering Sea coastlines. Research findings advance scholarly understandings of coastal ice conditions in the Bering Sea, and the geographic as wellas meteorological factors that enable their presence.
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    Developing a Topographic Model to Predict the Northern Hardwood Forest Type within Carolina Northern Flying Squirrel (Glaucomys sabrinus coloratus) Recovery Areas of the Southern Appalachians
    Evans, Andrew M.; Odom, Richard H.; Resler, Lynn M.; Ford, W. Mark; Prisley, Stephen P. (Hindawi, 2014-08-28)
    The northern hardwood forest type is an important habitat component for the endangered Carolina northern flying squirrel (CNFS; Glaucomys sabrinus coloratus) for den sites and corridor habitats between boreo-montane conifer patches foraging areas. Our study related terrain data to presence of northern hardwood forest type in the recovery areas of CNFS in the southern Appalachian Mountains of western North Carolina, eastern Tennessee, and southwestern Virginia. We recorded overstory species composition and terrain variables at 338 points, to construct a robust, spatially predictive model. Terrain variables analyzed included elevation, aspect, slope gradient, site curvature, and topographic exposure. We used an information-theoretic approach to assess seven models based on associations noted in existing literature as well as an inclusive global model. Our results indicate that, on a regional scale, elevation, aspect, and topographic exposure index (TEI) are significant predictors of the presence of the northern hardwood forest type in the southern Appalachians. Our elevation + TEI model was the best approximating model (the lowest AICc score) for predicting northern hardwood forest type correctly classifying approximately 78% of our sample points. We then used these data to create region-wide predictive maps of the distribution of the northern hardwood forest type within CNFS recovery areas.
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    Ecotone response to climatic variability depends on stress gradient interactions
    Malanson, George P.; Resler, Lynn M.; Tomback, Diana F. (2017-01-19)
    Background Variability added to directional climate change could have consequences for ecotone community responses, or positive and negative variations could balance. The response will depend on interactions among individuals along environmental gradients, further affected by stress gradient effects. Methods Two instantiations of the stress gradient hypothesis, simple stress and a size-mediated model, are represented in a spatially explicit agent based simulation of an ecotone derived from observations of Abies lasiocarpa, Picea engelmannii, and Pinus albicaulis in the northern Rocky Mountains. The simple model has two hierarchically competitive species on a single environmental gradient. The environment undergoes progressive climate change and increases in variability. Because the size model includes system memory, it is expected to buffer the effects of extreme events. Results The interactions included in both models of the stress gradient hypothesis similarly reduce the effects of increasing climatic variability. With climate amelioration, the spatial pattern at the ecotone shows an advance of both species into what had been a higher stress area, but with less density when variation increases. In the size-mediated model the competitive species advances farther along the stress gradient at the expense of the second species. The memory embedded in the size-mediated model does not appear to buffer extreme events because the interactions between the two species within their shifting ecotone determine the outcomes. Conclusions Ecotone responses are determined by the differences in slopes of the species response to the environment near their point of intersection and further changed by whether neighbor interactions are competitive. Interactions are more diverse and more interwoven than previously conceived, and their quantification will be necessary to move beyond simplistic species distribution models.
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    Estimating Impervious Surface Cover in Flathead County, Montana
    Skeen, James Andrew (Virginia Tech, 2017-06-22)
    Northwest Montana has seen a significant increase in its population in the past twenty years. The increase in population, and associated development, is thought to be associated with "amenity migration"; people moving to an area to exploit the recreational opportunities that are unique to that area. Impervious surfaces can serve as a suitable proxy for tracking the spread of various anthropogenic influences on an ecosystem; it impacts groundwater recharge, increases overall surface runoff as well as pollution and sediment load, and fragments landscapes. In this study, an Artificial Neural Network model was developed to update NLCD impervious surface product (2011) in Flathead County, Montana. Four Landsat 8 images from 2015 and 2016 were used to characterize imperviousness. This multi-temporal analytical method was designed to reduce the spectral confusion between impervious surface and soil/agricultural lands. We compared the neural network-predicted impervious surface maps with 2011 NLCD. When all four neural network prediction images agreed with a change of 50% or more from the 2011 NLCD map, the average of those four images replaced that pixel from the 2011 imperviousness map. Compared to the ground truth, the method used showed significant promise, with an R2 of 0.73 and RMSE of 0.123. A comparison of the artificial neural network model results and the 2011 NLCD data showed a continuation of urbanization trends; the urban cores of towns in the study remain static while the majority of impervious surface development takes place along the perimeter of urban areas.
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    The evaluation of land consolidation policy in improving agricultural productivity in China
    Jin, Xiaobin; Shao, Yang; Zhang, Zhihong; Resler, Lynn M.; Campbell, James B. Jr.; Chen, Guo; Zhou, Yinkang (Springer Nature, 2017-06-05)
    China is presently undergoing rapid economic development and unprecedented urbanization. Concerns over food security have prompted the Chinese government to implement large-scale land consolidation projects. However, no formal evaluation has been conducted on such projects. Thus, effectiveness of land consolidation policy remains uncertain. We obtained detailed geo-spatial information for 5328 land consolidation projects implemented between 2006 and 2010, and used time-series MODIS NDVI (2006-2016) data to assess effectiveness of China's land consolidation policy in improving agricultural productivity. Our results show that the overall effectiveness of land consolidation in improving agricultural productivity is low, which lies in contrast to optimistic estimates based on regional statistical analysis and theoretical approaches. For projects (n = 560) implemented in 2006, about 29.5% showed significant (p < 0.05) increasing trends of MODIS NDVI after implementation of land consolidation. For 2007-2010, lower percentages (e.g., 25.9% in 2007 and 13.5% in 2010) of projects showed significant increasing trends. Furthermore, we found effectiveness of land consolidation projects displayed clear regional differences and driving factors are inconsistent with policy design. We anticipate our research to be a starting point for a more comprehensive evaluation involving longer time-series and higher spatial resolution data.
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    Fire History of an Acidic Barrens Complex: A Methods Assessment of Fire Return Intervals
    Lawrence, Nathaniel Jo-Walker (Virginia Tech, 2019-03-22)
    Fire-scarred trees provide an important source of data and direct evidence for understanding past fires and vegetation dynamics. Although dendrochronological fire scar records provide fine-scale temporal and spatial resolution, limitations exist in the development, analysis, and interpretation of these fire history datasets. In order to assess these limitations, we applied a systematic gridded sampling scheme to a 4-hectare study area located in the Ridge and Valley Province of northeastern Pennsylvania. We mapped and described a total of 155 fire-scarred trees within a 50-meter resolution grid, noting the species, health status, and basal scar orientation for each tree. Additionally, we cut a full or partial cross section from 58 fire-scarred pitch pine (Pinus rigida) for the purpose of assessing multiple "filtering" techniques and for the development of a fire interval simulation model. The simulation model randomly selected trees from each grid cell to estimate fire return intervals at multiple spatial scales. Our results indicate that fire return intervals are dependent upon the definition of "recorder" years and influenced by various filtering methods, including minimum number and minimum percentage of trees scarred. For example, the number and length of fire intervals was greater when years prior to the initial scar were considered "non-recording" vs. "recording" and when a percentage scarred filter was applied. The simulation model provides an additional range of fire interval estimations that can be used by land managers to guide forest restoration and fire management objectives.
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    A geospatial analysis of multi-hazard risk in Dharan, Nepal
    Aksha, Sanam K.; Resler, Lynn M.; Juran, Luke; Carstensen, Laurence W. (2020-01-01)
    Natural hazard risk assessment generally focuses on a single hazard type, such as earthquakes, landslides, or floods. This emphasis tends to consider physical processes in isolation. However, most locations are simultaneously at risk to multiple, interacting hazards that generate cascading effects or synergies. Although scholars have proposed a multi-hazard risk framework based on probabilities, the quality and quantity of data required for such an approach are often unavailable in developing countries. Using geospatial and socioeconomic data, this study represents a first step in assessing multi-hazard risk in the city of Dharan, Nepal. Three hazards-landslides, floods, and earthquakes-were considered for an integrated hazard assessment using statistical methods and the Analytic Hierarchy Process (AHP). We employed a Social Vulnerability Index (SoVI) to create a vulnerability map of the study area, which was then combined with a multi-hazard hazard map to produce a total risk map. Our results indicate that eastern Dharan along the Seuti River and southwestern Dharan on the left bank of the Sardu River are at high risk to multiple hazards. Central Dharan and the hills in the western portion of the city are categorized as low risk areas. Data limitations, such as availability and spatial resolution, did not allow for dynamic modeling; however, our results identified the spatial extent of low to high risk areas, which can inform future disaster planning. For example, the methodology and results of this study could assist in the development of disaster risk reduction programs and policies.