Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2008.

Thesis (Ph. D.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Anthropogenic change in the Great Plains of North America within the past two centuries has facilitated extensive woody encroachment by eastern redcedar (Juniperus virginiana, hereafter redcedar). Conversion of grassland to redcedar woodland occurs rapidly as a result of the interaction between changing disturbance and land use patterns. In addition, redcedar encroachment causes compositional shifts in grassland floral and faunal assemblages, and may alter abiotic factors such that grassland restoration efforts are limited. The objectives of this study were to: 1) track vegetation and faunal assemblages in grasslands along a gradient of redcedar encroachment, 2) assess the capacity for experimental tree removal to promote re-colonization of grasslands by associated flora and fauna, and 3) examine the influence of scale on spatial relationships between small-mammal abundance and redcedar cover. During the first phase of my study, I examined herbaceous vegetation, woody vegetation, and small-mammal assemblages at grassland sites along a redcedar encroachment gradient in north-central Oklahoma. I noted hump-shaped trends in the capture rate, species diversity, and species evenness of small mammals along the redcedar encroachment gradient. In addition, higher levels of encroachment were associated with compositional shifts from grassland- to woodland-associated small mammals. Characteristics of the small-mammal assemblage along the gradient corresponded to increases in redcedar cover and the frequency of episodic management events within the past two decades. Experimental redcedar removal during the second phase of my study generally increased vegetation and faunal diversity in 2 years following treatment, and treatment sites having the highest pre-treatment levels of redcedar cover exhibited the greatest responses to tree removal. The results of my study suggested that within the time frame I examined, redcedar encroachment had altered the biotic characteristics of this system, but did not facilitate abiotic shifts capable of constraining rapid grassland recovery. Tree removal also appeared to modulate the effects of consecutive drought and flood years on small-mammal diversity during post-treatment. During the third phase of my study, I examined the strength of association between differences in percent redcedar cover and spatial abundance patterns of 4 common small-mammal species. I examined small-mammal abundance at three relatively small spatial scales (38, 154, and 616 m2) to determine how redcedar-mammal associations were stronger with increases in spatial scale. In addition, I determined whether the influence of spatial scale on redcedar-mammal associations varied along a gradient of redcedar encroachment. The strength of redcedar-mammal associations increased with spatial scale, but was strongest at sites having the lowest levels of encroachment. These results corresponded to variation in the spatial distribution of redcedar cover and compositional differences in the small-mammal species assemblage along the encroachment gradient. Studies examining the effects of woody encroachment will extend our understanding of successional processes and ensure that appropriate management is implemented in the conservation of these imperiled grassland ecosystems.

No description available.

Meadows are important within forest ecosystems because they provide diverse species habitats, facilitate water cycling, help with sediment capture, aid in carbon sequestration, and create natural fire breaks in forested regions. However, fire suppression, poor grazing practices, and climate change have accelerated the encroachment of conifers into historical meadow habitat. This has led to an extensive loss of meadow habitat within the Sierra Nevada and Cascade Mountain Ranges. Therefore, the purpose of this study is to quantify changes in percent soil moisture and groundwater levels following the removal of encroached lodgepole pine (Pinus contorta) in a historic meadow habitat near Lake Almanor, California. A before-after control-intervention (BACI) study design was used, with Marian Meadow (MM) as the control and Rock Creek Meadow (RCM) as the restored meadow. Soil moisture and groundwater level data was collected one year before (water year 2019), and three years after (water years 2020-2023) the removal of lodgepole pine from RCM in the fall of 2020. This data was then analyzed using multiple linear regression and estimated marginal means (EMMs) models. Percent soil moisture increased each year after restoration, with significant increases from pre-restoration values occurring in year 2 and year 3 post-restoration. The overall mean soil moisture content increased from 30.69% (pre-restoration) to 40.42% by the 3rd year post-restoration. Groundwater has had a much more mixed response to restoration, with the 1st year post-restoration seeing a significant decrease in groundwater availability. Years 2 and 3 showed gradual recovery of groundwater levels, although on average they were still less than pre-restoration groundwater levels. This can likely be attributed to moderate drought occurring in the 2020 and 2021 water years. Sources of variability include the 2021 Dixie Fire which burned through both meadows at different severity levels, gaps in the data due to issues with the data loggers, differences in snowmelt timing, and differences in soil attributes. Collectively, however, all these factors converge toward a wetter meadow habitat. Hopefully, the results of this research will help promote a better understanding of how meadow restoration can improve California forestland management.

Doctor of Philosophy / Biology / Walter K. Dodds / Ari M. Jumpponen / Due to agricultural practices and urbanization, tallgrass prairie ecosystems have become threatened as < 5% of its historical coverage exists today. The small remainder of praire that does exist is further threatened by the encroachment of woody plant species. Woody plant encroachment may not only alter prairie ecosystem function, but also prairie microbial communities responsible for these functional processes. Further, prairies are high disturbance ecosystems, especially prairie streams which are hydrologically harsh. They support communities that frequently undergo succession due to recurring flood and drought conditions, yet little is known about the response of microbial communities to these disturbances. In my dissertation, I first address the degree of woody vegetation expansion in riparian corridors (parallel to streams) in watersheds with variable fire frequency and grazing. I found that the rate of riparian woody expansion declines with higher fire intervals and is not affected by grazing, but even annual burns may not prevent woody plant expansion in riparian zones from occurring. Second, I quantified the effect of using restorations of riparian corridors, through removal of woody plants, on physical, chemical, and microbial community (bacteria and fungi) dynamics across stream to upslope soils. Removal restoration causes a decrease in NH₄⁺ and soil water content, and causes streams and upslope soils to become similar in fungal community richness unlike forested landscapes. Bacterial communities were minimally impacted by removals, but were highly structured among stream to upslope soils due to multiple environmental gradients (i.e., pH, NO₃⁻, soil moisture). Lastly, I examined the successional development of biofilm-associated microbial communities in a prairie stream from both a functional and structural perspective. I found that biofilm microbes exhibited strong successional trajectories, with communities developing towards net autotrophy and therefore becoming reliant upon in-stream derived carbon. Further, bacterial communities displayed spatial differences, but much stronger temporal patterns in community composition were detected. These studies highlight how woody plant encroachment may influence stream ecosystems in addition to spatiotemporal trends in microbial community assembly.

Master of Science / Department of Biology / Samantha Wisely / As human populations increase world-wide, land use and land cover are altered to support the rapid anthropogenic expansion. These landscape alterations influence patterns of zoonotic infectious disease emergence and propagation. It is therefore becoming increasingly important to study emerging and re-emerging diseases to predict and manage for future epidemics. Studies of directly-transmitted infectious diseases should consider three components of disease epidemiology: characteristics of the pathogen, ecology of the host, and habitat configuration of the underlying landscape. I studied the influence of both the host ecology of the striped skunk (Mephitis mephitis) and the alteration of the underlying landscape on the epidemiology of rabies virus in the Flint Hills of Kansas. This tall-grass prairie is experiencing woody expansion due to anthropogenic disturbance, altering the landscape on which the rabies virus emerges and spreads. We first studied the behavioral and social ecology of the striped skunk using field and genetic methods. We concluded that 1) striped skunks reached high population densities in anthropogenically disturbed habitats, 2) these individuals were not closely related, and 3) contact rates could be influenced by temperature. Using habitat-specific skunk densities from this initial study, we created spatially-explicit contact networks of skunk populations across the Upper Kansas River Watershed and simulated the emergence and spread of rabies through the system. This modeling approach revealed a threshold of forest habitat beyond which striped skunks became increasingly connected and the rabies virus reached greater extents across the landscape. Based on these findings we recommend fire regimes and land cover alterations to reduce woody encroachment across the Flint Hills and to avoid future disease epidemics in the region.

International Telemetering Conference Proceedings / October 22-25, 2001 / Riviera Hotel and Convention Center, Las Vegas, Nevada / This paper presents initial results of an investigation on bandwidth efficient waveforms for telemetry, tracking and commands (TT&C). Included in the investigation are waveforms that are currently being considered by the International Consultative Committee for Space Data Systems (CCSDS) and American Institute of Aeronautics and Astronautics (AIAA) for standards, advanced waveforms and others that have the potential to become future standards. The goal of this investigation is to recommend a suite of bandwidth efficient modulation schemes for further investigation. This suite of modulation scheme should be suitable for various TT&C applications with data rates ranging from a few hundreds Bit Per Second (bps) to a few hundreds Mega bps (Mbps). First, the philosophy of waveform evaluation is described. The description includes a list of waveform attributes leading to quantitative and qualitative figures of merit for bandwidth efficient waveforms. Then quantitative results for the two most important waveform attributes (bandwidth efficiency and bit error rate performance) are presented. These results will be used by a follow-on study to significantly reduce the number of candidate waveforms, so that all attributes can be more thoroughly evaluated.

Habitat loss, habitat fragmentation and species invasions have been recognized as three of the leading threats to biodiversity. I examined the effects of habitat loss and fragmentation on native and invasive plants in central Texas. During the last century, the density and abundance of woody plants has been increasing in the savannas of eastern Edwards Plateau. This process, known as woody plant encroachment, not only reduces the amount of open herbaceous habitat but also fragments that habitat creating smaller and more isolated patches. In three studies, I investigated the consequences of this habitat loss and fragmentation for plants which do not occur under the cover of woody plants including native grasses and forbs and the invasive Eurasian bunchgrass, Bothriochloa ischaemum (King Ranch Bluestem). In the first study, I show that woody plant encroachment reduces native herbaceous species richness (the number of species in a given area). Using a collection of historical aerial photographs, I demonstrate that current native herbaceous species richness was most strongly related to recent habitat amount, but to the degree of habitat fragmentation at least 50 years ago. In a second study, I show that the presence of B. ischaemum was negatively related to the degree of fragmentation in the surrounding landscape. Finally, I found that B. ischaemum had higher rates of germination and growth in experimental plots where the species commonly lost with woody plant encroachment were removed than in unmanipulated control plots. Together, this work suggests that woody plant encroachment is directly slowing the spread of an invasive species while indirectly facilitating its establishment. / text

Egypt witnesses an increasing population growth concomitant with limited water and agricultural land resources. The objectives of this study were to utilize remotely sensed data for the inventory of agricultural lands in the Nile Delta, monitoring spatial and temporal variations in agricultural lands and quantifying agricultural land losses due to urbanization. Inventory of agricultural lands was designed using two approaches: thresholding and linear mixture analysis. We utilized 12 images from the Landsat satellite: 4 from Multi-Spectral Scanner (1972), 4 from Thematic Mapper (1984) and 4 from Thematic Mapper (2003) covering the entire Nile Delta. In addition, a set of 480 NDVI images were obtained from the Advanced Very High Resolution Radiometer (AVHRR) sensor that cover the period 1984-2003. Landsat images were subjected to atmospheric, radiometric and geometric corrections as well as image mosaicking. Normalized Difference Vegetation Index (NDVI) was applied and thresholding for agricultural land cover revealed that the areal extent of agricultural lands was 3.68, 4.32 and 4.95 million acres (one acre = 0.96 Egyptian Feddan) in 1972, 1984 and 2003, respectively. Linear mixture analysis of the AVHRR-NDVI with the TM-NDVI images showed that agricultural lands approached 4.11 and 5.24 million acres in 1984 and 2003, respectively. Using multitemporal Principal Component Analysis (PCA) for the TM and AVHRR images proved that reclamation activities were mostly along the western margins of the Nile Delta. Spatio-temporal analysis showed that middle delta has the highest agricultural vigor compared with the margins. Agricultural land loss was estimated in some cities within the delta as well as in Greater Cairo area. We studied the land cover classification and change in Greater Cairo area based on 5 Landsat images acquired in 1972, 1984, 1990, 1998 and 2003. Agricultural lands lost 28.43% (32,236 acres) between 1972 and 2003 with an annual loss of 1040 acres. Agricultural lands on the peripheries of Cairo and its satellite towns were the most vulnerable areas. Soil salinization was another limiting factor for land reclamation. The main conclusion confirms that remote sensing is an accurate, efficient and less expensive tool for the inventory and monitoring agricultural land change in Egypt.