The Greenbelt Corridor (GBC), located in a floodplain of the Elm Fork of the Trinity River, contains patches of bottomland forest and serves as part of Lake Lewisville’s flood control backwaters. This study examines forest structure and composition in relation to topographic position and forest stage in the GBC. Thirty two plots were surveyed within various stage classes, topographic positions, and USDA soil types. Trees were identified and measured for height and DBH. Density, basal area, and importance value for each of species was calculated. Soil and vegetation were analyzed using ANOVA, Principal Component Analysis, Canonical Correlation, Canonical Correspondence Analysis and Cluster Analysis. Tests confirmed that calcium carbonate and pH show significant differences with topographic positions but not with forest stage. Potassium shows no significant difference with soil texture class. Sand shows a strong negative correlation with moisture, organic matter, organic carbon and negative correlation with calcium carbonate and potassium. Silt shows positive correlation with moisture, organic matter, organic carbon, and calcium carbonate. Clay shows strong positive correlation with moisture, organic matter and organic carbon but negative correlations with pH. Swamp privet is dominant tree types in wetland forest. Sugarberry cedar elm, green ash and American elm are widely distributed species in the study area covering low ridges, flats, and slough. In total, density is significantly different in wetland low forest and late successional stage and basal area is significantly different in early successional stage and late successional stage. Other results show that clay is negatively correlated with American elm but positively correlated with cedar elm. Organic matter and moisture shows a strong positive correlation with cedar elm. Calcium carbonate is associated with green ash and swamp privet, sand is associated with sugarberry and red mulberry, silt and pH with cedar elm and bur oak.

The impact of the small stock industry on Succulent Karoo vegetation has long been acknowledged, and there is a need for researchers and managers to better understand the dynamics and processes leading to vegetation degradation and recovery. Despite the fact that these arid systems tend to hold high demographic inertia, as well as being prone to sudden and unpredictable events, there are few data-sets that are long enough (>50 yrs) to adequately distinguish 'noise' from true changes. This study examines an extensive data set of plant % cover, recorded using a rapid transect step-point technique, for the period between 1971 and 2002 throughout the Ceres Karoo. Correspondence analysis (CA) ordinations were used to show plant community changes from year to year at two sites: one that has been rested for many decades, and one that has used the Group Camp system since 1970. CA ordinations were also used to depict changes between 1992 and 2002 on three farms using different grazing systems. Results are discussed against the backdrop of the Stock Reduction Scheme initiated in the 1970's. Of the two farms examined from 1971 to 2002, the one using the group camp approach has shown an initial lag-period of about 10 years, and a subsequently steady and directional turnover of plant communities, increasing in cover of desirable species, until 2002. The rested farm showed no identifiable change. Of the farms studied between 1992 and 2002, a clear separation was found between the one using the Group Camp system and the others that are only grazed in winter. The former farm appeared to be showing the greatest amount of change. These results challenge the opinion that rested arid region veld is unlikely to recover. On the contrary, there has been a move toward more desirable veld since the 1970's in land that has not even been rested, but has had relatively reduced stock numbers. The more rested lands appear to be healthier than those that have been more frequently grazed, but they are not showing clear signs of change, supporting theories that arid region vegetation dynamics are characterised by a state and transition type of model. An important pattern to note is that changes from a degraded to a more desirable veld are characterised by a long lag period of more than 10 years, with subsequent changes occurring throughout a 20-year period. Thus the importance of allowing rangelands sufficient time to recover is highlighted, as is the importance of establishing, and continuing existing, long-term data sets.

A research report submitted in partial fulfilment of the requirements for the degree of Master of Science in Environmental Science (Coursework and Research Report) to the Faculty of Science, University of the Witwatersrand, Johannesburg, 2017. / Various studies have been conducted on the determinants of herbaceous vegetation composition and structure in savannas, but there is still no consensus on the extent of the role played by each. This is particularly so for disturbed savannas in communal rangelands. This study aimed to investigate the relative influence of rainfall, catenal position and distance from village on composition and structure of herbaceous vegetation in communal rangelands of Bushbuckridge, Mpumalanga Province in South Africa. The study used pre-existing data collected in 2012 in 56 plots located across nine villages in three rainfall zones: Low (<600 mm), Medium (600-700 mm) and High (>700 mm). In each zone, the communal rangelands of three villages were sampled in upslope and downslope positions and across three distance (disturbance) categories of, 0-599 m, 600-1799 m and >1800 m relative to nearest villages. The composition-related measures investigated were: absolute and relative abundance of species present, species richness, Simpson’s Diversity Index and relative abundance of perennial and annual grasses, as well as categories of forbs whilst the herbaceous structure measures used were distance in meters measured along transect line to perennial grass tuft and grass basal cover. Both individual and interactive effects of the rainfall zone, landscape position, and distance from village on herbaceous composition and structure were investigated using bivariate and multivariate statistics. Both grass species richness and Simpson’s Diversity Index were significantly higher in the high rainfall zone than in the low and medium rainfall zones. Perennial grasses in all rainfall zones heavily dominated the herbaceous layer, with the mean percentage perennial grass contribution being lowest in the high rainfall zone whilst the low rainfall zone had the highest. The percentage composition of annual grasses was highest in the medium rainfall zone and lowest in the low rainfall zone whilst it was intermediate in the high rainfall zone. The mean distance to perennial grass, which is an index of density of perennial grass tufts, was significantly higher in the high rainfall zone than in the low rainfall zones. The mean percentage grass basal cover was higher in low rainfall zone than in high rainfall zone. The mean species richness in the upslope and downslope catenal positions was not significantly different which was contrary to what was expected. Mean Simpson’s Diversity Index was higher on the downslope position than on the upslope catenal position. The relative abundance of perennial grasses between the upslope and downslope catenal position was not significantly different. The proportion of perennial grasses was more than that of annual grasses and other life forms sampled. Neither mean distance to perennial grass nor basal cover differed significantly between catenal positions. It was established in this study that closest plots to villages had 22% more species than the plots between medium and far plots from the villages. Near the villages (0-599 m), the species richness was found to be higher than in the medium (600-1799 m) and (>1800 m) distance categories. The mean Simpson‘s Diversity Index in all distance (disturbance) categories were found to be not significantly different. There was no significant difference in the percentage of perennial grass among the disturbance gradient categories. The perennial grasses were consistently dominant over the annual grasses along the disturbance gradients. The distance to perennial grass indicated no difference across all distance gradients. Percentage basal cover decreased with increasing distance from settlements. The composition and occurrence of grass species were associated with different environmental gradients studied. There was significant interactive effect due to a combination effect of rainfall, topographical gradients and distance gradient on the distance to perennial grass. However, the mean distance to perennial was lower at distance and rainfall combination, though was not significant. The interactive effect on basal cover due to a combination effect of rainfall, catenal position and distance gradient was found to be not significant. Overall, the herbaceous composition and structure was more strongly impacted by rainfall zone than by catenal position. The herbaceous composition and structure was affected by disturbance gradient specifically on species richness and grass basal cover only, while there was no effect on Simpson’s Diversity Index, perennial grass percentage, and distance to perennial grass as measured along transect line. It was also established that there was association of species with environmental gradients. It is recommended that in future a multi-year study on the same variables that have been studied here be undertaken in order to establish long-term trends on the effect of the gradients on herbaceous vegetation. It must be ensured also that there be representativity of disturbance gradients samples when designing sampling programme. It will also be beneficial to establish the density per village or stocking rates of different villages and the management aspects of the stock and how it is related to herbaceous composition and structure. Such studies will provide further knowledge on the extent of human induced disturbance like grazing in the communal rangelands given a set of environment gradients. / LG2018

Double-crested Cormorants are expanding their breeding range to historic wintering and migratory regions, such as Guntersville Reservoir in Alabama. This study lends insight into how cormorants breeding in a temperate ecosystem impact plants, trees, soil and bird communities as well as home range and movement of cormorants during the breeding season and whether they reside on this reservoir year-round. Results suggest that breeding cormorants have a negative impact on this ecosystem and do not move far from colony sites. Stable isotopes from cormorants and prey fish suggest that cormorants are migrating from this system after breeding, potentially to a marine source. This study corroborates past studies of negative impacts of cormorant colonies, and provides novel results of how southeastern cormorants use and move on Guntersville Reservoir. This thesis can provide biologists information on how best to control populations and mitigate impacts on this and other similar southeastern systems.

During the April 25 – 28, 2011 severe weather outbreak, 350 tornadoes were confirmed across 21 states, making the event the largest 3-day outbreak in U.S. History. Of the 350 tornadoes, 13 were of EF4 or EF5 strength. Due to complex terrain and vegetation in northeastern Alabama, northwestern Georgia, and eastern Tennessee, only four tornadoes were analyzed in this study. Abrupt changes in vegetation and the related sensible and latent heat fluxes have been shown to enhance convective activity along and near the resulting land surface discontinuities. This study analyzed heightened convective activity (analyzed by looking at cloud-to-ground lightning data) along each tornado track on days of weak synoptic forcing. Post- tornado months showed no signs of enhanced convective activity along any of the tornado tracks analyzed in this study, which could be attributed to several factors including study period, duration of intensity, tornado track length and width, and land cover.

The U.S. Environmental Protection Agency has mandated that states must include the use of biological assessments in their water quality laws to assess the biological integrity of aquatic systems. The Floristic Quality Assessment Index (FQAI), which uses wetland vegetation to assess the biological integrity of an ecosystem, has not been tested in Mississippi. The purpose of this study was to test the efficiency of the FQAI in wetlands along a gradient of human influence. Coefficients of conservatism (CC) were assigned to plant species based on their tolerance to disturbance and fidelity to habitat. A negative correlation was found between the FQAI and level of human disturbance for 53 sites surveyed in the summer of 2004. Based on the results of this study, the FQAI and the average CC could be effective tools for monitoring wetland management and restoration and for identifying areas of high conservation value in Mississippi.

Methods for woody plant herbicide screening were assayed with the goal of reducing resources and time required to conduct screenings for new products. Past studies have demonstrated reductions in required screening resources (time, amount of herbicide active ingredient, and size of seedlings) can be achieved relative to field exclosure screenings. Rapid screening methods including, greenhouse seedling screening, germinal screening, and seed screening were performed using triclopyr and 8 experimental herbicides supplied by Dow AgroSciences (DAS). Five woody species were included in screenings: black locust, loblolly pine, red maple, sweetgum, and water oak. Two groups of seedlings were used in greenhouse screening: 1-year-old (1-0) and 2-year-old (2-0). Seedling age was not calendar years, but was the number of greenhouse growing seasons seedlings experienced prior to herbicide treatment. Height and mortality responses showed that 1-0 seedlings were more susceptible to herbicide injury than 2-0 seedlings. Significant linear regression models were produced correlating 1-0 seedling pre-dormancy with post dormancy responses, shortening the length of that screening to 11 weeks from treatment to results. Species and herbicide specific models were produced correlating 2-0 seedling responses to 1-0 seedling data, germinal responses to 1-0 seedling data, and seed responses to 1-0 seedling data. 1-0 seedling pre to post dormancy predictions were more successful than other models. Results suggest that rapid screening methods have some usefulness in early stages of product development to determine herbicide activity and spectrum of efficacy to guide planning of larger scale field trials, resulting in savings of time and resources. / Master of Science

Tsunamis are among the most threatening natural hazards that can affect coastal communities and infrastructures. In order to provide useful information for coastal protection, one of my aims in this dissertation is to identify the physical metrics that better represent the damage cause by tsunamis. I approach this problem by carrying out three-dimensional-SPH numerical simulations of solitary waves which allow to track spatial-temporal evolution of physical variables during their breaking. By comparing these evolutions it is possible to visualize the complex hydrodynamic process that occurs during breaking. Results show that the highest danger lies in the environment of the shoreline. However the highest vulnerability of coastal communities and infrastructures lies onshore where they find themselves more exposed to the destructive capacity of extreme tsunami waves. In this regard, the second main goal in this dissertation is to understand how coastal vegetation reduces and modifies the onshore wave inundation. I address this problem by using shallow water equations and Serre-Green-Naghdi equations employed in a set of two-dimensional depth-integrated simulations. Analysis of results indicate the existence of a transition zone located between where runup is not affected at all and where runup suffers the maximum reduction by the vegetation. This infers the requirement of a minimum length of the vegetated barrier in order to achieve the maximum runup reduction under a specific set properties such as barrier location, barrier width, beach slope and/or wave amplitude. Overall we conclude, after intense validation work, that numerical approaches are very convenient tools to analyze difficult wave processes. However it is necessary to be aware of the limitation of each numerical approach. / Ph. D.

Warm Springs Mountain (WSM), a priority conservation area for The Nature Conservancy in Bath County, Virginia, is home to a rare montane pine barren and large tracts of uninterrupted mixed pine and deciduous forest extending east into the George Washington National Forest. Limited documentation of past disturbances and their influence on WSM forests presents challenges for land managers desiring to understand historic conditions for these ecosystems. The only formal study of vegetation dynamics on WSM noted an absence of pitch pine (Pinus rigida Mill.) regeneration and an increase in fire-intolerant species during recent decades in the pine barren community that is probably linked to fire suppression. Dendrochronological studies of disturbance history in the central and southern Appalachians have mostly focused on ridgetop and southwestern-facing slopes. This study examines long-term forest dynamics in the pine- and oak-dominated forests on southeastern slopes of Warm Springs Mountain and downslope from the higher elevation pine barren using dendrochronology and vegetation analysis. We studied trees in six 20 x 50 m plots to develop a tree ring chronology and document changes in stand composition and structure through time. We found an increase in fire-intolerant species and decline in fire-dependent pines and oaks through time. Pitch pines have not recruited since 1954 in our sites due to a lack of burning, while Acer rubrum L. has produced high numbers of seedlings in recent years. This study of vegetation dynamics over space and time will provide insights for land managers and inform fire restoration practices. / Master of Science

Yes / In 1970 a set of maps was published which summarized the results of an extensive survey of the vegetation of Ilkley Moor. This paper presents new maps showing the distribution of selected vegetation communities based on a detailed survey undertaken in 1983-84, and examines the changes which have occurred in the period 1964--1984. Comparison of the maps reveals that Calluna vulgaris and Pteridium aquilinum have increased their occupancy of the moor, whilst there has been a marked reduction in the abundance of Empetrum nigrum and Eriophorum spp. These changes indicate that the degradation of the moor which was recorded during the 1960s was reversed, at least partially, between 1964 and 1984.