No description available.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 9, 2010). Includes bibliographical references.

No description available.

This study compares the soils, floristic composition, phytosociological structure and history of seven Brazilian savannas in the Amazon basin: those at Alter do Chao, Amapa, Roraima and SE Humaita are islands in rain forest; and those at Chapada dos Parecis, Redencao, and Carolina are on the periphery (northern border) of the central Brazilian savannas (the so-called 'cerrado'). A total of 26 transects were sampled by the PCQ method (for trees with dbh greater than or equal to 5 cm) and additional tree species were recorded by 'wide patrolling'. A total of 101 species were recorded from the transects and another 43 species were recorded by 'wide patrolling'. Byrsonima crassifolia, B. coccolobifolia, Curatella americana, Salvertia convallariodora and Plathymenia reticulata occurred in most or all sites, but no species occurred in all transects. The number of species in the isolated savannas decreased with the distance from the central Brazilian core savanna area. Both cluster analysis (based on the S0rensen Similarity Index) and ordination (DCA), showed that the disjunct and non-isolated peripheral areas were in floristically distinct groups. Five surface soil samples (0 - 10 cm) were collected from each of the 26 transects. Two soil cores (up to 4 m depth), one located in the savanna and the other from the nearest forest present, were taken from each study site for carbon isotope analysis. All the sites had acidic soils (pH 4.5 - 5.2) and a wide range of concentrations of aluminium (0.12 - 1.49 meq 100g-1); most of the other soil properties varied significantly within study sites. An ordination (PCA) distinguished the soils from Amapa, Alter do Chao, Redencao and Roraima, but did not distinguish the disjunct sites from non-isolated peripheral ones. The soil delta 13C values of all the disjunct savannas indicated a vegetation change in the past from C3 to C4 plants, showing that forest (or at least a vegetation with few C4 plants) formely covered these sites. 14C dating indicated that the disjunct savannas are of relatively recent origin, e.g. Humaita was dated at about 2,000 years BP, and hence that they are not remnants of a more widespread Pleistocene savanna in the Amazon.

A research report submitted to the Faculty of Science in partial fulfilment of the requirements for the degree of Master of Science. Johannesburg, 31 August 2012. / Unable to load abstract.

The human-induced changes of the Earth's land surfaces have been unprecedented, with outcomes often indicating degradation and loss of environmental quality. Mato Grosso State in Brazil, location of the study area, underwent extensive land-use and land-cover changes in recent decades with the rates, patterns and consequences poorly documented until now. In this context, the aim of the present research is to propose a multidisciplinary approach for quantifying historical land-use and environmental changes in the southeast part of this State, where the Cerrado biome (Brazilian savannas) has been intensively converted into agricultural lands. The methodology includes three parts: remote sensing change detection, land vulnerability mapping, and identification of key environmental indicators. Land-use/cover information was extracted from a temporal remote sensing dataset using an object-oriented classification approach, and the changes quantified employing a post-classification method. In addition, the study area was assessed for its vulnerabilities, focusing mainly on erosion risks, wetlands, and areas with limited or no suitability for crops. Finally, key environmental indicators were identified from the preceding steps and analyzed within the Organisation for Economic Co-operation and Development (OECD) Pressure-State-Response (PSR) framework. The results provided an improved mapping of the Cerrados natural vegetation conversion into crops and pastures, and indicate that the Cerrado vegetation was intensively converted and also became more fragmented in the time frame studied. Between 1985 and 2005 the area lost approximately 6491 km 2 of Cerrados (42 %). Modeling based on the Universal Soil Loss Equation indicated significant increase in erosion risk from 1985 to 2005 mainly related to the increase in crop areas and the crops' encroachment into more fragile lands.The identification of environmental indicators rendered complex environmental information more generally accessible by structuring it within the PSR framework.The indicators captured key information about land-use and environmental changes in the area, showing that agricultural expansion is the major human activity exerting pressure on natural resources at a landscape scale, and that the pattern of change included high rates of crop expansion and the use of fragile environments such as wetlands and sandy erodable soils.

Tropical savannas and woodlands are the dominant vegetation cover in Southern Africa covering 4 million km2. Their large spatial extent means they are potentially a globally important store of biomass carbon with implications for global climate, and an area of high biodiversity value. They provide natural resources such as food, fuel and timber that help sustain the livelihoods of over 100 million people. The ability of these savanna woodlands to maintain these important ecological functions is under question due to increases in land use and land cover change. This thesis addresses a set of science questions aimed at (i) improving our knowledge of the amount of carbon and biodiversity stored in these ecosystems and how they co-vary, (ii) how these variables are spatially distributed at landscape scales and the factors which underlie these patterns, and (iii) how they respond over time to human disturbance. In Chapter 2 I examine how patterns in aboveground woody carbon storage (AGC) are linked to differences in forest structure, tree species diversity and floristic composition across a recently established network of 25 permanent sample plots in south-east Tanzania. Large stems were a significant contributor to plot-level AGC stocks with the top 3% of individuals (>40cm) in terms of size containing 35% of the total measured C. This data can potentially be used to simplify future measurements of biomass in these systems. Tree species diversity was positively related to AGC indicating the potential to align forest conservation efforts. The linear relationship suggests a functional relationship between the variables and is consistent with ecological theory on niche complementarity and selection effects, however based on the available data the mechanisms underlying this relationship can only be theorised. Changes in tree species composition were also noted across plots with differences in vegetation structure between plots explaining 16% of the variation in composition, with environmental differences related to climate and soils explaining only 3%. In Chapter 3, the focus shifts to understanding larger-scale spatial patterns in AGC. Field plots are spatially limited in this regard, therefore radar remote sensing data was used to generate a map of AGC in order to improve our knowledge on what principally controls its spatial variability at landscape scales. Results showed that factors related topography, climate and soils explained very little of the variation in C stocks across the landscape (r2 = 15 – 20%). Differences in slope angle and topographic position were important in discriminating between low biomass savannas and moderate biomass woodlands, while differences in annual precipitation were more important in separating woodlands and denser forests. A large proportion of the variation in C stocks (~80%) was unexplained highlighting the role of unmeasured variables. It is suggested that fire may play a key role in shaping patterns in tree species composition and C stocks across these landscapes. This data has important implications for a local REDD+ project which is aiming to generate carbon credits through improved fire management. In the second part of the thesis the attention shifts to understanding the long-term ecological impacts of shifting cultivation and the sensitivity and resilience of these woodlands to anthropogenic change. In Chapter 4 I examined how carbon stored in trees and soils recover across a 40-year chronosequence of abandoned agricultural land, and how this patchy disturbance impacts spatial pattern in tree species composition and diversity. I show that re-growing woodlands can act as carbon sinks through the accumulation of woody biomass (0.83 tC ha-1 yr-1), with soil texture having no clear impact on accumulation rates. Re-growing woodlands were also found to contain considerable biodiversity value by promoting novel species assemblages. Bulk soil carbon stocks appeared to be largely unaffected by the full cycle of shifting cultivation. However in Chapter 5 I show evidence of a previously unquantified legacy effect of land clearance on soil CO2 production with more recently abandoned fields (c. 6 years) exhibiting significantly higher efflux rates than the older abandonments (15 -25 years) and mature woodlands. Total soil nitrogen was the most important predictor of soil respiration across the plots (r2 = 0.3) followed by fine root density (r2 = 0.12). Soils in the younger sites were found to be more nitrogen rich which was used to explain the greater CO2 fluxes in these areas, however, it is still unclear why this pattern exists. The thesis concludes by discussing the wider implications of the results, as well as outlining further work needed to solidify some of the conclusions drawn in this thesis.

No description available.

Thesis (M.S.)--Mississippi State University. Department of Agricultural and Biological Engineering. / Title from title screen. Includes bibliographical references.

The intent of this thesis is to set out new data relating to the climate of the savanna in the Rupununi district of Guyana, and to comment thereon with reference to the causes and continuing existence of that savanna. To indicate the significance of the data and the pertinence of the comments it will be necessary to review recent discussion of the nature and causes of savanna in general. [...]