Universiẗat, Diss., 2006--Würzburg. / Erscheinungsjahr an der Haupttitelstelle: 2005. Dateien im PDF-Format.

Philosophiae Doctor - PhD / In the Succulent Karoo biome of South Africa vegetation degradation by overgrazing is a recognized threat to biodiversity. In the eastern Little Karoo region of the Western Cape Province, ostrich farming has degraded large areas of natural vegetation, particularly in the Gannaveld habitat of the Oudtshoorn basin. Little quantified vegetation data exists on the impacts of degradation and the composition of the Gannaveld vegetation types. This study quantifies the composition of Oudtshoorn Gannaveld and the impacts of degradation on this critically endangered vegetation type. The diversity of this vegetation type is added to by the occurrence of mima-like circular soil mounds, termitaria, which support distinctive plant assemblages. Perennial plant data and soil data were collected from the largest remaining remnant of Oudtshoorn Gannaveld perceived to contain different levels of degradation from near pristine to severely degraded. The results show 72 species in 49 genera and 17 families were recorded with the Aizoaceae, Asteraceae and Amaranthaceae families being dominant. The off termitaria plant community is dominated by the Asteraceae, Aizoaceae and Crassulaceae families while the on termitaria community is dominated by the Asteraceae, Amaranthaceae and Zygophyllaceae families. Four levels of degradation were identified in each of the broader on and off termitaria communities. It was found that grazing and trampling induced degradation on termitaria results in the loss of perennial plant cover and plant litter and an increase in bare ground while degradation off termitaria results in a loss of species. There are changes in soil chemistry both on and off termitaria as a result of vegetation degradation. Degradation results in palatable species being replaced by unpalatable and disturbance indicating species. Perennial plant cover off termitaria is resilient to grazing and trampling, however species richness, plant functional type composition and the abundance of individual species are not. Species richness on termitaria is resilient to grazing and trampling but cover, plant functional type composition and the abundance of individual species are not. Degradation results in shifts from succulent and woody shrub dominated communities to dwarf succulent and dwarf succulent shrub dominated communities. These changes hold implications for agriculture,biodiversity conservation and the provision of ecosystem services.

Grazing by domestic livestock is one of the primary ways by which humans have modified landscapes. At low stocking rates livestock grazing can modify vegetation community composition, but at high stocking rates grazing can also reduce vegetation productivity and initiate soil erosion, leading to land degradation. The country of Iceland has undergone severe land degradation over the past 1100 years, with over half of the former vegetation cover being lost, and the remainder having depleted productivity. This work focuses upon the role that grazing by domestic livestock played in this degradation, and how the interactions between farm management, vegetation cover and climate affected grazing patterns in space and time. The aims of the research were achieved by constructing an environmental simulation model, called Búmodel, which allowed a cross-disciplinary approach that integrated landscape ecology, environmental archaeology and historical analysis. Búmodel was loosely coupled with GIS so that spatially based model inputs and outputs could be displayed and analysed in map form. The purpose of Búmodel was to predict spatial and temporal patterns of vegetation biomass production and utilisation (through grazing and hay-making) with a view to commenting on vegetation degradation in the pre-modern period (pre-1900 AD). The model was parameterised using contemporary and historical Icelandic agricultural data. Model validation was undertaken using sensitivity tests and comparison with data from an independent grazing experiment in the north of Iceland. Búmodel was then applied to two contrasting study areas: Vestur- Eyjafjallahreppur, a farming community on the south coast of Iceland, and Hofstaðir, a farm estate in the north east of the country, situated inland by Lake Mývatn. These applications demonstrated the importance of farm management in avoiding land degradation and in ameliorating the impact of climate. They also established the usefulness of Búmodel as a tool for the investigation of human and environmental interactions in Iceland.

An investigation of temporal dynamics of El Niño–Southern Oscillation (ENSO) and spatial patterns of dryness/wetness period over arid and semi-arid zones of Central Asia and their relationship with Normalized Difference Vegetation Index (NDVI) values (1982-2011) have explored in this article. For identifying periodical oscillations and their relationship with NDVI values have selected El Nino 3.4 index and thirty years of new generation bi-weekly NDVI 3g acquired by the Advanced Very High Resolution Radiometer (AVHRR) satellites time-series data. Based on identification ONI (Oceanic Nino Index) is a very strong El Nino (warm) anomalies observed during 1982-1983, 1997-1998 and very strong La Nino (cool) period events have observed 1988-1989 years. For correlation these two factors and seeking positive and negative trends it has extracted from NDVI time series data as “low productivity period” following years: 1982-1983, 1997 -1998; and as “high productivity period” following years: 1988 -1989. Linear regression observed warm events as moderate phase period selected between moderate El Nino (ME) and NDVI with following eriods:1986-1987; 1987-1988; 1991-1992; 2002-2003; 2009-2010; and moderate La Niña (ML) periods and NDVI (1998-1999; 1999-2000; 2007-2008) which has investigated a spatial patterns of wetness conditions. The results indicated that an inverse relationship between very strong El Nino and NDVI, decreased vegetation response with larger positive ONI value; and direct relationship between very strong La Niña and NDVI, increased vegetation response with smaller negative ONI value. Results assumed that significant impact of these anomalies influenced on vegetation productivity. These results will be a beneficial for efficient rangeland/grassland management and to propose drought periods for assessment and reducing quantity of flocks’ due to a lack of fodder biomass for surviving livestock flocks on upcoming years in rangelands. Also results demonstrate that a non-anthropogenic drivers of variability effected to land surface vegetation signals, nderstanding of which will be beneficial for efficient rangeland and agriculture management and establish ecosystem services in precipitation-driven drylands of Central Asia.

Land degradation, a phenomenon referring to (drought) in arid, semi-arid and dry sub-humid regions as a result of climatic variations and anthropogenic activities most especially in the semi-arid lands of Sudan, where vast majority of the rural population depend solely on agriculture and pasture for their daily livelihood, the ecological pattern had been greatly influenced thereby leading to loss of vegetation cover coupled with climatic variability and replacement of the natural tree composition with invasive mesquite species. The principal aim of this study is to quantitatively examine the vigour of vegetation in Sudan through different vegetation indices. The assessment was done based on indicators such as soil adjusted vegetation index (SAVI). Cloud free multi-spectral remotely sensed data from LANDSAT imagery for the dry season periods of 1984 and 2009 were used in this study. Results of this study shows conversion of vegetation to other land use type. In general, an increase in area covered by vegetation was observed from the NDVI results of 2009 which is a contrast of that of 1984. The results of the vegetation indices for NDVI in 1984 (vegetated area) showed that about 21% was covered by vegetation while 49% of the area were covered with vegetation in 2009. Similar increase in vegetated area were observed from the result of SAVI. The decrease in vegetation observed in 1984 is as a result of extensive drought period which affects vegetation productivity thereby accelerating expansion of bare surfaces and sand accumulation. Although, increase in vegetated area were observed from the result of this study, this increase has a negative impact as the natural vegetation are degraded due to human induced activities which gradually led to the replacement of the natural vegetation with invasive tree species. The results of the study shows that NDVI perform better than by SAVI.

Ao longo de várias décadas vem se intensificando a urbanização no interior de áreas de mananciais da Região Metropolitana de São Paulo - RMSP. Como resultado tem-se a diminuição da cobertura vegetal, a poluição de mananciais e a precariedade das ocupações informais, a colocar em risco a vida de milhares de pessoas. O principal objetivo desta tese é avaliar que os instrumentos da nova legislação de mananciais não foram suficientes para uma efetiva melhora e de que os ajustes da nova legislação ainda que tenham promovido um avanço e uma certa contenção do quadro de degradação ambiental e social, ainda carecem de uma maior integração entre os agentes públicos do Estado e dos Municípios envolvidos na aplicação dos instrumentos previstos. Para tanto foi adotado um recorte territorial abrangendo municípios da RMSP e distritos do município de São Paulo que estivessem total ou parcialmente abrangidos pela LPM/1975-1976, a fim de avaliar, caso a caso, o crescimento demográfico, a expansão urbana e a diminuição da cobertura vegetal dentro e fora de mananciais. Constatamos um adensamento nos territórios abrangidos pela LPM/1975-1976 selecionados para estudo, o que implica mudanças nos padrões de ocupação e uma possível diminuição da pressão sobre os remanescentes florestais. Não obstante as medidas emergenciais levadas a efeito nessas áreas, o passivo ambiental ainda é significativo, exigindo ações coordenadas e integradas dos agentes públicos do Estado e municípios envolvidos, visando à melhoria das condições ambientais e de qualidade de vida de seus habitantes e à preservação dos mananciais de abastecimento público. Entendemos que tais movimentos podem constituir o caminho para a construção de áreas urbanas com um mínimo de sustentabilidade ambiental, tendo como horizonte futuro a possibilidade de existirem cidades sustentáveis, espaço de convivência de toda sua população. / During several decades the urbanization around areas of water spring in the \"São Paulo Metropolitan Region (RMSP)\"has become more intense. As a result of this process, the increase of informal occupancy, the decrease of vegetation in the affected areas and pollution of the water spring put the life of thousands of people at risk. This thesis evaluates that the legislation dedicated to water springs was not sufficient in providing a solution to the problems above. The instruments provided by the new legislation - though successful in improving the overall picture of social and environmental degradation of the spring regions - remain mostly unenforced due to a lack of integration between the state and city government levels. In order to show this result, a sample of territories of the RMSP and districts of the city of São Paulo was chosen among those covered by the Water Supply Protection Law - LPM/1975-1976. Case by case, demographic increase, urban expansion and the decrease in vegetation around spring regions was researched. We observed an increase of population density in the sampled territories encompassed by the LPM/1975-1976, which implies a change in the patterns of occupancy and less degradation of areas of forests possibly. Although emergency actions were taken, the environmental degradation is far reaching. The preservation of the water and vegetation of the spring and the improvements of life quality of the local population require coordinated effort from public agents in the state and city levels. In our understanding, these coordinated actions may form a path to the ultimate goal of constructing urban areas with environmental sustainability.

Ao longo de várias décadas vem se intensificando a urbanização no interior de áreas de mananciais da Região Metropolitana de São Paulo - RMSP. Como resultado tem-se a diminuição da cobertura vegetal, a poluição de mananciais e a precariedade das ocupações informais, a colocar em risco a vida de milhares de pessoas. O principal objetivo desta tese é avaliar que os instrumentos da nova legislação de mananciais não foram suficientes para uma efetiva melhora e de que os ajustes da nova legislação ainda que tenham promovido um avanço e uma certa contenção do quadro de degradação ambiental e social, ainda carecem de uma maior integração entre os agentes públicos do Estado e dos Municípios envolvidos na aplicação dos instrumentos previstos. Para tanto foi adotado um recorte territorial abrangendo municípios da RMSP e distritos do município de São Paulo que estivessem total ou parcialmente abrangidos pela LPM/1975-1976, a fim de avaliar, caso a caso, o crescimento demográfico, a expansão urbana e a diminuição da cobertura vegetal dentro e fora de mananciais. Constatamos um adensamento nos territórios abrangidos pela LPM/1975-1976 selecionados para estudo, o que implica mudanças nos padrões de ocupação e uma possível diminuição da pressão sobre os remanescentes florestais. Não obstante as medidas emergenciais levadas a efeito nessas áreas, o passivo ambiental ainda é significativo, exigindo ações coordenadas e integradas dos agentes públicos do Estado e municípios envolvidos, visando à melhoria das condições ambientais e de qualidade de vida de seus habitantes e à preservação dos mananciais de abastecimento público. Entendemos que tais movimentos podem constituir o caminho para a construção de áreas urbanas com um mínimo de sustentabilidade ambiental, tendo como horizonte futuro a possibilidade de existirem cidades sustentáveis, espaço de convivência de toda sua população. / During several decades the urbanization around areas of water spring in the \"São Paulo Metropolitan Region (RMSP)\"has become more intense. As a result of this process, the increase of informal occupancy, the decrease of vegetation in the affected areas and pollution of the water spring put the life of thousands of people at risk. This thesis evaluates that the legislation dedicated to water springs was not sufficient in providing a solution to the problems above. The instruments provided by the new legislation - though successful in improving the overall picture of social and environmental degradation of the spring regions - remain mostly unenforced due to a lack of integration between the state and city government levels. In order to show this result, a sample of territories of the RMSP and districts of the city of São Paulo was chosen among those covered by the Water Supply Protection Law - LPM/1975-1976. Case by case, demographic increase, urban expansion and the decrease in vegetation around spring regions was researched. We observed an increase of population density in the sampled territories encompassed by the LPM/1975-1976, which implies a change in the patterns of occupancy and less degradation of areas of forests possibly. Although emergency actions were taken, the environmental degradation is far reaching. The preservation of the water and vegetation of the spring and the improvements of life quality of the local population require coordinated effort from public agents in the state and city levels. In our understanding, these coordinated actions may form a path to the ultimate goal of constructing urban areas with environmental sustainability.

In order to understand the dynamics of desertification after the 1980s droughts, the trends and changes of photosynthetically active fraction of the vegetation cover of the semi-arid region of West Africa have been analyzed across three ecoclimatic entities. This study focuses on six countries (Senegal, Mauritania, Mali, Burkina-Faso, Niger and Benin) that reflect quite well the human and environmental context of semi-arid regions. The main objective of this thesis is to check in the before-mentioned biophysical and human context, if the state of the vegetation improves because of more favourable rainfall conditions, or if, conversely, the long environmental deterioration during recent decades has a healthy dose of irreversibility for several years. The process of investigation proceeds in three stages defined by geographical scales and a geoclimatic gradient. At the regional level, we compared vegetation productivity data from 1982-1999 time series of NOAA-AVHRR NDVI data to rainfall data. We analyzed data from 315 rain gauges distributed across five countries (Senegal, Mauritania, Mali, Burkina-Faso and Niger) with annual average isohyets ranging from 100 to 900 mm. For trends analysis, we used the ratio of the integrated vegetation index (iNDVI) during the crop-growth period (June to October) to the May to October sum of rainfall (RR). This ratio (iNDVI/RR), a proxy of the Rain Use Efficiency, is widely used by ecologists as an indicator for detecting desertification processes. Overall, our results show a significant increase of the net primary production as a response of post-drought rainfall increase. However, the trends of iNDVI/RR ratio suggest that most of the studied stations (54%) in sahelian and sahelo-sudanese belts were stable and 31.4% showed strong to very strong negative change in iNDVI/RR ratio, while 13.3% of the stations showed a moderate decrease and only 1.3% showed a positive trend. At the country level, similar trends were recorded throughout 128 stations in Burkina Faso located between the 500 mm and 1100 mm isohyets. In fact, more than half the studied stations showed a stability of iNDVI/RR ratio. However, 39.8% of them show a negative trend from low to high, while only 2.4% of them show a slight positive trend. In addition, a comparison with more detailed local case studies confirmed these observed trends. However, the obtained results for wetter stations in the southern part of the country should be taken with precaution, as the relationship between NDVI and rainfall tends to weaken when annual rainfall is higher than 1000 mm. Overall, the negative trends highlight a gradual decline in plant productivity. These results recorded in 44.7% of the analyzed stations may reflect ongoing desertification processes in the sahelian and sahelo-sudanian zones over the past two decades. At the local level, a structural characterization of woody units in three bioclimatic regions of the sudanian zone (900 mm 1200 mm) in the north of Benin was conducted to assess their degradation status. We recorded the structural characteristics of stands (basal area, density), species diversity as well as disturbances type and intensity. Multivariate analysis revealed a gradient of productivity between the three regions: there was a high diversity of woody stands in the south-sudanian sector, while the north-sudanian and sudano-sahelian sectors were dominated by savannas and shrub, which had low productivity. The productivity gradient is influenced by a disturbance gradient suggesting that the decline in productivity is stronger from south-sudanian to the sudano-sahelian region. In addition, the spatial component of the observable changes in vegetation cover has been mapped by remote sensing in a restricted area of the sudanian zone in northern Benin with SPOT-XS data over the period 1986-2005. Over the past two decades, 19.6% of the woody stands have completely disappeared; 12.9% of this extinction of woody stands was due to deforestation, and 13.9 % due to degradation processes. In contrast to these trends, 21.8% of the study area were stable, while less than a third (31.7%) of the area were experiencing woody recovery (reforestation). The analysis also reveals significant disparities in the rates of change of the identified land use class units. These variations are more pronounced for the woody units and agricultural land than in villages. These results suggest that land cover degradation throughout the study area is primarily due to anthropogenic factors (livestock and agricultural expansion, logging, breeding). In fact, this area is a preferred destination for agricultural migrants fleeing the unpredictable climatic conditions of the drier semi-arid areas. Overall, our results highlight the rapid decline of vegetation resources, challenging assumptions that the impact of ongoing desertification processes is mixed, outside of the arid and semi-arid regions of West Africa. The developed framework is easily reproducible and allows the implementation of a reliable diagnosis on the state of the vegetation cover from accessible and inexpensive data. Its implementation should facilitate the development of managerial techniques for better assistance to the poor, especially vulnerable to the gradual degradation of their environment.