No description available.

The goals of this research are to identify the major constraints to plant succession in degraded cerrado vegetation. The area selected for this research, is located on the right bank of the Araguaia River in Goias State (Brazil). Floristic composition survey, seed rain and soil seed bank assessments were conducted in four forest fragments and in a degraded area. Planted seedlings, Soil translocation, Seed translocation and Artificial perches were also investigated. Floristic composition survey showed a richness of 145 species for the whole area and absolute density of 623.89 individuals.ha-1 for the degraded area and a range from 1333.72 to 2247.27 individuals.ha-1 for forest fragments. Seed rain survey resulted in 87 species identified, and annual seed arrival was 2.36 seeds.m-2 for the degraded area and 103.75 seeds.m-2 to 236.25 seed.m-2 to forest fragments. Soil seedbank analysis found a richness of 33 species and 87% of germinated seeds were from non-woody plants. The mean seed density of woody plants was 0 for the degraded area and ranged from 25 seeds.m-2 to 257.50 seed.m2 for forest fragments. Introducing seedlings showed a seedling survival rate of 38% after 24 months observation. Enterolobium sp and Inga spp showed higher rates of growth and positive interaction with fertilizer. The application of Tanglefoot, showed no significant results in any treatment. Treatments with fertilizer had less herbivory registered. Luehea candicans showed higher rate of herbivory. Seedling mortality was lower in fenced blocks and indicated Inga spp with lowest rate. Amongst nucleation strategies Seed translocation recruited more individuals after two years, followed by perches and soil seed bank translocation, but perches recruited more different species and had the same rate for seedling survival when compared to seed rain translocation. The results from this study show that succession in degraded Cerrado may be constrained by biotic and abiotic barriers.

No description available.

In the savanna woodlands of Southern Africa, locally know as miombo, carbon cycling is poorly quantified and many of the key processes remain obscure. For example, seasonal constraints on productivity and leaf display are not well understood. Also, fire is known to be a key process, with around 50% of the annual global area burned occurring in Africa, but detailed understanding of its ecological effects is lacking. Land use change and woodland degradation are changing the structure and functioning of these tropical woodlands, which cover 2.7 million km2 of Southern Africa and provide ecosystem services which support the livelihoods of over 100 million people. In this thesis I quantify the major carbon stocks of the woodlands in Nhambita Regulado, Gorongosa District in Sofala Province, Mozambique. I also examine processes that affect these stocks, including fire and clearance for agriculture. Furthermore, I quantify the seasonal cycle of leaf display, and its relationship to climate. I conducted a series of experimental burns and found that fire intensity was strongly related to rates of top-kill and root stock mortality. Top-kill rates decreased as tree diameter increased up to 10 cm DBH. After this point increased size did not affect top-kill rates, possibly because of accumulated wounds and rottenness. I then extrapolated these results to long term predictions of tree populations and carbon stocks by modelling the interactions of fire, mortality and tree growth. The model was able to successfully predict woody vegetation structure at two sites with known fire regimes, including a 50-year fire experiment in Marondera, Zimbabwe. The results show that annual fires in miombo suppress all woody vegetation. Low intensity fires every 2.5 years are required to maintain observed stem biomass in Nhambita. High intensity fires lead to high top-kill rates (12%), even among large stems. Manipulating fire intensity rather than frequency seems to be the most practical approach to limiting degradation by fire in these ecosystems. Using a three year time series of hemispherical photographs of the tree canopy, combined with satellite data, I find that tree leaf phenology is not directly related to seasonal rainfall patterns, both in Nhambita and across Southern Africa. Pre-rain green-up is the dominant phenology, from the semi arid savannas of the south of the continent to the wet miombo of the Congo basin. Wet miombo woodlands have longer periods of green-up before rain onset (mean 60 days) compared with dry miombo (37 days). Green up-dates show little interannual variability but large spatial variability. The importance of pre-rain green-up in determining how these ecosystems will respond to changing rainfall patterns is unknown, but is an important area for future study. I quantified carbon stocks in the Nhambita woodlands in the soil (69% of total carbon stocks of 111 tC ha-1), tree stems (19%) and roots (8%) as well as other smaller pools. An allometric relationship between root and stem biomass and stem diameter was developed, and used to evaluate the uncertainties in stem carbon estimation at plot and landscape scale. We find that the uncertainty (95% confidence intervals) at plot scale can be quite large (60% of the mean) but this is reduced to around 25% at landscape scale. Strategies for effective inventories of miombo woodland are presented. Using a chronosequence of abandoned farmland, we estimate that stem biomass recovers from clearance after around 30 years of abandonment. Changes in soil carbon stocks are less well understood and need further work. This thesis concludes by outlining further work needed to model the carbon cycle of these woodlands, as well as discussing the implication of pre-rain green-up for satellite observations of land cover changes and biomass mapping.

Faculty of Science School of Animal,Plants and Enviromental Science 0204279a craigm.kznwildlife.com / Fire is a key determinant of savanna dynamics, and would thus have a major influence on the vegetation dynamics of Mkuzi Game Reserve. Given this logic, it is an important and commonly used management tool in this reserve. Its main uses in the reserve are for either removing moribund material or for reducing woody plant encroachment, both of which normally entail dry season burns. As a consequence, fire often results in a green flush of vegetation that is highly favoured by grazing herbivores. A further management goal is maintaining or improving biological diversity by promoting vegetation heterogeneity. Current policy prescribes this should be achieved through point-source ignitions rather than by block-burning, which was the earlier practice. This study explores spatial and temporal fire patterns at a landscape scale in Mkuzi Game Reserve using Geographic Information Systems (GIS). Much of our understanding of the dynamics of fire has previously been determined at a plot scale and scaling up of these insights to a landscape scale is problematic, hence this project aimed to contribute to our understanding of the dynamics of fire at a landscape scale. The study also specifically examined how the fire regime in the reserve has changed with a change in the burning philosophy and strategy, namely from block burning to the point source ignition (PSI) strategy, which began to be implemented in the mid-1980's. Fire frequency was related to both geological type and vegetation type. The fact that geology was related to fire frequency was not surprising because the relationship between geology and vegetation in the reserve has previously been established. The varying amount of herbaceous material per vegetation type apparently influenced fire frequency. Spatial variation in fire frequency was also positively related to rainfall variation over the reserve, while the total area burnt per annum was positively related to the preceding wet season rainfall, but not for years with a high dry season rainfall. The influence of rainfall on grass production and thus fuel load explained these relationships. In addition, there was some evidence of a carry over effect of rainfall where the previous wet season rainfall together with the preceding wet season rainfall influenced total annual area burnt, but this was only significant for years when dry season rainfall was low. Contrary to an expected negative influence, dry season rainfall had no effect on the total annual area burnt. Grazer biomass had a significant limiting effect on fire frequency over the reserve (spatially), most likely due to consumption of herbaceous ii material, but there was no relationship between grazer biomass and total annual area burnt (temporally). Dry season burns were significantly larger than wet season burns and can be attributed to the more favourable fuel condition during the dry season. Intense burns were also generally larger than the cooler burns, namely those rated as patchy/very patchy and clean. This was mainly attributed to a high fuel load which is critical for intense fires but also positively influences the spread of fire. The comparison of the block burning strategy and the point source ignition (PSI) strategy showed that fire frequency was greater during the PSI burning period than during the block burning period. The total area burnt per annum was greater during the PSI burning period than during the block burning period, but individual burn sizes were not significantly different between the two strategies. Evidence showed that individual burns that occurred during the PSI period had boundaries that were more irregular than those of block burns. Fires were most common during the dry season for both burning strategies, but the proportion of the burns that occurred during the dry season was greater for the PSI burning period than for the block burning period. Evidence also showed that a much greater emphasis was put on applying dry season prescribed burns during the PSI period than during the block burning period. A greater effort was also made during the PSI period to burn firebreaks, which were only implemented during the dry season. Arson fires (started deliberately or accidentally by neighbours) were more common during the block burning period than during the PSI period, while under both burning strategies, they were more common during the dry season than the wet season. There was no distinguishable difference in the burn intensity patterns between block and PSI burning, that is, the proportions of burns in the different burn intensity classes were not significantly different between the two burning strategies. Although the contribution of the individual fire barrier types showed some change with a change from block burning to a PSI strategy, the combined contribution of natural barriers did not increase, and that of management barriers did not decrease, as would have been expected. In addition, natural and management barriers were apparently of equivalent importance during both burning strategies.

The thesis presents a thorough, in-depth study that fills some of the gaps in the knowledge of the impacts of woodland utilisation in communal areas. The chosen case study villages are in Bushbuckridge, a government gazetted Integrated Sustainable Rural Development programme node, making the results pertinent to sustainable energy policy reform in South Africa. A case-study of two villages was used to investigate the spatial and structural changes in fuelwood supply in response to fuelwood extraction as well as the changes in use-patterns over time. A survey of the structure and composition of the woody vegetation and wood harvesting patterns around the villages was conducted and compared against historical data, spanning 17 years. Total wood stock in the communal woodlands of both villages declined over the study period; the loss being greater in Welverdiend. Significant, negative change in the structure and species composition, particularly of species that are commonly harvested for fuelwood has occurred in Welverdiend but not in Athol. The absence of negative impacts in Athol implies that harvesting regimes here are more sustainable but it is more likely that this is due to the lower human population and lower fuelwood extraction pressure. The changes in woodland structure were linked to landcover change patterns that occurred in the villages over the last 44 years, from their creation through forced resettlements on old farms in the area. Landcover change patterns were similar in both villages since 1965 but there was significantly greater woodland loss in Welverdiend (48% woodland loss) in comparison to Athol (25% woodland loss). The systematic loss of woodland areas to agricultural fields was linked to expanding residential areas due to human population growth. Deforestation occurred where woodlands were already impacted through selective harvesting. The physical changes in woodland structure and landcover were linked to a detailed socio-economic analysis of the two villages, providing critically important data for the sustainable management of woodlands in South Africa. The impact of access to electricity on fuelwood consumption rates was carried out through analysis of the economic, time and opportunity costs of fuelwood collection, compared against the different fuelwood availability in each village. In Welverdiend demand for fuelwood has so far proved inelastic; households have adjusted their fuelwood collection regimes, going on fewer collection trips but spending longer times for each trip but ultimately household investment is similar to that in Athol. Fuelwood demand is maintained in Welverdiend by the availability of purchased fuelwood and harvesting in new sites. A model to predict the socio-economic factors at the household and per capita level which affect fuelwood consumption was developed. Revealing in the process that households with access to electricity used less fuelwood annually and the amounts of fuelwood used were influenced by the household perceptions of fuelwood scarcity in the village, Household population size had a direct bearing on the likelihood of households switching to electricity with every addition to the household size decreasing the likelihood of switching by 48%. This study has major implications for the government’s on-going rural electrification programme. Interventions are required that raise awareness about fuelwood availability trends, based on landscape developments and targeting women as the main users of fuelwood.

A pressão antrópica sobre o cerrado vem transformando sua paisagem em um mosaico de fragmentos naturais imersos em uma matriz antropizada. A qualidade da vegetação dos fragmentos remanescentes depende em grande parte das populações de polinizadores, dos quais as abelhas são o grupo mais representativo. As abelhas sem ferrão (Apidae: Meliponini) compõem a maior biomassa de polinizadores nesse bioma. Seus ninhos são feitos usualmente em cavidades de troncos ou no solo e algumas espécies constróem ninhos expostos. Os fatores que levam os meliponíneos a nidificarem em uma determinada região são, a princípio, a disponibilidade de recursos (sítios de nidificação e alimento) e o comportamento competitivo intra e interespecífico. Mas esses não são os únicos determinantes, pois os fatores que levam as populações a se manterem, se expandirem ou se reduzirem nessa região estão ligados também à resposta de cada espécie ao grau de antropização da paisagem. O objetivo geral dessa tese foi investigar como fatores naturais e antrópicos afetam a nidificação de meliponíneos em ambiente de cerrado, visando responder às seguintes questões: a) Diferenças estruturais entre fitofisionomias de cerrado se refletem na composição de espécies? b) Como a redução das áreas naturais de cerrado e sua substituição por paisagens rurais e urbanas afetam as populações de ninhos de meliponíneos? e c) Como o relacionamento genético e a obtenção de recurso alimentar afetam a distribuição das colônias em uma área de cerrado? Para responder a essas questões, esta tese foi dividida em três capítulos: No capítulo 1, o objetivo foi compreender se e como a distribuição dos ninhos de Meliponini variaria entre três fisionomias de cerrado, campo sujo, campo cerrado e cerradão em Itirapina, SP, e como essa variação estaria relacionada a diferenças na disponibilidade de sítios de nidificação e de alimento em cada uma delas. Foi realizado um levantamento dos ninhos e uma avaliação da quantidade e composição de espécies de árvores em cada uma dessas fisionomias, além da contagem de plantas floridas durante 20 meses. Foram localizados 50 ninhos de Meliponini, sendo 17 no campo sujo (todos de Trigona spinipes), 19 no campo cerrado (18 de T. spinipes e um de Melipona quadrifasciata), 12 no cerradão (cinco de T. spinipes, três de Tetragonisca angustula, dois de Leurotrigona muelleri, um de Trigona hyalinata e um de Plebeia droryana) e dois de T. spinipes fora da área amostrada. A maior quantidade de árvores foi encontrada no cerradão, enquanto o maior número de plantas floridas foi encontrado no campo sujo. No capítulo 2, o objetivo foi avaliar o efeito da substituição das áreas naturais de cerrado por paisagens agrícolas e urbanizadas sobre as populações de Meliponini como um todo, e particularmente sobre abelhas Melípona. Os resultados obtidos em 31 levantamentos de ninhos em áreas de cerrado, além do levantamento feito em Itirapina, foram relacionados ao grau de antropização da paisagem. A avaliação da paisagem foi feita por meio da análise e classificação de imagens de satélite do entorno dos levantamentos. A riqueza de espécies de Meliponini se correlacionou negativamente com a proporção de áreas rurais, mas a composição de espécies se correlacionou positivamente. A composição de espécies se relacionou positivamente ao porte da vegetação também. Por sua vez, a densidade de ninhos e a composição de espécies de Melípona se correlacionaram negativamente com a proporção de áreas rurais. No capítulo 3, o objetivo foi verificar o grau de relacionamento genético e sua influência na distribuição das colônias de T. spinipes na paisagem, a distância utilizada para o forrageamento e o compartilhamento ou não de alimento entre colônias. Para isso, realizamos um estudo com marcadores de microssatélites entre as colônias levantadas no capítulo 1, além um experimento de distância de forrageamento. As colônias vizinhas apresentaram um baixo grau de relacionamento genético entre si, mas as operárias coletadas em uma mesma flor apresentaram alto grau. A distância de forrageamento foi maior que a distância entre colônias vizinhas. Concluiu-se que: a) Fitofisionomias campestres podem apresentar uma abundância de ninhos maior do que fitofisionomias florestais, mas as fitofisionomias florestais podem apresentar uma riqueza maior de espécies. O tamanho da amostra pode subestimar a riqueza de espécies das fitofisionomias florestais. A relação positiva entre a composição de espécies de Meliponini e o porte da vegetação indica que há preferência de algumas espécies por determinada fitofisionomia. No entanto, a detecção de um padrão torna-se difícil dada a ubiquidade das espécies de comportamento mais plástico. b) A antropização pode ter um efeito negativo sobre as populações de Meliponini, podendo levar à perda de espécies. Para espécies de comportamento mais plástico, as áreas antropizadas não oferecem limitação de recursos, mas para espécies de comportamento mais restritivo, a substituição das áreas naturais pode ter um efeito deletério sobre suas populações. c) O baixo grau de relacionamento genético entre colônias próximas indica que não há limitação de fluxo gênico para T. spinipes. A capacidade de suas operárias em dominar um recurso floral pode excluir competitivamente abelhas de espécies menos agressivas. Se a matriz antropizada apresentar limitação de recursos, espécies de comportamento menos agressivo poderão não conseguir obter recursos alimentares, ficando isoladas em fragmentos de áreas naturais. O isolamento pode levar à perda de variabilidade genética e, consequentemente, à perda de espécies. Portanto, políticas de conservação que visem a proteção das espécies de Meliponini devem levar em conta não apenas a quantidade de árvores de uma região, mas também a qualidade e a heterogeneidade da vegetação, tanto nas áreas de proteção ambiental quanto nas áreas entre elas. / The antropic pressure over the Cerrado has been transforming its landscape into a mosaic of fragments surrounded by an antropized matrix. The quality of the vegetation of the remaining fragments largely depends on the pollinators populations, which the bees are the most representative. The stingless bees (Apidae: Meliponini) compound the biggest biomass of this biome. Their nests are usually made inside trunk or soil cavities, but some species make exposed nests. The factors that lead Meliponini to nest in a given region are, at first, the resources availability (nest sites and food) and the intra- and interspecific competitive behavior. However, these are not the sole determinants, because the factors that lead to maintain, expand or reduce populations sizes are also related to the response of each species to the landscape antropization degree. The main general goal of this thesis was to investigate how natural and antropic factors affect the Meliponini nesting in Cerrado areas, seeking to answer the following questions: a) Do structure differences among cerrado phytophysiognomies reflect in Meliponini species composition? b) How do the reduction of Cerrado natural areas and their replacement by rural and urban landscapes affect the Meliponini nest populations? and c) How do the genetic relationship and the obtaintion of food resources affect colony distribution in a Cerrado area? To answer these questions, this thesis was split in three chapters: In chapter 1, the objective was to understand if and how the Meliponini nest distribution would vary among three Cerrado phytophysiognomies, namely campo sujo, campo cerrado and cerradão in Itirapina, SP, and how this variation would be related to differences in nesting sites and food availability in each one of them. A nest survey and an evaluation of the trees amount and species composition were undertaken in each phytophysiognomie, besides flowering plants count over 20 months. We found 50 Meliponini nests, being 17 in campo sujo (all belonging to Trigona spinipes), 19 in campo cerrado (18 of T. spinipes and one of Melipona quadrifasciata), 12 in cerradão (five of T. spinipes, three of Tetragonisca angustula, two of Leurotrigona muelleri, one of Trigona hyalinata and one of Plebeia droryana) and two nests of T. spinipes outside the sampled area. The highest amount of threes was found in cerradão while the highest amount of flowered plants was found in campo sujo. In chapter 2, the objective was to evaluate the effect of replacement of natural Cerrado areas by rural and urban landscapes over general Meliponini populations and particularly over Melípona bees. The results of 31 nests surveys in Cerrado areas besides those conducted in Itirapina were correlated to the antropization degree of the landscape. Landscape evaluation was undertaken by analysis and classification of satellite images from the surveyed surrounding areas. The Meliponini species richness was negatively related to the proportion of rural areas, but species composition was positively related. Species composition was positive related to vegetation size too. I turn, both Melípona nests density and Melípona species composition were negatively related to the proportion of rural areas. In chapter 3, the objective was to verify the degree of genetic relationship and its influence over T. spinipes colony distribution in the landscape, the foraging distance and if there was or was not sharing food among colonies. To accomplish this, a microsatellite markers study was undertaken among colonies found in chapter 1, plus a foraging range experiment. Neighbor nests shown a low genetic relationship degree among them, but workers collected at the same flower showed a high degree of genetic relationship. Foraging distance was farther than the distance between neighbor colonies. We conclude that: a) Grassland phytophysiognomies may show a nest abundance higher than forest phytophysiognomies, but these can show a higher species richness. Sample size can underestimate species richness in forest phytophysiognomies. The positive relationship between Meliponini species composition and vegetation size indicates that there are preferences of some species to some phytophysiognomies. However, the ubiquity of species with a plastic behavior may difficult the finding of a pattern. b) Antropization may have a negative effect over Meliponini population, leading to species loss. To the species with a more plastic behavior, antropized areas do not offer resources limitation, but to species with a more restrictive behavior, the replacement of natural areas may have a deleterious effect on their populations. c) The low degree of genetic relationship among neighbor nests indicates that there is no genetic flow limitation to T. spinipes. The ability of T. spinipes workers to dominate a flower resource may competitively exclude less aggressive bees. If the antropized matrix presents resource limitation, less aggressive species may not obtain food resources, becoming isolated in fragments of natural areas. The isolation may lead to loss of genetic variability and consequentially to species loss. Thus, conservation policies aiming at Meliponini species protection must take in account not only the amount of trees of a given region, but also the quality and heterogeneity of vegetation, as much in areas of environmental protection as the areas among them.

Savannas comprise over one eighth of the world's land surface with some 50 Mha in North America alone. They are productive systems supporting a high level of both faunal and floral diversity and are of increasing socioeconomic importance. The maintenance and formation of savannas have been attributed to climate, soils, herbivory and fire. However, the reasons for the coexistence of trees and the grass layer have still to be determined. These two contrasting life forms create a complex of intra- and interspecific positive, negative, and neutral interactions, few of which have been quantified. Under lower-than-average rainfall, tree effects on grasses in a Prosopis savanna in northern Texas were largely neutral with few measurable competitive or facultative effects from the tree canopy. However, grasses demonstrated increased productivity where belowground competition with neighboring trees was removed. Similarly, tree growth increased following the removal of grasses under and around individual trees, particularly on shallower soils, but only during a season of significant precipitation. Low intensity burning of grasses enhanced growth of adult trees, but patterns were inconsistent between two different sites. Moderate clipping around individual trees had no apparent effect on tree growth. Intraspecific competition between savanna trees was not evident, but may have been blurred by an extensive, lateral distribution of near-surface roots. Overall, tree intraspecific competition was neutral regardless of soil depth, suggesting lateral tree roots may be only used opportunistically. Although some competitive relationships were verified, the differences in the responses between the two years of study, and at different sites indicated that soil depth and climate may have overriding impacts on tree-grass interactions and savanna dynamics in this system.

Savannas comprise over one eighth of the world's land surface with some 50 Mha in North America alone. They are productive systems supporting a high level of both faunal and floral diversity and are of increasing socioeconomic importance. The maintenance and formation of savannas have been attributed to climate, soils, herbivory and fire. However, the reasons for the coexistence of trees and the grass layer have still to be determined. These two contrasting life forms create a complex of intra- and interspecific positive, negative, and neutral interactions, few of which have been quantified. Under lower-than-average rainfall, tree effects on grasses in a Prosopis savanna in northern Texas were largely neutral with few measurable competitive or facultative effects from the tree canopy. However, grasses demonstrated increased productivity where belowground competition with neighboring trees was removed. Similarly, tree growth increased following the removal of grasses under and around individual trees, particularly on shallower soils, but only during a season of significant precipitation. Low intensity burning of grasses enhanced growth of adult trees, but patterns were inconsistent between two different sites. Moderate clipping around individual trees had no apparent effect on tree growth. Intraspecific competition between savanna trees was not evident, but may have been blurred by an extensive, lateral distribution of near-surface roots. Overall, tree intraspecific competition was neutral regardless of soil depth, suggesting lateral tree roots may be only used opportunistically. Although some competitive relationships were verified, the differences in the responses between the two years of study, and at different sites indicated that soil depth and climate may have overriding impacts on tree-grass interactions and savanna dynamics in this system.

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