<p>Boundary-layer flow over bodies such as aircraft wings or turbine blades is characterized by a pressure gradient due to the curved surface of the body. The boundary layer may experience modal and non-modal instability, and the type of dominant instability depends on whether the body is swept with respect to the oncoming flow or not. The growth of these disturbances causes transition of the boundary-layer flow to turbulence. Provided that they are convective in nature, the instabilities will only arise and persist if the boundary layer is continuously exposed to a perturbation environment. This may for example consist of turbulent fluctuations or sound waves in the free stream or of non-uniformities on the surface of the body. In engineering, it is of relevance to understand how susceptive to such perturbations the boundary layer is, and this issue is subject of <em>receptivity analysis</em>.</p><p> </p><p>In this thesis, receptivity of simplified prototypes for flow past a wing is studied. In particular, the three-dimensional swept-plate boundary layer and the boundary layer forming on a flat plate with elliptic leading edge are considered. The response of the boundary layer to vortical free-stream disturbances and surface roughness is analyzed, receptivity mechanisms are identified and their efficiency is quantified.</p> / 76218 VR Receptivity

Boundary-layer flow over bodies such as aircraft wings or turbine blades is characterized by a pressure gradient due to the curved surface of the body. The boundary layer may experience modal and non-modal instability, and the type of dominant instability depends on whether the body is swept with respect to the oncoming flow or not. The growth of these disturbances causes transition of the boundary-layer flow to turbulence. Provided that they are convective in nature, the instabilities will only arise and persist if the boundary layer is continuously exposed to a perturbation environment. This may for example consist of turbulent fluctuations or sound waves in the free stream or of non-uniformities on the surface of the body. In engineering, it is of relevance to understand how susceptive to such perturbations the boundary layer is, and this issue is subject of receptivity analysis.   In this thesis, receptivity of simplified prototypes for flow past a wing is studied. In particular, the three-dimensional swept-plate boundary layer and the boundary layer forming on a flat plate with elliptic leading edge are considered. The response of the boundary layer to vortical free-stream disturbances and surface roughness is analyzed, receptivity mechanisms are identified and their efficiency is quantified. / QC 20101022 / 76218 VR Receptivity

The combined effects of food availability and predation risk on fish foraging behavior have been investigated via both laboratory and field experiments, primarily in temperate, freshwater systems and during daylight hours. In contrast, relatively little attention has been directed towards fish foraging decisions along subtropical shorelines, which serve as nursery grounds for a variety of economically important fishes, as well as at night, when many species emerge from refuges to feed. The mangrove-seagrass ecotone and adjacent seagrass beds constitute nocturnal feeding grounds for fish secondary-tertiary consumers. In subtropical Biscayne Bay, Florida (USA), I investigated the influences of food and risk on nocturnal seagrass use by gray snapper (Lutjanus griseus), bluestriped grunt (Haemulon sciurus), great barracuda (Sphyraena barracuda), and seabream (Archosargus rhomboidalis) along a distance gradient, spanning from the mangrove fringe to 120 m from shore. This was accomplished by conducting a series of integrated field and laboratory studies, including: (1) nocturnal seine sampling to determine fish abundance patterns in relation to the mangrove-seagrass interface; (2) fish stomach content analysis to reveal feeding habits and trophic relationships; and (3) diel field tethering experiments to explore nearshore gradients in predation pressure. With these data I tested a priori predictions of fish distributions relative to food and predation risk that were generated from foraging theory: (1) fishes will be distributed across the distance gradient in proportion to their food supply (i.e., ideal free distribution, IFD); or (2) fishes will avoid high risk areas such that their abundances will be lower than predicted by food resources in high-risk habitats (i.e., food-risk trade-off). Results revealed that fish assemblage composition differed by season and distance from shore, with the zone nearest the mangroves generally harboring the lowest densities of late-stage juvenile fishes. Stomach content analysis demonstrated that gray snapper fed on a variety of small fishes and crustaceans, while bluestriped grunt fed primarily on caridean shrimp. Seabream fed almost exclusively on vegetation and great barracuda was almost entirely piscivorous; however, seasonal shifts in diet and feeding habits were evident. Seasonal shifts in major food resource use generally did not correspond with changes in relative abundance of food supply. Seasonal trophic niche breadth differences were evident for gray snapper, great barracuda and bluestriped grunt, while niche breadth was equivalent between seasons for seabream. Based on seasonal food supply in the environment, niche breadth values did not match basic foraging theory predictions, which state niche breadth should expand as preferred food resources become scarce. Tethering experiments indicated that predation rates were highest nearest the mangrove edge and decreased with increasing distance from shore. Moreover, predation pressure at night was nearly twice as high compared to the day. Testing these data against my predictions from foraging theory, I found that none of the fishes examined (gray snapper, seabream and bluestriped grunt) were distributed according to IFD. Seabream and gray snapper avoided foraging close to the mangrove-edge, where their food was most abundant, but risk was highest. Bluestriped grunt appeared to forage randomly across the distance gradient despite spatial variation in food and predation risk. Overall, results suggest that: (1) spatial patterns of utilization of seagrass habitat adjacent to the mangrove-seagrass ecotone differs by species, life-stage and season; (2) Seasonal shifts in diet were not correlated with changes in relative abundance of food supply; (3) trophic niche breadth of late juveniles did not expand with declines in their food resources; (4) the mangrove-seagrass ecotone appears to serve as a hunting corridor for predators targeting juvenile fishes moving about the mangroves; and (5) two of the three species examined appeared to give up food in return for safety by avoiding foraging near the mangroves, despite high food availability.

Boundaries between adjacent habitats can create unique biotic and abiotic conditions, varying species compositions and abundances between the edge and interior of habitats. As habitats become fragmented, the relative amount of edge increases. Understanding the role that habitat edges have in determining species compositions and abundances is fundamental for conservation and management of habitats, particularly those under threat from fragmentation. Seagrass habitats are common nearshore habitats that harbour a rich and diverse faunal assemblage that are under threat worldwide from human disturbance. Human induced fragmentation, and the propensity of seagrass to form naturally patchy landscapes, makes it an ideal system to study the effects of edges on fauna. / Evidence of fish displaying edge effects in seagrass habitats is equivocal. Assessment of fish edge effects was done by sampling seven positions within seagrass habitats at fine spatial scales. Strong, consistent patterns in fish distributions demonstrated clear edge effects both within and alongside seagrass at these sites. The total number of fish sampled was greater at the seaward seagrass edge than the seagrass middle, but there was little difference between the seagrass middle and the shoreward seagrass edge. Four individual fish species showed preferences for the seagrass edges. Further investigation revealed that patch size could influence the magnitude of edge effects in seagrass beds. Fish were sampled in ten variously sized seagrass patches in three positions within each patch. Two species showed variations in edge effects across patches which could be attributed to the area of the patch. Changes in patch size can influence the magnitude of edge effects that species display, suggesting that patch area effects (fish density varying with patch size) could be caused by edge effects. / Food availability and predation are mechanisms commonly used to explain edge effect patterns. Gut analysis was done on Stigmatopora nigra sampled at the edge and middle of patches to determine if prey consumption varied between positions, and explain S. nigra distribution. There was little difference in prey consumed by S. nigra at the edge and middle of patches, suggesting that food was unlikely to be causing S. nigra edge effects, or that the influence of prey distribution was being masked by other factors such as seagrass structure. Predator abundances and foraging efficiency may vary at the edge and middle of patches, and consequently influence the distribution of prey fish within patches. Underwater videos were placed at four positions within seagrass habitats to assess predator distributions. Predatory Australian salmon, Arripis spp., spend more time over adjacent sand than other positions, while small potential prey species (King George whiting, Sillaginodes punctata, recruits) appear to prefer the middle of seagrass patches, possibly to avoid encounters with salmon. To test if the predator-prey distributions reflected actual predation pressure, a tethering experiment was done to determine if predation was causing edge effects in small fishes. / King George whiting recruits and pipefish (Stigmatopora spp.) were tethered at each of the four positions at different depths. Survival time of whiting recruits was greater in the middle of shallow seagrass patches than other positions. Few pipefish were preyed upon, and survival time was lower over sand adjacent to seagrass than at the seagrass edge or middle. Video footage revealed that salmon was the dominant predator of both whiting recruits and pipefish. The distribution of predators and associated predation can explain edge effects for some species (whiting) but other mechanisms, or a combination of mechanisms, are determining edge effects for other species (pipefish). / Edge effects were common amongst fish species in seagrass habitats, and included permanent, temporary and predatory species. Patch size was found to influence the extent of the edge effect. There was little evidence to support prey consumption as an underlying mechanism causing higher fish abundances at the interior or edge of patches, however there was evidence that predation could be causing edge effects. Changes in fish distributions within seagrass patches due to patch size and predation when seagrass undergoes fragmentation need to be considered by not only ecologists, but also by managers in the development of plans for seagrass conservation. Future studies should investigate the relative contribution of different edge characteristics in determining the degree of seagrass edge effects.

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Planet Earth is undergoing a rapid rate of ecosystem conversion and degradation and one of the major challenges of current environmental science is to contribute to the management and conservation of biodiversity through the development of tools for assessing environmental change. The main goal of this doctoral dissertation is to contribute to the scientific literature on remote sensing tools for monitoring tropical dry forests, which is one of most important global change frontiers. This thesis is composed of five chapters which have the goals of covering the following specific goals: 1) To estimate the extent and geographic distribution of the neotropical dry forest. 2) To evaluate the potential use of satellite-detected fires as deforestation predictors in tropical dry forest and 3) To evaluate the potential of remote sensing techniques to detect edge effects in tropical dry forest. Before assessing the main goals of the thesis, in chapter two, Integrating Remote Sensing and Biodiversity research, we stress out the necessity of integrated assessments using multiple spatial and spectral resolution sensors over a wide array of ecosystems in order to find relevant ecosystem properties that would be sensitive to species richness. Chapter three, Extent and Conservation of tropical dry forests in the Americas, describes a regional scale mapping effort using coarse-scale imagery (MODIS 500-m) of the extent and geographical distribution of tropical dry forests that introduces several innovations to previous assessments. Based on these techniques, the total current extent of tropical dry forest in the Americas is 519,597 Km2. I also found that 66% of the ecosystem has been already converted to other land uses while only 4.5 % of is under protected areas. Chapter four, MODIS Active fires and deforestation in tropical dry forest landscapes, we show correlations patterns between the number of MODIS Active Fires and forest cover change in four tropical dry forest landscapes in Latin America. At the Santa Cruz site (Bolivia), correlations were strong and significant while at Chamela Site (Mexico) and the Mata Seca site (Brazil) correlations were moderate but significant as well. In the Machango site (Venezuela), active fires showed no correlation to deforestation events. In general, our findings show that fires detected by the MODIS sensor may be used as predictors of deforestation in tropical dry forest ecosystems. Chapter five, Edge influence on canopy openness and understory microclimate in two Neotropical dry forest fragments, addresses one of the most characteristic features of fragmented tropical forests: the increase in disturbance near the edges of the fragment or what is known as edge effects. Results in gap fraction and Fraction of Intercepted Photosynthetically Active Radiation (FiPAR) show that edge influence at tropical dry forest sites extend to at least 300-m. Finally, Chapter Six, Remote sensing of edge effects in dry forest fragments using CHRIS/Proba Imagery, shows an assessment of changes in the fraction of intercepted photosynthetically active radiation (FiPAR) across four edge-to-interior transects in tropical dry forests fragments and their correlation to spectral vegetation indices (SVIs) computed from the hyperspectral and multiangular CHRIS sensor on board the Proba platform. Results show that the use of spectral vegetation indices for identifying and quantifying edge effects in tropical forests have the potential to improve modeling of forest disturbance in fragmented landscapes. The work contained in these five chapters address issues that are critical to the advancement of tropical dry forest monitoring. These studies contribute to the current scientific literature on the use and application of optical remote sensing tools, not only applicable in tropical dry forests, but for tropical forest conservation at the continental, regional and local level.

As florestas representam o mais importante reservatório de carbono (C) dentre os ecossistemas terrestres e sua conversão para usos antrópicos da terra pode afetar o estoque de C na vegetação e no solo. Esse processo pode ser mediado pela composição e configuração da paisagem, em particular em função dos efeitos de borda nas áreas florestais e pelas mudanças no tipo de uso do solo e na idade das matas. Este trabalho tem como objetivo investigar como a distância da borda, as mudanças de uso do solo, a matriz e a idade da mata impactam os estoques de C na vegetação e no solo em paisagens fragmentadas de Mata Atlântica. Para isso, foram escolhidos doze fragmentos florestais (14 - 235 ha) em duas classes de idade (jovens: =70 anos) e em contato com diferentes tipos de matriz (plantações de Eucalipto, que têm menor contraste com a floresta, e campo antrópico, com maior contraste), onde foram estimados os estoques de C acima e abaixo do solo ao longo de dois transectos com 130 x 5 m perpendicular à borda de cada fragmento. No total foram amostrados 1.310 troncos e coletadas amostras de solo em três profundidades entre 0-30 cm e em quatro distâncias da borda, além de amostras de solo nos dois tipos de matriz. O estoque de C foi calculado por equações alométricas para a vegetação e por oxidação do C orgânico para o solo. Concorreram modelos lineares mistos com o estoque de C na vegetação ou no solo em função de diferentes combinações das variáveis: idade do fragmento, tipo de matriz e a distância da borda. Para o estoque de carbono no solo também concorreram modelos com combinações entre tipo de uso do solo e a declividade do terreno. O estoque de C teve média de 14,84 ± 5,67 Mg ha-1 na vegetação e 74,86 ± 19,0 Mg ha-1 no solo da floresta (profundidade 0-30 cm). O estoque de C na vegetação foi, conforme esperado, menor nas bordas de fragmentos antigos com matriz de campo, principalmente nos primeiros 40 m. No entanto, contrariamente ao esperado, em fragmentos jovens, o estoque de C foi invertido, sendo maior nas bordas, principalmente em contato com a matriz de eucalipto e nos primeiros 40 m da borda. Esse padrão foi determinado principalmente pela contribuição de C das árvores com DAP 10-20 cm, as quais foram responsáveis por grande parte do estoque de C (46%). O estoque de C no solo não foi explicado pela idade, matriz ou distância da borda, mas varia com a declividade dependendo do tipo de uso do solo: aumentou na floresta, diminuiu no eucaliptal e não variou no campo. Os resultados sugerem que os efeitos de borda têm um impacto diferente na biomassa aérea em fragmentos antigos (remanescentes) e jovens (regenerantes). Assim, os efeitos de borda podem estar beneficiando a comunidade vegetal presente nos fragmentos jovens e prejudicando a comunidade dos fragmentos antigos. O estoque de C do solo é pouco sensível às alterações da estrutura florestal (i.e. aos efeitos de borda e da idade da mata), porém responde ao tipo de uso do solo, sendo perdido quando este uso é mais intenso. Em suma, os resultados mostram que os estoques de C em paisagens que sofreram longo processo de desmatamento e fragmentação, como as da Mata Atlântica, são bastante heterogêneos e modulados pela estrutura da paisagem. Esse processo levou a importantes perdas nos estoques aéreos, enquanto os estoques no solo ainda permanecem altos, em particular em áreas florestais ou menos manejadas. Esse padrão espacial heterogêneo nos estoques de C em paisagens fragmentadas deve ser considerado em políticas públicas que visem fomentar serviços ecossistêmicos de regulação climática em florestas tropicais / Among terrestrial ecosystems, the forests compose the most important carbon reservoir and its conversion for anthropogenic use may affect the stored carbon in both vegetation and soil. In this context, the landscape structure (composition and configuration) can strongly modulated this process throughout edge effects and consequently by changes on land use and forest age. We aim investigate how edge effects, the changes on land use, the type of matrix and the forest age affects the carbon stock in fragmented landscapes in the Brazilian Atlantic Forest. For this, were chosen twelve forest fragments (14-235 ha) in two age classes (second growth =70 years) and in contact with different kinds of matrix (eucalyptus plantations - less contrasting edge and anthropogenic fields - more contrasting edge). In each forest fragment was stablished two perpendicular transects to the forest edge (130 x 5 m) were the stored carbon below and above-ground were estimated. In total were sampled 1.310 trunks and 756 soil samples in both types of matrix in four edge distances and carbon stored was calculated using alometric equations for vegetation and carbon organic oxidation for soil. Linear Mixed Models were building where the carbon stored above and below-ground could be a function of different combining variables: forest age, matrix type and edge distance. For the stored carbon below-ground were also included in the models the soil type and soil slope. The mean stored carbon above and below-ground was respectively 14.84 ± 5.67 Mg.ha-1 and 74.86 ± 19.0 Mg.ha-1. The stored carbon above-ground was lower in the edge (mainly first 40 m) in the most contrasting matrix (anthropogenic fields). However, unlike our hypothesis the stored carbon was reverse in the youngest forests with higher values in the edge (mainly in eucalyptus matrix and in the first 40m of the edge). This pattern can be assigned by the higher number of trees with DAP 10-20 which were responsible of the major part of the stored carbon (46%). The stored carbon below-ground has no relationship with the forest age, with the matrix type, neither with the edge distance. Although, it varies with the slope and land use: increase in the forest and decrease in eucalyptus plantations and does not change in the anthropogenic fields. Our results suggests that edge effects has different impact on stored carbon above-ground in old-growth and second-growth forests. The microclimatic changes due edge effects seems benefits second-growth forest composition while in old-growth forests, the opposite seems occurs. The carbon stored below-ground is little sensitive to changes on forest structure (i.e. edge effects and forest age), for another hand, it seems be strongly related with the land use type where the higher losses occurs when the land use is more intense. Nevertheless, the stored carbon above-ground are very heterogeneous and it should be due the intense process of deforestation and fragmentation of the Atlantic Forest. This intense process lead to important losses of stored biomass while the stored carbon below-ground remains higher mainly in forested areas or lesser managed lands. This heterogeneous pattern of stored carbon found in fragmented landscapes should be considered by decision makers aiming the provision of regulation ecosystem services mainly related to climate change in tropical forests

Florestas tropicais comportam dois terços de todas as espécies existentes no mundo, mas a perda de habitat, fragmentação e alteração na qualidade do habitat estão levando esta biodiversidade à extinção. Apesar de haver uma extensa literatura sobre este assunto, há um consenso geral de que o conhecimento gerado por muitos estudos é dependente do contexto e permeado por dificuldades metodológicas, como a alta correlação entre os fenômenos ocorrentes em paisagens alteradas pela ação humana e a miríade de respostas biológicas encontradas entre espécies. Desta forma, há ainda muita incerteza sobre a generalidade dos padrões observados e sua efetiva aplicação para a conservação de áreas naturais. Assim, nesta tese o objetivo foi de contribuir para esta discussão ao responder as seguintes perguntas: (i) Qual papel que bordas ecossistêmicas e efeitos de borda desenvolvem em comunidades naturais? (ii) A comunidade de aves é afetada pela fragmentação do habitat de maneira semelhante em matas primárias e secundárias? (iii) Seriam os efeitos de área e de borda análogos, e estariam estes associados em uma relação causal? (iv) Como a comunidade de aves se comporta com relação à variação na cobertura florestal, configuração do fragmento e qualidade do habitat, e será possível separar o efeito de cada variável? (v) Diferenças no protocolo amostral poderiam alterar as estimativas de atributos da comunidade e mudar a magnitude dos padrões ecológicos observados assim como a probabilidade de detectá-los? E (vi) qual estratégia é mais eficiente em identificar locais com alta integridade da comunidade, espécies indicadoras ou métricas indicadoras, como métricas da paisagem? Para responder estas perguntas foram usados dados provenientes de mais de 7000 aves capturadas com redes de neblina em 65 pontos amostrais localizados em seis paisagens de diferentes proporções de cobertura florestal e graus de perturbação na Mata Atlântica do Planalto Atlântico Paulista. Os resultados mostram que: (i) bordas estão presentes tanto em habitats naturais quanto alterados pela ação humana e produzem grandes efeitos sobre espécie e comunidades; (ii) apesar de matas secundárias possuírem uma comunidade de aves empobrecida, a forma como as aves são afetadas pela fragmentação nestes habitats é semelhante a matas primárias; (iii) efeitos de borda não são apenas análogos, mas podem ser a causa dos efeitos de área de fragmento; (iv) os efeitos de mudanças na cobertura florestal, configuração do fragmento e qualidade do habitat são altamente correlacionados e só podem ser separados com o uso de técnicas estatísticas que controlem explicitamente esta correlação; (v) a forma como o protocolo de amostragem é estruturado temporalmente afeta os padrões encontrados da relação espécie-área em paisagens fragmentadas; e por fim, (vi) métricas indicadoras, produzem resultados mais fortes e consistentes do que espécies indicadoras na identificação de áreas com alta integridade da comunidade. Assim, conclui-se que as aves de sub-bosque na Mata Atlântica são fortemente afetadas pela perda de habitat, fragmentação e mudanças na qualidade do habitat, mas esta influência é muito dependente do contexto temporal e espacial em que o estudo é realizado. Ainda, devido à baixa consistência dos resultados obtidos com amostras de curta duração, aliado ao grande poder explicativo dos modelos contendo métricas da paisagem, métricas indicadoras devem ser consideradas como a melhor estratégia para a identificação de áreas com alta integridade da comunidade. / Tropical forests hold two thirds of all species in the world, but alterations in habitat cover, fragmentation and quality are driving tropical biodiversity to the brink of extinction. Despite the extended literature on this subject, there is a general agreement that the knowledge gained from many of these studies are context-specific and pervaded by methodological difficulties, such as high inter-correlations among many phenomena in human-altered landscapes and diverse biological responses to landscape change that depend on species traits. Because of these issues, there is great uncertainty about the generality of observed patterns and the effective application of results in the conservation of natural areas. Thus, in this thesis the aim was to bring light to some of these concerns by answering the following questions: (i) What is the role of ecosystem boundaries and edge effects on natural communities? (ii) Do bird communities show similar patterns of responses to habitat fragmentation in secondary forests as those previously reported for primary forest? (iii) Are edge and area effects on bird species functionally similar and even causally associated? (iv) How does a tropical understory bird community respond to the highly inter-correlated variation in forest cover, patch configuration and habitat quality; and is it possible to set these influences apart? (v) Could differences in sampling protocol alter community estimates or change the magnitude of ecological trends and the probability of detecting them? And (vi), which strategy is more efficient in identifying sites with the highest community integrity, indicator species or structural indicators, such as landscape metrics? To address these questions I used data from more than 7000 birds captured using mist nets in 65 sites from six landscapes with different proportions of forest cover and habitat degradation in the Atlantic Forest of Brazil. The results showed that: (i) edges are ubiquitous features of natural and human-altered landscapes and strongly influence most species; (ii) even though the bird community in secondary forests is degraded relative to primary communities, birds from these areas show similar responses to edge and area effects found for primary forests; (iii) edge effects are not only functionally similar, but might also be the main drivers of area effects in fragmented landscapes; (iv) the effects of changes in forest cover, patch configuration and habitat quality are highly confounded and without the use of analyses that explicitly model this correlation it is impossible to pull apart the relative influence of each variable; (v) the way the sampling protocol is designed temporally affects the perceived patterns of how species respond to area effects; and finally, (vi) structural indicators generate stronger and more consistent results than indicator species in predicting changes in community integrity. In conclusion, the results show that understorey birds are highly affected by changes in habitat cover, fragmentation and habitat quality in the Atlantic forest, but this influence is strongly dependent on the temporal and spatial context of the study. Also, because of the low consistency of results obtained from short-surveys, and the large explanatory power of models containing landscape metrics, structural indicators should be viewed as the best strategy for identifying sites with high community integrity.

I examined the effect of sugarcane plantations on small mammal communities at 3 sites in the Lowveld of Swaziland during the dry and wet seasons of 2008. I evaluated changes in species abundance and community parameters in relation to distance to the interface, as well as the relationship between small mammal communities and environmental variables. I used pitfall arrays and Sherman live traps to sample small mammals along 9 traplines at the land-use interface and on a gradient extending 375 m into each land-use. I used point-centered-quarter, range pole, and line-transect sampling to characterize plant community structure. Two generalist small mammal species had increased abundance as distance into the sugarcane increased. Two species with wide geographic ranges appeared to select areas within 75 m of the interface. Four species with restricted habitat tolerances or diets were negatively affected by sugarcane, as was 1 species that selects for low ground cover. Two species may have avoided the interface. For the majority of species in the Lowveld, sugarcane does not provide habitat. Sugarcane monocultures > 375 m in width may form a barrier to movement of small mammal species. Species richness and diversity significantly decreased at the interface of 2 sites, however, 1 site had increased diversity associated with the interface. My analysis indicated a difference in community composition between the 2 land-uses and differences between the farthest interior conservation area (375 m)-interface (0 m) and the farthest interior sugarcane (375 m). There was no difference in community composition between seasons or distances within the conservation area. The farthest interior sugarcane trapline had distinctness from other traplines within the sugarcane, and may be of importance for minimizing the effects of habitat fragmentation in lowveld savanna. The effects of sugarcane did not extend into adjoining natural vegetation. My results indicated grass biomass, litter depth and shrub density played important roles in structuring the communities. Between sites, variation in community structure attributable to the sugarcane interface varied. The site with poorest vegetative cover had the highest relative importance of distance to the interface. One species (Steatomys pratensis) was negatively affected by distance to the interface.

This is a new method of determining magnetization strength, direction, and paleopole location from magnetic anomalies across edges of the equatorial band of magnetic sources on Mars. Different assumed locations of paleopoles result in different inducing field directions in the vicinity of an edge. Thus, with different paleopoles, the resulting magnetic fields from the edges of magnetic sources are different, and correlate differently with the observed fields. Best correlating observed and computed magnetic edge effect fields yield the potential paleopoles. The total gradient (TG) of the z-component magnetic field was used to identify the edges of magnetization boundaries. Three edge segments yielded meaningful paleopoles. They are: (15°S, 285°E)/(0°, 292.5°E) across the northeast trending edge east of Tharsis; (15°N, 195°E) across the southern boundary located in the Terra Cimmeria and Terra Sirenum area; and (15°S, 165°E)/(45°S, 180°E) across the northeast edge of Hellas Planitia. The effective magnetization in these regions (assuming 40km magnetic layer thickness) is 7.02, 42.13-94.79, and 2.63-3.51 A/m, respectively. Evidence from the overlap of regions of TG and chronostratigraphy suggests that the dynamo was active during the Noachian and may have been active in the early Hesperian.