No description available.

This study presents new data on soil organic matter dynamics in relation to two forest types in a strongly seasonal lowland rainforest in Korup National Park, SW Cameroon. Organic matter dynamics at the start of the wet season were investigated by quantifying changes in the amount of the standing crop of surface organic matter and light fraction soil organic matter (LF.SOM) in five replicate plots with low (≤ 15%) basal area ectomycorrhizal trees ≥ 30 cm gbh (LEM forest type), and five with high (≥ 45 %) basal area ectomycorrhizal trees (HEM forest types). Soil samples were collected in the wet season from three soil depths: an organic-enriched layer (0 - 3 cm), 3 - 8 cm and >8 cm layers, in both HEM and LEM forest types, in 1993 (3 harvests), and in 1994 (8 harvests). LF.SOM and heavy fraction soil organic matter (HF.SOM) were separated from < 2 mm whole soil using tap water and/or saturated NaI solution (density 1.65 g cm^-3). Other pools of organic matter quantified included that in the > 2 mm soil fraction and in the < 2 mm sieved whole soil. LF.SOM accounted for 10 - 40 % soil organic matter, 7 - 34 % carbon, 2 - 28 % N and 2 - 25% P of the < 2 mm whole soil across forest types and down the soil profile. The > 2 mm soil fraction accounted for 14 - 21% carbon, 11 - 20 % N, and 6 - 22% P of total soil (i.e. <2 mm whole soil + > 2 mm soil fraction). The amount of LF.SOM was not significantly different between the two forest types at all depths. Both the amount of the standing crop of surface organic matter and LF.SOM declined as the wet season progressed. However, the amount of LF.SOM declined faster (55 %) in the LEM forest than in the HEM forest (22 %). On the other hand, the amount of HF.SOM increased over the same period. A vertical gradient in LF.SOM content was observed.

No description available.

No description available.

The distribution of species in space is determined by the species dispersal capacity, adaptation to environmental conditions, and response to predators and competitors. To determine the importance of dispersal limitation, environmental filtering, and species interactions on the distribution of species in the Brazilian Amazonian forest, I sampled termites in a large area of Brazil. I investigated patterns in species occurrence that could indicate competition and predation structuring termite communities, and analyzed the association of termite abundance and species richness with the density of ant predators. The spatial distribution of termites, and their association with climatic and edaphic conditions were also used to infer about the effects of dispersal limitation and environmental filtering. A total of 271 termite species and 4,389 colonies was found in the 148 transects sampled. Predator density was the strongest predictor of termite abundance and species richness at small spatial scales, but the turnover in termite species composition was mostly associated with measures of soil texture. At broad spatial scales, soil chemistry, climate, and isolation by distance were associated with termite abundance, species richness, and species composition. These results suggest that both species interactions, their association with the environment, and their dispersal capacity determine their distribution. Nevertheless, dispersal limitation seem to be stronger over large areas, whereas environmental filtering can act both at small and large geographic scales.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第19070号 / 人博第723号 / 新制||人||173(附属図書館) / 26||人博||723(吉田南総合図書館) / 32021 / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 市岡 孝朗, 教授 加藤 眞, 教授 瀬戸口 浩彰 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DGAM

Tropical forests, which provide important ecosystem functions and services, are increasingly threatened by anthropogenic pressures. This has resulted in an urgent need to understand tree species diversity of those forests. Where knowledge of that diversity is largely from the botanical surveys and local ecological studies, data must inevitably be up-scaled from point observations to the landscape and regional level if a holistic perspective is required. This thesis explores aspects of the spatio-temporal heterogeneity of canopy reflectance patterns over the forests of French Guiana, in order to assess whether this information could help defining an ecologically consistent forest typology. To gain insight into both the spatial and temporal heterogeneity of French Guiana’s forests, instrumental artefacts affecting the satellite data first had to be addressed. Data used in this study represent the spectral response of forest canopies, and the way in which such data are captured makes them susceptible to the ‘bi-directional reflectance distribution function’ (BRDF). BRDF indicates that objects do not reflect light in equal proportions in all directions (isotropically). Thus, forest canopies will reflect light anisotropically depending on factors including canopy roughness, leaf optical properties and inclination, and the position of the sun relative to the sensor. The second chapter of this thesis examines how BRDF affects the canopy reflectance of forests in French Guiana, and how not correcting for BRDF affects spectral classifications of those forests. When monthly reflectance data corrected for the artefact are examined, these suggest seasonally-occurring changes in forest structure or spectral properties of French Guiana’s forests. The third chapter of this thesis thus examines temporal effects of BRDF, and used cross-regional comparisons and plot-level radiative transfer modelling to seek to understand the drivers of the monthly variation of the forests’ canopy reflectance. For the latter, the Discrete Anisotropic Radiative Transfer (DART) model was used along with aerial laser scanning (ALS) observations over different forest structures, indicating that the observed variation in reflectance (and derivatives known as vegetation indices) could not be explained by monthly variations in solar direction. At the regional scale, it was also demonstrated that forests in the Guiana Shield possess temporal variation distinct from forests in central Africa or northern Borneo, forests also lying just above the Equator. Had the observed temporal variation in vegetation indices been the result of BRDF, it would have been expected that the forests in the three zones would have similar patterns of variation, which they did not. Central African forests appear to have their greening synchronized with rainfall, whereas forests in the Guianas appear synchronized with the availability of solar radiation. Further analysis of the vegetation index time-series of observations also indicated that different types of forests in French Guiana possess distinct patterns of temporal variation, suggesting that tropical forest types can be discriminated on the basis of their respective “temporal signatures.” That was exploited in the fourth chapter of the thesis, which maps forests in French Guiana based on their combined spatio-temporal canopy reflectance patterns and by so doing presents a novel way of addressing forest typology, based on ecologically meaningful information. The thesis presented demonstrates that it is possible to adequately address remote sensing data artefacts to examine patterns of spatial and temporal variation in tropical forests. It has shown that phenological patterns of tropical rainforests can be deduced from remote sensing data, and that forest types can be mapped based on spatio-temporal canopy reflectance patterns. It is thus an important contribution to understand the ecology of tropical forests in French Guiana and to improve the toolbox of scientists dealing with the identification of spatio-temporal patterns observable in forests at the landscape level.

En 1988, après deux décennies de régime militaire, le Brésil rédige une nouvelle constitution afin de bâtir une nation fondée sur la démocratie, le multiculturalisme et l’intégration. C’est dans ce cadre que (re)naissent les quilombos, communautés afro-descendantes auxquelles est accordée, en guise de réparation historique, la propriété collective de leurs terres. Sont ainsi démarqués des territoires différenciés pour des populations spécifiques au nom de la diversité. Mais une telle mesure peut-elle suffire à assurer la durabilité de ces communautés noires rurales ? Pour répondre à cette question, nous recourons à trois études de cas, trois communautés quilombolas (Amazonie, Etat du Pará pour deux d’entre elles et vallée du Ribeira, Etat de São Paulo) dont nous croisons les caractéristiques et les trajectoires, les structures et les stratégies. Il s’agit, de cette façon, d’observer les mécanismes de leur durabilité, à partir d’un double point de vue. Le point de vue social d’abord, que nous évaluons en nous appuyant sur les travaux d’Elinor Ostrom et sa théorie des biens communs. Mais aussi un point de vue territorial qui, nous le supposons, permet d’enrichir l’observation des systèmes sociaux et de leurs mécanisme d’adaptation et de démontrer les enjeux territoriaux de la durabilité elle-même. Finalement, l’étude de nos trois cas permet de mettre en évidence que la « quilombolisation » des communautés semble remplir partiellement ses objectifs, en assurant des garanties territoriales et sociales certes, mais en rencontrant quelques difficultés à les inscrire pleinement dans le temps long. / In 1988, after two decades of military regime, Brazil writes a new constitution in order to build a nation founded on democracy, multiculturalism and integration. In this framework, Quilombos are reborn. They are afro-descendant communities to whom is given, as a historical redemption, the collective tenure of their lands. Differentiated territories are tenured for specific populations on behalf of diversity. But can such a measure be sufficient to ensure the sustainability of these black rural communities? To answer this question, we focus on three case studies, three Quilombola communities (two in the Amazon, State of Pará and one in the Ribeira Valley, State of São Paulo) and we cross their features and trajectories, their structures and strategies. In this way, the aim is to observe the mechanisms of their sustainability, from a double point of view. A social point of view, first, that we assess by relying on Elinor Ostrom’s studies and her theory of Commons. But a territorial point of view too, that, we assume, completes the observation of social systems and their adaptation mechanisms and demonstrate the territorial stakes of the sustainability. Finally, the three case studies highlight that the “quilombolization” of the communities seems to partially fulfill its objectives, ensuring territorial and social guarantees, but still having some difficulties to last. / Em 1988, após duas décadas de governo militar, o Brasil escreve uma nova constituição para construir uma nação fundada sobre a democracia, o multiculturalismo e a integração. É nesse marco que (re)nascem os quilombos, comunidades afrodescendentes as quais é concedida, como reparação histórica, a propriedade coletiva de suas terras. Assim são demarcados territórios diferenciados par populações específicas em nome da diversidade. Mas, será que tal medida poda ser suficiente para garantir a sustentabilidade dessas comunidades negras rurais? Para responder a esse pergunta, mobilizamos três estudos de caso, três comunidades quilombolas (da Amazônia, Estado do Pará e do vale do Ribeira, Estado de São Paulo) das quais cruzamos as características e as trajetórias, as estruturas e as estratégias. Trata-se, dessa forma, de observar os mecanismos de sua sustentabilidade, a partir de um duplo ponto de vista. O ponto de vista social primeiro, que avaliamos nos apoiando nos trabalhos de Elinor Ostrom e sua teoria dos bens comuns. Mas também um ponto de vista territorial que, assumimos, permite enriquecer a observação dos sistemas sociais e seus mecanismos de adaptação e de demonstrar os desafios territoriais da própria sustentabilidade. Finalmente, o estudo de nossos três casos permite evidenciar que a “quilombolização” das comunidades parece cumprir parcialmente seus objetivos, assegurando garantias territoriais e sociais, mas encontrando algumas dificuldades para inseri-las plenamente no tempo longo.

Tropical forests, which provide important ecosystem functions and services, are increasingly threatened by anthropogenic pressures. This has resulted in an urgent need to understand tree species diversity of those forests. Where knowledge of that diversity is largely from the botanical surveys and local ecological studies, data must inevitably be up-scaled from point observations to the landscape and regional level if a holistic perspective is required. This thesis explores aspects of the spatio-temporal heterogeneity of canopy reflectance patterns over the forests of French Guiana, in order to assess whether this information could help defining an ecologically consistent forest typology. To gain insight into both the spatial and temporal heterogeneity of French Guiana’s forests, instrumental artefacts affecting the satellite data first had to be addressed. Data used in this study represent the spectral response of forest canopies, and the way in which such data are captured makes them susceptible to the ‘bi-directional reflectance distribution function’ (BRDF). BRDF indicates that objects do not reflect light in equal proportions in all directions (isotropically). Thus, forest canopies will reflect light anisotropically depending on factors including canopy roughness, leaf optical properties and inclination, and the position of the sun relative to the sensor. The second chapter of this thesis examines how BRDF affects the canopy reflectance of forests in French Guiana, and how not correcting for BRDF affects spectral classifications of those forests. When monthly reflectance data corrected for the artefact are examined, these suggest seasonally-occurring changes in forest structure or spectral properties of French Guiana’s forests. The third chapter of this thesis thus examines temporal effects of BRDF, and used cross-regional comparisons and plot-level radiative transfer modelling to seek to understand the drivers of the monthly variation of the forests’ canopy reflectance. For the latter, the Discrete Anisotropic Radiative Transfer (DART) model was used along with aerial laser scanning (ALS) observations over different forest structures, indicating that the observed variation in reflectance (and derivatives known as vegetation indices) could not be explained by monthly variations in solar direction. At the regional scale, it was also demonstrated that forests in the Guiana Shield possess temporal variation distinct from forests in central Africa or northern Borneo, forests also lying just above the Equator. Had the observed temporal variation in vegetation indices been the result of BRDF, it would have been expected that the forests in the three zones would have similar patterns of variation, which they did not. Central African forests appear to have their greening synchronized with rainfall, whereas forests in the Guianas appear synchronized with the availability of solar radiation. Further analysis of the vegetation index time-series of observations also indicated that different types of forests in French Guiana possess distinct patterns of temporal variation, suggesting that tropical forest types can be discriminated on the basis of their respective “temporal signatures.” That was exploited in the fourth chapter of the thesis, which maps forests in French Guiana based on their combined spatio-temporal canopy reflectance patterns and by so doing presents a novel way of addressing forest typology, based on ecologically meaningful information. The thesis presented demonstrates that it is possible to adequately address remote sensing data artefacts to examine patterns of spatial and temporal variation in tropical forests. It has shown that phenological patterns of tropical rainforests can be deduced from remote sensing data, and that forest types can be mapped based on spatio-temporal canopy reflectance patterns. It is thus an important contribution to understand the ecology of tropical forests in French Guiana and to improve the toolbox of scientists dealing with the identification of spatio-temporal patterns observable in forests at the landscape level.