L’objectif de ce travail était de caractériser la variabilité saisonnière des échanges gazeux des arbres de la canopée en forêt tropicale humide guyanaise confrontés à des saisons sèches.L’étude s’est orientée sur la mesure des flux de carbone et d’eau au cours des saisons sèches dans deux habitats contrastés du point de vue hydrique, afin de préciser leur sensibilité et réponse à la sècheresse. Nos résultats montrent qu’une proportion non négligeable d’arbres ne subit pas de sécheresse marquée en saison sèche, malgré la forte diminution de la teneur en eau du sol en surface. Nous faisons l’hypothèse que ces arbres possèdent alors des racines en profondeur qui leur permettent d’accéder aux horizons qui restent humides malgré la faible pluviométrie. Durant les longues saisons sèches, nous observons une diminution de l’assimilation nette de CO2 foliaire, de l’efflux de CO2 des troncs ou de la densité de flux de sève, et dans une moindre mesure de la respiration foliaire. Cette diminution concerne un nombre plus important d’arbres, quand l’intensité de la sécheresse est plus forte (2008 par rapport à 2007). Néanmoins, de grandes différences de réponse à la sècheresse du sol ont été observées, suggérant des sensibilités et des mécanismes de réponse différents entre ces arbres. En habitat de bas-fond, nous montrons une plus faible diminution des flux carbonés et hydriques en saison sèche, suggérant un accès pour ces arbres aux horizons humides, proches de la nappe phréatique. Par ailleurs, nos résultats suggèrent pour certains arbres un effet négatif des conditions d’anoxie sur ces flux en saison des pluies.Si l’accentuation de l’intensité des saisons sèches en forêt tropicale humide Amazonienne se confirme, comme suggérée par les modèles climatiques, ce travail suggère des modifications rapides de la composition spécifique des forêts, au profit des espèces plus résistantes aux contraintes hydriques / The aim of this work was to characterize the seasonal variations in leaf and trunk gas exchange of tropical rainforest canopy trees exposed to dry seasons. This study focused on measuring gas exchange (CO2 and H2O) at the leaf and trunk level during dry seasons in a Terra firme forest and in a seasonally flooded forest in order to specify their sensitivity and response to drought.Our results showed that part of the studied trees do not encounter a large reduction in soil water content during dry seasons, suggesting that they display deep rooting systems.During long dry periods, we recorded a decrease in leaf photosynthesis, trunk CO2 efflux or sap flow density, and foliar respiration to a lesser extent, for a majority of the trees. Nevertheless, large differences among trees in their response to these conditions were observed, suggesting distinct sensitivities and response to soil drought among trees. Furthermore, these variations were greatest when soil drought was highest (2008 as compared to 2007).In seasonally flooded forest, the decrease in gas exchange was less, suggesting that these trees do have access to wet layers during the dry season, close to the groundwater. However, during wet seasons, we observed a negative effect of anoxia for some trees, whereas others did not display any response, suggesting large differences in tolerance to anoxia among trees abundant in these seasonally flooded forests.We conclude that would seasonal soil droughts increase over the next decades, large vegetation changes might occur because of the large differences among trees in their functional response to soil drought conditions

Submitted by Natalie Mendes (nataliermendes@gmail.com) on 2015-11-18T00:32:31Z No. of bitstreams: 1 Disserta??o - Marcelo dos Santos Silva - 2013.pdf: 7962051 bytes, checksum: 4e7968dec1d69dfb701ea5b5c43215dd (MD5) / Made available in DSpace on 2015-11-18T00:32:31Z (GMT). No. of bitstreams: 1 Disserta??o - Marcelo dos Santos Silva - 2013.pdf: 7962051 bytes, checksum: 4e7968dec1d69dfb701ea5b5c43215dd (MD5) Previous issue date: 2013-03-25 / Conselho Nacional de Pesquisa e Desenvolvimento Cient?fico e Tecnol?gico - CNPq / This study aimed to contribute to the knowledge of wood anatomy of the Atlantic Forest woody species, discussing their ecological/functional value, in addition to qualifying these species for energy generation and/or papermaking, based on derived values from measurements of the fibers and the bulk density. Serra da Jiboia is one of the areas indicated as priority for conservation of the Atlantic Forest and considered of extreme biological importance in terms of vegetation. Three to ten samples of 25 species were collected in the Serra da Jiboia, El?sio Medrado, Bahia. The portion from 1 to 3 cm from the bark was considered for making a macerate, histological slides, and measurement of the bulk density. The results are shown in two chapters and two appendices. In chapter 1, the existence of ecological trends for the Atlantic Forest of Serra da Jiboia was examined. The high frequency for growth rings boundaries distinct, diffuse porosity, absence of vessel arrangement, simultaneous presence of multiple and solitary vessels, simple perforation plates, tangential diameter of vessel larger than 350 ?m, nonseptate fibers, fiber length between 900-1600 ?m, fibers with simple to minutely bordered pits, rays per millimeter: 4-12, rays and/or axial elements irregularly storied and presence of inorganic inclusions. Most of these characteristics were interpreted as ecological trends for the Atlantic Forest of Serra da Jiboia, based on an analysis of the literature about their functional meanings and their correlation with the environmental characteristics of this environment. A smaller amount was assessed as arising from general evolutionary trends for the angiosperms. The conduction area, mesomorphy and vulnerability index, showed wide variation. More integrated studies involving wood anatomy which consider other aspects of the plants should be developed for a better understanding of the ecologic trends as well as its contrasting variations. In chapter 2, in which the anatomical and physical qualification of the wood for paper and/or energy production was made, four derived values ? wall fraction, flexibility coefficient, Runkel ratio and slenderness ratio ? and bulk density were measured. None of the species displayed all of the derived values optimal for paper production, although if each derived value is considered separately many of them could be qualified for this purpose. Most of the species were considered appropriate for power generation because they exhibit high wall fraction, Runkel ratio and high bulk density, and low flexibility coefficient. Aspidosperma discolor, Helicostylis tomentosa, Miconia amoena and Myrsine guianensis stand out from the rest. In conclusion, Serra da Jiboia proves to be a potential area for sustainable management studies of economically viable timbers. / Esse trabalho teve como objetivo contribuir para o conhecimento da anatomia do lenho de esp?cies arb?reas da Mata Atl?ntica, discutindo seu valor ecol?gico/funcional, al?m de qualificar estas esp?cies para gera??o de energia e/ou fabrica??o de papel, baseando-se nos valores derivados das dimens?es das fibras e na densidade aparente. A Serra da Jiboia ? uma das ?reas indicadas como priorit?rias para conserva??o da Mata Atl?ntica e classificada como de extrema import?ncia biol?gica no quesito vegeta??o. Foram coletadas de tr?s a dez amostras de 25 esp?cies nesta ?rea, localizada no munic?pio de El?sio Medrado, Bahia. Considerou-se a por??o entre 1-3 cm a partir da casca para confec??o de macerado, das l?minas histol?gicas e aferi??o da densidade aparente. Os resultados est?o apresentados em dois cap?tulos, e dois ap?ndices. No cap?tulo 1, examinou-se a exist?ncia de tend?ncias ecol?gicas para a Mata Atl?ntica da Serra da Jiboia, registrou-se alta frequ?ncia para an?is de crescimento distintos, porosidade difusa, aus?ncia de arranjo dos vasos, presen?a simult?nea de vasos solit?rios e m?ltiplos, placa de perfura??o simples, comprimento dos elementos de vasos maior que 350 ?m, fibras com ar?ola das pontoa??es simples a reduzida, presen?a de fibras n?o septadas, comprimento da fibra entre 900-1600 ?m, 4-12 raios por mil?metro, raios e elementos axiais n?o estratificados e presen?a de inclus?es inorg?nicas. A maioria destas caracter?sticas foi interpretada como tend?ncias ecol?gicas para a Mata Atl?ntica atrav?s da discuss?o com a literatura sobre seus significados funcionais e a correla??o destes com as caracter?sticas ambientais desse ambiente. Uma menor quantidade foi avaliada como decorrente das tend?ncias evolutivas gerais para as angiospermas. A ?rea de condu??o, ?ndice de vulnerabilidade e mesomorfismo apresentaram grande varia??o, trabalhos mais integrativos, envolvendo a anatomia da madeira, que considerem outros aspectos das plantas, devem ser desenvolvidos para uma melhor compreens?o das tend?ncias ecol?gicas, bem como da varia??o que se contrap?em a esta. No cap?tulo 2, no qual ? feita a qualifica??o anat?mica e f?sica da madeira para fabrica??o de papel e/ou produ??o de energia, quatro valores derivados ? fra??o parede, coeficiente de flexibilidade, ?ndice de Runkel e ?ndice de enfeltramento ? e a densidade aparente foram mensurados. Nenhuma esp?cie apresentou todos os valores derivados ?timos para a produ??o de papel, embora se considerado cada valor derivado isoladamente muitas delas podem ser qualificadas positivamente para este fim. A maioria das esp?cies apresentou-se aptas ? gera??o de energia por exibirem fra??o parede, ?ndice de Runkel e densidade aparente alta e baixo coeficiente de flexibilidade, destacando-se Aspidosperma discolor, Helicostylis tomentosa, Miconia amoena e Myrsine guianensis. Conclui-se, portanto, que a Serra da Jiboia apresenta-se como uma ?rea em potencial para estudos de manejo sustent?vel de madeiras economicamente vi?veis.

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La distribution de l'abondance des espèces en un site, et la similarité de la composition taxonomique d'un site à l'autre, sont deux mesures de la biodiversité ayant servi de longue date de base empirique aux écologues pour tenter d'établir les règles générales gouvernant l'assemblage des communautés d'organismes. Pour ce type de mesures intégratives, le séquençage haut-débit d'ADN prélevé dans l'environnement (" ADN environnemental ") représente une alternative récente et prometteuse aux observations naturalistes traditionnelles. Cette approche présente l'avantage d'être rapide et standardisée, et donne accès à un large éventail de taxons microbiens jusqu'alors indétectables. Toutefois, ces jeux de données de grande taille à la structure complexe sont difficiles à analyser, et le caractère indirect des observations complique leur interprétation. Le premier objectif de cette thèse est d'identifier les modèles statistiques permettant d'exploiter ce nouveau type de données afin de mieux comprendre l'assemblage des communautés. Le deuxième objectif est de tester les approches retenues sur des données de biodiversité du sol en forêt amazonienne, collectées en Guyane française. Deux grands types de processus sont invoqués pour expliquer l'assemblage des communautés d'organismes : les processus "neutres", indépendants de l'espèce considérée, que sont la naissance, la mort et la dispersion des organismes, et les processus liés à la niche écologique occupée par les organismes, c'est-à-dire les interactions avec l'environnement et entre organismes. Démêler l'importance relative de ces deux types de processus dans l'assemblage des communautés est une question fondamentale en écologie ayant de nombreuses implications, notamment pour l'estimation de la biodiversité et la conservation. Le premier chapitre aborde cette question à travers la comparaison d'échantillons d'ADN environnemental prélevés dans le sol de diverses parcelles forestières en Guyane française, via les outils classiques d'analyse statistique en écologie des communautés. Le deuxième chapitre se concentre sur les processus neutres d'assemblages des communautés.[...] / Integrative patterns of biodiversity, such as the distribution of taxa abundances and the spatial turnover of taxonomic composition, have been under scrutiny from ecologists for a long time, as they offer insight into the general rules governing the assembly of organisms into ecological communities. Thank to recent progress in high-throughput DNA sequencing, these patterns can now be measured in a fast and standardized fashion through the sequencing of DNA sampled from the environment (e.g. soil or water), instead of relying on tedious fieldwork and rare naturalist expertise. They can also be measured for the whole tree of life, including the vast and previously unexplored diversity of microorganisms. Taking full advantage of this new type of data is challenging however: DNA-based surveys are indirect, and suffer as such from many potential biases; they also produce large and complex datasets compared to classical censuses. The first goal of this thesis is to investigate how statistical tools and models classically used in ecology or coming from other fields can be adapted to DNA-based data so as to better understand the assembly of ecological communities. The second goal is to apply these approaches to soil DNA data from the Amazonian forest, the Earth's most diverse land ecosystem. Two broad types of mechanisms are classically invoked to explain the assembly of ecological communities: 'neutral' processes, i.e. the random birth, death and dispersal of organisms, and 'niche' processes, i.e. the interaction of the organisms with their environment and with each other according to their phenotype. Disentangling the relative importance of these two types of mechanisms in shaping taxonomic composition is a key ecological question, with many implications from estimating global diversity to conservation issues. In the first chapter, this question is addressed across the tree of life by applying the classical analytic tools of community ecology to soil DNA samples collected from various forest plots in French Guiana. The second chapter focuses on the neutral aspect of community assembly.[...]

A growing body of work reveals that animal-mediated pollination is negatively affected by anthropogenic disturbance. Landscape-scale disturbance results in two often inter-related processes: (1) habitat loss, and (2) disruptions of habitat configuration (i.e. fragmentation). Understanding the relative effects of such processes is critical in designing effective management strategies to limit pollination and pollinator decline. I reviewed existing published work from 1989 to 2009 and found that only six of 303 studies separated the effects of habitat loss from fragmentation. I provide a synthesis of the current landscape, behavioral, and pollination ecology literature in order to present preliminary multiple working hypotheses to explain how these two landscape processes might independently influence pollination dynamics (Chapter 2). Despite the potential importance of independent effects of habitat fragmentation, effects on pollination remain largely untested. Studies designed to disentangle the independent effects of habitat loss and fragmentation are essential for gaining insight into landscape-mediated pollination declines. I also found that the field of landscape pollination ecology could benefit from quantification of the matrix, landscape functional connectivity, and pollinator movement behavior. To test the hypothesis that pollinator movement can be influenced by landscape configuration, I translocated radio-tagged hummingbirds across agricultural and forested landscapes near Las Cruces, Costa Rica (Chapter 3). I found return paths were on average more direct in forested than in agricultural landscapes. In addition, movement paths chosen in agricultural landscapes were more forested than the most direct route suggesting that hummingbirds avoided crossing open areas when possible. To determine if differences in pollinator movement translated to differences in plant reproduction, I tested the relative importance of landscape composition versus configuration on the reproductive success of Heliconia tortuosa, a hummingbird-pollinated forest herb (Chapter 4). I used a stratified random sampling design to select sites across orthogonal gradients in patch size, amount of forest, and elevation. I tested four landscape change hypotheses (i.e., local, landscape composition, landscape fragmentation, and fragmentation threshold). I found that Heliconia reproduction supported both the local site and landscape fragmentation hypotheses. Seed set increased with increasing forest patch size independent of amount of forest in the surrounding landscape. I also found that increasing patch size positively influenced the relative abundance of pollinators. The observed differences in seed set likely resulted from differences in hummingbird movements (Chapter 3) and/or abundance under different landscape configurations. / Graduation date: 2013

The development of human societies rests on functioning ecosystems. This thesis builds on integrated theories of linked social-ecological systems and complex adaptive systems to increase the understanding of how to strengthen the capacity of ecosystems to generate services that sustain human well-being. In this work, I analyze such capacity in human-dominated production ecosystems in Tanzania and Madagascar, and how this capacity is related to local management practices. Resilience of social-ecological systems refers to the capacity to buffer change, to re-organize following disruption, and for adaptation and learning. In Papers I and II, qualitative interview methods are used for mapping and analyses of management practices in the agroecosystem of the Mbulu highlands, Northern Tanzania. Practices such as soil and water conservation, maintenance of habitats for pollinators and predators of pests, intercropping, and landscape diversification, act to buffer food production in a variable environment and sustain underlying ecological processes. The practices are embedded in a decentralized but nested system of institutions, such as communal land rights and social networks, that can buffer for localized disturbances such as temporary droughts. Paper II compares these findings with practices in a farming system in Sweden, and suggests that similar mechanisms for dealing with uncertainty and change can exist in spite of different biophysical conditions. In Papers III and IV, interviews are combined with GIS tools and vegetation sampling to study characteristics and dynamics of the dry forests of Androy, southern Madagascar. Paper III reports on a previously underestimated capacity of the dry forest of southern Madagascar to regenerate, showing areas of regeneration roughly equal areas of degenerated forest (18 700 ha). The pattern of forest regeneration, degradation, and stable cover during the period 1986-2000 was related to the enforcement of customary property rights (Paper III). Paper IV reports on a network of locally protected forest patches in Androy that is embedded in a landscape managed for agricultural or livestock production and contributes to the generation of ecosystem services and ecosystem resilience at a landscape scale. Forest protection is secured by local taboos that provide a well-functioning and legitimate sanctioning system related to religious beliefs. In Paper V, two spatial modeling tools are used to assess the generation of two services, crop pollination and seed dispersal, by the protected forest patches in southern Androy. The functioning of these services is dependent on the spatial configuration of protected patches in the fragmented landscape and can be highly vulnerable to even small changes in landscape forest cover. In conclusion, many of the identified practices are found to make ecological sense in the context of complex systems and contribute to the resilience of social-ecological systems. The thesis illustrates that the capacity of human-dominated production ecosystems to sustain a flow of desired ecosystem services is strongly associated with local management practices and the governance system that they are embedded in, and that, contrary to what is often assumed, local management can and does add resilience for desired ecosystem services. These findings have substantial policy implications, as insufficient recognition of the dynamics of social-ecological interactions is likely to lead to failure of schemes for human development and biodiversity conservation.

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On the frontier of biodiversity-rich tropical forests, how land is used has an important role in buffering the primary ecosystem. Unsustainable small-scale cattle farming endangers soil quality and degrades the landscape. Silvopasture is a type of agroforestry that provides both ecological and livelihood benefits. A number of projects have been implemented across the tropics to encourage silvopasture adoption, with varying success. This dissertation questions the reasons for variable outcomes among participants within these projects: what motivates smallholders to adopt innovative land-use practices, and what form of incentives may help to overcome obstacles and catalyse adoption. This dissertation contributes to the ongoing debate on payments for ecosystem services, specifically about their suitability and effectiveness. To understand what influences decisions to adopt sustainable land-use practices, I review systematically and quantitatively the literature on adoption predictors, and I empirically analyse participation and short-term adoption in a pilot project for planting fodder trees in the border of a protected forest in Chiapas, Mexico, using primary and secondary data. I focus on subjective perspectives and livelihood strategies of actual and potential participants as explanatory variables, which have received unduly scarce attention in past studies. This lack of attention is partially caused by the difficulties of operationalising internal variables. I address this challenge by developing an analytical approach that increases the precision of the resulting perspectives in Q methodology. I cluster livelihood strategies and model adoption. This in-depth case-study suggests the type of incentives that are adequate to encourage adoption of sustainable land-use practices. Results indicate that payments may not be the best incentive for pioneer adopters, and that the adoption process is composed of separate individual steps, which are influenced distinctly by identifiable predictors, such as livelihood diversity. Uncovering this heterogeneity of motivations towards adoption provides useful knowledge for designing more effective external policy interventions.

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