Made available in DSpace on 2014-06-11T19:30:57Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02-25Bitstream added on 2014-06-13T20:01:09Z : No. of bitstreams: 1 manzatto_ag_dr_rcla.pdf: 670572 bytes, checksum: 214e3956624d3fad7ce979a8133dfb58 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / As alterações na estrutura e na composição florística de um fragmento de floresta estacional Semidecidual foram descritos para o período de 14 anos (1989 - 2003). Esse fragmento, denominado Mata da Fazenda São José (MFSJ), apresentou para o período de estudo um aumento na densidade arbustivo-arbórea, entretanto houve uma diminuição da área basal total para a comunidade. A composição florística apresentou grande dinamismo, registrando a perda de 42 espécies e o ingresso de 38. As espécies dominantes apresentaram variações nos seus valores de densidade relativa, demonstrando que a estrutura fitossociológica é dinâmica, alterando-se ao longo do tempo. As análises multivariadas da vegetação indicaram a presença de quatro grupos vegetacionais relacionados aos quatro subgrupos edáficos identificados na área de estudo. As análises quantitativas e qualitativas da estrutura da comunidade demonstraram diferenças em cada um destes subgrupos, os quais apresentaram, ao longo do período de estudo, diferenças referentes às suas alterações na estrutura e na substituição das espécies. Essa característica tem modulado ao longo do tempo e projetado uma comunidade altamente diversificada, apresentando peculiaridades quanto às áreas que constituem o mosaico sucessional. / Changes in the structure and composition in the tropical semideciduous forest were described in 14-year-period. The studied fragment called Mata da Fazenda São José (MFSJ) presents under the studied period an increasing scrubs and trees density rate, however there was a decreasing rate on its total community basal area. The floristic composition showed great dynamism, indicating 42 species loss and 38 species gain. The main species presented variability on its relative density, demonstrating that the phytosociological structures is dynamic and changes as time passes by. The multivariate analysis of vegetation indicated four vegetation groups, related to the four different soil subgroups found on the study area. The quantitative and qualitative analysis over the community structures, presented differences on each of these groups which presented, along the studies period, differences related to its structure changing and species substitution. This characteristic has modulated and projected a highly diversified community showing different characteristics on the fields compounding the succession patch.

Tree-ring data serves as a chronicle of the past environment and provides long-term records about climate variations, volcanic eruptions, glacial activity and many others processes. Over the past few decades, dendrochronology has become common in studying disturbances. This thesis is focused on release detection methods (i.e. abrupt growth after death of neighbouring tree(s)) and their application. The presented review showed that despite the some uncertainties in methodological approaches, release detection is a reliable tool for forest disturbance reconstruction. In this thesis, release detection was applied in various forest ecosystems for reconstruction of disturbances and their effects. The achieved results importantly contribute to the understanding of the ecological processes concerning forest management, long-term changes in natural forest ecosystems, forest diversity and the impact of global changes.

Orientador: Marco Antonio de Assis / Banca: Ivan Schiavini / Banca: Ricardo Ribeiro Rodrigues / Banca: Osmar Cavassan / Banca: Frederico Augusto Guimarães Guilherme / Resumo: As alterações na estrutura e na composição florística de um fragmento de floresta estacional Semidecidual foram descritos para o período de 14 anos (1989 - 2003). Esse fragmento, denominado Mata da Fazenda São José (MFSJ), apresentou para o período de estudo um aumento na densidade arbustivo-arbórea, entretanto houve uma diminuição da área basal total para a comunidade. A composição florística apresentou grande dinamismo, registrando a perda de 42 espécies e o ingresso de 38. As espécies dominantes apresentaram variações nos seus valores de densidade relativa, demonstrando que a estrutura fitossociológica é dinâmica, alterando-se ao longo do tempo. As análises multivariadas da vegetação indicaram a presença de quatro grupos vegetacionais relacionados aos quatro subgrupos edáficos identificados na área de estudo. As análises quantitativas e qualitativas da estrutura da comunidade demonstraram diferenças em cada um destes subgrupos, os quais apresentaram, ao longo do período de estudo, diferenças referentes às suas alterações na estrutura e na substituição das espécies. Essa característica tem modulado ao longo do tempo e projetado uma comunidade altamente diversificada, apresentando peculiaridades quanto às áreas que constituem o mosaico sucessional / Abstract: Changes in the structure and composition in the tropical semideciduous forest were described in 14-year-period. The studied fragment called Mata da Fazenda São José (MFSJ) presents under the studied period an increasing scrubs and trees density rate, however there was a decreasing rate on its total community basal area. The floristic composition showed great dynamism, indicating 42 species loss and 38 species gain. The main species presented variability on its relative density, demonstrating that the phytosociological structures is dynamic and changes as time passes by. The multivariate analysis of vegetation indicated four vegetation groups, related to the four different soil subgroups found on the study area. The quantitative and qualitative analysis over the community structures, presented differences on each of these groups which presented, along the studies period, differences related to its structure changing and species substitution. This characteristic has modulated and projected a highly diversified community showing different characteristics on the fields compounding the succession patch / Doutor

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2017-12-11T12:45:44Z No. of bitstreams: 1 PGEF16MA067.pdf: 68542 bytes, checksum: 23aa33dada350b049cf9be80cf0294d9 (MD5) / Made available in DSpace on 2017-12-11T12:45:44Z (GMT). No. of bitstreams: 1 PGEF16MA067.pdf: 68542 bytes, checksum: 23aa33dada350b049cf9be80cf0294d9 (MD5) Previous issue date: 2016-06-24 / FAPESC / Uniedu / This dissertation aimed to identify the impact of reservoir filling of a hydroeletric power station on the floristic-structural compostion of the tree component in ecotonal fragment between Mixed Ombrophilous Forest and Deciduous Forest, located in the municipality of São José de Cerrito, SC. Two survey were conducted: in the first and second year after the reservoir water filling. For this, 48, 200 m2, plots were allocated through stratified systematic sampling, in three sectors: bottom (sector 1), adjacent to the reservoir, middle slope and upper slope. The trees within plots with circumference at breast height (cbh) ≥ 15,7 cm were identified and measured (cbh), and, in the second evaluation year, the dead trees were counted and recruits incorporated to survey. In each plot, the following environmental variables were obtained: edaphic, topographic and environmental impact. The data were analyzed by phytosociological estimates, demographic dynamics, multivariate analysis and modelling techniques. In the first year, the high number of dead trees (second greatest value of relative importance in community: 9.59%) stood out, with a significantly great number in the sector 1 (p < 0,05), which could be associated to the proximity to water reservoir. The dynamics demonstrated stability in richness and individuals number, whereas there were differences among sectors, with sector 1 presenting greater basal area loss (2.51%.year-1) than others. There was a weak relation between dynamics and evaluated environmental variables, indicating that the trees development is mostly associated to non-evaluated variables, such as reservoir influence. Thus, the present study indicates that the first effects of reservoir can be observed two years after the process of water filling / A presente dissertação objetivou identificar o impacto do enchimento do reservatório de uma Usina Hidreletrica (UHE) na composição florístico-estrutural do componente arbóreo de um fragmento em ecótono entre Floresta Ombrófila Mista e Floresta Estacional Decidual localizado no município de São José do Cerrito, SC. Foram realizadas duas avaliações: no primeiro e no segundo ano após o enchimento do reservatório. Para isso, foram alocadas 48 parcelas de 200 m² cada, de forma estratificada-sistemática, em três setores do fragmento: adjacente às margens do reservatório (setor 1), meio da encosta e topo da encosta. Os indivíduos arbóreos dentro das parcelas com circunferência a altura do peito (CAP) ≥ 15,7 cm foram identificados e mensurados (CAP), sendo que, no segundo ano de avaliação, os indivíduos mortos foram quantificados e os recrutas incorporados ao levantamento. Em cada parcela, foram mensuradas as variáveis ambientais: características edáficas, topográficas, de luminosidade e de impacto ambiental. Os dados foram analisados por estimativas fitossociológicas, cálculos de dinâmica, análises multivariadas e técnicas de modelagem. Destaca-se, no primeiro ano, o elevado número de indivíduos mortos (segundo maior valor de importância na comunidade: 9,59%), sendo significativamente maior no setor 1 (p < 0,05), o que pode estar associada à maior proximidade com a lâmina d’água. A dinâmica apresentou estabilidade na riqueza e em número de indivíduos, porém, entre os setores houve distinções, sendo o setor 1 caracterizado pela maior taxa de perda em área basal (2,51%.ano-1). Houve pouca relação das taxas de dinâmica com as variáveis ambientais analisadas, indicando que a maior influência encontrada sobre o desenvolvimento das árvores está associada a variáveis não utilizadas nas análises, como a influência do reservatório. Assim, o presente estudo indica que, dois anos após o enchimento do reservatório, foi possível perceber os primeiros efeitos do enchimento do lago da hidrelétrica na comunidade arbórea

Le rôle joué par les forêts tropicales dans le cycle du carbone à l'échelle planétaire est majeur. Tant par les énormes quantités stockées sous forme de bois, que par les flux de CO2 séquestrées annuellement dans les troncs et le sol. Plusieurs études mettent en évidence des changements structuraux au sein des forêts pantropicales durant les 20 dernières années, notamment une augmentation de la dynamique (recrutement et mortalité) (Lewis et al. 2004b; Phillips et al. 2004b) et de la biomasse aérienne ligneuse en forêt Amazonienne (Baker et al. 2004a). Ces changements de dynamique ont été mis en relation avec une disponibilité accrue en ressources auparavant limitantes (azote et CO2) et donc liés aux changements climatiques globaux. Cependant, les processus de régénération après perturbation dans un peuplement forestier génèrent, eux aussi, une réelle accumulation de biomasse. Des perturbations endogènes (chablis, glissements de terrains) ou exogènes (sécheresses, tempêtes ou actions anthropiques) pourraient être à l'origine de ces fluctuations de dynamique forestière. Sans une connaissance approfondie de l'état initial des forêts étudiées, il semble difficile de distinguer, localement, une accumulation de biomasse liée à un effet de régénération de celle liée à un forge climatique. La présente thèse cherche à investiguer s'il existe des stades de régénération au sein d'un même massif forestier, qui illustreraient différentes perturbations asynchrones. Ces stades sont déterminés sur la base de la structure forestière (densité, diamètre quadratique moyen) et au travers de l'architecture des arbres. Après avoir estimé les flux, stocks et bilans de biomasse sur le site d'étude, ceux-ci sont mis en relation avec des stades de régénération, pour montrer que les parcelles sont formées d'une majorité de stades en croissance et que cela engendre une accumulation nette de carbone durant la période de suivi (1991-2009). / As living trees constitute one of the major stocks of carbon in tropical forests, assessing the role of these ecosystems in the carbon cycle received an increasing scientific and political interest. A better understanding of variations in the dynamics and structure of tropical forests is necessary to predict the potential of these ecosystems to lose or store carbon, and to understand how they recover from disturbances. Recent findings showed an increase of the turn-over in pantropical forests (Phillips et al. 2004a) and an increase of above-ground biomass in neotropical forests (Baker et al. 2004a). These results were attributed to an increasing availability of abiotic ressources (CO2, nitrogen) enhancing forest dynamics. Nevertheless, these findings were controversial and some scientists pointed out statistical and methodological errors (Lewis et al. 2006a; Wright 2006).The present project is based on a very different point-of-view and makes a nother interpretation of these results. The main hypothesis of this study is that the observed changes in forest dynamics around the Amazonian basin and in French Guyana are the consequence of natural endogenous processes. Tropical forests are facing recurring disturbances of various intensities and scales, ranging from tree fall (several square meters) to major drought linked to El Niño events (thousands of hectares). Thus forests would never reach equilibrium, but would rather fluctuate between short periods of disturbance and long periods of regeneration. The main findings of this study are that forests at our site can be seen as a mosaic of areas at different structural and dynamical stages, most of them increasing in mean stem diameter and accumulating biomass. The overall biomass balance is a net biomass increase that might mainly be related to endogenous forest dynamic.

As florestas tropicais exibem elevada biodiversidade e desempenham um importante papel no ciclo global do carbono. Porém, essas florestas têm sido impactadas aceleradamente nos últimos anos. No Brasil, a floresta tropical Atlântica está restrita a aproximadamente 7 % de sua extensão original e seus remanescentes ainda sofrem ameaças. Com isso, informações sobre a dinâmica da vegetação desse bioma são importantes para entender o funcionamento desse ecossistema e servem de subsídio para auxiliar em sua conservação e restauração. No presente estudo, os principais processos que regem a dinâmica de uma floresta (mortalidade, recrutamento e crescimento) foram estimados em duas fisionomias distintas da floresta tropical Atlântica. Além disso, a variação líquida da biomassa acima do solo (BAS) também foi estimada. Para o presente estudo foram utilizadas cinco (5) parcelas permanentes de um (1) hectare inseridas no projeto temático Gradiente Funcional, sendo: quatro (4) na floresta de Terras Baixas e uma (1) na floresta de Restinga. Os inventários foram realizados no momento da implantação das parcelas permanentes (2006) e após dois (2) anos. Os resultados obtidos demonstraram que a Restinga (1635 ind.ha-1) possui maior densidade total de indivíduos vivos com o DAP \'>OU=\'4,8 cm que a Terras Baixas (1221 ind.ha-1). O estoque de biomassa acima do solo (BAS) foi maior na Terras Baixas (212,3 Mg.ha-1) que na Restinga (166,3 Mg.ha-1) (DAP \'>OU=\'4,8 cm). A distribuição dos indivíduos nas classes de diâmetro influenciou essas diferenças estruturais: a Restinga possui maior densidade total de indivíduos na menor classe de diâmetro e a floresta de Terras Baixas possui maior densidade de indivíduos na maior classe. Tal fato também impactou a distribuição do estoque de BAS nas classes de diâmetro: a floresta de Restinga estoca mais biomassa na classe de 10-30 cm e a floresta de Terras Baixas na maior classe de DAP, \'>OU=\'50 cm. A mediana da taxa de incremento diamétrico da comunidade arbórea não diferiu entre os dois tipos de floresta, sendo igual a 1,0 mm.ano-1 na Restinga e 0,8 mm.ano-1 na Terras Baixas (DAP \'>OU=\'4,8 cm). Diferenças na taxa de incremento diamétrico com relação às formas de vida (árvores e palmeiras) foram observadas. A taxa de incremento diamétrico das árvores apresentou relação positiva com o aumento das classes de DAP e o índice de iluminação de copa. O mesmo padrão não foi observado para as palmeiras. A taxa de mortalidade da comunidade arbórea foi semelhante entre os dois tipos de floresta, sendo igual a 2,46 % na Restinga e 2,00 % na Terras Baixas (DAP \'>OU=\'4,8 cm). A taxa de recrutamento também foi semelhante entre as florestas, sendo igual a 1,42 % na Restinga e 1,36 % na floresta de Terras Baixas. A variação líquida da BAS foi maior nas Terras baixas (0,64 Mg.ha-1.ano-1) que na Restinga (0,32 Mg.ha-1.ano-1). Por fim, a floresta tropical Atlântica apresenta maior densidade de indivíduos vivos, menor estoque de BAS, menor taxa de incremento e reposição quando comparada com outras florestas tropicais, possivelmente devido à distribuição da precipitação ao longo do ano / Tropical forests display a biodiversity unmatched by any other vegetation type and play an important role in the global terrestrial carbon cycle. However, tropical forests have been severely impacted in the last years. In Brazil, the tropical Atlantic forest is restricted to approximately 7 % of its original extension and its fragments still remain threatened. Hence, information regarding the vegetation dynamic of this important biome is important to understand the functioning of this ecosystem and support conservation and restoration actions. Here, the principal processes that drive forest dynamics (mortality, recruitment and growth) were estimated for two tropical Atlantic forest types. Additionally, the net aboveground biomass change (AGB) also was estimated. In this study, five one-hectare permanent plots established by the Gradiente Funcional project were adopted: four (4) plots in lowland and one (1) in seasonally flooded Atlantic forest. The forestry inventories were performed in the same time of permanent plot establishment (2006) and after two (2) years (2008). The results showed that the seasonally flooded Atlantic forest has greater total stem density (DBH \'>OU=\'4.8 cm) than lowland Atlantic forest, equal to 1635 ind.ha-1 in seasonally flooded and 1221 ind.ha-1 in lowland forest. The aboveground biomass (AGB) was greater in lowland than in seasonally flooded forest, equal to 166.3 Mg.ha-1 in seasonally flooded and 212.3 Mg.ha-1 in lowland forest (4,8 cm DBH). The distribution of trees among DBH classes influenced these structural differences: the seasonally flooded forest has high stem density at smaller DBH size class while the lowland forest has high stem density at larger DBH size class. In addition, that variation in size structure also impacted the AGB distribution among DBH classes: the seasonally flooded Atlantic forest has more AGB in the 10-30 cm DBH class and the lowland Atlantic forest has more AGB in the large size class ( \'>OU=\'50 cm). The median growth rate of tree community did not differ between the two forest types, equal to 1.0 mm.yr-1 in seasonally flooded and 0.8 mm.yr-1 in lowland forest ( \'>OU=\'4.8 cm DBH). Differences in growth rates regarding the life forms (tree and palm) were observed. Tree growth rates showed positive relationship with crown illumination index and DBH classes. The same tendency was not observed for palm life form. The mortality rate of tree community did not differ between the two forest types, equal to 2.46 % in seasonally flooded and 2.00 % in lowland forest ( \'>OU=\'4.8 cm DBH). The recruitment rate also did not differ between the two forest types, equal to 1.42 % in seasonally flooded and 1.36 % in lowland forest (\'>OU=\'4.8 cm DBH). The lowland Atlantic forest AGB net change (0.64 Mg.ha-1.yr-1) was higher than seasonally flooded Atlantic forest (0.64 Mg.ha-1.yr-1). Finally, the tropical Atlantic forest has higher stem density, lower AGB, lower growth and turnover rates than other tropical forests probably due to rainfall distribution among year

As florestas tropicais exibem elevada biodiversidade e desempenham um importante papel no ciclo global do carbono. Porém, essas florestas têm sido impactadas aceleradamente nos últimos anos. No Brasil, a floresta tropical Atlântica está restrita a aproximadamente 7 % de sua extensão original e seus remanescentes ainda sofrem ameaças. Com isso, informações sobre a dinâmica da vegetação desse bioma são importantes para entender o funcionamento desse ecossistema e servem de subsídio para auxiliar em sua conservação e restauração. No presente estudo, os principais processos que regem a dinâmica de uma floresta (mortalidade, recrutamento e crescimento) foram estimados em duas fisionomias distintas da floresta tropical Atlântica. Além disso, a variação líquida da biomassa acima do solo (BAS) também foi estimada. Para o presente estudo foram utilizadas cinco (5) parcelas permanentes de um (1) hectare inseridas no projeto temático Gradiente Funcional, sendo: quatro (4) na floresta de Terras Baixas e uma (1) na floresta de Restinga. Os inventários foram realizados no momento da implantação das parcelas permanentes (2006) e após dois (2) anos. Os resultados obtidos demonstraram que a Restinga (1635 ind.ha-1) possui maior densidade total de indivíduos vivos com o DAP \'>OU=\'4,8 cm que a Terras Baixas (1221 ind.ha-1). O estoque de biomassa acima do solo (BAS) foi maior na Terras Baixas (212,3 Mg.ha-1) que na Restinga (166,3 Mg.ha-1) (DAP \'>OU=\'4,8 cm). A distribuição dos indivíduos nas classes de diâmetro influenciou essas diferenças estruturais: a Restinga possui maior densidade total de indivíduos na menor classe de diâmetro e a floresta de Terras Baixas possui maior densidade de indivíduos na maior classe. Tal fato também impactou a distribuição do estoque de BAS nas classes de diâmetro: a floresta de Restinga estoca mais biomassa na classe de 10-30 cm e a floresta de Terras Baixas na maior classe de DAP, \'>OU=\'50 cm. A mediana da taxa de incremento diamétrico da comunidade arbórea não diferiu entre os dois tipos de floresta, sendo igual a 1,0 mm.ano-1 na Restinga e 0,8 mm.ano-1 na Terras Baixas (DAP \'>OU=\'4,8 cm). Diferenças na taxa de incremento diamétrico com relação às formas de vida (árvores e palmeiras) foram observadas. A taxa de incremento diamétrico das árvores apresentou relação positiva com o aumento das classes de DAP e o índice de iluminação de copa. O mesmo padrão não foi observado para as palmeiras. A taxa de mortalidade da comunidade arbórea foi semelhante entre os dois tipos de floresta, sendo igual a 2,46 % na Restinga e 2,00 % na Terras Baixas (DAP \'>OU=\'4,8 cm). A taxa de recrutamento também foi semelhante entre as florestas, sendo igual a 1,42 % na Restinga e 1,36 % na floresta de Terras Baixas. A variação líquida da BAS foi maior nas Terras baixas (0,64 Mg.ha-1.ano-1) que na Restinga (0,32 Mg.ha-1.ano-1). Por fim, a floresta tropical Atlântica apresenta maior densidade de indivíduos vivos, menor estoque de BAS, menor taxa de incremento e reposição quando comparada com outras florestas tropicais, possivelmente devido à distribuição da precipitação ao longo do ano / Tropical forests display a biodiversity unmatched by any other vegetation type and play an important role in the global terrestrial carbon cycle. However, tropical forests have been severely impacted in the last years. In Brazil, the tropical Atlantic forest is restricted to approximately 7 % of its original extension and its fragments still remain threatened. Hence, information regarding the vegetation dynamic of this important biome is important to understand the functioning of this ecosystem and support conservation and restoration actions. Here, the principal processes that drive forest dynamics (mortality, recruitment and growth) were estimated for two tropical Atlantic forest types. Additionally, the net aboveground biomass change (AGB) also was estimated. In this study, five one-hectare permanent plots established by the Gradiente Funcional project were adopted: four (4) plots in lowland and one (1) in seasonally flooded Atlantic forest. The forestry inventories were performed in the same time of permanent plot establishment (2006) and after two (2) years (2008). The results showed that the seasonally flooded Atlantic forest has greater total stem density (DBH \'>OU=\'4.8 cm) than lowland Atlantic forest, equal to 1635 ind.ha-1 in seasonally flooded and 1221 ind.ha-1 in lowland forest. The aboveground biomass (AGB) was greater in lowland than in seasonally flooded forest, equal to 166.3 Mg.ha-1 in seasonally flooded and 212.3 Mg.ha-1 in lowland forest (4,8 cm DBH). The distribution of trees among DBH classes influenced these structural differences: the seasonally flooded forest has high stem density at smaller DBH size class while the lowland forest has high stem density at larger DBH size class. In addition, that variation in size structure also impacted the AGB distribution among DBH classes: the seasonally flooded Atlantic forest has more AGB in the 10-30 cm DBH class and the lowland Atlantic forest has more AGB in the large size class ( \'>OU=\'50 cm). The median growth rate of tree community did not differ between the two forest types, equal to 1.0 mm.yr-1 in seasonally flooded and 0.8 mm.yr-1 in lowland forest ( \'>OU=\'4.8 cm DBH). Differences in growth rates regarding the life forms (tree and palm) were observed. Tree growth rates showed positive relationship with crown illumination index and DBH classes. The same tendency was not observed for palm life form. The mortality rate of tree community did not differ between the two forest types, equal to 2.46 % in seasonally flooded and 2.00 % in lowland forest ( \'>OU=\'4.8 cm DBH). The recruitment rate also did not differ between the two forest types, equal to 1.42 % in seasonally flooded and 1.36 % in lowland forest (\'>OU=\'4.8 cm DBH). The lowland Atlantic forest AGB net change (0.64 Mg.ha-1.yr-1) was higher than seasonally flooded Atlantic forest (0.64 Mg.ha-1.yr-1). Finally, the tropical Atlantic forest has higher stem density, lower AGB, lower growth and turnover rates than other tropical forests probably due to rainfall distribution among year

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La compréhension de la coexistence des espèces végétales et leur l’assemblage dans les communautés naturelles reste un des objectifs fondamentaux de l’écologie, et c’est un enjeu majeur dans le contexte actuel des changements globaux. Ce travail de thèse a consisté à apporter des éléments de compréhension quant aux effets des facteurs abiotiques et biotiques pour l’assemblage des communautés d’arbres en milieu tempéré. Ces questions nécessitent d’être considérées sur le long terme, ce qui est particulièrement difficile en milieu forestier du fait de leurs dynamiques lentes. C’est pourquoi nous avons utilisé ici une approche originale basée sur un modèle mécaniste de dynamique forestière. Dans la filiation des études empiriques basées sur les traits fonctionnels en écologie des communautés, nous avons cherché à identifier les signatures fonctionnelles du filtre environnemental et de la compétition dans l’assemblage des communautés forestières, et ce le long d’un gradient de productivité en Europe centrale. Nos résultats montrent que le filtre environnemental est un déterminant majeur de la structure des communautés en restreignant la gamme de variation des traits, avec des effets plus marqués dans les milieux très contraignants et peu productifs. Par ailleurs, nos résultats montrent que la compétition pour la lumière mène à une convergence de la structure fonctionnelle des communautés, convergence d’autant plus forte que les milieux sont productifs. Dans le but d’approfondir la compréhension des mécanismes d’assemblages et de coexistence, nous avons montré qu’une augmentation de la variabilité climatique interannuelle n’aboutit pas systématiquement à une perte de diversité, et pourrait même favoriser la coexistence en modifiant le pouvoir compétitif relatif des espèces au cours du temps. Enfin, nous avons montré que les différences de valeurs de traits des espèces d’arbres pouvaient favoriser leur coexistence via des réponses différentielles des espèces à la variabilité climatique interannuelle et aux conditions de lumière. L’ensemble de ces résultats apporte de nouveaux éléments quant à la compréhension de la structuration des communautés forestières, et propose une vision intégrative des processus complexes d’assemblage et de coexistence au sein des communautés. / Understanding the coexistence of plant species and their assembly within natural communities remains one of the fundamental goals of ecology, and this major challenge appears even more crucial in the current context of global change. The aim of this work was to better understand how the abiotic and biotic factors determined tree communities’ assembly in temperate forests. These questions can only be considered on the long term, which is especially difficult for forest ecosystems because of their slow dynamics. Therefore we used an original approach based on a forest dynamic model. Following trait-based empirical studies in community ecology, we tried to identify the functional signatures of environmental filtering and competition in forest communities along a productivity gradient in Central Europe. Our results showed that environmental filtering is a major determinant of community structure as it reduced the trait range all along the gradient, with stronger effects in harsh sites with low productivity. Further looking for identifying underlying causal processes, we showed that competition for light led to a convergence of functional community structure, and that this convergence increased with site productivity. Furthermore, our results suggested that inter-annual climatic variability does not systematically result in biodiversity loss, and could even promote species coexistence through changes in the hierarchy of competitors over time. Finally, we showed that differences in trait values of tree species could promote coexistence through differential species responses to inter-annual climatic variability and to light conditions. These findings bring new insights regarding the understanding of tree communities’ structure, and they provide an integrative understanding of the complex processes driving community assembly and species coexistence in natural forests.

Pour de nombreux écologistes, les forêts tropicales sont synonymes de richesse et de diversité spécifique ; aussi l'existence de forêts monodominantes, à savoir de forêt dominée par une seule espèce, reste un formidable énigme. Nous présentons ici la première étude de l'autécologie d'une nouvelle espèce monodominante : Spirotropis longifolia (DC) Baill. (Leguminosae-Papilionoideae) se développant en Guyane française. La monodominance du S. longifolia est très importante, ce dernier pouvant représenter jusqu'à 70% du peuplement. Par ailleurs, le cortège floristique associé à cette espèce diffère largement de celui de la forêt adjacente, très diversifiée. La monodominance du S. longifolia ne peut être expliquée ni par des conditions pédologiques particulières ni par l'absence de compétiteur dans ses peuplements. Nous suggérons en revanche que ses étonnantes capacités à réitérer et à marcotter lui permettent d'installer de maintenir sa monodominance. Nous avons de plus développé un jeu de marqueurs microsatellites et constitué une banque de gènes au cours d'une importante campagne de terrain. Nous proposons une nouvelle classification de la monodominance afin de mieux appréhender les processus écologiques qui lui sont associés, et y replaçons le S. longifolia. Enfin, nous mettons en perspective nos résultats avec la gestion des peuplements naturels. / Large expanses of forest dominated by a single tree species, i.e. monodominant forests, occur through the tropics and remain an long-standing conundrum to most ecologists. In French Guiana, we described a new monodominant tree species: Spirotropis longifolia (DC) Baill. (Leguminosae-Papilionoideae), and studied, for the first time, its autecology. We reported a strong monodominant feature (up to 70 % of stems >10 cm in d.b.h.) and a marked difference between floristic composition of the dominated and adjacent, highly diverse, stands. The monodominance of S. longifolia was supported neither by peculiar soil conditions nor by a lack of competitors but may be owned to its astonishing self-coppicing and layering abilities which induce a sharp spatial structure. We also developed a set of microsatellite markers and conduct a large field survey to built up a gene data base. Facing the variety of ecological processes involved in monodominance, we identified a lack of conceptual framework, set a new classification of monodominance and positioned S. longifolia within. We finally discuss these results in the frame of the forest management.