La Nouvelle-Calédonie qui présente une biodiversité à la fois exceptionnelle et très menacée, fait partie des points chauds de biodiversités définis à l'échelle globale comme zones prioritaires pour la conservation. Les incendies, d'origines anthropiques et constituant l'une des principales menaces pesant sur les écosystèmes naturels néo-calédoniens, conduisent à un recul des forêts denses humides (forêts par la suite) principalement au profit des savanes sur substrats volcano-sedimentaires. Au cours de cette thèse, les processus écologiques mis en jeu dans les dynamiques des forêts et des savanes, liés aux variations du régime d'incendie, ont été étudiés à différentes échelles spatiales et temporelles. L'analyse de la distribution spatio-temporelle des forêts et des savanes à l'échelle du paysage a mis en évidence différents facteurs dirigeant la dynamique paysagères et identifié des zones de recolonisation forestière. Différents modèles de succession secondaire et cortèges d'espèces pionnières ont été identifiés à partir de l'analyse de ces zones de recolonisation. La mesure de traits fonctionnels et l'utilisation de modèles semi-physiques de dommages causés par les incendies ont révélé une faible tolérance aux incendies de ces espèces. Enfin, une analyse multivariée de la structure, de la composition floristique et des conditions micro-climatiques des zones clés de transitions entre la savane et la forêt a permis de mieux comprendre les processus d'expansion et de contraction forestière. / New Caledonia, which presents both an exceptional and highly endangered biodiversity, is one of the worldwide biodiversity hotspots for conservation priority. Human-induced fires, which are one of the main threats to natural ecosystems in New Caledonia, lead to the expansion of savannas on volcano-sedimentary substrates at the expense of rainforests. In this thesis, the ecological processes, which are involved in the dynamics of rainforests and savannas and related to changes in fire regime, have been studied at different spatial and temporal scales. The analysis of the spatio-temporal distribution of rainforests and savannas across the landscape allowed us to both point-out the different drivers of their dynamics and to identify areas of rainforest recolonization. Different secondary succession patterns and pioneer species assemblages were identified from the analysis of these areas of recolonization. The analysis of measured functional traits and the use of semi-physical models of fire-caused damages highlighted the low tolerance of these pioneer species to fire. Finally, a multivariate analysis of the structure, the floristic composition and the micro-climatic conditions of transitional zones between savanna and rainforest, has allowed us to better understand the processes of rainforest's expansion and contraction. This thesis opens a new field of research in New Caledonia with important implications in rainforest's restoration and sustainable management.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The subtropical seasonal forests located on the brazilian southern plateau (BSP) of Rio Grande do Sul state (Brazil) represent an extension from the Misiones province flora, considered one of the most threatened ecosystems in the world. BSP represents the largest forested areas of the state, most of the them are secondary forests, originate from agricultural abandonment areas. In many cases, these forests are source of shelter and food for livestock. Given the importance of the BSP for biodiversity conservation and maintenance of ecological services is little knowledge how these forests regenerate after impact. This doctoral thesis has been organized into four chapters, the first three describe and evaluate the secondary succession in soils and forest vegetation after abandonment of agricultural activities. Thirtyfive preserved forests at different ages (5 to> 100 years) with low environmental variability were sampled with standardized inventory methodology, for analyzes of the soil and vegetation attributes. Specifically, the questions that this study sought to answer were: 1) how soil attributes to change (11 chemical and three texture) along a forest succession and what are the best indicators of change, 2) are linear floristic changes along succession and what floristic similaririty between ages, chronosequence, successional stages and stages of development of the forests? 3) how structural attributes of vegetation (13 attributes) changes along a chronosequences and what the best indicators of changes? The results showed that the chemical properties of soil and structure vegetation changed significantly and not predictable for a single attribute along chronosequences forests. Only discriminant analysis aproach was possible to characterize the ages of forest using a group of soil and structure attibutes. The floristic composition also varied substantially where few species can be listed as indicators of a particular stage of development. Floristic patterns emerged only when pooled data from aged forests. The last chapter evaluated the effect of cattle grazing in 35 forests with different ages (5 to > 100 years) and three levels of impact (forests with current impact of cattle grazing, forests excluding grazing 10 years ago and forests without cattle grazing). Standardized inventory in all these forests were employed for analysis of soil and vegetation in order to compare and evaluate the effect and magnitude of the impact of grazing on forest ecosystem. The most adverse effect ocurred in the soil (chemical and texture) than in the floristic composition and structure of vegetation. However, the impact of grazing on soil and tree component can be recovered in 10 years after sttoped the activity in forest ecosystems. These results are important to impact monitoring, restoration and sustainable management projects in the largest and most endangered ecological corridor in Rio Grande do Sul State. / As florestas estacionais subtropicais localizadas na região do rebordo do Planalto Meridional (RPM) do Rio Grande do Sul representam uma extensão da flora proveniente da província Misiones (Argentina), essa considerada um dos ecossistemas mais ameaçados do mundo. O RPM comporta a maior área de floresta do estado que são principalmente compostas de florestas secundárias originadas do abandono de áreas agrícolas. Em muitos casos, as florestas remanescentes são utilizadas como fonte de abrigo e alimento para o gado. Dado a importância das florestas do RPM para conservação da biodiversidade e para a manutenção dos serviços ecológicos, sabe-se pouco como essas florestas se regeneram após o impacto. A presente tese de doutorado foi organizada em quatro capítulos, os três primeiros buscaram descrever e avaliar a sucessão secundária nos solos e da vegetação florestal após o abandono da atividade agrícola. Foram amostradas 35 florestas preservadas em diferentes idades (5 a >100 anos) com inventários padronizados, e em menor variação ambiental possível, para análises das características do solo e da vegetação. De forma específica, o estudo procurou responder as seguintes questões: 1) como muda os atributos do solo (11 variáveis químicas e três físicas) ao longo da sucessão florestal e quais os melhores indicadores dessa mudança; 2) existe mudanças florísticas lineares ao longo da sucessão e qual a similaridade florística entre idades, cronossequências, estágios sucessionais e nas fases de desenvolvimento da floresta? 3) como mudam os atributos estruturais da vegetação (13 atributos) ao longo da sucessão e quais os melhores indicadores dessas mudanças? Os resultados demonstraram que os atributos químicos do solo e da estrutura da vegetação mudaram significativamente nas florestas ao longo da sucessão, no entanto, as mudanças não foram lineares ou previsíveis, o que não permitiu elencar um único atributo eficiente para caracterizar uma idade de floresta. Somente com o emprego da análise discriminante foi possível identificar grupos de variáveis do solo e da estrutura da vegetação eficientes para classificar as diferentes idades de florestas. A composição florística também variou e algumas poucas espécies podem ser elencadas como indicadoras de uma determinada fase de desenvolvimento. O último capítulo avaliou o efeito do pastoreio bovino em 35 florestas com diferentes idades (5 a > 100 anos) e níveis de impacto (florestas com impacto atual de pastoreio bovino, florestas com exclusão do pastoreio a 10 anos e florestas sem pastoreio bovino). Foram realizados inventários padronizados em todas essas florestas para análise do solo e vegetação com objetivo de comparar e avaliar o efeito e a magnitude do impacto do pastoreio no ecossistema florestal. O impacto do pastoreio foi mais significativo no solo (química e textura) do que na composição florística e estrutura da vegetação, sendo possível elencar maior número de indicadores ambientais no primeiro caso. No entanto, o impacto do pastoreio no solo e no componente arbóreo pode ser recuperado em 10 anos de abandono da atividade nos ecossistemas florestais. Os resultados apresentados fornecem importantes subsídios para programas de monitoramento de impacto, recuperação de ecossistemas degradados e manejo de espécies silvícolas nesse que é o maior e mais ameaçado corredor ecológico do estado do Rio Grande do Sul.

Folgende Themenkomplexe wurden behandelt: Biogeographie, Pflanzendiversität, Verbreitungsmuster von Lebensformen und Arten in Mikrohabitaten sowie entlang ökologischer Gradienten, Epiphyt-Porophyt-Beziehungen, Vergesellschaftung, Sekundärsukzession und die Auswahl von Indikatorarten. Zum ersten Mal wird bei einer derartigen Untersuchung die sekundäre Sukzession von Kryptogamengesellschaften in tropischen Bergregenwäldern voll berücksichtigt. Die Untersuchung wurde im Einzugsgebiet des Río Savegre auf der pazifikseitigen Abdachung der westlichen Cordillera de Talamanca (Costa Rica) durchgeführt.Kapitel 1 gibt eine generelle Einführung in Tropische Bergregenwälder und die Bedeutung von Moosen und Makroflechten als wichtige Komponenten dieser Ökosysteme. Der Leser wird in das Untersuchungsgebiet, sein Klima, seine Geologie und seine Vegetation eingeführt.Im Kapitel 2 werden die pflanzengeographischen Muster der Moose montaner Eichenwälder der Cordillera de Talamanca dargestellt und diskutiert.Kapitel 3 diskutiert Diversität, Mikrohabitatdifferenzierung und Lebensformenspektren der Moose in einem hochmontanen Eichenwald Costa Ricas. Es wurde versucht, die Moosflora aller Mikrohabitate eines Eichenwaldes, inklusive der Strauch- und Bodenschicht zu erfassen. Kapitel 4 und 5 beinhalten die Beschreibung epiphytischer Kryptogamengesellschaften (Moose und Makroflechten) in Primär- und Sekundärwäldern. Mit Hilfe einer aus dem Alpinismus abgeleiteten Klettertechnik wurden Bäume von der Stammbasis bis in die Zweige der äußeren Krone beprobt. Die Vegetationsaufnahmen repräsentieren die Variation der epiphytischen Vegetation. Prozentuale Deckungsgrade der rindenbewohnenden Moose und Makroflechten wurden geschätzt und mit Hilfe einer Detrended Correspondence Analysis (DCA)' und nicht-metrischer Multi-response Permutation Procedure (MRPP)' verglichen. Rindenproben der untersuchten Bäume wurden mit deionisiertem Wasser extrahiert und der pH-Wert bestimmt.Kapitel 4 behandelt die epiphytischen Kryptogamengemeinschaften auf den dominierenden Baumarten (Quercus copeyensis und Q. costaricensis) primärer, hochmontaner Eichenwälder Costa Ricas. Kapitel 5 vergleicht Artenreichtum, Vergesellschaftung und Ökologie der epiphytischen Kryptogamen in primären und sekundären hochmontanen Eichenwäldern Costa Ricas. Quercus copeyensis-Bäume der oberen Baumschicht von Primär- und Sekundärwäldern wurden beprobt mit dem Ziel einen Einblick in Regenerationspotential, -muster und -prozesse der Epiphytensukzession nach anthropogener Störung zu erhalten.

Though succession is a widely studied process, there are only a few reports dealing with changes in plant functional types in the course of succession. Even fewer studies are dealing with agricultural, wet meadows, which are under continuous impact of mowing. The aim of this work is to fill this gap. The studied area is situated in south part of CHKO Slavkovský Les (region of Karlovy Vary, West Bohemia). In previous works grasslands on arable field after 15, 35 and 55 years after abandoned and continual grasslands in last 100 years were detected from historical agriculture maps. The releves on all types of grassland were made and the species pool was investigated. I this work I investigate the functional types and live-history traits of these species and I also look for Ellenberger values and changes of abiotic environment. The result suggests that the late - successional species are long-lived and have slower live cycle (they mature later). Their seeds are less persistent and have worse dispersal ability. Their seedlings are more viable and the species invest more to aboveground biomass than to underground. Late-successional species also flower earlier and shorter time, what seems to be an adaptation to mowing. I found no relationship between successional age in which the species occur and seed mass,...