Myrmarker har en stor roll i regleringen av den globala kolbalansen och koncentrationerna av koldioxid och metan i atmosfären, vilket gör dem till speciellt viktiga ekosystem ur ett klimatförandringsperspektiv. Förändringar av myrmarker genom naturlig utveckling eller antropogen påverkan kan därför få långtgående störningar av myrars klimatreglerande funktion. Mikroorganismer har en avgörande roll i biogeokemiska processer genom att t ex bryta ned organisk material i mark och därmed styra kolets kretslopp. För att förstå hur myrsystemen reagerar på störningar är det därför väsentligt att veta hur mikroorganismsamhällena reagerar genom förändringar i sammansättning och biogeokemisk aktivitet. Målet för studierna, som ligger till grund för denna avhandling, var att undersöka hur mikroorganismsamhällen i myrar reagerar på uppvärmning genom klimatförändring och ökade kväve- (N) och svavel- (S) halter i nederbörd. High through-put sekvensering användes för att studera taxonomiska och funktionella egenskaper hos mikroorganismerna i myrar och quantative PCR användes för att mer specifikt studera de metanbildande arkeorna. Två fältkampanjer vardera omfattande tre ombrotrofa myrar med olika klimatförhållanden och olika mängder N och S inederbörden användes för att undersöka lokala och storskaliga effekter på myrars mikrobiella samhällen. Resultaten visade att latudinell variation i geoklimatologiska förhållanden (temperatur ochnederbördsmängd) och deposition av näringsämnen hade en påverkan på sammansättningen av de mikrobiella samhällena och aktiva metanbildare förr än variationen i den kemiska miljön inom varje specifik myr. Myrväxtsamhällenas sammansättning för en specifik myr visades sig i stor utsträckning styra sammansättningen av motsvarande mikrobiella samhälle i torvprofilen. Detta framgick klart av i en analys av samexisterande nätverk av mikroorganismsamhällen och motsvarande växtsamhällen i en studie av tre geografiskt skilda myrar med olika kvävedeposition. Effekterna av klimatförändring och nederbörd med olika mängder av N och S studerades mer specifikt genom att analysera de mikrobiellasamhällena i  ett långliggande (18 år) försök. Påverkan av var och en av dessa manipulationer antingen förstärktes eller minskades, när de förekom i kombinationer. Ökad kvävedeposition var den faktor som hade starkast effekt. De långvariga störningarna medförde stora förändringar i den mikrobiella taxonomin inom samhällena. Detta återspeglades dock inte i den fysiologiska kapaciteten, vilket visar att det finns en stark buffring i myrarnas mikrobiella funktion. Detta tyder på att framtida utveckling av myrar i relation till olika störningar sannolikt inte kommer att påverka myrarnas roll för kolbalans och växthusgasutbyte med atmosfären. / Peatlands play a substantial role in regulating the global carbon balance and concentrations of the greenhouse gases CO2 and CH4 in the atmosphere, and are thus of utmost importance from a climate change perspective. Any changes of peatland functions due to natural or anthropogenic perturbations may result in changes in these ecosystem services. Soil microbial communities are essential drivers of biogeochemical processes, including the carbon cycle. In order to fully understand the effect of environmental perturbations on peatland functions, it is essential to understand how microbial communities are affected. The aim of the research presented in this thesis was to investigate the responses of the peat microbial communities to climate change and increased precipitation of nitrogen(N) and sulfur (S) compounds. High-throughput sequencing approaches were used to investigate the taxonomic and functional composition of microbial communities, and quantitative PCR was used to specifically target the methanogen community. Two field studies including three ombrotrophic peatlands each that differed in climatological conditions and atmospheric N and S depositions, were used to investigate and compare the effect of large- and local-scale environmental conditions on microbial communities. The results show that the variation in geo-climatological (temperature and precipitation) and atmospheric deposition conditions along the latitudinal gradient modulate the peat microbial community composition and the abundance of active methanogens to a greater extent thansite-related microhabitats. Furthermore, a tight coupling between the plant community composition of a site and the composition of its microbial community was observed, and was found to be mainly driven by plants rather than microorganisms. These co-occurrence networks are strongly affected by seasonal climate variability and the interactions between species in colder areas are more sensitive to climate change. The long-term effects of warming and increased N and S depositions on the peat microbial communities were further investigated using an 18-year in-situ peatland experiment simulating these perturbations. The impacts of each of these perturbations on the microbial community were found to either multiply or counteract one another, with enhanced N deposition being the most important factor. While the long-term perturbations resulted in a substantial shift in the taxonomic composition of microbial communities, only minor changes occurred in genome-encoded functional traits, indicating a functional redundancy. This could act as a buffer maintaining ecosystem functioning when challenged by multiple stressors, and could limit future changes in greenhouse gases and carbonexchange.

Budongo Forest Reserve (BFR) is a flagship reserve for primate conservation due to its abundant chimpanzee (Pan troglodytes) population, and its current management policy for multiple economic, conservation and environmental benefits. The identification and better understanding of the structure and dynamics of the forest/plant community types, patterns of species distribution and quantitative properties of their diversity is important to the conservation and sustainable management of tropical rainforests. This study seeks to contribute to a better understanding of the BFR forest community types, species diversity patterns and environmental correlates, as well as natural regeneration processes (i.e. seedling establishment and sprouting). Data on vegetation and environmental variables were collected using rectangular 50 x 100m (0.5 ha) plots, sub-divided into five equal contiguous (20 x 50 m) 0.1 ha sub-plots. Data on land-use/cover changes, and relevant associated socio-economic parameters were collected through the analysis of multi-temporal satellite imagery and field observations, as well as interviews of local households and key informants. The study revealed significant land-use/cover changes, with the area under sugarcane cultivation increasing over 17-fold, from 690 ha in 1988 to 12729 ha in 2002, with a concomitant loss of about 4680 ha (8.2% loss) of forest/woodland, mainly in the southern part of BFR. These changes are attributed to agricultural expansion, a rapidly increasing human population, exacerbated by large influxes of refugees, lack of alternative sources of income, conflicts of interest and political interference in the management of BFR, and an unclear land tenure system. The need for more land for agricultural expansion and the loss of woodlands (a source of building materials and fuelwood for the local communities) is leading to the invasion of and encroachment on BFR, which threatens plant and wild animal conservation. The study revealed that the vegetation of BFR is formed by a mosaic of plant communities, with the major forest types being; Pseudospondias microcarpa Swamp Forest, Funtumia elastica - Pouteria altissima, Lasiodiscus mildbraedi - Khaya anthotheca and Cynometra alexandri - Rinorea ilicifolia forest communities. Canonical correspondence analysis (CCA) indicated that soil nutrients (Si, Ca, N, Fe and Li) and anthropogenic disturbances are the main factors controlling forest community patterns. The variances explained as a proportion of total inertia were relatively high (0.53 and 0.56 for basal area and abundance, respectively), showing how well the measured variables explained species composition. These plant communities differed significantly in terms of woody species diversity and richness; being highest in the Pseudospondias microcarpa swamp and lowest in the Cynometra alexandri-Rinorea ilicifolia forest. However, about 48 species were shared between the forest community types. A total of 269 species representing 171 genera and 51 families was recorded. Fisher’s alpha-diversity ranged 4.45-30.59 and 3.07-29.7 for stem diameters ≥2.0 cm and ≥10 cm, respectively, being significantly higher for stem diameters ≥2.0 cm. The use of stem diameters ≥2.0 cm unveiled 53 more species (19.7%), with only 216 species recorded for the standard ≥10 cm dbh minimum size usually applied in tropical forests. A SHE analysis also showed greater richness (ln(S)) and H diversity for the >2.0 cm than the ≥10cm stem diameters. Hence, the study reaffirmed that the use of 10 cm as a minimum dbh in woody plant diversity studies in forests, where many tree species rarely exceed 10 cm stem diameter, is highly likely to underestimate diversity and richness, potentially biasing the understanding of diversity patterns. The most speciose families were Euphorbiaceae, Fabaceae, Rubiaceae, Moraceae, Meliaceae, Rutaceae, Annonaceae, and Flacourtiaceae, accounting for 147 species. Families with the highest Familial Importance values (FIV) were; Fabaceae (17.5), followed by Euphorbiaceae (16.3), and Ulmaceae (8.35). The BFR exhibits characteristics intermediate between log-normal and log-series species-abundance distributions, indicating a community with a small number of abundant species and a relatively large proportion of rare species. Both Whittaker’s (βw) and the Morisita-Horn Index measures of β-diversity consistently showed higher β-diversity for logged and arboricide treated areas, followed by logged only, and then nature reserve historical management practice types. β-diversity was relatively high at the total forest community scale, but lower for stem diameter ≥2.0 cm than ≥10.0 cm data. Environmental variables significantly explained 66.5% and 61.9% of the variance in species composition for stem diameter ≥2.0 cm and ≥10.0 cm data, respectively. Hence, the variation in species composition of BFR is characterised by significant spatial patterns, and the patterns in β-diversity are to a great extent associated with environmental heterogeneity (i.e. soil nutrients, topographic and light gradients) and anthropogenic disturbances. Investigation of natural regeneration showed that sprouting is generally common among the woody species, with both canopy and sub-canopy trees sprouting prolifically. Of the 122 species affected by ii harvesting, and tree and branch fall disturbances, 199 (97.5%) from 31 families sprouted from the cut stumps, with only Caloncoba crepiniana (De Wild. & Th.Dur.) Gilg exhibiting both stem and root sprouting. Stump basal diameter, height, bark-thickness, and height of stump above the ground at which the first sprout emerged, were significant predictors of sprouting ability among individuals. Number of sprouts/stump differed significantly among families, species, and stump size-classes. Of the 241 seedling species, representing 46 families, about 30.3% were rare (only 2-10 individuals); while 12% were very rare (only 1 individual each). Cynometra alexandri C.H. Wright and Lasiodiscus mildbraedii Engl. were the most abundant seedlings and also among the most widely distributed species in the forest. Analysis of similarity (ANOSIM) revealed significant differences in seedling composition between transects, but not between topographic positions or historical management practice types. Canonical Correspondence Analysis (CCA) showed that the measured environmental variables significantly explained 59.4% of the variance in seedling species distributions, with the three most important variables being organic matter, titanium and leaf area index (LAI; an indicator of light availability below the canopy). Hence, the important mechanisms influencing regeneration via seedlings in BFR operate through the soil system, and the ground and canopy vegetation characteristics. Nine of the 15 intensively studied multiple-use species, namely L. mildbraedii, Celtis Mildbraedii Engl., Pouteria altissima (A. Chiev.) Aubrev. & Pellegr., Chrysophyllum albidum G. Don., C. alexandri, Diospyros abyssinica (Hiern) F. White, Funtumia elastica (Preuss) Stapf., Chrysophyllum perpulchrum Hutch. & Dalz, and Antiaris toxicaria (Pers.) Lesch. had highly negative size-class distribution (SCD) slopes and substantial seedling regeneration. While Alstonia boonei De Wild. and Cordia millenii Bak. had weakly negative SCD slopes and pulsed or sporadic regeneration patterns. The wide distribution of seedlings for a variety of species, and with most of the intensively studied species having population structures showing healthy regeneration patterns, suggests that BFR is currently experiencing a continuous regeneration phase. In conclusion, the gradients in the vegetation of BFR are a reflection not only of site conditions as shown by the edaphic and abiotic factors, but also the history of human interventions.

A bacia hidrográfica do Rio Corumbataí é de extrema importância para o desenvolvimento sustentável da região por ser o principal manancial para o abastecimento de 8 municípios: Piracicaba, Charqueada, Rio Claro, Santa Gertrudes, Ipeúna, Itirapina, Corumbataí e Analândia. Devido à importância das florestas nativas na manutenção da qualidade e quantidade dos recursos hídricos e ao elevado índice de fragmentação, tem ocorrido um acréscimo nessa região das ações que visam a recuperação e a conservação da cobertura florestal. A constatação de que grande parte dessas ações poderá ser comprometida ao longo do tempo, em função da falta de esclarecimentos sobre a complexidade florestal da região, motivou a realização da caracterização fitogeográfica nessa área. Uma etapa dessa caracterização foi realizada por meio do reconhecimento geral da cobertura florestal, utilizando-se técnicas de interpretação de imagens orbitais digitais, checagens de campo e reconhecimento aéreo. Paralelamente foi realizado um amplo levantamento bibliográfico, no qual obtiveram-se as informações necessárias para a identificação dos aspectos fisionômicos das formações florestais e a realização das análises de composição florística e similaridade (Índice de Jaccard e Coeficiente de Aglomeração). Ao todo foram identificadas 7 formações florestais pertencentes à composição fitogeográfica da bacia, sendo: Estacional Semidecidual, Estacional Semidecidual Aluvial, Estacional Semidecidual Submontana, Estacional Decidual, Floresta Paludosa, Cerradão e Cerrado. A análise geral da composição florística demonstrou a ocorrência de uma alta diversidade nesse mosaico florestal, na qual foram identificadas 487 espécies arbóreas-arbustivas pertencentes a 72 famílias e 212 gêneros. Também pôde-se verificar que do total de espécies apenas 10 espécies são generalistas, ou seja, ocorrem em todas as formações e, 163 espécies são exclusivas, ou seja, ocorrem numa formação especificamente. A análise da similaridade pelo índice de Jaccard demonstrou que as maiores semelhanças florísticas ocorrem entre as florestas Semidecidual e Semidecidual Aluvial e entre o Cerrado e o Cerradão. Os resultados do coeficiente de aglomeração demonstrou haver alta heterogeneidade florística entre as formações e que estas se organizam em 2 grandes grupos, o das Florestas Estacionais com a Floresta Paludosa e o do Cerrado com o Cerradão. Para compreender melhor a organização do mosaico florestal da Bacia do Corumbataí, realizou-se o mapeamento e o georreferenciamento dos pontos de ocorrência das formações fitogeográficas e, posteriormente, fez-se a associação destes com diferentes características ambientais da região. Com isto, identificou-se os fatores edáficos que condicionam as áreas de ocorrência de cada formação e, consequentemente, obteve-se uma visão global da distribuição geográfica das formações, concluindo que: as florestas Semidecidual, Semidecidual Aluvial e Paludosa ocorrem em toda a extensão da bacia; a floresta Semidecidual Submontana, o Cerrado e o Cerradão ocorrem com maior freqüência nas regiões leste e norte; e a floresta Estacional Decidual ocorre no sul, precisamente no município de Piracicaba. Por fim, são feitas recomendações para a recuperação e a conservação florestal na bacia que podem subsidiar futuras ações conservacionistas. / The Corumbatai River Basin is of great importance to the sustainable development of its region, for it is the main source of treatable water supplied to homes, industries and public use of 8 of the following municipalities: Piracicaba, Charqueada, Rio Claro, Santa Gertrudes, Ipeúna, Itirapina, Corumbatai and Analândia. Given the importance of native forests in the maintenance of quality and quantity of the watershed, associated to the great degree of fragmentation, there has been occurring an increase of actions aimed at recovering and conservation of the natural vegetation. The evidences that during the time the most part of this actions can be compromised due to the deficiency of explanation about the forest complexity, this has motivated this work of phytogeographic characterization in the region. One phase of this characterization has taken place with the general forest coverage reconnaissance, using the interpretation techniques of digital orbital imagery, field checking and aerial reconnaissance. Moreover, a ample bibliographical review was undertaken, through which the necessary information were obtained for the identification of physiognomic aspects of the forest formation and to the analysis of floristic composition and similarity (Jaccard’s Coefficient and Agglomerate Classification). There were 7 forest formation identified in total, which belong to a phytogeographical composition of the riverbasin, which are: Seasonal Semidecidual Forest, Seasonal Alluvial Semidecidual Forest, Submontana Semidecidual Forest, Seasonal Deciduous Forest, Flooded Forest, Savanna Forest and Savanna. The general analysis of the floristic composition demonstrated the occurrence of high diversity in the forest mosaic, in which were identified 487 arboreal species, belonging to 72 families and 212 genera. It was also possible to verify that from the total number of species, only 10 species are general, that is, they occur in all formation. Moreover, 163 species are exclusively, that is, they occur in a specific formation only. The analysis of similarity by the Jaccard index demonstrated that the majority of floristic similarities occur among the Semidecidual Forests and the Alluvial Semidecidual Forest and the Savanna and Savanna Forest. The results of the agglomerate classification demonstrated to have high floristic heterogeneity among the formation and that these are organized in 2 large groups: the Seasonal Forests with Flooded Forest and of the Savanna with Savanna Forest. To best understand the organization of this forest mosaic within the Corumbatai Basin, a georefferenced mapping system was created, showing the points of occurrence of the phytogeographical formation and, afterwards, these were associated with the different environmental characteristics of the region. After having that done, it was identified the edafic factors that impose conditions to the areas of occurrence of each formation and, consequently, it was possible to obtain a general view of the geographical distribution of the different formation, which allowed for the following conclusion: the Semidecidual, Semidecidual Alluvial and Flooded Forest occur in all the extension of the riverbasin; the Semidecidual Submontana, the Savanna and the Savanna Forest occur with higher frequency in the east and north regions; and the Seasonal Deciduous Forest occur mostly in the south, precisely in the Piracicaba municipality. Finally, some recommendations are made for the recovery and conservation of the forests within the Corumbatai Riverbasin, which can subsidize future conservationist actions.

A bacia hidrográfica do Rio Corumbataí é de extrema importância para o desenvolvimento sustentável da região por ser o principal manancial para o abastecimento de 8 municípios: Piracicaba, Charqueada, Rio Claro, Santa Gertrudes, Ipeúna, Itirapina, Corumbataí e Analândia. Devido à importância das florestas nativas na manutenção da qualidade e quantidade dos recursos hídricos e ao elevado índice de fragmentação, tem ocorrido um acréscimo nessa região das ações que visam a recuperação e a conservação da cobertura florestal. A constatação de que grande parte dessas ações poderá ser comprometida ao longo do tempo, em função da falta de esclarecimentos sobre a complexidade florestal da região, motivou a realização da caracterização fitogeográfica nessa área. Uma etapa dessa caracterização foi realizada por meio do reconhecimento geral da cobertura florestal, utilizando-se técnicas de interpretação de imagens orbitais digitais, checagens de campo e reconhecimento aéreo. Paralelamente foi realizado um amplo levantamento bibliográfico, no qual obtiveram-se as informações necessárias para a identificação dos aspectos fisionômicos das formações florestais e a realização das análises de composição florística e similaridade (Índice de Jaccard e Coeficiente de Aglomeração). Ao todo foram identificadas 7 formações florestais pertencentes à composição fitogeográfica da bacia, sendo: Estacional Semidecidual, Estacional Semidecidual Aluvial, Estacional Semidecidual Submontana, Estacional Decidual, Floresta Paludosa, Cerradão e Cerrado. A análise geral da composição florística demonstrou a ocorrência de uma alta diversidade nesse mosaico florestal, na qual foram identificadas 487 espécies arbóreas-arbustivas pertencentes a 72 famílias e 212 gêneros. Também pôde-se verificar que do total de espécies apenas 10 espécies são generalistas, ou seja, ocorrem em todas as formações e, 163 espécies são exclusivas, ou seja, ocorrem numa formação especificamente. A análise da similaridade pelo índice de Jaccard demonstrou que as maiores semelhanças florísticas ocorrem entre as florestas Semidecidual e Semidecidual Aluvial e entre o Cerrado e o Cerradão. Os resultados do coeficiente de aglomeração demonstrou haver alta heterogeneidade florística entre as formações e que estas se organizam em 2 grandes grupos, o das Florestas Estacionais com a Floresta Paludosa e o do Cerrado com o Cerradão. Para compreender melhor a organização do mosaico florestal da Bacia do Corumbataí, realizou-se o mapeamento e o georreferenciamento dos pontos de ocorrência das formações fitogeográficas e, posteriormente, fez-se a associação destes com diferentes características ambientais da região. Com isto, identificou-se os fatores edáficos que condicionam as áreas de ocorrência de cada formação e, consequentemente, obteve-se uma visão global da distribuição geográfica das formações, concluindo que: as florestas Semidecidual, Semidecidual Aluvial e Paludosa ocorrem em toda a extensão da bacia; a floresta Semidecidual Submontana, o Cerrado e o Cerradão ocorrem com maior freqüência nas regiões leste e norte; e a floresta Estacional Decidual ocorre no sul, precisamente no município de Piracicaba. Por fim, são feitas recomendações para a recuperação e a conservação florestal na bacia que podem subsidiar futuras ações conservacionistas. / The Corumbatai River Basin is of great importance to the sustainable development of its region, for it is the main source of treatable water supplied to homes, industries and public use of 8 of the following municipalities: Piracicaba, Charqueada, Rio Claro, Santa Gertrudes, Ipeúna, Itirapina, Corumbatai and Analândia. Given the importance of native forests in the maintenance of quality and quantity of the watershed, associated to the great degree of fragmentation, there has been occurring an increase of actions aimed at recovering and conservation of the natural vegetation. The evidences that during the time the most part of this actions can be compromised due to the deficiency of explanation about the forest complexity, this has motivated this work of phytogeographic characterization in the region. One phase of this characterization has taken place with the general forest coverage reconnaissance, using the interpretation techniques of digital orbital imagery, field checking and aerial reconnaissance. Moreover, a ample bibliographical review was undertaken, through which the necessary information were obtained for the identification of physiognomic aspects of the forest formation and to the analysis of floristic composition and similarity (Jaccard’s Coefficient and Agglomerate Classification). There were 7 forest formation identified in total, which belong to a phytogeographical composition of the riverbasin, which are: Seasonal Semidecidual Forest, Seasonal Alluvial Semidecidual Forest, Submontana Semidecidual Forest, Seasonal Deciduous Forest, Flooded Forest, Savanna Forest and Savanna. The general analysis of the floristic composition demonstrated the occurrence of high diversity in the forest mosaic, in which were identified 487 arboreal species, belonging to 72 families and 212 genera. It was also possible to verify that from the total number of species, only 10 species are general, that is, they occur in all formation. Moreover, 163 species are exclusively, that is, they occur in a specific formation only. The analysis of similarity by the Jaccard index demonstrated that the majority of floristic similarities occur among the Semidecidual Forests and the Alluvial Semidecidual Forest and the Savanna and Savanna Forest. The results of the agglomerate classification demonstrated to have high floristic heterogeneity among the formation and that these are organized in 2 large groups: the Seasonal Forests with Flooded Forest and of the Savanna with Savanna Forest. To best understand the organization of this forest mosaic within the Corumbatai Basin, a georefferenced mapping system was created, showing the points of occurrence of the phytogeographical formation and, afterwards, these were associated with the different environmental characteristics of the region. After having that done, it was identified the edafic factors that impose conditions to the areas of occurrence of each formation and, consequently, it was possible to obtain a general view of the geographical distribution of the different formation, which allowed for the following conclusion: the Semidecidual, Semidecidual Alluvial and Flooded Forest occur in all the extension of the riverbasin; the Semidecidual Submontana, the Savanna and the Savanna Forest occur with higher frequency in the east and north regions; and the Seasonal Deciduous Forest occur mostly in the south, precisely in the Piracicaba municipality. Finally, some recommendations are made for the recovery and conservation of the forests within the Corumbatai Riverbasin, which can subsidize future conservationist actions.

L’objectif principal de la thèse était de caractériser les impacts de différents types de gestion pastorale (bovins, équins, caprins) sur les communautés végétales de « nouveaux écosystèmes » fortement anthropisés que sont les digues et remblais de la réserve de Donzère-Mondragon dans la basse vallée du Rhône. Différents outils ont été utilisés (relevés de végétation, analyses de sols, analyses minérales des herbages, télédétection, SIG, etc.) à des échelles spatiales différentes afin de dégager les interrelations entre les différents niveaux d’organisation et fonctionnalités de la végétation. En effet, l’émergence des « nouveaux écosystèmes » oblige les gestionnaires à reconsidérer les principes initiaux de la gestion conservatoire. Dans notre étude, il a pu être démontré que les systèmes de pâturage faisant appel à des troupeaux d’herbivores dont l’organisation est adaptée pour maintenir l’ouverture des milieux, augmentent la richesse spécifique, la diversité et l’hétérogénéité de la végétation à court terme (3-5 années) par rapport à l’absence de gestion ou aux interventions mécaniques. Les analyses montrent également que les espèces annuelles qui apparaissent sont appétentes et contribuent à augmenter la valeur fourragère de certains faciès du site pâturé par les chevaux. Ces herbivores ont également un impact sur la banque de graines permanente du sol en augmentant son hétérogénéité et la densité de graines viables sous les faciès les plus pâturés. Le pâturage des vaches et des chevaux confirme une corrélation entre l’indice de végétation (NDVI) obtenu après l’analyse de photographies aériennes, la biomasse et la richesse en espèces végétales. Les estimations d’indices de consommation de la ronce sous SIG ont permis d’apprécier l’efficacité de l’action des chèvres. Ces différents résultats, pour les modalités testées, correspondent bien à ceux déjà obtenus lors d’applications de systèmes pastoraux en milieux naturels. Des expérimentations devraient également être menées à l’avenir via des systèmes de pâturage mixtes notamment bovin-caprin et équin-caprin pour accroître l’effet de la restauration aux dépens de la colonisation d’arbustes compétitifs dont la ronce. La gestion pastorale appliquée devrait néanmoins être pensée sur le moyen terme, si possible via des contrats pluriannuels, favorisant la durabilité de cette méthode de gestion et de ses effets dans le temps. / The main objective of the thesis was to characterize the impacts of different types of pastoral management (cattle, horses, goats) on "new ecosystems" plant communities. Our experimentations were conducted in highly anthropized dykes and embankments of the Donzère-Mondragon reserve in the lower Rhone valley. Various tools were used (i.e. vegetation surveys, soil analyzes, grassland mineral analyzes, remote sensing, GIS, etc.), and at different spatial scales in order to identify the interrelationships between the different levels of vegetation organization and functions. Indeed, the emergence of "new ecosystems" requires managers to reconsider the initial principles of conservation management. Our study showed that, in the short term (3-5 years), grazing systems using herds of herbivores, whose organization is adapted to maintain open habitats, increase species richness, diversity and heterogeneity of plant communities compared to lack of management or mechanical interventions. Moreover, the annual species that appear are appetizing and contribute to increase the forage value of the site grazed by horses. These herbivores also have an impact on the permanent seed bank by increasing both its heterogeneity and the density of viable seeds under the most grazed patches. Grazing of cattle and horses confirm a correlation between the vegetation index (NDVI), biomass and plant species richness. Finally, we evaluated the efficacy of goats’ action on bramble via consumption indices calculated using GIS. Our different results are in the line with those already obtained in natural environments. Future experiments should test the effects of mixed grazing systems, particularly cattle, goats and horses, on the colonization dynamic of competitive shrubs such as brambles. Applied pastoral management should be considered in the medium term, via multi-year contracts to promote the sustainability of this management method and its effects over time.

Le processus d’urbanisation conduit à un ensemble de transformations et perturbations qui peuvent avoir des conséquences sur la flore spontanée. Ce travail de thèse porte sur les communautés végétales des espaces herbacés ordinaires distribués au sein 3 aires urbaines de l’ouest de la France : Angers, Nantes et la Roche-sur-Yon. A travers deux approches, taxonomique et fonctionnelle, l’objectif est d’analyser les variations de diversités et de composition floristiques le long de gradients paysagers (notamment d’urbanisation et de connectivité des habitats). Ces milieux apparaissent diversifiés, tout en ne présentant qu’un faible nombre d’espèces exotiques. Le gradient urbain-rural structure les communautés, établissant notamment de fortes distinctions dans leurs compositions spécifiques, et ce, malgré l’absence de variations en terme de richesse et d’homogénéisation. Ces distinctions sont en lien avec des traits relatifs à leurs exigences écologiques (habitat, pH, humidité, lumière)et au niveau de perturbation plus élevé en ville. Ces relations varient malgré tout selon que l’on considère l’abondance locale ou régionale des espèces suggérant que d’autres mécanismes viennent s’ajouter à ces processus de filtre. La mesure in situ de trois traits fonctionnels (hauteur, SLA et phénologie) montre également l’importance de ce processus de filtre sur les espèces à un niveau intraspécifique. L’ensemble des résultats montre la façon dont ces espèces communes s’assemblent au regard des processus écologiques à l’oeuvre dans des environnements urbains, et permet d’ouvrir des perspect / The process of urbanisation leads to a series of transformations and disturbances that may have consequences for wild plant communities. This thesis presents a study of the plant communities of ordinary grasslands distributed among three cities of western France: Angers, Nantes and La Roche-sur-Yon. Using both taxonomical and functional approaches, the aim is to analyse the variation in plant diversity and composition along landscape gradients, in particular those of urbanisation and habitat connectivity. Such grassland habitats appear to be diverse, despite a low number of exotic species. The urban-rural gradient structures such communities, in particular by strongly modifying species composition; and this despite an absence of variation in species richness or of homogenisation. These modifications in community structure are linked to traits for ecological requirements (for habitat, pH, humidity or light)or for adaptation to higher levels of disturbance in towns. These relationships vary according to species’ local or regional abundance, suggesting that other mecanisms accompany the filtering process. Taking into account three functional traits (height, SLA and phenology) measured in situ shows that the filtering process also has consequences at intraspecific level. Taken together, the results show how common species are assembled in response to ecological processes operating in urban environments and open up new perspectives and applications for the integration of grassland plant communities into biodiversity conservation objectives in urban areas

Throughout arid and semi-arid inland Australia, many extensive floodplains occur in association with rivers which are amongst the most hydrologically variable in the world. As rainfall in these areas is characteristically low and patchy, conditions in Australia's 'dryland' floodplains fluctuate unpredictably between extended periods of drought and huge floods that transform vast areas into wetlands, often for months at a time. Vegetation in these floodplains is commonly dominated by short grass and forb associations and patches of open succulent shrubland which are attributed with high ecological and socio-economic values due to their provision of habitat to a diverse array of terrestrial and aquatic fauna and their productive native pasture growth. In temperate and tropical floodplains, a substantial number of studies have shown that plant community composition and structure is determined primarily by flow and alterations to flow in these areas, through water extraction or river regulation, have resulted in many changes to the vegetation including loss of biodiversity and mass invasions of exotic species. Despite increasing pressure for water resource development in 'dryland' regions, relatively little is known regarding the effects of highly variable flows on the vegetation dynamics of arid floodplains, particularly in Australia. This thesis addresses this knowledge gap by examining the role of flow in the vegetation dynamics of a large arid floodplain in central Australia: the Cooper Creek floodplain. The effects of flow on plant community dynamics, from an organism level to that of the landscape, are examined across a range of spatial and temporal scales. Results are presented from a two year temporal vegetation survey during which time two flood pulse events of differing sizes occurred. A large-scale spatial survey was also conducted to determine the effects of flood history on spatial variation in plant community composition and structure. The composition of the soil seed bank and its contribution to vegetation dynamics were additionally investigated through a series of germination trials. Amongst common arid floodplain plants, life history traits that enable persistence under variable hydrological conditions were also considered via several experiments aimed at determining the effects of flow on the outcomes of various life history stages including germination, growth and dispersal. Throughout the study, results are presented for plant groups that were predefined on the basis of life form, life span and taxonomic divisions within these categories. Plant community composition and structure in the Cooper Creek floodplain exhibits significant shifts both temporally, in response to flood pulse wetting and drying, and spatially, in response to flood history. Flood pulse inundation has the potential to influence each life history stage across the range of plant groups present and the outcomes of these appear to be determined by hydrological attributes such as flood pulse timing, duration and rate of drawdown. Vegetation consequently exhibits gradual zonation on a gradient of flood frequency along which plant groups occur at predictable locations depending on their life history traits and recent hydrological conditions. A substantial proportion of species display ruderal life history traits including large, persistent soil seed banks and rapid life cycles which enable escape in time from the stresses associated with flooding and drought. These species, mostly comprising annual monocots and forbs, are widespread throughout the landscape and their presence in the extant vegetation is related primarily to the time since the last flood pulse event and the hydrological attributes of this. Perennial species, particularly shrubs, do not appear to rely similarly on the soil seed bank for recruitment and their distribution in the floodplain vegetation is likely to be determined more by their ability to tolerate either flooding or drought. Overall, this study demonstrates that flow, despite its variability, has an overriding influence on vegetation dynamics in the arid floodplain of the Cooper Creek. The spatial and temporal variability of flow maintains a heterogeneous mosaic of plant communities of differing composition and structure. Given this close relationship between flow and vegetation dynamics, anthropogenic alterations to flow are likely to result in changes to the vegetation including homogenisation of plant communities across the floodplain landscape and eventual loss of biodiversity.

L’attività di ricerca ha previsto il confronto fra due siti inquinati da metalli pesanti e due siti controllo naturali. Contrariamente ai parametri chimico-fisici e ai contenuti in metallo dei suoli, le analisi vegetazionali non hanno evidenziato differenze significative tra i siti. E’ stata necessaria la messa a punto strumentale di tecniche ICP-OES, ED(P)XRF per la calibrazione empirica di un XRF portatile, per le osservazioni puntiformi in situ di suoli e flora ed è stata modificata la metodica ufficiale per le stime della biodisponibilità dei metalli pesanti nei suoli inquinati. 6 specie comuni ai 4 siti sono state valutate per i loro TF e BAF. Viene confermata la specie-specificità del TF e del BAF per il quale è stato elaborato un inedito algoritmo per un corretto confronto tra le specie. Tra le sei specie, Silene Alba ha i migliori TF e BAF. Successivamente, sono state valutate alcune caratteristiche del Pennisetum clandestinum, candidato per la fitodepurazione: tollera le concentrazioni di arseniato tipiche dei suoli inquinati, l’arseniato è un inibitore competitivo del trasporto del fosfato, possiede un’elevata velocità di assorbimento dell’arseniato che accumula nella radice, ma non lo trasloca nella frazione epigea, parte dell’As(V) viene ridotto ad As(III) che viene efflusso dalla radice / The research has provided a comparison between two heavy metals polluted sites and two natural control sites. Unlike physical-chemical parameters and metal content in the soils, vegetation analysis showed no significant differences between sites. The development and optimization of instrumental techniques ICP-OES and ED(P)XRF was necessary to calibrate empirically a portable XRF for soil and flora point observations in situ and the official method for estimation of bioavailability of heavy metals in polluted soil was changed. Six species, common to the four sites, were evaluated for their TF and BAF. Were confirmed the TF and the BAF species-specificity for which it was developed a novel algorithm to obtain a correct comparison among species. Among the six species, Silene Alba has the best TF and BAF. In the second stage, some characteristics of Pennisetum clandestinum, candidate for the phytoremediation, were assessed: it tolerates arsenate concentrations typical of polluted soil, arsenate is a competitive inhibitor of phosphate transport, it has a high uptake rate of arsenic that accumulates in the root, but it doesn’t move in the aboveground fraction and part of As(V) is reduced to As(III), which is efflux from roots.

Subsistence harvesting pressure in most African countries focuses on the small and mostly unreproductive trees found in the understorey stratum and can have potentially insidious ecological effects. Harvest intensities at Ongoye Forest Reserve (OFR) vary significantly across the forest (range = 87 - 567 stumps ha-1), with harvesting focussed exclusively on poles from tree species that grow only in the understorey. Growing evidence indicates that seedling establishment from the pool of species available beneath a closed canopy is greatly influenced by the differential ability of species to take advantage of the short burst of resources in newly-created understorey gaps. Seedling dynamics in these gaps may determine forest tree diversity and dynamics and consequently harvest gaps have the potential to significantly affect natural forest dynamics. This study examined seedling establishment beneath intact understorey and within artificially created understorey gaps of different sizes (single stem gaps, two stem gaps, four stem gaps, eight stem gaps and control ‘gap’, where no stems were removed) that simulated different spatial scales of harvesting intensity of understorey trees. This experiment examined the proposition that successful seedling establishment and natural succession is strongly dependent on the scale of harvesting. Seedling abundance, species richness, irradiance (photosynthetically active radiation and the red to far-red ratio), soil nutrient composition and herbaceous layer cover was measured in each gap size in 2005 before harvesting, and again in 2007. The mean seedling abundance was not significantly different among gap treatments, although there was a trend towards more seedlings in 2005 than 2007. Seedling abundance in all gaps was greater than at control sites beneath the intact understorey. There was a continuous increase in seedling richness in 2007. An average species richness of 4.3 was recorded in the control sites, beneath a shaded understorey. Here, seedling richness increased by 18.24% with the removal of a single understorey tree (Gap 1). Species richness increased with increasing experimental gap size increased so that the greatest mean species richness (6.2 species) was recorded where eight neighbouring trees were removed (Gap 8). Light transmission reaching the seedling stratum was greater in larger gaps and there was a trend towards more seedlings and greater species richness in the higher light environments of such gaps. Soil nutrient levels did not influence seedling abundance and species richness in gaps. The herbaceous layer suppressed seedling establishment. In the largest gaps (115.4m2) created by harvesting, seedling composition was more deterministic than in small gaps where seedling establishment and density was random, accordingly there were more species in larger gaps from a more defined species assemblage. Current harvesting levels of pole-sized understorey trees, where only small gaps are created in the understorey, are unlikely to alter forest dynamics and species composition at OFR. This study demonstrates that harvesting eight adjacent trees crosses the harvest intensity threshold between sustainable natural tree dynamics and a potential successional shift to an alternative state. Clearly, for natural dynamics to be maintained harvesting intensities will have to be regulated. / http://hdl.handle.net/10413/631 / Thesis (M.Env.Dev.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.

Fire plays an important role in structuring and maintaining savanna grassland ecosystems. Although regular fires are a characteristic feature of savannas, the effects of fire frequency on these systems are less well known, particularly with respect to how frequency of fire influences large herbivore distribution and behaviour. The expectation is that large herbivores should be attracted to frequently burned sites as a consequence of changes in forage quality and quantity, and/or vegetation structure and composition. The former could be driven by alterations in soil nutrients, such as N and P. Alterations in vegetation also could be important in determining risk of predation. For example, an increase in woody vegetation could decrease predator visibility making large herbivores more vulnerable to predation. The objectives of this study were to investigate the effects of long-term alterations in fire frequency on herbivore distribution and behaviour, as well as the mechanisms (soil nutrients, vegetation structure and composition, and forage quality and quantity) potentially driving the distribution of large herbivores. To address these objectives, I conducted large herbivore surveys on a bi-weekly basis from 2009-2010 in a series of plots in the Experimental Burn Plots (EBPs) burnt at different frequencies (annual, triennial and unburnt) over the last five decades at three study sites in the Kruger National Park, South Africa. Surveys also were conducted on new plots that were established adjacent to the long-term plots. These new plots have a fire return interval of 4 years which is similar to the triennially burned plots of the EBPs. They were established in the landscape adjacent to the EBPs to assess whether the responses of herbivores to fire observed in the EBPs reflected was at landscape level. The distribution of all large herbivore species combined and of grazers (e.g. zebra) or browsers (e.g. kudu) only were not affected by fire frequency. In contrast, the abundance of mixed-feeders, such as impala, was significantly higher in the unburnt (control) and annually burned plots than the triennially burned plots. Although season did not have a significant impact on the distribution of browsers and mixed-feeders, overall more grazers were recorded across all burn treatments in the dry season compared to the wet season. Similar patterns of herbivore distribution were observed between the new plots and the triennially burned EBP plots, suggesting that responses observed to the long-term fire frequency treatments reflects herbivore responses at the landscape level. The long-term fire frequency treatments significantly affected soil nutrients (N, organic C, P, and K were significantly lower with annual burning), vegetation structure (abundance of woody plants were greater in unburned plots), and forage quantity (unburned plots had higher biomass) but not quality. More frequent fires improved visibility by reducing tree height and density and herbaceous biomass, thereby potentially reducing predation risk, when compared to less frequent burning. As a result, herbivores selected sites with more frequent fires. The behaviour of the herbivore species investigated was predominantly influenced by seasonal-induced changes to their environment rather than fire frequency. In the wet season irrespective of the burning treatment visibility was low due to high rainfall that increases plant biomass, whereas in the dry season visibility was improved because there is little to no rainfall. This potential alteration in predation risk likely resulted in herbivores being more vigilant in the wet season than the dry season. Overall, results from this study suggest that the combination of fire frequency and season drive herbivore distribution and behaviour by altering mainly the vegetation structure which can influence predation risk. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.