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The savanna woodlands of Southern Africa, colloquially termed the miombo, are poorly described in terms of biodiversity compared to other biomes. They have therefore been underrepresented in the wider understanding of how land use intensification is shaping global biodiversity. Land use change is known to reduce biodiversity and disrupt intactness of ecological communities with consequences for ecosystem functioning, resilience, and services. Miombo woodlands are described as biodiversity hotspots due to a high endemism of species and the presence of megafauna. At the same time, they are also considered dynamic socio-ecological systems shaped by disturbances and the land use activities of people. The patterns of biodiversity change in these tropical ecosystems may, therefore, have their own unique contexts, understanding of which will be essential for biodiversity and land use management in these ecosystems. In this thesis, I identified the patterns of biodiversity change in response to the two major land use practices in the two dominant woodland types in southern African woodlands: the selective logging due to charcoal production in the mopane woodlands, and agricultural expansion in the miombo. I also examined the impact of two main disturbance agents, humans and elephants, on habitat structure and biodiversity in mopane woodlands. Across all chapters in this thesis, I investigated the effects of land use change and habitat modification on biodiversity empirically using chronosequences. To understand biodiversity change, I employed a hierarchical multilevel modelling approach making inferences at the three levels of ecological communities: species, community, and meta-community (set of ecological communities at different sites). I selected six villages in the charcoal production hotspot of southern Mozambique and carried out field surveys for three taxonomic groups: trees, mammals and ground beetles. I modelled the counts of trees and beetles and incidence of mammals using meta-community occurrence models in a Bayesian framework with the intensity class of the villages, above-ground biomass and land cover type as predictors. The results suggested that the species richness of trees and mammals declined by 12 and 8.5 % respectively while that of beetles increased by 3.5%, albeit non-significantly. In addition, the beta diversity of trees decreased while that of mammals increased. The results show that while both trees and mammals reduced in richness, they responded differently to charcoal production in terms of community organisation. The trees underwent subtractive homogenisation (decrease in alpha and beta diversities) primarily because of deterministic processes induced by selective harvesting of tree stems for charcoal. Mammal communities, on the other hand, showed subtractive heterogenization (decrease in alpha, but increase in beta diversity) mainly due to random extinctions. In the agriculture frontier of miombo-dominated northern Mozambique, I investigated the effects of fragmentation and habitat loss caused by agricultural expansion on diversity and composition of trees and mammals. I modelled the occurrences of trees and mammals using occupancy models with the fragmentation and quantity of woodland cover as predictors. The model showed that most tree species (n=10), mainly the timber and firewood species, linearly declined in population size as fragmentation increased. Mammals, on the other hand, showed a nonlinear response. Seven mammal species increased at the lower levels of fragmentation. However, at the higher levels, none of the mammal species increased while two declined. Similarly, the species richness of trees linearly declined, while that of mammals increased up to a fragmentation level of 55-65% and declined above this limit. The beta diversity of trees increased with fragmentation while that of mammals decreased. The results suggest that, although fragmentation reduces species richness of both trees and mammals, it affects their species compositions in different ways. Trees undergo subtractive heterogenization due to random species losses while mammals experience subtractive homogenisation mainly due to the combined effects of fragmentation-led habitat loss and intensified hunting. Finally, this study concludes that, above 75% fragmentation or below 26% habitat quantity, both taxonomic groups endure biodiversity loss. The threshold results here corroborate similar habitat quantity thresholds (20-30%) observed elsewhere in different ecosystems. However, they differ with the widespread notion that above 30% habitat quantity, the effect of fragmentation is non-existent. The results here emphasize that taxonomic groups respond differently, the diversity and population size of mammals reduced only after the habitat threshold, whereas, those of trees showed linear decrease with fragmentation most likely due to fragmentation-led habitat loss. Lastly, I examined the effects of disturbance by humans and elephants on habitat structure and bird diversity by conducting a space for time substitution comparison in the mopane woodlands of Zambia. To examine the woodland structure, I modelled the structural attributes of habitat (stem diameter, stand density, and basal area) using mixed models with the proportion of affected stems by humans and elephants as explanatory variables. I found that elephant disturbance was associated with higher stem diameters, low stand densities, but no change in basal area. Human disturbance, on the other hand, was related to reductions in stand density and basal area, but no change in the stem diameter. Further, I tested species and functional diversity of birds against the covariates of habitat structure and disturbance. I found that bird communities reduced in species richness in both, human as well as elephant disturbed areas. However, the functional diversity did not change with elephant disturbance. I concluded that human disturbance reduces woody biomass (basal area is correlated with woody biomass) of mopane woodlands and functional diversity of birds whilst elephants do not. In this thesis, I conclude that human driven land use change in the miombo woodlands erodes alpha diversity of all taxonomic groups. However, increases in beta diversity of mammals with charcoal land use and trees in agricultural land use may maintain their diversities at the meta-community level.

Rivers and their catchments are under mounting pressure from direct channel modification, intensification of land use, and from a legacy of decades of channelisation. Recent legislation, in the form of the EU Water Framework Directive, places a greater emphasis on the management of water bodies as holistic systems, and includes the explicit consideration of hydromorphological quality, which describes the hydrologic and geomorphic elements of river habitats. These are defined specifically as hydrological regime, river continuity and river morphology. This appreciates that sediment and flow regimes, along with the channel structure, provides the 'template' on which stream ecological structure and function is built. Invertebrate fauna contribute significantly to the biodiversity of rivers, and often form the basis of monitoring river health. However much of the fundamental ecological knowledge base on the response of invertebrates to hydromorphological change needed to make informed decisions and accurate predictions, is either lacking, inadequate or contradictory. This thesis addresses some of the key potential shortcomings in recent bio-assessment that others have alluded to, but which have rarely been explored in the context of direct channel manipulations. By using two case studies of, realignment in a natural upland catchment, and flood protection engineering in an urban stream, this study investigates the sensitivity of hydromorphological impact assessment methods that rely on biodiversity patterns of benthic riverfly (Ephemeroptera, Plecoptera and Trichoptera) larva. This work employed widely used biomonitoring indices of benthic riverfly larva abundance, species richness, alpha and beta diversity, and community composition, applied over a range of spatial scales, in combination with spatially contemporaneous physical habitat data, to describe and explain community changes in response to disturbance, and patterns of natural variation. The effects of restoration were investigated using a high degree of sample replication within channels and across the wider catchment, as well as contrasting spring and autumn seasons. To assess change in a small urban channel, approaches that explicitly consider spatial elements of community data, using spatial eigenvectors analysis, were applied to spatially detrend community data and directly investigate spatial patterns. Restoration of the Rottal Burn was found to be successful in restoring habitat diversity and geomorphic processes, and in turn increasing reach scale species richness and beta diversity through the gradual arrival of rare and specialist taxa into novel habitats. Catchment scale replication revealed high variation in diversity indices of modified and undisturbed streams, and a strong temporal pattern related to antecedent flow conditions. Channels with greater habitat heterogeneity were able to maintain high gamma diversity during times of high flow stress by providing a number of low flow refuges along their length. The urban Brox Burn had surprisingly high riverfly richness and diversity driven by small scale hydraulic heterogeneity, created by bed roughness resulting in a range of microhabitats. Riverfly community responses to direct channel dredging could not be detected by measurements of average richness and diversity, however distinct changes were seen in gamma diversity, the identity of community members and their arrangement among sample patches. Impacts of sediment pollution release due to engineering were short lived and apparently had little detrimental impact on biodiversity. Strong spatial patterns of community assembly on the stream bed were uncovered, relating to longitudinal, edge and patchy patterns. Significant habitat drivers of community composition were confounded by high amounts of spatial autocorrelation, especially hydraulic variables. Due to the strongly physical and spatial nature of hydromorphological disturbance, turnover of species between sample locations at a range of scales, and the spatial arrangement of habitats and communities is of more use for detecting these types of subtle changes compared to mean richness or diversity. These findings have implications for the targeting of resources for monitoring of restoration, or engineering disturbances, in order to be sensitive to hydromorphological change. Efforts should target the main area of natural variability within the system, either replicating sampling in time or space to distinguish effects of impact. Spatial patterns, measures of beta diversity and species identity can be better exploited to identify systems with functioning geomorphological processes. Channel typologies proved misleading, and quantification of habitat and selection of control sites using multiple pre-defined criteria should be carried out. Studies of restoration operations and engineering impacts provide considerable opportunities for advancing our knowledge of the mechanisms that drive community response under a range of conditions to improve impact detection.

Sites left to spontaneous vegetation succession and those technically reclamed were studied and compared on dumps in the Most Region, NW Czech Republic. Data were sampled in summer 2008 and 2010. Species composition and species diversity were analyzed using phytosociological reléves arranged along 100m transects. Alfa- and beta-diversity were evaluated. There were significant differences between sites in alfadiversity. Beta-diversity was highest in the spontaneously re-vegetated sites. There were also differences in species composition among the studied sites. I consider using spontaneous succession as appropriate in restoration of land disturbed by brown coal mining. It is a good alternative to expensive technical reclamation.

Submitted by Marlene Santos (marlene.bc.ufg@gmail.com) on 2018-07-12T20:09:09Z No. of bitstreams: 2 Tese - João Fabrício Mota Rodrigues - 2017.pdf: 7026938 bytes, checksum: bb5eb1fc81f363b414aa3c9e80fb3429 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-07-13T10:42:29Z (GMT) No. of bitstreams: 2 Tese - João Fabrício Mota Rodrigues - 2017.pdf: 7026938 bytes, checksum: bb5eb1fc81f363b414aa3c9e80fb3429 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-07-13T10:42:30Z (GMT). No. of bitstreams: 2 Tese - João Fabrício Mota Rodrigues - 2017.pdf: 7026938 bytes, checksum: bb5eb1fc81f363b414aa3c9e80fb3429 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-05-03 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Understanding the processes that shape the current distribution patterns of species is one of the main goals of Ecology. In this thesis, we aimed to understand which factors are related to the distribution of the turtle diversity, a group of ectothermic animals whose diversity patterns are still little known, over time and space. To that end, we used distribution data from continental chelonian species, as well as life history information (habitat type and body size), and reconstructed a phylogenetic hypothesis for the group using molecular data. Turtles had a burst of lineage diversification during the irradiation of the Emydidae family, which is probably linked to an event of ecological opportunity. In addition, aquatic animals had higher rates of diversification than terrestrial animals, which helps to explain the current greater diversity of aquatic animals. Turtle richness distribution along the continents is mainly influenced by climatic variables such as temperature and precipitation, but the time when lineages first colonized the continental regions also influences this pattern. Beta diversity among chelonian communities is mainly influenced by the geographical distance between communities, and communities from different biogeographic realms are structured by different drivers. Finally, body size diversity of turtles is also influenced by temperature, and small animals are more common in cold areas. / Compreender os processos responsáveis pelos padrões de distribuição atuais das espécies é um dos principais objetivos da Ecologia. Nesta tese, visamos entender quais fatores estão relacionados à distribuição da diversidade de quelônios, grupo de animais ectotérmicos cujos padrões de diversidade ainda são pouco conhecidos, ao longo do tempo e do espaço. Para esse fim, usamos dados de mapas de distribuição das espécies de quelônios continentais, além de informações de história de vida (tipo de hábitat e tamanho corporal), e reconstruímos uma hipótese filogenética para o grupo usando dados moleculares. O grupo dos quelônios apresentou uma explosão de diversificação durante a irradiação da família Emydidae, o que está provavelmente ligado a um evento de oportunidade ecológica. Além disso, animais aquáticos apresentaram taxas de diversificação mais elevadas que os animais terrestres, o que ajuda a explicar a maior diversidade de animais aquáticos atuais. A distribuição da riqueza de quelônios ao longo dos continentes é influenciada principalmente por variáveis climáticas tais como temperatura e precipitação, porém o intervalo de tempo desde o qual as áreas foram colonizadas também influencia nesse padrão. A diversidade beta entre as comunidades de quelônios é influenciada principalmente pela distância geográfica entre as comunidades, e comunidades de diferentes de domínios biogeográficos são estruturadas de modo diferenciado. Finalmente, a diversidade de tamanhos corporais dos quelônios também é influenciada pela temperatura, de modo que animais menores são mais comuns em áreas mais frias.

Submitted by JÚLIO HEBER SILVA (julioheber@yahoo.com.br) on 2017-05-25T20:22:07Z No. of bitstreams: 2 Tese - Juliana Simião Ferreira - 2013.pdf: 2071806 bytes, checksum: 8202c30edb9d0103d57d3b98ce204f2c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-05-26T14:46:31Z (GMT) No. of bitstreams: 2 Tese - Juliana Simião Ferreira - 2013.pdf: 2071806 bytes, checksum: 8202c30edb9d0103d57d3b98ce204f2c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-05-26T14:46:31Z (GMT). No. of bitstreams: 2 Tese - Juliana Simião Ferreira - 2013.pdf: 2071806 bytes, checksum: 8202c30edb9d0103d57d3b98ce204f2c (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2013-05-20 / Headwater streams biodiversity is very important to the maintenance of the biological integrity found in the whole hydrological basin. Therefore, understanding the processes generating and/or influencing biodiversity in such environments may contribute to future aquatic integrity monitoring programs and to the strategic planning for both species and community conservation found within the every stream networks. The main goals of the current study were to: i) identify landscape and spatial environmental predictors responsible for the structure of aquatic insects communities (Trichoptera); ii) identify which hierarchical scale within the hydrologic basins is responsible for the highest biodiversity variation, what may provide subsidies for future studies and planned conservation of lotic environments. In order to achieve such goals, we did different studies with specific objectives directed to (i) measure the contribution of environmental and spatial variables while determining species richness and composition within Trichoptera communities, separately considering species with wide and narrow spatial distribution; (ii) measure the influence of landscape attributes such as vegetation cover in different spatial scales on species richness and bet diversity, as well on the different trophic functional groups found within the Trichoptera community; (iii) evaluate the effects of nested headwater streams community structure embedded within superior hierarchical levels (e.g. microbasins, subbasins, and the whole catchment), as well as the effects of the environmental and spatial predictors on alpha, beta and gamaTrichoptera diversity considering different spatial scales. All studies were performed with a set of biological data sampled in 48 headwater streams within two hydrographic basins locate within the state of Goiás, Brazil, with different land use regimes. Within those streams, local environmental variables (physical-chemical variables and habtat integrity), landscape attributes (vegetation cover, and land use classification), and also the biological data regarding the Trichoptera insects were sampled. In the first study, we observed that compositional changes within the Trichoptera communities was determined by local processes, especially for genus with wider distribution, while the communities of those species with narrower distribution were probably structured by other factors not measured here. This study reinforces that the use of community deconstruction related to specific species attributes (e.g. spatial distribution) contributes to a better comprehension of the processes determining the metacommunities structure. In the second study, we verified that landscape attributes within the hydrologic basin, such as vegetation quality around the streamlet and vegetation cover up to 200m from the streamlet, are important predictors to the structure and functioning of Trichoptera communities. In the third study, results indicate that the variation in alpha, beta and gama diversities depend on the spatial scale considered and that the environmental degradation affects distinctly such patterns. We were able to verify that the structure of Trichoptera communities is determined by environmental factors, mainly in the local scales, such as water physical-chemical parameters and vegetation cover. Additionally, we observed that that the spatial scale within which the diversity is maximized is on catchment scale, reinforcing the need to increase the spatial scales considered in such studies in order to obtain a higher diversity for the Trichoptera in headwater streams. Finally, these studies confirm the vulnerability of Trichoptera communities to the variability on water quality and landscape changes, supporting the use of these organisms as indicators and reinforcing the need of conservation strategies which consider the aquatic diversity within each streamlet embedded in hydrologic basin elsewhere. / A diversidade biológica em riachos de cabeceira é muito importante para a manutenção da integridade de toda a bacia hidrográfica. Então, entender os processos que geram e/ou influenciam a diversidade nestes ambientes pode contribuir para futuros programas de monitoramento da integridade aquática e para o planejamento estratégico para a conservação de espécies e de comunidades das redes hidrográficas. O presente estudo teve por objetivo principal identificar os preditores ambientais locais, de paisagem e espaciais em múltiplas escalas responsáveis pela estruturação das comunidades de insetos aquáticos (Trichoptera). Além disso, objetivou verificar a escala hierárquica de bacias hidrográficas responsável pela maior variação da diversidade e desta forma, subsidiar futuros estudos e planejamento para conservação de ambientes lóticos. Para tanto, foramrealizados diferentes estudos com objetivos específicos direcionados a(i)medir a contribuição relativa de variáveis ambientais e espaciais na determinação da riqueza e composição taxonômica das comunidades de Trichoptera, considerando separadamente os táxons com distribuição ampla e restrita em riachos de nascente do bioma Cerrado, (ii)medir a influência dos atributos da paisagem como cobertura vegetal em diferentes escalas espaciais sobre a riqueza e diversidade beta, bem como sobre diferentes grupos tróficos funcionais da comunidade de Trichoptera, (iii) avaliar o efeito da estrutura aninhada de pequenos riachos de cabeceira inseridos dentro de níveis hierarquicamente superiores (microbacias, sub-bacias e bacias), bem como o efeito dos preditores ambientais e espaciais na diversidade alfa, beta e gama de insetos aquáticos. Todos os estudos foram realizados com o conjunto de dados amostrados em 48 riachos de nascente em duas bacias hidrográficas em Goiás, Brasil, com padrões de uso do solo distintos. Nestes riachos amostramos variáveis ambientais locais (físico-química e integridade de habitat) e de paisagem (índice de cobertura vegetal e uso do solo), assim como os insetos aquáticos da ordem Trichoptera.No primeiro estudo, observamos queamudança na composição das comunidades de Trichoptera foi determinada por processos locais, principalmente para os gêneros de distribuição mais ampla, enquanto os restritos provavelmente foram estruturados por outros fatores aqui não investigados. Este estudo reforça que o uso da abordagem de desconstrução da comunidade em função dos atributos das espécies contribui para uma melhor compreensão dos processos determinantes das metacomunidades. No segundo estudo, verificamos que as características da paisagem dentro da bacia de drenagem, como qualidade da mata em torno do riacho e da cobertura vegetal em escalas de até 200m do riacho, são importantes preditores da estrutura e funcionamento das comunidades de Trichoptera. No terceiro capítulo, os resultados indicam que a variação na diversidade alfa, beta e gama é dependente da escala espacial, e que o grau de degradação regional afeta distintamente estes padrões. Desta forma, podemos verificar que a estrutura das comunidades de Trichoptera é determinada por fatores ambientais, principalmente, na escala local, tanto as características da água como de cobertura vegetal. Além disso, observamos que a escala espacial em que a diversidade é maximizada é na escala de sub-bacia, reforçando a necessidade de ampliar as escalas espaciais para se obter a maior diversidade deste grupo em riachos de cabeceira. Por fim, estes trabalhos confirmam a vulnerabilidade das comunidades de Trichoptera à variações na qualidada de água e de modificações na paisagem como intensificação do uso do solo, o que suporta o uso destes como indicadores, além de reforçar a necessidade de estratégias para conservação que considere a diversidade aquática em riachos pertencentes a redes hidrográficas.

Abstract Describing how and why species composition of ecological communities varies across spatial and temporal scales is a primary objective for ecological research. A key challenge is to distinguish changes in community composition resulting from external factors from the natural background variability. In this thesis I aimed to study: 1) the level of temporal variation in community composition of stream macroinvertebrates, 2) the role of different environmental factors to temporal variability, 3) the effect of temporal variability on bioassessment outcomes, and 4) comparability of different approaches to study community variability through time. A majority of the studied macroinvertebrate communities showed lower level of inter-annual variation, i.e. temporal turnover, than expected by chance. The observation of high community stability was further supported by the low level of inter-annual variation in taxonomic completeness (quotient of observed and expected number of species, O/E). Despite the low absolute variation in O/E, ecological status assessments varied annually. Thus the use of one year data may bias management decisions. Macroinvertebrate communities experienced similar dynamics across several spatial extents, from riffles within a stream to streams among regions, suggesting that large-scale extrinsic factors are the major driver of community dynamics. Especially climatically exceptional years may have a strong imprint on community variability. However, at the within-stream scale, coherence was lower than expected, indicating that community dynamics may be driven by different processes at different spatial extents. Stream macroinvertebrate community dynamics were strongly related to in-stream vegetation, temporal variability decreasing with increasing macrophyte cover. Importantly, the effect of in-stream vegetation on temporal turnover of macroinvertebrate communities was masked by the stochastic effect of habitat connectivity, suggesting that unless stochastic effects are controlled for, the role of deterministic processes may be obscured, thus affecting our ability to understand and predict community changes through time. In addition, different approaches to study temporal variability may disagree on estimates for the level of temporal turnover and factors explaining it – a fact that should be taken into account when planning and comparing studies. / Tiivistelmä Yksi ekologisen tutkimuksen keskeisistä tavoitteista on kuvata, miten ja miksi eliöyhteisöjen koostumus muuttuu paikasta ja ajankohdasta toiseen. On tärkeää pystyä erottamaan erilaisten ulkoisten tekijöiden aiheuttamat muutokset luonnollisesta taustavaihtelusta. Väitöskirjani tavoitteena oli selvittää 1) miten paljon virtavesien pohjaeläinyhteisöissä tapahtuu ajallista vaihtelua 2) mitkä ympäristötekijät vaikuttavat yhteisöjen ajalliseen vaihteluun 3) miten ajallinen vaihtelu vaikuttaa ympäristön tilan arviointiin ja 4) kuinka vertailukelpoisia ovat eri lähestymistavat ajallista vaihtelua tutkittaessa. Valtaosa tutkituista pohjaeläinyhteisöistä vaihteli vuosien välillä vähemmän kuin olisi sattumalta odotettavissa osoittaen varsin suurta ajallista pysyvyyttä. Käsitystä yhteisöjen pysyvyydestä tuki myös vähäinen vuosittainen vaihtelu ekologista tilaa kuvaavassa taksonomisessa eheydessä (=havaitun ja odotetun lajiston suhde O/E). Huolimatta näennäisen pienestä vaihtelusta O/E suhteessa paikkakohtaiset tilaluokka-arviot saattoivat vaihtua vuodesta toiseen. Yhden vuoden aineistoon perustuvat tilan arvioinnit voivat siis johtaa virheellisiin johtopäätöksiin. Pohjaeläinyhteisöjen ajallinen vaihtelu oli samankaltaista eri mittakaavoilla niin peräkkäisten koskipaikkojen kuin eri alueilla sijaitsevien purojen välillä. Suuren mittakaavan ympäristötekijät näyttävät siis säätelevän eliöyhteisöjen ajallista vaihtelua. Erityisesti ilmastotekijöiltään poikkeukselliset vuodet säätelevät eliöyhteisöjä, ja niiden vaikutus voi näkyä vielä useiden vuosien kuluttua. Vaihtelun samankaltaisuus peräkkäisten koskipaikkojen välillä oli kuitenkin odotettua pienempää. Yhteisöjä voivat siis säädellä osittain eri tekijät eri mittakaavoilla. Tutkittujen pohjaeläinyhteisöjen ajallisen vaihtelun voimakkuus liittyi erityisesti vesikasvillisuuden määrään: vaihtelu väheni kasvillisuuden lisääntyessä. Kasvillisuuden määrän vaikutus peittyi kuitenkin satunnaisten tekijöiden alle. Jos satunnaisia tekijöitä ei huomioida, deterministiset syy-seuraussuhteet voivat jäädä huomaamatta heikentäen mahdollisuuksiamme ymmärtää ja ennustaa eliöyhteisöjen vaihtelua. Lisäksi eri lähestymistavat ajallista vaihtelua tutkittaessa voivat johtaa erilaisiin arvioihin vaihtelun suuruudesta ja siihen vaikuttavista tekijöistä, mikä tulisi ottaa huomioon tutkimuksia suunnitellessa ja niiden tuloksia vertailtaessa.

Light is essential component of forest ecosystem, as limited light availability in forest-floor restricts herb and tree seedlings growth. Importance of light availability for maintaining plant species diversity and community structure wasn't sufficiently evaluated in the Czech Republic. This study focus on the ecological relevance of light availability on both landscape and local scale. Relationship of light to cover, diversity and species composition was quantified in the thesis. Dominant tree species affected light availability and its spatial variability. Light availability was along the soil reaction and slope most influential factor for large-scale species diversity. Within-site light variability affected plant diversity more than soil reaction variability. Measuring light by means of hemispherical photography seems to be an appropriate for studies like this. Light availability influnence on community compostition is weak in comparison with other environmental gradients.

La hausse de l’urbanisation et la hausse d’introduction des espèces exotiques qui l’accompagne sont parmi les plus grands risques pour la biodiversité. Les espèces exotiques peuvent non seulement affecter la diversité alpha et réduire les populations d’espèces indigènes, mais également entrainer des changements de la biodiversité bêta. Toutefois, ces phénomènes sont complexes et la littérature sur le sujet présente des résultats variés. C’est pourquoi le but de cette recherche est d’étudier l’influence des espèces exotiques et envahissantes sur la diversité alpha et bêta de 61 boisés urbains de la grande région de Montréal. Nos résultats ont montré que les espèces envahissantes ont un effet plus grand que les espèces non envahissantes sur la diversité alpha. Elles sont toutes deux associées à une hausse de la richesse totale et de la diversité alpha. Toutefois, une hausse du couvert des espèces envahissantes est associée à une diminution de la richesse et du couvert des espèces indigènes. Nos résultats ont également montré qu’un grand couvert en espèces envahissantes provoque des changements significatifs de la diversité bêta en réduisant la différence entre les sites. À l’opposé, lorsque la richesse en espèces exotiques est grande, nous avons observé une différenciation en espèces indigènes qui serait expliquée par la diminution de leur richesse. Pour finir, nous avons constaté que les espèces exotiques et envahissantes sont associées à un changement significatif de la composition en espèces. Nos résultats suggèrent que les espèces exotiques, tout particulièrement les espèces envahissantes, sont associées à des changements importants de la diversité des boisés urbains. Toutefois, des études supplémentaires sont nécessaires pour confirmer si elles sont responsables de ces changements ou simplement le symptôme de perturbations sous-jacentes. / Urbanization and exotic species introduction associated with it are among the most important causes of the current biodiversity crisis. These disturbances are associated with a decrease in native species alpha diversity and with changes in beta diversity worldwide. However, those changes are complex, and studies on this subject show mixed results. Consequently, the impact of exotic species on native flora is still up for debate. In this context, we aimed to study the relationship between exotic and invasive species on the diversity of 61 forest patches in the Metropolitan region of Montreal. Our analysis showed that invasive species had slightly more impact on native diversity than non-invasive ones. However, the effects of invasive and non-invasive species were similar. They both added to the total richness, and their richness was associated with an increase of alpha diversity. They were also associated with a decrease in native species cover and the invasive species with a reduction of native richness. We also found that a high cover in exotic species, especially invasive ones induced homogenization in urban forest patches. However, at high richness, they tend to induce differentiation in native species beta diversity, caused by a decrease in native species richness. Finally, we found that exotic species induce significant changes to the species composition of the forest patches. Our results suggest that exotic species, especially invasive ones, are associated with significant changes in urban forest diversity. However, further research is needed to verify if they are direct actors in those changes or symptoms of underlying disturbances.

L’objectif de ce mémoire était d’évaluer l’influence de la latitude, de variables abiotiques et du type de tourbières (bog ou fen) sur la diversité des plantes vasculaires et des bryophytes. Des inventaires ont été réalisés dans 380 tourbières du nord-ouest du Québec (49° à 55° N). Les effets de la latitude, de la continentalité, du climat et de variables abiotiques locales sur la diversité α (richesse spécifique et dispersion fonctionnelle), la diversité β (indices LCBD) et la composition ont été évalués pour les deux groupes de plantes. La diversité α des bryophytes augmentait vers le nord, alors que la diversité α des plantes vasculaires présentait des patrons différents dans les bogs et les fens en réponse à la latitude. Il y avait une homogénéisation taxonomique et fonctionnelle vers le nord pour les deux groupes de plantes et dans les deux types de tourbières. Les variables environnementales avaient des effets différents sur les deux groupes de plantes, dépendamment de l’indicateur de biodiversité utilisé. La composition taxonomique et fonctionnelle des bryophytes et des plantes vasculaires étaient principalement structurées par les conditions locales contrastantes entre les bogs et les fens, tandis que les variations bioclimatiques le long du gradient latitudinal jouaient un rôle secondaire. Les futures études et politiques de gestion des milieux naturels devraient tenir compte de plus d’un indicateur de diversité et considérer les différences entre les deux écosystèmes et les deux groupes de taxons afin de planifier les efforts de conservation et afin d’évaluer les effets des changements environnementaux. / This study aimed to evaluate the influence of latitude, abiotic variables on vascular and bryophyte diversity in bogs and fens. Inventories were conducted in 380 peatlands in northeastern Québec (49° to 55° N). Changes in α-diversity (species richness and functional dispersion), β-diversity (LCBD indices) and composition in response to latitude, continentality, climate, and local abiotic variables were evaluated for both plant groups. Bryophyte α-diversity increased northward, while vascular α-diversity showed contrasting patterns in bogs and fens in response to latitude. Environmental variables had different effects on both species’ groups, and patterns varied depending on the diversity indicator used, as α- and β-diversity and functional and taxonomic diversity were often decoupled. There was taxonomic and functional homogenization with latitude for both groups of plants in both habitats. Bryophyte and vascular taxonomic and functional composition were primarily structured by contrasting local conditions in bogs and fens, while bioclimatic variations along the latitudinal gradient played a secondary role. These results highlight the contrasting biodiversity patterns in both peatland types and the importance of local habitat conditions in structuring vascular and bryophyte biodiversity. Therefore, future studies and policies should include more than one diversity indicator and consider the differences between ecosystems and taxon groups when evaluating the effects of environmental changes on biodiversity and planning conservation.