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111	Grassland type and seasonal effects have a bigger influence on plant functional and taxonomical diversity than prairie dog disturbances in semiarid grasslands Rodriguez-Barrera, Maria Gabriela, Kühn, Ingolf, Estrada-Castillón, Eduardo, Cord, Anna F. 21 May 2024 (has links) Prairie dogs (Cynomys sp.) are considered keystone species and ecosystem engineers for their grazing and burrowing activities (summarized here as disturbances). As climate changes and its variability increases, the mechanisms underlying organisms' interactions with their habitat will likely shift. Understanding the mediating role of prairie dog disturbance on vegetation structure, and its interaction with environmental conditions through time, will increase knowledge on the risks and vulnerability of grasslands. Here, we compared how plant taxonomical diversity, functional diversity metrics, and community-weighted trait means (CWM) respond to prairie dog C. mexicanus disturbance across grassland types and seasons (dry and wet) in a priority conservation semiarid grassland of Northeast Mexico. Our findings suggest that functional metrics and CWM analyses responded to interactions between prairie dog disturbance, grassland type and season, whilst species diversity and cover measures were less sensitive to the role of prairie dog disturbance. We found weak evidence that prairie dog disturbance has a negative effect on vegetation structure, except for minimal effects on C4 and graminoid cover, but which depended mainly on season. Grassland type and season explained most of the effects on plant functional and taxonomic diversity as well as CWM traits. Furthermore, we found that leaf area as well as forb and annual cover increased during the wet season, independent of prairie dog disturbance. Our results provide evidence that grassland type and season have a stronger effect than prairie dog disturbance on the vegetation of this short-grass, water-restricted grassland ecosystem. We argue that focusing solely on disturbance and grazing effects is misleading, and attention is needed on the relationships between vegetation and environmental conditions which will be critical to understand semiarid grassland dynamics under future climate change conditions in the region. info:eu-repo/classification/ddc/570 ddc:570 info:eu-repo/classification/ddc/500 ddc:500
112	Small remnant habitats : Important structures in fragmented landscapes Lindgren, Jessica January 2017 (has links) The world-wide intensification of agriculture has led to a decline in species richness due to land use change, isolation, and fragmentation of natural and semi-natural habitats in agricultural and forestry landscapes. As a consequence, there is a current landscape management focus on the importance of green infrastructure to mitigate biodiversity decline and preserve ecosystem functions e.g. pollination services and pest control. Even though intensification in agriculture has been ongoing for several hundreds of years, remnant habitats from earlier management practices may still be remaining with a surprisingly high plant richness. Preserving these habitats could help conserving plant species richness in agricultural landscapes, as well as other organisms that are dependent on plants for food and shelter. In this thesis I focus on two small remnant habitats; midfield islets and borders between managed forest and crop field in southeastern Sweden. In the past, both habitats were included in the grazing system and therefore often still have remnant population of grassland specialist species left today. I have used these two remnant habitats as model habitats to investigate the effect of landscape factors and local factors on species richness of plants, flower morphologies and plants with fleshy fruits. Additively, I analysed the effect of surrounding landscape and local openness on the functions; pollination success, biological pest control of aphids and seed predation on midfield islets. One of my studies showed that spatial distribution and size of the habitat affected plant species richness. Larger habitat size and higher connectivity between habitats increased species richness of plants in the habitats. Openness of the habitats was shown to be an important factor to increase species richness and richness of flower morphologies, both on midfield islets and in forest borders. Even though midfield islets had the highest species and morphology richness, both habitat types are needed for habitat complementary as forest borders have more plants with fleshy fruits and a higher richness of plant species that flowers in spring/early summer. It was also shown that a more complex forest border, not just with gaps in the canopy, but also with high variation in tree stem sizes increases plant species richness in the field layer. The conclusion is that by managing small remnant habitats to remain or become more semi-open and complex in their structure, would increase species richness of plants, grassland specialist species, and flower morphologies. It would also increase some ecosystem functions as seed predation and biologic pest control of aphids are more effective close to trees. If both midfield islets and forest borders would be managed to be semi-open, the area and connectivity of semi-open habitat would increase in the agricultural landscape, which may also improve pollination success as the connectivity between populations has a possibility to increase. Grassland specialist species are clearly abundant in the small remnant habitats. As the decline of semi-natural grasslands is causing a decline in grassland specialists’ species, not only plants, I recommend that small remnant habitats are included in conservation and management plans and strategies to improve habitat availability and connectivity for grassland species in agricultural landscapes. / <p>Research funder Ekoklim. Project:4339602.</p><p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p> Alpha-diversity Beta-diversity Biological pest control Canopy cover Connectivity Ecosystem function Fleshy fruits Forest edge Forest management Forest specialist species Fragmentation Functional diversity Gamma-diversity Grassland specialist species Green infrastructure Habitat amount hypothesis Island biogeography Midfield islets Plant diversity Plant-pollinator interaction Pollination Remnant habitat Seed predation Small habitats Species richness Structural heterogeneity Ecology Ekologi Miljö- och naturvårdsvetenskap Physical Geography Naturgeografi
113	Methodological investigations on vegetation typology and phytogeography of rain forests of tropical Africa Senterre, Bruno B.M.L. 17 June 2005 (has links) I. An original methodological discussion is proposed on the problem of the typology of tropical rain forest’s plant communities, based on the study of forest types across gradients of continentality and elevation, within Atlantic central Africa. These investigations were based on the statement that the main problems in forest typology are related to the non-zonal or zonal character of the different vegetation types and to non considering the relations and differences between forest strata. II. Field data consisted in phytosociological homogeneous sample plots localized within different recognized phytogeographical entities, in a region of tropical Africa where these entities are known to be well conserved. A total of 37 such plots were inventoried in the region extending from the littoral forests of Ndoté, Equatorial Guinea, which are wet evergreen forests, to the continental forests of the Dja, Cameroon, known as evergreen seasonal forests. The studied region also included the oriental Atlantic forests of Equatorial Guinea, known as moist evergreen forests or caesalp forests. In various parts of this continentality gradient, some plots were localized within climax non-zonal formations, namely the submontane rain forests. The emphasis was put on the vegetation of the Monte Alén National Park. The sampling methodology was willing to be as "complete ", including all strata, "quantitative ", enumerating all individuals, and "representative ", within each stratum, as possible. These multi-layers plots were realised using nested sub-plots, with a sampling size of 100 individuals for every ligneous stratum recognized (dominant trees, dominated trees and shrubs) and a sampling size of 200m² for the herbaceous and suffrutex stratum. Forest types were defined independently for each stratum and the differences were analysed. A method was proposed for the simultaneous analysis of all floristic data, converting and standardizing the values from ligneous strata, on the one hand, and from understorey strata, on the other hand. III. Ten forest types were described using IndVal and discussed in the general context of the guineo-congolian region, from a syntaxonomic view point (agglomerative classification) and from a phytogeographical view point (divisive classification). Homologies between these two approaches are described. The proposed phytogeographical system is based on an "open " conception of hierarchical classifications, combining advantages of agglomerative and divisive classifications. In concrete terms, the non-zonal criteria, for example the submontane variants, are categorised separately and in analogy with the zonal criteria, related to the usual phytochoria. Analysis of ecological relationships for the 10 communities showed that the main variables related to the floristic variability in our mainland rain forests are elevation, rainfall, hygrometry (estimated using bryophytes cover levels) and distance to the ocean. The two extremes on the vertical microclimatic gradient, dominant trees stratum and herbaceous stratum, give similar typologies, however canonical analysis showed that for the herbaceous layer, non-zonal variables (hygrometry and elevation) were gaining more importance when the influence of the two zonal variables was attenuated. In every case, spatial autocorrelation was less important than the environment in explaining floristic variability but its role increased in the spatial arrangement of understorey species, whose dispersal capacity is generally lower than canopy trees. The phytosociological, phytogeographical and ecological description of forest types is accompanied by a physiognomical description using biological types spectrum, as well as architectural models, leaf sizes, etc. With regard to diversity, we have demonstrated that species richness was higher from upper to lower strata because of the accumulation in lower strata of species from various strata. On the other hand, the proper stratum diversity, i.e. the structural set, decreased from dominant trees to shrubs. The proper diversity of the herb layer showed relatively high figures mainly due to the higher individual density in relation to the existence of microstrata. Within the 37 sample plots, 1,050 taxa have been identified to species or morpho-species levels, for a total of 25,750 individuals. These taxa represent 442 genus among 104 families. The richest forest type is found on the foothills of the Niefang range, on the windward side. This forest type is also characterised by a high number of oligotypic genus and by species belonging to functional types indicators of glacial refuges. These functional types are defined on the basis of the dispersal capacity and on kind of stand needed for effective germination. We formulated the hypothesis that this kind of "foothills refuge ", characterised by his zonal nature, could have been one of the rare refuges for species from mainland rain forests, while montane and fluvial refuges would mainly have preserved species from non-zonal forest types: (sub)montane and riverine. Based on indicator species of submontane forests, a potential distribution map of this forest type has been realised at the Atlantic central African scale. More than 400 submontane forest localities have been mapped. These forests begin at 400m of altitude near the ocean, and progressively at higher altitude for increasing distance to the ocean. Many lowland localities also comprised submontane species, which could indicate the existence of ecological transgressions. These transgressions would allow migratory tracks for submontane species between isolated mountain ranges, not only during glacial periods, through heights at the northern and southern borders of the congo basin, but also contemporarily through the lowland riverine forest network, in the centre of this basin. Finally, a special attention has been attributed to littoral forests and to some cases of choroecological transgressions, coupled to the ecological equalization phenomenon. plant diversity foothills refuge glacial refuge environmental stability conservation rarefaction curves individuals-area curves species-area curves compensations écologiques Guinée Equatoriale Monte Alén Monts de Cristal Réserve de Ndoté rainforest transgression Monte Alén Cristal mountains strate forestière sous-bois ensemble structural groupe écologique modèles architecturaux guilde types fonctionnels synusie genres monotypiques genres paucispecifiques diversité végétale courbes aire-espèces courbes individus-espèces courbes de raréfaction courbes aire-constance aire minimale morpho-espèces pléistocène constancy-area curves minimal area structural ensemble understorey ecological group synusia oligotypic genus Réserve de Biosphère du Dja Cameroun Quaternaire glaciation refuge glaciaire refuge de pied de massifs montagneux stabilité environnementale conservation transgression forestière phytosociology plant community phytogeography open classification non-zonal nested plots forest types IndVal morphospecies pleistocene littoral forest rain forest afromontane submontane altitudinal belt glaciation Quaternary Equatorial Guinea ecological equalization continentality continentalité étage d’altitude forêt littorale forêt dense humide afromontagnard submontagnard IndVal types forestiers phytosociologie phytogéographie classification ouverte azonal relevés emboîtés multistrates monotypic genus architectural model guild plant functional type Ndoté Reserve Cameroon Dja Biosphere Reserve forest stratum forest layer understory
114	Recherches méthodologiques pour la typologie de la végétation et la phytogéographie des forêts denses d'Afrique tropicale Senterre, Bruno 17 June 2005 (has links) I. An original methodological discussion is proposed on the problem of the typology of tropical rain forest’s plant communities, based on the study of forest types across gradients of continentality and elevation, within Atlantic central Africa. These investigations were based on the statement that the main problems in forest typology are related to the non-zonal or zonal character of the different vegetation types and to non considering the relations and differences between forest strata.<p><p>II. Field data consisted in phytosociological homogeneous sample plots localized within different recognized phytogeographical entities, in a region of tropical Africa where these entities are known to be well conserved. A total of 37 such plots were inventoried in the region extending from the littoral forests of Ndoté, Equatorial Guinea, which are wet evergreen forests, to the continental forests of the Dja, Cameroon, known as evergreen seasonal forests. The studied region also included the oriental Atlantic forests of Equatorial Guinea, known as moist evergreen forests or caesalp forests. In various parts of this continentality gradient, some plots were localized within climax non-zonal formations, namely the submontane rain forests. The emphasis was put on the vegetation of the Monte Alén National Park.<p><p>The sampling methodology was willing to be as "complete ", including all strata, "quantitative ", enumerating all individuals, and "representative ", within each stratum, as possible. These multi-layers plots were realised using nested sub-plots, with a sampling size of 100 individuals for every ligneous stratum recognized (dominant trees, dominated trees and shrubs) and a sampling size of 200m² for the herbaceous and suffrutex stratum.<p><p>Forest types were defined independently for each stratum and the differences were analysed. A method was proposed for the simultaneous analysis of all floristic data, converting and standardizing the values from ligneous strata, on the one hand, and from understorey strata, on the other hand.<p><p>III. Ten forest types were described using IndVal and discussed in the general context of the guineo-congolian region, from a syntaxonomic view point (agglomerative classification) and from a phytogeographical view point (divisive classification). Homologies between these two approaches are described. The proposed phytogeographical system is based on an "open " conception of hierarchical classifications, combining advantages of agglomerative and divisive classifications. In concrete terms, the non-zonal criteria, for example the submontane variants, are categorised separately and in analogy with the zonal criteria, related to the usual phytochoria.<p><p>Analysis of ecological relationships for the 10 communities showed that the main variables related to the floristic variability in our mainland rain forests are elevation, rainfall, hygrometry (estimated using bryophytes cover levels) and distance to the ocean. The two extremes on the vertical microclimatic gradient, dominant trees stratum and herbaceous stratum, give similar typologies, however canonical analysis showed that for the herbaceous layer, non-zonal variables (hygrometry and elevation) were gaining more importance when the influence of the two zonal variables was attenuated. In every case, spatial autocorrelation was less important than the environment in explaining floristic variability but its role increased in the spatial arrangement of understorey species, whose dispersal capacity is generally lower than canopy trees. The phytosociological, phytogeographical and ecological description of forest types is accompanied by a physiognomical description using biological types spectrum, as well as architectural models, leaf sizes, etc.<p><p>With regard to diversity, we have demonstrated that species richness was higher from upper to lower strata because of the accumulation in lower strata of species from various strata. On the other hand, the proper stratum diversity, i.e. the structural set, decreased from dominant trees to shrubs. The proper diversity of the herb layer showed relatively high figures mainly due to the higher individual density in relation to the existence of microstrata. Within the 37 sample plots, 1,050 taxa have been identified to species or morpho-species levels, for a total of 25,750 individuals. These taxa represent 442 genus among 104 families. The richest forest type is found on the foothills of the Niefang range, on the windward side. This forest type is also characterised by a high number of oligotypic genus and by species belonging to functional types indicators of glacial refuges. These functional types are defined on the basis of the dispersal capacity and on kind of stand needed for effective germination. We formulated the hypothesis that this kind of "foothills refuge ", characterised by his zonal nature, could have been one of the rare refuges for species from mainland rain forests, while montane and fluvial refuges would mainly have preserved species from non-zonal forest types: (sub)montane and riverine.<p><p>Based on indicator species of submontane forests, a potential distribution map of this forest type has been realised at the Atlantic central African scale. More than 400 submontane forest localities have been mapped. These forests begin at 400m of altitude near the ocean, and progressively at higher altitude for increasing distance to the ocean. Many lowland localities also comprised submontane species, which could indicate the existence of ecological transgressions. These transgressions would allow migratory tracks for submontane species between isolated mountain ranges, not only during glacial periods, through heights at the northern and southern borders of the congo basin, but also contemporarily through the lowland riverine forest network, in the centre of this basin. Finally, a special attention has been attributed to littoral forests and to some cases of choroecological transgressions, coupled to the ecological equalization phenomenon.<p> / Doctorat en sciences agronomiques et ingénierie biologique / info:eu-repo/semantics/nonPublished Sciences exactes et naturelles Agronomie générale Phytogeography -- Africa, Sub-Saharan Forest surveys -- Africa, Sub-Saharan Phytogéographie -- Afrique noire Inventaires forestiers -- Afrique noire submontane afromontane rain forest littoral forest pleistocene morphospecies IndVal forest types nested plots non-zonal open classification phytogeography plant community phytosociology transgression forestière conservation stabilité environnementale refuge de pied de massifs montagneux refuge glaciaire glaciation Quaternaire Cameroun Réserve de Biosphère du Dja oligotypic genus synusia ecological group understorey structural ensemble minimal area constancy-area curves pléistocène morpho-espèces aire minimale courbes aire-constance courbes de raréfaction courbes individus-espèces courbes aire-espèces diversité végétale genres paucispecifiques genres monotypiques synusie types fonctionnels guilde modèles architecturaux groupe écologique ensemble structural sous-bois strate forestière Cristal mountains Monte Alén rainforest transgression Réserve de Ndoté Monts de Cristal Guinée Equatoriale compensations écologiques species-area curves individuals-area curves rarefaction curves environmental stability glacial refuge foothills refuge plant diversity altitudinal belt Quaternary Equatorial Guinea ecological equalization continentality continentalité étage d’altitude forêt littorale forêt dense humide afromontagnard submontagnard types forestiers phytosociologie phytogéographie classification ouverte azonal relevés emboîtés multistrates monotypic genus architectural model guild plant functional type Ndoté Reserve Cameroon Dja Biosphere Reserve forest stratum forest layer understory

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