Evolution régressive récente de la végétation des tourbières hautes à sphaignes en Haute Ardenne (Hautes-Fagnes, Belgique)

Doctoral thesis (1999)

In temperate Europe, intact raised bogs from Northern Germany to the French Massif Central are part of rare postglacial ecosystems that one can consider as natural or very close to the natural state ... [more ▼]

In temperate Europe, intact raised bogs from Northern Germany to the French Massif Central are part of rare postglacial ecosystems that one can consider as natural or very close to the natural state. Unfortunately, many of them have been degraded or highly disturbed by intense human activities. Some of them, however, kept a subintact central part. This is the case for the three big raised bogs situated in the Hautes-Fagnes plateau in Belgium: the fagne Wallonne, the fagne de Clefaye and the Misten raised bogs. Their vegetation belongs to the Vaccinio oxycocci-Sphagnetea magellanici Br.-Bl. & Tx. 43 and Eriophoro vaginati-Sphagnetalia papillosi Tx. 70. But the legal conservation measures are not sufficient to guarantee their protection : in the course of the last 30 years, 10 to 25% of the area covered with intact raised bogs of the Hautes-Fagnes plateau have been degraded, mainly invaded by Molinia caerulea. Although it is important to bring forward such alarming observations, it is more essential to understand exactly the origin of the factors causing the degradation, if suitable measures to thwart the factors that condition them, and try to attenuate if not suppress their harmful effects, and thereby restore the conditions that will enable the natural vegetation from these environments to recover the lost areas. Here are the main objectives of this work: • To highlight the current and recent ecological and phytodynamic consequences of the degradation of the raised bogs; • To identify and date the causes of the degradation that struck the intact parts of the raised bogs present on the Hautes-Fagnes plateau; • To examine the practical management measures in the short-, medium-, and long-term taken in Belgium and abroad in order to restore the natural evolution of the peatlands. Studies of the vegetation The vegetation maps, on a scale of 1/250, indicate that, despite some differences, the degradation phenomenon seems to begin in the same way in the three bogs. We can notice: • an invasion by Molinia caerulea of the intact peat areas (in sometimes very high tussocks) but also its presence, in a more diffuse form, within the -narrowzones of transition and even among typical bog species; • a soil draining, resulting in the proliferation of Ericaceae, especially around relatively intact zones; • the existence of Deschampsia flexuosa, which seems to be linked to rather steep slopes at the edge of zones exclusively colonised by Molinia caerulea,; • the poor representation, both in terms of quality as quantity, of bryophytes; fewer than 10 species of peatmosses occur in these peatlands, where they are often little or ill-developed; • the occupation of peat bogs by relatively exclusive species (Empetrum nigrum, Molinia caerulea and other very thick Ericaceae bushes) which prevent other peat forming communities from developing. The analysis of the vegetation releves taken along three transects shows that the Misten bog appears as the most intact one (or the best preserved one) based on the cover, distribution and vitality of peatmosses, although as indicated by the vegetation map, Molinia caerulea surrounds this raised bog. The fagne de Clefaye peat bog seems much drier and the percentage of peatmosses cover is lower compared to the Misten bog. Some Empetrum nigrum clumps no longer contain any mosses. On the other hand, this bog holds more Sphagnum species than either of the other two bogs investigated. The raised bog of the fagne Wallonne is the most degraded one (at least the north-west part of it). The complexity of the problem composed already the focus of several studies as part of a graduate work. In order to have some idea of the evolution of the vegetation, all the releves which have been carried out along the transects of the three bogs have been the subject of an observation follow-up. Even if six or seven years between the vegetation releves is too short a time to show some significant evolution in a peat bog, the results nonetheless enable to bring to the fore some trends in the evolution of the vegetation present in the main bogs of the haut-plateau, Along the itemised transect, the vegetation of the peat bog seems to be stable and optimal for a peat forming activity typical of an ombrotrophic raised bog, to develop. The northern part of the fagne Wallonne bog shows much more worrying signs of evolution (heaths developing quickly) or signs of degradation of its vegetation (reduction of the number of peatmosses, increasing density of Molinia caerulea, and invasion by Betula alba subsp. glutinosa). The vegetation of the fagne de Cléfaye bog clearly evolves towards a drier phase (high intensification of heaths development) without leading to the rarefaction of peatmosses. We wanted to put these evolutional studies in a broader context and take advantage of previous studies carried out on the haut-plateau in similar conditions. Despite the interpretation difficulties that were met, the different studies allow to assert that there has been a quick change in the vegetation of the raised bogs in the last forty years. Are we in the presence of a Natural evolution or a degradation process? The ground cover in the northern part of the fagne Wallonne bog shows obvious signs of degradation. The southern part of it as well as the fagne de Cléfaye bog show instead an evolution of the vegetation towards a stage heavily composed of heaths, with, however, a strong reduction of peatmosses. The Misten bog seems to experience the slowest evolution: is this a former evolution stage of the vegetation or is the balance achieved? Hydrological studies In natural conditions, the fluctuations of the water table of an ombrotrophic bog on a one-year scale remain modest: about 10 centimetres from one season to the other. It is thus interesting to check if the variations of the water table level are of the same nature in different spots of the three studied bogs or if the alteration phenomena, that are visible at the vegetation level and are present on the three bogs also appear in the behaviour of water tables at the surface of these bogs. Based on the follow-up of the 148 dip wells scattered on the three peat bogs, it appears that the Misten bog water table level is the most stable one. This means that the peat forming species, present on the fagne de Clefaye and especially in the studied part of the fagne Wallonne, are constantly subjected to fluctuations (which are sometimes significant) of the water table level. Now, if the peatmosses usually spread according to a humidity gradient, some of them tolerating a greater distance of the water table level than others, it does not mean however that a same species can survive such variations. The dip wells maps and the 3-dimensional representations of the water table enable to better understand the spreading of the vegetation at the surface of the bog. But these measures also reveal the presence of pedological phenomena, natural or not, such as drainage ditches, outlet, exploitation scar, fissures in the peat mass and others, that very much influence the variation of the water table level and thereby the surface vegetation in the short-, medium-, and long-term Paleo-ecological studies In order to better understand the evolution of raised bogs and especially try to find signs of their degradation, it is essential to investigate the peat lying right under the present vegetation. All the steps that have been set about within this context tried to answer the following questions: Is there a link between the vegetation present at the surface and the recent peat composition lying right under? Is there a link between the recently formed peat composition and the water table level observed on the peat bog? Are the microfossils, that are contained in the peat, affected by variations of the water table? Can we draw differences in the composition of the peat according to how far the boring has been carried out from the current active central zone of the peat bog? It clearly appears that the composition of the peat varies according to the type of present vegetation under which the sample was taken and the range of fluctuations of the water table level recorded on this spot. On the Misten peat bog, the palynological study of peat borings 10 m away from one another allowed to show that peat layers representing the same paleobotanical event(s) do not have the same thickness in each boring and can even be absent. In the same way, at a constant rate of pollen, the accumulation speed of the peat is higher in the bog centre compared to its margins. If one considers a same paleo-botanical event, and thus a same period of time, one can see that the pollen concentration is inversely proportional to the thickness of the peat. Two distinct parts are visible on the borings of the Misten peat bog surface: the upper part, the most recent one, characterised by the influence of the topographic position of the boring on the peat forming speed; the lower part, the oldest one, in which the influence is less pronounced. Thanks to different dating techniques (l4C, pollen concentrations and reference borings), this boundary between the two parts can approximately be dated back to the middle of the 14th century. This phenomenon should be related to an anthropogenic phenomenon rather than to a climatic one, given the short distance separating the borings. It would rather be the result of the manual exploitation of the peat than the harmful effects of the Eupen ditch which was dug much later (1774). A lot of microfossils, identifiable or not, present in the borings (rhizopodes, conidia ...) can doubtless be used as degradation indicators. Of course, these studies need to be deepened and systematised before going any further. What emerges especially from these studies is that when one undertakes regeneration attempts on a peat bog, one should not only take the present vegetation and hydrological parameters into account, but also the peat structure and composition, in at least the upper part of the deposits. Research and management Although acting on the current evolution of the Belgian bogs appears essential in order to prevent them from disappearing, it is clear that restoration measures that were appropriate elsewhere, cannot be applied to other areas without some thorough knowledge of the ecological parameters that govern them. The obvious result of this work is that the scientific follow-up of the management measures that have been taken is not only imperative, but that prior study measures of the sites and their characteristics are indispensable. This type of study is heavy because it requires an important investment from the researcher and often causes a lot of damage to the studied flora and fauna. However, these studies are necessary to understand the peatland systems and should even be complemented by further studies (lysimetric, structural or chemical...) . The standardisation of the data gathering system, the improvement of the information techniques and the management of the results organised in a way that allows all the researchers to consult them should contribute towards some lightening of the work. The computer science and the miniaturised electronic technology could improve the efficiency of the measures implemented, thereby benefiting the researcher and the reserve. Given the implied advanced technologies, these modern studies and data gathering processes would be expensive but it is cheap in comparison to the costs of the heavy works that are to be undertaken in the hope of preserving the raised bogs. Moreover, such a preparation of management measures can only improve their efficiency. If, despite all the efforts, the preservation of the jewels of the state nature reserve of the Haute-Fagnes is jeopardised, these studies will at least allow to go further in the understanding of the raised bogs systems. [less ▲]

Perspective and limit of candidate gene marker’s technology in animal breeding.

in Congresso de Melhoramento Genetico (1999, November)

Le comportement migrateur des poissons en Wallonie. Caractérisation biologique et implication pour une gestion durable des populations.

Conference (1999, November)

Experimental Infection of Specific Pathogen-Free New Zealand White Rabbits with Five Strains of Amyxomatous Myxoma Virus

in Journal of Comparative Pathology (1999), 121(4), 369-84

Myxomatosis is a specific disease of the European rabbit (Oryctolagus cuniculus) due to a virus belonging to the genus Leporipoxvirus. Forty-seven years after its deliberate introduction into Europe, the ... [more ▼]

Myxomatosis is a specific disease of the European rabbit (Oryctolagus cuniculus) due to a virus belonging to the genus Leporipoxvirus. Forty-seven years after its deliberate introduction into Europe, the clinical aspects and the epizootiology of myxomatosis have changed. Two forms (nodular and amyxomatous) of the disease have been identified to date. A comparative study was made of the clinical signs, pathogenesis and gross lesions observed in male specific pathogen-free New Zealand White rabbits inoculated with five strains of amyxomatous myxoma virus. All five strains induced the characteristic amyxomatous myxomatosis clinical syndrome with clinical signs that differed only in intensity. The varying clinical intensity, together with the results of virological examination question the virulence of at least three of the five strains. Genomic analysis confirmed that the five strains came from the Lausanne strain introduced in 1952 in France and not from an unnoticed introduction of a Californian strain of myxoma virus. No link was found between the amyxomatous myxoma virus strains and the SG33 vaccine strain. 1999 Harcourt Publishers Ltd. [less ▲]

Définir la jeunesse ? D'un bout à l'autre du monde

Book published by Les Presses de l'Université Laval (1999)

Cet ouvrage réunit des chercheurs d'un bout à l'autre du monde autour d'une même question, l'étude de la jeunesse. De quelle manière faut-il aborder cette période du cycle de vie dont on parle avec ... [more ▼]

Cet ouvrage réunit des chercheurs d'un bout à l'autre du monde autour d'une même question, l'étude de la jeunesse. De quelle manière faut-il aborder cette période du cycle de vie dont on parle avec abondance sans bien savoir comment la définir ? Les mots sont non seulement porteurs de sens, mais servent aussi à orienter l'action. Les notions d'insertion, d'intégration ou de socialisation héritées de la tradition sociologique sont aujourd'hui récupérées dans des politiques où les jeunes se sentent souvent happés. Le statut d'acteurs qu'on leur a reconnu au beau temps de l'action étudiante ne continue-t-il à s'appliquer que dans les sociétés où les jeunes sont majoritaires ? Les sociétés vieillissantes laissent-elles un peu de place aux jeunes pour l'élaboration de stratégies ? Les études qui portent aujourd'hui sur la jeunesse impliquent de démêler les intentions derrière les discours. Dans un contexte de mutation ou de (ré)invention du lien social, le pari à relever n'en est que plus passionnant. [less ▲]

A Cell Type-Specific and Gap Junction-Independent Mechanism for the Herpes Simplex Virus-1 Thymidine Kinase Gene/Ganciclovir-Mediated Bystander Effect

in Clinical Cancer Research : An Official Journal of the American Association for Cancer Research (1999), 5(11), 3639-44

Tumor cells expressing the herpes simplex virus type 1 thymidine kinase (HSV-tk) gene are killed by nucleoside analogues such as ganciclovir (GCV). GCV affects not only the cells expressing HSV-tk but ... [more ▼]

Tumor cells expressing the herpes simplex virus type 1 thymidine kinase (HSV-tk) gene are killed by nucleoside analogues such as ganciclovir (GCV). GCV affects not only the cells expressing HSV-tk but also neighboring cells that do not express the gene; this phenomenon commonly is called "bystander effect." GCV metabolites transfer via gap junctional intercellular communication (GJIC) accounts for the bystander effect in different cell lines, but other mechanisms have also been described. In this study, we analyzed the mechanisms of the bystander effect in two cell lines exhibiting different capacities of communication (DHD/K12 and 9L). The 9L cells exhibited a very good bystander effect, which was completely blocked by a long-term inhibitor of GJIC, 18 alpha-glycyrrhetinic acid. DHD/K12 cells exhibited a moderate bystander effect that was not abolished by 18 alpha-glycyrrhetinic acid or 1-octanol, another strong inhibitor of GJIC. Interestingly, we also observed a bystander effect in cultures where HSV-tk-expressing DHD/K12 cells were physically separated from their untransfected counterparts but grown in the same medium. Moreover, the transfer of filtered conditioned medium from GCV-treated HSV-tk-expressing DHD/K12 cells to DHD/K12 parental cells induced a decrease of survival in a concentration-dependent manner, suggesting that the bystander effect in this cell line was mediated by a soluble factor. [less ▲]

Airway Mast-Cell Activation in Asthmatics Is Associated with Selective Sputum Eosinophilia

in Allergy (1999), 54(11), 1188-93

BACKGROUND: Tryptase is a serine endoprotease selectively released from mast cells. Although mast cells are known to be activated after experimental allergic provocation, their role in naturally occurring ... [more ▼]

BACKGROUND: Tryptase is a serine endoprotease selectively released from mast cells. Although mast cells are known to be activated after experimental allergic provocation, their role in naturally occurring asthma is still debated. METHODS: We have investigated the levels of tryptase in the whole induced sputum collected from 51 asthmatics (31 atopic and 20 intrinsic) seen in our outpatient clinic and 22 normal nonatopic healthy volunteers. Tryptase was measured by a new immunoassay based on B12 monoclonal antibody recognition of total tryptase (UniCAP System, Pharmacia) with a sensitivity of 1 ng/ml. RESULTS: While being below the threshold of detection in all normal volunteers, tryptase was detectable in the sputum from 9/51 asthmatics (18%) including five atopic and four intrinsic asthma cases. In these patients, among whom three were asymptomatic asthmatics, the values ranged between 1 and 6.1 ng/ml. The asthmatics with detectable sputum tryptase had greater sputum eosinophil counts (P<0.05) but lower neutrophil counts (P<0.05) than those in whom tryptase was undetectable. When compared to control subjects, asthmatics without tryptase had still greater eosinophil counts (P<0.0001) but also raised neutrophil counts (P<0.05). No significant difference could be found between asthmatics with tryptase and those without tryptase with respect to the age, the baseline lung function, the methacholine bronchial responsiveness, and the frequency of treatment with inhaled steroids. CONCLUSIONS: With the UniCAP System, tryptase was detectable in the sputum from 18% of asthmatics irrespective of atopy and current symptoms. Asthmatics with tryptase appeared to have a selective increase in sputum eosinophil counts while those without tryptase displayed a mixed sputum granulocyte infiltration with raised eosinophil and neutrophil counts. [less ▲]

Régénération osseuse: on touche au but!

in Journal du Dentiste, cahiers scientifiques (1999)

Exercices excentriques appliqués au traitement des tendinites

in Actes du Congrès Eurokiné 1999 (1999, November)

Miscibility of poly(vinylidene fluoride) and poly(methylmethacrylate-co-zinc polyacrylate) ionomers

in Polymer (1999), 40(24), 6831-6839

A random copolymer of methyl methacrylate and 5.7 mol.% of acrylic acid has been neutralized by zinc cation to different extents in order to study the effect of zinc carboxylate pendant groups on the ... [more ▼]

A random copolymer of methyl methacrylate and 5.7 mol.% of acrylic acid has been neutralized by zinc cation to different extents in order to study the effect of zinc carboxylate pendant groups on the miscibility of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). The interaction parameter (χ) has been calculated from the experimental depression of the PVDF melting point. χ is minimum at zinc carboxylate content of 2.8 mol.%. The dynamic mechanical analysis of the PVDF-PMMA ionomer binary blends does not agree with the additivity rule of the properties, consistently with the phase morphology that changes with composition. Blends are indeed amorphous as long as the PVDF content does not exceed 40 wt.%, otherwise, semicrystalline PVDF coexists with an amorphous mixed PVDF/copolymer phase. [less ▲]