Options
Gobat, Jean-Michel
Nom
Gobat, Jean-Michel
Affiliation principale
Fonction
Professeur honoraire
Email
jean-michel.gobat@unine.ch
Identifiants
Résultat de la recherche
Voici les éléments 1 - 10 sur 136
- PublicationAccès libre
- PublicationAccès libreWhat does "lignoform" really mean?(2018-9-6)
; ; Among the many studies devoted to deadwood, very few have considered it in a broader ecosystemic context, especially in relation to the underlying humiferous topsoil. In order to fill this gap, we detail here the concept of lignoforms, humus forms strongly linked to deadwood and mostly ignored by humus forms specialists. After presenting the main characteristics of deadwood, the main actors involved in its life cycle and its important and varied roles in many ecosystems, we explain how to describe and study lignoforms. We also propose new diagnostic horizons for these particular humus forms, as well as a classification system, including an identification key (see Appendix A Identification key for lignoforms). Finally, we discuss some important issues pertinent to continuing to improve knowledge of these common but little studied humus forms. - PublicationAccès libreTerrestrial humus systems and forms - Specific terms and diagnostic horizons(2018-1-16)
; ; - PublicationAccès libreTerrestrial humus systems and forms - Keys of classification of humus systems and forms(2018-1-16)
; ; ; - PublicationAccès libre
- PublicationAccès libreDes formes d'humus au bois mort et du bois mort aux formes d'humus : contribution à l'étude des formes d'humus et des communautés lombriciennes en zone forestière subalpine, avec une emphase particulière sur le bois mort(Neuchâtel : Université de Neuchâtel, Faculté des sciences, 2016)
; ; Le Bayon, ClaireCette thèse s’inscrit dans une recherche plus vaste, le projet DecAlp. Celui-ci se déroule dans les Alpes italiennes (province de Trente) et est mené conjointement par de nombreux chercheurs. Il a pour principal objectif l’élaboration d’un modèle de décomposition et d’intégration du bois mort au sol. Cette thèse y occupe une place centrale en se concentrant sur les formes d’humus qui jouent un rôle charnière entre les parties aériennes et souterraines du système étudié.
Une première partie est consacrée à la description des formes d’humus. Deux méthodologies complémentaires sont développées à deux échelles spatiales différentes et agrémentées de nombreux documents pratiques. Ces deux échelles spatiales permettent d’effectuer plus aisément le lien entre les différentes thématiques de recherche du projet DecAlp (allant par exemple du bassin versant et du peuplement forestier aux communautés microbiennes du sol). Ces méthodes sont ensuite appliquées aux sites d’étude afin d’y collecter des données utiles à l’ensemble du projet.
Les outils de recherche ainsi développés pour l’étude des formes d’humus permettent de passer, schématiquement, du descriptif au fonctionnel. Cela est illustré tout au long du manuscrit, notamment par différents articles préparés pour publications scientifiques ainsi que par des chapitres acceptés pour un livre à paraître prochainement.
Une autre partie du manuscrit est consacrée aux lignoformes, les formes d’humus inféodées au bois mort. La manière adéquate de les décrire est développée, ainsi qu’une synthèse de la littérature expliquant les différentes origines possibles des lignoformes et leurs rôles dans les écosystèmes. Un nouveau système de classification des lignoformes est élaboré et présenté, accompagné d’une clé dichotomique. Il inclut de nouveaux horizons caractéristiques et de nouvelles références. Cette partie est complétée par une base de données (photos, descriptions et caractéristiques physico-chimiques) destinées à de futures recherches dans ce domaine original et prometteur.
La dernière partie du manuscrit concerne les relations entre les conditions environnementales (formes d’humus, valeurs écologiques indicatrices révélées par l’étude de la végétation, accumulations de débris ligneux) et les communautés de vers de terre. Les différents types de formes d’humus identifiés se distinguent significativement entre eux par leurs propriétés physico-chimiques et les communautés lombriciennes qu’ils abritent. Ces dernières sont également influencées par la présence ou non d’accumulations de débris ligneux fins. Cette partie démontre l’importance de descriptions adéquates d’un milieu et de son hétérogénéité afin de pouvoir comprendre, protéger et conserver des prestations écosystémiques essentielles à l’homme pour son bien-être social, économique et culturel.
Les nombreuses données inédites acquises permettront à l’ensemble des membres du projet DecAlp de réaliser prochainement un ou plusieurs articles de synthèse générale concernant les aspects fonctionnels globaux du système étudié, notamment le rapport à un éventuel réchauffement climatique. Les résultats obtenus pourront alors être transposés à une échelle plus large, étant donné que les différents processus et entités écosystémiques documentés et décrits ici sont également généralisables à de nombreux autres types d’écosystèmes., This thesis is part of a larger research, the DecAlp project. This latter is conduct in the Italian Alps (Trentino, I) and involved numerous researchers with the shared goal of elaborating a model for wood decomposition and its incorporation into the soil. This thesis focuses mainly on the humus forms. They occupy a key role in the DecAlp project as they allow linking the aerial and the underground parts of the studied system.
A first part is devoted to the description of humus forms. Two complementary methodologies are developed at two different spatial scales and are complemented by many practical documents. These two spatial scales allow linking more easily the different research topics of the DecAlp project (ranging from watersheds and forest stands to the soil microbial communities). These methods are then applied to the study sites in order to collect data useful for the whole project.
The research tools developed for the study of humus forms can then be used to understand the ecosystem and its processes. This is illustrated throughout the manuscript by including various articles prepared for scientific publications as well as chapters accepted for a forthcoming book.
Another part of the manuscript is devoted to the lignoforms, humus forms linked to the dead wood. The proper way to describe them is explain and followed by a synthesis of the literature showing the various possible origins of lignoforms and their roles in ecosystems. A new system of classification for the lignoforms is developed and presented (including a dichotomous key). This system includes new horizons and new references. This part is completed by a database (photos, descriptions and physicochemical characteristics) for future research in this original and promising topic.
The last part of the manuscript concerns the relationships between environmental conditions (humus forms, indicator ecological values revealed by the study of vegetation, woody debris accumulations) and the earthworm communities. The various types of identified humus forms are significantly different according to their physicochemical properties. They shelter different earthworm communities which can also be influenced by the presence or absence of fine woody debris accumulations. This part demonstrates the importance of adequate descriptions of an environment and its heterogeneity in order to understand, protect and preserve ecosystem services which are useful to social, economic and cultural human well-being.
The numerous new data acquired will be useful to all the members of the DecAlp project to write a synthesis paper concerning the overall functional aspects of the studied system, including the effects of a possible global warming. The results obtained here could then be transposed to a larger scale, since the various ecosystem features described are also generally applicable to many other types of ecosystems. - PublicationAccès libreAre urban soils similar to natural soils of river valleys?(2015-8-14)
; ; Purpose Urban soils and soils of river valleys are constituted of heterogeneous materials that have been manipulated, disturbed or transported at different spatial and temporal scales. Despite these similarities, little is known about soil evolution in urban soils and their comparison with natural soils remains therefore highly useful. We hypothesized that, according to their degree of perturbation, urban soils and natural soils of river valleys have similar soil processes related to their structure, physical and chemical characteristics. Materials and methods Using a synchronic approach, we compared two soil gradients, one located in the natural reserve of the Allondon River (canton of Geneva, Switzerland) and the other in and around the city of Neuchâtel, Switzerland. A total of five alluvial and 18 urban soil profiles were described according to vegetation type and alluvial terraces formed at different distances from the river for the river valley ecosystem and to soil age for the urban ecosystem. Correlations between soil gradients and classical physical (soil depth, particle-size distribution, coarse fraction) and chemical (Corg, pHH2O, Ptot, Ntot, CaCO3, CEC and C/N ratio) parameters of soils were first tested in order to identify similarities and differences among soil gradients. Data of soil properties were then clustered hierarchically in order to identify soil group classification. Results and discussion Our results showed similarities and differences between soil gradients. In the urban context, soil thickness was positively correlated to soil age, while the coarse fraction, sand content and C/N were negatively correlated to soil age gradient. In soils of the river valley, most of the chemical variables were either negatively (pHH2O and CaCO3) or positively (CEC, Corg and Ntot) correlated to soil distance from the river. These differences between gradients can be mainly explained by parent material, depositional conditions and land use which can influence soil processes. However, alluvial soils were well clustered with two identified urban soil groups according to soil maturity. Evolved alluvial soils far from the river were grouped with natural and near natural urban soils. Conversely, “young” perturbed alluvial soils were most clustered with human-made soils. Conclusions From the two selected soil gradients, soils on alluvial sediments are similar to urban soils in some characteristics. However, parent material, depositional conditions and soil and vegetation interactions on soil processes (e.g. matter cycle, energy flux) still need more investigation. This study contributes to the development of a natural soil reference for urban soils. - PublicationAccès libreEffects of endogeic earthworms on the soil organic matter dynamics and the soil structure in urban and alluvial soil materials(2015-1-1)
; ; ; Earthworms are considered as key actors of soil processes at different spatial and temporal scales and provide essential ecosystem services linked to climate regulation or primary production. However, little is known about their basic functional roles (e.g. organic matter decomposition, soil structuring processes) in perturbed systems such as urban or alluvial soils. Alluvial soils are characterized by regular physical perturbation through flooding and associated erosion/sedimentation processes which are rather similar to perturbations (e.g. temporal instability, spatial heterogeneity) affecting urban soils. Due to their close soil characteristics, we hypothesized that in both cases, soil functioning is similarwith respect to soil fauna activity. Under controlled conditions, our objective was to investigate the effects of two endogeic earthworm species, Allolobophora chlorotica (pink morph) and Aporrectodea rosea (the two most abundant species found in the studied urban site), on soil organic matter (SOM) dynamics and soil structure (network of earthworm burrows) comparing an urban and an alluvial soil. We investigated the growth of individuals (weight gain and reproduction success) and assessed their effects on SOMdecomposition (cumulative C–CO2 emission, nitrogen and phosphorus mineralization) and soil structure (macroporosity, total length and connectivity of segments) after one and three months of incubation. Our results showed higher growth of A. rosea in the alluvial soil compared to the urban soil. However, the total length of burrows, carbon and nitrogen mineralization were often higher in the urban soil especially when the two species were combined. This trend can be mainly explained by lower organic matter content found in the urban soil whichmay influence positively the burrowing activity and negatively the growth of earthworms. Endogeic earthworms appear a key feature of the soil functioning in the urban context through their roles on organic matter transformation, the formation and maintenance of the soil structure. - PublicationAccès libreBas-marais et prairies humides du Haut-Jura: relations sol-végétation et évolution(2015)
; Vittoz, PascalLes marais sont des écosystèmes à grande valeur écologique. Ils abritent une importante diversité de milieux, et contiennent des espèces végétales spécialisées et particulièrement adaptées aux sols temporairement ou partiellement saturés en eau. Depuis quelques années, de nombreuses études ont démontré que les marais subissent actuellement des transformations dans beaucoup de pays, bien qu’ils soient pour la plupart protégés. En effet, la plupart de ces écosystèmes semi-naturels semblent être menacés par les activités humaines, comme les pratiques agricoles (enrichissement en nutriments, abandon de la fauche ou de la pâture), mais également par les changements climatiques. Ces facteurs ont un impact négatif sur l’écologie, le fonctionnement et la qualité de ces écosystèmes, altérant les conditions hydrologiques et provoquant par conséquent de profondes transformations dans les communautés végétales, avec par exemple la disparition de nombreuses espèces spécialistes typiques de ces écosystèmes.
Dans cette recherche, il a été question d’étudier l’évolution, sur une durée d’environ 40 ans (1974 – 2012), de quelques milieux végétaux présents dans une zone particulière du Jura, plus précisément à la Vallée de Joux (Suisse, canton de Vaud) et à Chapelle-des-Bois (France, départements du Jura et du Doubs). Une partie de cette recherche (approche diachronique) a pour objectif de détecter d’éventuels changements floristiques dans cinq types de milieux représentant des bas-marais et des prairies marécageuses (Caricion fuscae, Caricion davallianae, Calthion, Filipendulion et Molinion). Pour cela, 110 relevés phytosociologiques faits entre 1974 et 1988 par Jean-Daniel Gallandat sont relocalisés sur le terrain et revisités en 2012 et 2013 (surface hétérogène mais identique entre chaque paire d’« ancien-nouveau » relevés), puis comparés. Puis, dans un deuxième temps, les causes de ces changements sont estimées d’une part grâce aux valeurs indicatrices de Landolt, puis, fait nouveau dans ces milieux humides, par l’utilisation des conditions édaphiques et notamment des formes d’humus. Comme ces dernières n’ont jamais été décrites auparavant dans les sites d’étude, cette étude des formes d’humus a été complétée, aux mêmes emplacements, par l’étude des sols et de la végétation actuels (sur une surface identique de 25 m2) ceci afin d’avoir une caractérisation ou un aperçu actuel des différents milieux végétaux inventoriés avec leurs sols et leurs formes d’humus (approche synchronique).
L’approche synchronique a permis d’identifier actuellement plusieurs communautés végétales présentes parfois sur plusieurs types de sols ou de formes d’humus différents. De plus, cette étude simultanée de plusieurs paramètres a permis d’obtenir une meilleure compréhension du fonctionnement et de l’écologie actuels de ces milieux. Ces milieux sont complètement dépendants de la présence et de la chimie de l’eau (taux de carbonates et taux en nutriments notamment), mais également de la présence de bétail. Cette approche a également permis d’émettre des hypothèses sur la stabilité actuelle de ces milieux mais aussi sur les potentiels changements de dynamique du milieu grâce aux listes floristiques ainsi qu’aux séquences d’horizons des formes d’humus. Des changements de végétation semblent être inévitables dans le futur si les conditions environnementales et anthropiques actuelles des sites prospectés restent les mêmes.
La comparaison des 110 anciens relevés effectués entre 1974 et 1988 avec les nouveaux relevés de 2012 et 2013 a permis de détecter des changements de végétation et de diversité spécifique dans les milieux humides prospectés, que cela soit au niveau des bas-marais, des prairies humides oligotrophes à Molinia caerulea ou des prairies humides plus eutrophes. L’utilisation simultanée des valeurs indicatrices de Landolt et des formes d’humus a permis de suggérer que ces différents milieux humides sont particulièrement menacés par une eutrophisation. Cette eutrophisation peut être due à un ensemble de sources différentes qui s’additionnent les unes aux autres et dont il est difficile d’identifier exactement la part de responsabilité. 1) Les changements de pratiques agricoles, avec notamment l’arrêt de la fauche et de la pâture, provoquent d’une part une prolifération des ligneux, et d’autre part, par l’accumulation de litière, une baisse de la lumière au niveau de sol ainsi qu’une augmentation de nutriments disponibles dans le milieu. 2) L’apport de nutriments peut également provenir par ruissellement des pâturages situés aux alentours des milieux humides prospectés. Cet apport sera d’autant plus important si l’utilisation de ces pâturages s’effectue plus intensivement. 3) L’apport d’azote provenant des dépôts atmosphériques a vraisemblablement également une part de responsabilité dans cette eutrophisation générale, comme cela l’a été suggéré dans plusieurs autres études. 4) Comme supposé par les formes d’humus, cette eutrophisation semble également provenir d’un assèchement, et semble toucher quelques marais uniquement. Ainsi, en période sèche, la minéralisation est accrue ce qui augmente le taux de nutriments disponibles ensuite pour les plantes. L’origine exacte de cet assèchement n’a pas pu être établie. Cependant, il semble que cet assèchement soit la conséquence d’une évapotranspitation augmentée résultant d’un abandon des pratiques agricoles (fauche et pâture). De plus, la présence de nombreux canaux de drainage particulièrement sur les sites de la Vallée de Joux semble également jouer un rôle dans cet assèchement, renforçant ainsi les effets induits par les changements de pratiques agricoles.
Cette thèse semble avoir permis de démontrer que les milieux étudiés, même s’ils sont protégés par des mesures, des lois ou des directives, ont subi et subissent encore actuellement de nombreuses dégradations qui, d’une part, altèrent la qualité, la biodiversité et le fonctionnement de ces milieux, et qui, d’autre part, ont un fort impact fonctionnel et visuel sur le paysage des montagnes jurassiennes. De nouvelles mesures de gestion sont donc nécessaires pour enrayer ou limiter ces modifications et maintenir au mieux ces milieux ainsi que leur fonctionnement. Ces nouvelles mesures devront impérativement concerner tous les paramètres nécessaires à la survie de ces milieux et possibles à modifier, comme la présence et la chimie de l’eau (taux en nutriments notamment) et la ré-introduction et le contrôle de pratiques agricoles extensives (fauche et pâture)., Wetlands are ecosystems of high conservation value. They are a great source of vegetation types and biodiversity and contain plant species specialized and adapted to permanently or temporary water-saturated soils. In order to maintain their species richness and their quality, these fragile ecosystems must be conserved.
However, several studies have demonstrated that some wetlands decreased in surface and in quality in many parts of the world since several years, although these biotopes are managed and protected by laws. Most of them are threatened by various factors linked to climate change and surrounding human activities, such as nutrient enrichment, desiccation and land-use changes. These factors have a negative impact on the ecology, the functioning and the quality of these wet ecosystems, altering the hydrological conditions and causing consequently dramatic transformations of the plant communities and a loss of many specialist species.
In this project, the principal purpose was to study the evolutionary dynamic on a temporal scale of 40 years (1974 – 2012) of some types of wetlands in a particular part of the Jura Mountains, and more precisely in the Vallée de Joux (Switzerland, canton of Vaud), and in Chapelle-des-Bois (France, Jura and Doubs departments). A part of this research (diachronic approach) was consecrated to the detection of possible vegetation changes in five types of wetlands (Caricion fuscae, Caricion davallianae, Calthion, Filipendulion, Molinion). For this, 110 former phytosociological relevés made between 1974 and 1988 by Jean-Daniel Gallandat were relocated, resurveyed in 2012 and 2013 (heterogeneous surface, but identical between each pair of « old – new » relevés) and compared. Then, the causes of these observed vegetation changes were estimated by, firstly, using Landolt values, and secondly, as it is the originality of this study, by using edaphic conditions and particularly by humus forms. As these humus forms have not yet be described in the study area, this humus forms study were completed in same plots by present soils and vegetation descriptions (identical surface of de 25 m2) in order to have a description or a current overview of vegetation, soils and humus forms present in the sampled study sites (synchronic approach).
The synchronical approach has enabled to identify at the moment many vegetal communities that are often characterized by different types of soils and humus forms. This part has also enabled to have a better understanding of the current functioning and the ecology of these environments. These biotopes are completely dependant on water presence and quality (especially carbonates and nutrients), but also by livestock. This approach has also enabled to make suppositions about the stability and the conservation’s state of these ecosystems, but also on potential dynamic’s changes thanks to floristic lists and horizons successions of humus forms. Some vegetation changes seem to be inevitable if the current environmental and anthropogenic conditions of the study sites are the same.
The comparison of the 110 former relevés with the new ones has enabled to detect many vegetation changes and species diversity in the study wetlands alliances, including fens, oligotrophic wet meadows as Molinion and eutrophic wet meadows. The simultaneous uses of Landolt values and humus forms have enabled to propose that these different wetlands are threatened by eutrophication. This input of nutrients can be due to a set of different added sources that are very difficult to detect one by one. 1) Changes in agricultural practices, with mowing or pasturing abandonment, cause on one hand, the development of woody species, and on the other by litter accumulation, a decrease of the aboveground light and consequently an increase of released nutrients. 2) The nutrient inputs can also result from the streaming coming from the surrounding pastures. These inputs will be more important if the use of these pastures is carried out more intensively. 3) Nutrients coming from atmospheric deposits have certainly also a responsibility in this general eutrophication as it was already suggested by other studies. 4) As supposed by humus forms, eutrophication can also come from a drying up. Thus, in dry period, the mineralization of the organical matter is increased, which causes an increase of the rate of nutrients available for the plants. This draining seems to concern only a few wetlands in the study area. The exact origin of these drying up could not be established in this study. However, it seems that it is the consequence of an increased evapotranspiration causing by an abandonment of agricultural practises (mowing and pasturing). Furthermore, the presence of artificial drains particularly in both sites of the Vallée de Joux could also play a role in this drying up, accentuating the effects induced by land-use changes.
This thesis demonstrated that the study wetlands, even that they are protected by measures or laws have been and are always suffering from numerous modifications that degrade the quality, the biodiversity and the functioning of these ecosystems. Furthermore, these degradations have a great functional and visual impact on the Jura Mountains landscape. New management measures are necessary to stop or reduce these modifications and to maintain these wetlands. These measures should absolutely concern all possible parameters necessary to the survival of these wetlands, as the presence and quality of water (nutrients rates notably) and the reintroduction and the control of agricultural extensive practices (mowing and/or pasturing). - PublicationAccès libreAre urban soils similar to natural soils of river valleys?(2015)
; ; Purpose Urban soils and soils of river valleys are constituted of heterogeneous materials that have been manipulated, disturbed or transported at different spatial and temporal scales. Despite these similarities, little is known about soil evolution in urban soils and their comparison with natural soils remains therefore highly useful. We hypothesized that, according to their degree of perturbation, urban soils and natural soils of river valleys have similar soil processes related to their structure, physical and chemical characteristics.
Materials and methods Using a synchronic approach, we compared two soil gradients, one located in the natural reserve of the Allondon River (canton of Geneva, Switzerland) and the other in and around the city of Neuchâtel, Switzerland. A total of five alluvial and 18 urban soil profiles were described according to vegetation type and alluvial terraces formed at different distances from the river for the river valley ecosystem and to soil age for the urban ecosystem. Correlations between soil gradients and classical physical (soil depth, particle-size distribution, coarse fraction) and chemical (Corg, pHH2O, Ptot, Ntot, CaCO3, CEC and C/N ratio) parameters of soils were first tested in order to identify similarities and differences among soil gradients. Data of soil properties were then clustered hierarchically in order to identify soil group classification.
Results and discussion Our results showed similarities and differences between soil gradients. In the urban context, soil thickness was positively correlated to soil age, while the coarse fraction, sand content and C/N were negatively correlated to soil age gradient. In soils of the river valley, most of the chemical variables were either negatively (pHH2O and CaCO3) or positively (CEC, Corg and Ntot) correlated to soil distance from the river. These differences between gradients can be mainly explained by parent material, depositional conditions and land use which can influence soil processes. However, alluvial soils were well clustered with two identified urban soil groups according to soil maturity. Evolved alluvial soils far from the river were grouped with natural and near natural urban soils. Conversely, “young” perturbed alluvial soils were most clustered with human-made soils.
Conclusions From the two selected soil gradients, soils on alluvial sediments are similar to urban soils in some characteristics. However, parent material, depositional conditions and soil and vegetation interactions on soil processes (e.g. matter cycle, energy flux) still need more investigation. This study contributes to the development of a natural soil reference for urban soils.