The relationship between vegetation change and rehabilitation management is investigated at a severely degraded cut-over lowland raised mire on the Wales/England border, managed by Natural England and The Countryside Council for Wales. Positive responses are confirmed 11 years after rehabilitation commenced, identifying trends towards raised mire as well as bog pool vegetation and water table thresholds associated with these trends have been established. A landscape-scale vegetation survey was carried out three times over 9 years. Species abundance was correlated with average seasonal water table height, time since rehabilitation, cutting type and survey year. Key species maps for the time series confirmed positive vegetation response, but slower than stipulated in the site management plan. There was a clear increase in the target peat-forming species (Sphagnum cuspidatum, Eriophorum angustifolium and E. vaginatum) as a direct response to rehabilitation and correlating positively with a high water table. Permanent quadrat vegetation monitoring was carried out three times at five-year intervals. Uncut areas and areas of recent commercial cuttings were rehabilitated earliest having significant increases in target mire species without the loss of other mire species from excess inundation. In the recent commercial cutting areas, a successional trend was identified, from a low water table to a fluctuating water table characterised by Molinia caerulea-rich vegetation, followed by a transition to stable, inundated conditions supporting Sphagnum cuspidatum/Eriophorum spp pool vegetation. A second successional trend, associated with the achievement of a near-surface, stable water table, saw the development of raised mire vegetation including Sphagna other than S. cuspidatum. This latter trend was primarily found in the uncut areas of the site but was also found to a lesser extent in recently cut-over areas where it was preceded by a fluctuating water table with a Calluna vulgaris- Molinia caerulea vegetation. A new survey related water table residence time calculated from hydrology data with vegetation for each quadrat. Analysis identified a mire pool vegetation type correlated with shallow, above surface flooding. A diverse mire vegetation type was also found which correlated with the water table staying within the upper 10cm of peat. The minimum threshold for establishment of Sphagnum species was found to be an average water table level within the range of 5.1 to 10cm below the peat surface. Higher cover of Sphagnum species was related to shallow flooding – suggesting that these conditions would be most efficient in re-establishing mire vegetation. 3 A base-line vegetation monitoring survey on an area immediately following deforestation and damming identified a subtle but positive response of the mire vegetation to management within one year.

Les tourbières représentent 2 à 3% des terres émergées et stockent entre 10 et 25% du carbone des sols. Les tourbières sont soumises à des contraintes anthropiques et climatiques importantes qui posent la question de la pérennité de leur fonctionnement en puits de C et de leur stock. Une meilleure compréhension de ces écosystèmes est nécessaire pour déterminer les facteurs et les effets et interactions de ces facteurs sur les émissions de gaz à effet de serre (GES). Ce travail a consisté à suivre les émissions de GES et les facteurs contrôlant dans La tourbière de La Guette (Sologne) pour établir son bilan de C. En parallèle des expérimentations sur l’effet de l’hydrologie sur les flux ont été menées, enfin un suivi sur 4 sites a été réalisé pour étudier la variabilité à l’échelle journalière. Les résultats de ces travaux montrent que la tourbière de La Guette a fonctionné en source de C (-220 ± 33 gC m-2 an-1) et ce malgré un niveau de nappe élevé. Ils montrent également l’importance de la variabilité spatiale des flux estimés à l’échelle d’un site. Les expérimentations confirment l’importance de l’hydrologie et suggèrent à haut niveau de nappe d’eau des phénomènes liés au transport des gaz. Enfin l’étude de la variabilité journalière montre que la sensibilité de la respiration à la température peut être différente le jour et la nuit et que la synchronisation entre les températures du sol et la respiration peuvent améliorer la représentation de cette dernière. / Peatlands cover only 2 to 3% of the land area but store between 10 and 25% of the soil carbon. The outcome of the anthropic and climatic pressure on these ecosystems is uncertain regarding their functions and storage. A better understanding of these ecosystems is needed to determine the factors and their interactions on greenhouse gas (GHG) emission. This work consist in monitoring GHG emissions and controlling factors in a Sphagnum peatland to estimate its carbon balance. Experimentation on mesocosms were carried out to explore the effect of hydrology on the fluxes and a monitoring on 4 sites was made to study the daily variability. Results show that La Guette peatland was a carbon source (-220 ± 33 gC m-2 an-1) in spite of the high water table level. The importance of the spatial variability measured in the site was also demonstrate. The hydrology effect was confirmed by the mesocosms experiments and high water table level shows that gas transport might have an effect. Finally the study of the daily variability show that the temperature sensitivity of the respiration might be different between day and night and that synchronizing soil temperatures and respiration can improve the respiration representation.