Dynamics of bog-pine-dominated mires in the Jura Mountains, Switzerland: Atentative scheme based on synusial phytosociology

A description of the bog-pine (Pinus uncinata var. rotundata) dominated veg etation of uncut oligotrophic mires affected by drainage is given. Surveys were carried out at 17 sites along the Jura Mountains (Switzerland and Fran ce) in 1993, 1994, and 1995. Raised bogs of the Jura are generally of small size, and most vegetation changes in them have occurred as a result of the indirect impact of peat cutting. This activity led to the peat drying out and to colonization by trees, in particular by bog-pines. Integrated synusial phytosociology was used to describe the vegetation wher e bog-pine, spruce, and birch occur. Two spatio-temporal levels of organiza tion were considered: the synusia and the phytocoenosis. At the phytocoenos is level, four vegetation types representing bog-pine stands of uncut and d eep oligotrophic peats are described with their constitutive synusial compo sition. They represent: (1) phytocoenoses developing in the open, wet centr al parts of the bogs, where trees are scattered and of small size, (2) phyt ocoenoses with layered tree stands of medium size and with a higher density , and (3) phytocoenoses with tall trees, developing generally near the edge of the bogs or close to peat cuttings. A generalized qualitative dynamic m odel of the vegetation in relation to the development of bog-pine trees was developed. It shows the spatial and temporal organization of the constitue nt synusiae, as well as other underlying hypothetical functional relations. The different bog-pine-dominated vegetation types described in this study a ppear to have coexisted since the origin of the Jura bogs as a result of lo cal polyclimaxes induced by differential waterlogged situations. They proba bly all belong to the same (primary) successional series, but have been aff ected by both autogenic and allogenic processes. During the development of the bogs the balance between the different communities changed. In particul ar, the vegetation types with dense and tall pine trees have undergone a dr astic expansion since the Jura bogs were first affected by drainage.