Spatio-temporal pattern of bog pine (Pinus uncinata var. rotundata) at the interface with the Norway spruce (Picea abies) belt on the edge of a raised bog in the Jura Mountains, Switzerland

In a bog site in way of paludification, a pine stand is declining, which presently is an infrequent phenomenon on the Swiss Jura scale. A transect was positioned in the bog, from the external and driest part (pine-spruce stand) towards the central and wettest part (pine stand). Water table, tree structure, tree age structure and pine radial growth were analysed with spatial and temporal references. The ground water level is very shallow and the hydrologic gradient is obvious during dry periods. Tree structure (height and diameter) is strongly linked to the hydrologic gradient. Two cohorts have invaded the bog with a 70-year-time period between them. The first one concerned the whole transect; it started around 1840 and could be related to a clear cutting on the fringe of the bog. After a quick initial radial growth, the pines reduced their radial growth abruptly (1870-1885), more quickly and strongly in the centre of the bog, where an important mortality was observed over the last 10 years. Bog pine can thus survive over decades with a very reduced growth and in very bogs probably constituted the bog pines' survival niche during paludification in the Jura bogs.