Volume 15 (2014 / 2015) Article 6

Enhanced sensitivity of a mountain bog to climate change as a delayed effect of road construction

by P. von Sengbusch

Published online: 02.01.2015

Summary

Trees of Pinus rotundata (bog pine) characterise many bogs in the mid-altitude mountains of central Europe (Switzerland, East and South Germany, Czech Republic). The research described here focuses on recent changes in the growth of bog pine on the Ennersbacher Moor, a mountain mire in the Black Forest (south-west Germany). An increase in the cover of bog pine is usually caused by drainage and subsequent drawdown of the water table. However, this bog has not been drained or directly disturbed in any other way. One possible explanation is that a road constructed in 1983 along one margin of the bog has diverted part of its water supply. Even though the road was designed to conduct potentially salt-contaminated drainage water away from the bog, its construction did not cause an immediate vegetation response in the 1980s and 1990s. Therefore, I hypothesise that it enhanced the sensitivity of the bog to climatic stress, predisposing it to a succession that was eventually triggered by a series of drought years in 2009–2011. Data collected near the centre of the bog over the period 1998–2014 indicate not only a distinct change in the relationship between height and trunk circumference of the trees, but also an increase of dwarf shrub cover and changes in the composition of Sphagnum communities. Although the pH of near-surface water may have increased slightly over this period, pH and EC values remain within typical ranges for raised bogs in the Black Forest. Examination of peat profiles revealed that the peat is more highly humified now than it was in 2002, and water table records from 2012–2014 show a greater amplitude of fluctuation than water table data collected in 1998–2001. Even though its mean level is only 105 mm below the ground surface, the water table is now observed to fall rapidly to depths of at least 350 mm during both wet and dry summers. Mapping surface (meso)topography and flow lines from the adjacent slope shows that the Ennersbacher Moor is not domed in this direction, so that water arriving from upslope would reach the bog centre if the road were not present. Overall, the results support the hypothesis that the observed succession is a delayed effect of construction of the road.

Citation

von Sengbusch, P. (2015): Enhanced sensitivity of a mountain bog to climate change as a delayed effect of road construction. Mires and Peat 15: Art. 6. (Online: http://www.mires-and-peat.net/pages/volumes/map15/map1506.php)

Reviewers

IMCG and IPS acknowledge the work of the reviewers.