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BENDAGHA, N., GÄRTNER, S., SAYER ,U., REIF, A. (2004): Vegetation, site conditions, and land use history of a Downy Oak forest in Tagolsheim, Alsace, France (in German language).

Ber. Naturforsch. Ges. Freiburg 94, 127-150.

 

The Downy Oak (Quercus pubescens) and the common Boxtree (Buxus sempervirens) in Alsace are rare woody species. While the Downy Oak forms zonal forests in submediterranean climatic regions in the south, it reaches the northern limits of its distribution north of the Alps. The Downy Oak forests there are preferably found on dry limestone slopes with south- and southwest exposition and are mostly surrounded by Beech dominated forest. In the study area a transitional forest type where Beech and Oak are directly in competition. When studying the site preferences of  Downy Oak, the ecotone from Downy Oak forests to neighboring forest types is of special interest. Aim of this study was to identify parameters wich explain the ecotone between Beech (Fagus sylvatica) and Downy Oak forests, with the main focus on soil water storage capacity and climate. Within the survey period from may until December 2003 the forest vegetation of the Buxberg in Tagolsheim have been characterised, described and cartographied. The study of the vegetation ist based on the phytosociological system of Braun-Blanquet. The particularity of this zone consist on the distibution of an Oak mixed forest in contact with a thermophile lime dry Beech dominating forest. Syntaxonomically, the Downy Oak forest can be integrated into the association of Quercetum pubescenti-petraeae with a subassociation of Buxus sempervirens. This forest is encircled by a  Carici-Fagetum with an association of Carex sylvatica. The ecotone between Beech and Downy Oak forest could not be classified in the phytosociological system because of the absence of diagnostical caracteristical species and differential species. In order to analyse the impact of the ecological factors that are relevant for this ecotone, two main factors have been investigated: soil water storage capacity with soil profiles as well as climate represented by solar radiation with the computer programm DACHrad. The results arising out of this analysis indicate that these two vegetation groups could be clearly distinguished  by drought due to solar radiation. The soil water storage capacity do not influence directly in this case the vegetation changing. The Downy Oak forests at the northern limits of its distribution seems to be restricted to dry soils, and slopes with south exposition and sufficiently high radiations which prevent Beech from dominating forests. Additionally, the areal of the Downy Oak is further limited throught the expansion of the common Boxtree wich forbid all kind of regeneration. In order to preserve the Downy Oak in this region, it has been suggested on the one hand to brake the expansion of the Boxtree and on the other hand to set up this protected biotope in a permanent monitoring area.

Keywords: Quercus pubescens, Buxus sempervirens, Drought, Insolation, Alsace

 

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