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The development of species composition and the structure of forests from the Black Forest to the Schwaebischen Alb – with particular emphasis on beech

concluded 12/2004


The study was carried out in association with the Graduiertenkolleg's 'Gegenwartsbezogene Landschaftsgenese' (Research Training Group's 'Formation and development of present day landscapes') project. The objective was to investigate the influence of natural and anthropogenic influences on the current species composition and to forecast the further development in the near future. To this end, three representative areas were selected from the varying landscapes of the central Black Forest region, the Baar-Schwarzwald and the Suedwestalb, and the results obtained from each of the sites compared. A further objective was to determine whether differences existed between the development in public and private forests. An additional issue requiring clarification was the extent to which pure spruce stands can be converted to mixed stands using naturally regenerated beech. In accordance with the objectives, the study was divided into three individual sub-projects:

1) Development of forest composition with human influence
In the first subproject, the historical development of forest structure in the three eras ‘devastation’, ‘reafforestation’ and ‘forest transformation’ was examined, as were the changes in species composition. This was based on the analysis of the available literature, supplemented by archive material.
In all three study areas the forests cleared up until the end of the 18th century and during World War II were principally replanted with spruce and pine. This resulted in large areas of conifer dominated forests. Since 1970 the transformation of these stands into more stable mixed stands has been strived for.
The study of the development of the forest structure over the last fifteen years was  made possible by comparing the results of the national forest inventories from 1986/88 and 2001/02. A significant reduction of the proportion of spruce and the area of pure spruce stands was observed in all three study areas, as well as an increase in the area of mixed stands.

2) State and development of forest composition in the small private forest sector
In the second sub-project the situation surrounding the small private forest sector was examined in an area in the central Black Forest and the current as well as the forecast tree species compositions investigated. The research area selected has a higher than average proportion of small private forests, at 63% of the forest area. A survey of the forest owners revealed that the proportion of conifer species, especially spruce, will continue to remain high in the future. A process of conversion away from pure conifer stands to mixed stands was also evident, however. The proffered state grants for afforestation projects requiring prior permission was seen to be having an impact. Between the years 1993-2002, young broadleaf species rich stands accounted for 80% of the afforestation grants allocated. At the same time, the study revealed that the majority of advance plantings and reafforested windthrow and bark beetle damaged stands were planted primarily with conifers. These results stemmed from an analysis of the applications submitted under the 'Naturnahe Waldwirtschaft' (nature orientated forestry) grant scheme in recent years. The backlog in terms of thinning and tending operations became very evident. There exists a danger that the insuffieciently thinned stands will become instable and the introduced admixed species will be lost .

3) Colonisation of conifer forests by beech
In the third subproject, the possibility of utilising the natural migration of beech into pure conifer stands for the purposes of forest transformation was examined. Regeneration data was collected in conifer stands to test this.
The most important results obtained were that young beech trees established themselves in pure conifer stands at distances of up to 60 m from the mother tree. A beech seedling density of ≥ 1 plant/m2 was observed up to 25 m from the mother tree. In terms of practical silviculture, this means that one old beech per hectare is sufficient to ensure the admixture of beech in the next stand generation. This will require intensive tending of the young growth, however. Should the beech trees of the subsequent generation be of acceptable quality, then individual young beech trees are not enough. In this case, groups of young beech trees are required.
On the south western Alb young spruce trees were not able to compete with ash and sycamore seedlings. Beech was also present in small quantities, which means that without silvicultural intervention the spruce stands will probably be replaced by ash-sycamore stands with individual beech trees in the next generation.
A tendency towards greater broadleaf species proportions in the young growth was also evident in the other two study areas. Imbalances arose as a result of browsing, however. Broadleaf species and fir were browsed preferentially, whereas spruce exhibited almost no damage. Consequently, browsing benefits the young spruce trees.

The results of the three subprojects indicate a move towards an increase in the area of mixed stands in both state and privately owned forests. The species composition in the state forests will evolve towards that of natural forests, in line with management guidelines. In the privately owned forests the stands will become increasingly mixed – the area of pure spruce stands is in decline – but spruce will remain the most important species, and the species proportions will vary only slightly. The natural migration of beech into conifer stands may be integrated into silvicultural treatments, but requires subsequent tending measures. 
Researcher: Monika Ganz
Supervisor: Prof. Dr. J. Huss
Thesis: http://www.freidok.uni-freiburg.de/volltexte/1616/
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