The common service tree is currently a rarity in our forests, and one of the four important native Sorbus species, along with the wild service tree, rowan and service tree. According to the results of National Forest Inventory 3 for Bavaria, it was found to account for 0.2 % of the area of our forests. The reason for this low share is its low competitive ability, which is due to its extremely high light requirement, combined with its slow growth rate. This is also why the distribution of the whitebeam in Bavaria is concentrated particularly on sparse forest structures with high light exposure and forest edges. Its advantage, however, is its ability to colonise sites with extremely unfavourable growing conditions. This explains the important role it plays in the restoration of protection forests in the Bavarian Alps, for example, where it can also be introduced on steep slopes with very adverse soil conditions.
Fig. 1: The whitebeam can colonise sites with extremely unfavourable growing conditions. Photo: Christoph Josten (LWF)
Integration of the whitebeam in forest development in times of climate change should also be advocated in lowland areas, as this tree species copes very well with drought and extreme radiation conditions (on open areas) thanks to the tomentose underside of its leaves (covered with densely matted woolly hairs), which help to reduce evaporation. This is one of the reasons why it is considered a pioneer tree species. Its integration as an enriching mixing element in future forests should therefore be considered.
The introduction of the whitebeam can however also be an enrichment in ecological terms. When it flowers in April/May each year, the whitebeam is a valuable source of food for insects. Its reddish-brown berries are also a valuable source of food for birds. In addition, the whitebeam’s foliage helps to fertilise and enrich the soil when it is shed in autumn. Whitebeam berries are naturally spread by birds, which pick up the red fruits and excrete the seeds undigested, often several kilometres away from the seed tree.
Fig. 2: The common whitebeam, with its characteristic white-haired leaf undersides and red berries. Photo: Christoph Josten (LWF)
For whitebeams to be preserved in our forests in the long term and their share in our forests to be actively increased, long-term support from the forest owner is necessary. This begins with the right choice of provenance.
As a mixing element, the whitebeam is mainly introduced through active planting. Planting material is offered by the tree nurseries. However, since the whitebeam forms hybrids with all other Sorbus species, there are a large number of regional subspecies in Bavaria (e.g. the Kordigast whitebeam, the Danube whitebeam). The plants should thus always be procured in consultation with the experts (foresters) on site.
The special ecological characteristics of this tree species, such as its high light requirement and slow growth, also mean it requires long-term silvicultural support from forest owners. It is for example necessary to relieve the whitebeam of competitive pressure at all stages of its growth.
Once successfully established, the trees must be checked regularly to determine whether competing tree species are threatening their survival and vitality. If this is the case, competitors within a radius of approx. 2 metres must be removed at an early stage; in later growth phases, care must be taken to ensure the crown is free and to allow undisturbed crown development. This is the only way to ensure that the tree species can be integrated as an enriching mixing element in the climate forests of the future. On the edges of forests and on disturbed areas and special sites, the whitebeam can initially establish itself successfully after planting or being seeded by birds. But even here, it needs help from the forest owner so as not to perish in the face of competition from other tree species.
To summarise, whitebeams are valuable trees for mixed forests in times of climate change. Although they require long-term silvicultural support if they are to survive in the stand or on the edge of the forest, the introduction and promotion of the whitebeam can nevertheless make a valuable contribution to the establishment of climate-stable forests, to risk diversification, and to the promotion of biodiversity.
