Water deficiency – Forests in danger?

Background

Vertrocknete Buchen aus einem Gefäßversuch
European beeches, dried out during a pot experiment (© Thünen-Institut/Jürgen Müller)

During a dry spring as typical in Brandenburg, water is limited for the forests. Does the water deficiency cause damage to the forest? How long can the forests bear this lack of water? It is known, that trees are adapted differentially to water shortage. But there is still a need for further research in the amount of loss in increment during long dry periods and dry successive years (droughts).

Water deficiency occurs if a plant needs more water than is available. Plants, soil and the meteorological conditions interact. At the Thünen-Institute we identify regions in Germany with recent and potential risk of water deficiency. By the use of models it is possible to reproduce how the water deficiency and decreasing available soil water affect trees.  

Especially young trees are vulnerable, as their roots are not deep and cannot reach deeper soil water. Thus they are in the focus of our experiments. In a rain-shelter experiment (Drylab) with eight lysimeters we examine the sensitivity of beeches with different origins to drought stress under controlled conditions. Out of this we derive indicators of critical drought stress. The following film shows, how it works (in German).

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For older trees the growth and thus the tree increment of high importance for potential yield. With the help of tree ring analysis we examine the tree growth of each year. With statistical approaches we connect the tree ring growth with the climatic conditions. With this we deduce the reaction of tree species or proveniences to an assumed climate change. Is there a high growth or are other tree species better adapted to the side conditions?

Measurment of the water fluxes in forests (© Thünen-Institut/Jürgen Müller)

Agriculture can adapt quite fast with its annual crops to dry climate, while planning periods in forestry are 100 years or longer. Thus already today decisions need to be made, determining the future conditions of the forests. It is the task of research to realize drought-related risks and to show options for action, as adaption of forestry like the selection of tree species or provenance.

Field laboratory "Drylab"

Informationen über die Bedeutung verschiedener Baumarten für den Wasserhaushalt finden Sie in dem Dossier "Wald und Wasser".