Climate change in the forest: Which tree species survive the drought?

Climate change in the forest: Which tree species survive the drought?

As climate change continues, research into water absorption and availability is critical to the future of our forests. A current study by the University of Göttingen provides information about the water absorption depth of tree species such as spruce, European beech and Douglas fir. The aim is to find out which tree species should be promoted during longer dry periods.

The results of this comprehensive study show that beech and Douglas fir have access to water from deeper soil layers, while spruce comes under greater stress in critical dry phases because it is dependent on water from the upper soil layers. These findings are particularly relevant, especially since mixed stands influence water uptake. In mixtures with conifers, beech absorbs more water from deeper layers than in pure stands.

Influence of tree species and mixed stands

The Göttingen University research team analyzed stable isotopes to distinguish water sources and evaluate different tree species under comparable conditions. The measurements were taken at four locations in Lower Saxony. These show that the influence of the tree species, the mix of tree species and the soil conditions are essential for water absorption. What is particularly critical is the fact that spruce stands are affected more quickly when there is a lack of water, meaning that switching to other tree species, such as Douglas fir, does not appear to be an optimal solution.

The positive reactions of beech to neighbors in mixed stands clearly show that their synergies can lead to better water access. In contrast, the mixture with beech affects the water absorption of the spruce. Although beech and Douglas fir are considered a compatible combination, both tree species could also experience difficulties in extreme drought.

Climate adaptation in silviculture

The Federal Institute for Geosciences and Natural Resources (BGR) and the Northwest German Forest Research Institute (NW-FVA) are investigating the effects of drought-tolerant species such as Douglas fir and Norway oak on the soil water balance under the “KLIBW-GW” project. The project, funded by the BMEL and BMUV and running until November 2024, aims to record the recharge rate of groundwater under tree species such as Douglas fir, red oak and spruce.

Groundwater recharge in particular is an important ecosystem service provided by forests. Current climate conditions are leading to a decline in these recharge rates, which calls for new forestry approaches. Deciduous trees such as red oak have the potential to increase groundwater recharge, while Douglas fir could lead to lower amounts of seepage.

Modeling the water balance

Water balance models based on physical laws are used in Bavaria to comprehensively analyze the water balance. These models, such as LWFBrook90, integrate soil and site properties with meteorological measurements to enable site-specific water balance representations. This precision is crucial to take into account the different water consumption of the main tree species.

These models comprehensively depict the water requirements of tree species such as spruce, pine, beech and oak as well as mixed stands. The data is processed in geographic information systems (GIS) in order to clearly present information relevant to decision-making for forestry practitioners.

The challenge posed by climate change requires new silviculture strategies to ensure the vitality of forests and their contribution to water supply through effective soil management. Both research approaches offer valuable insights into the adaptation of forests to changing climatic conditions and their influence on the water balance.