Background

Beech is the most important deciduous tree species in Bavaria and the key species of a variety of beech forest ecosystems. It offers a diversity of ecological and economical advantages, and is widely accepted as a robust and sustainable component of resilient mixed forests in Bavaria. However, an increase in frequency (and magnitude) of droughts and late frosts is very likely to be observed under climate change conditions in Bavaria - climatic extremes to which beech trees respond highly sensitive.

Fig. 1: Response of beech trees in the Bavarian Forest to a late frost event. The upper panel shows the canopy state at May 3rd 2011, just before the late frost event, and the lower panel shows the canopy state at May 4th 2011, just after the late frost event. The white areas signify regions of interests for image analysis to compute the duration of canopy recovery.

Image source: Menzel A., Helm R. & Zang C. (2015). Functional Plant Ecology, 6, 110.

HyBBEx investigates temporal legacies of these climate extremes, so-called hysteresis effects, which may range from dedicated recovery periods to mortality. Additional to important and directly practically relevant questions about the site-specific implications for growing beech, HyBBEx is especially concerned with the ecological perspective, with a focus on the carbon balance of beech forests — because hysteresis effects may turn forest ecosystems from carbon sinks to carbon sources, and can therefore directly impact important ecosystem services.

Fig. 2: Extraction of tree-ring samples in the Bavarian Rhoen. Time series of tree growth derived from tree-ring measurements are an important data source for HyBBEx, since trees store valuable information about recovery from climate extremes in their rings.

Image source: C. Zang (private)

Currently, we know only little about these hysteresis effects, and consequently even the most up-to-date ecosystem models cannot fully capture the recovery of ecosystem productivity after climatic extremes. Therefore, a realistic process-based projection of the ecosystem functioning of forests (and more specifically beech forests) is currently not possible. HyBBEx uses an innovative approach comprising data integration, and statistical and dynamical modelling, and model-data-fusion to achieve projections of ecosystem dynamics of Bavarian forest ecosystems through a better understanding of hysteresis effects. This enables HyBBEx to deliver both basic science contributions and insights in tree species suitability and ecosystem management that can directly be fed back into forestry practice. All in all, the project wants to contribute considerably to the improved understanding of climate change impacts on Bavaria, with a direct benefit for the development of regional adaptation strategies.