Modelling the impact of dead wood water retention in Central European Forests

In recent years, German forests have faced numerous stress episodes, such as droughts, heatwaves and insect outbreaks, leading to a significant rise in tree mortality. Consequently, deadwood production increased, partly outpacing extraction capacities. This trend coincides with a shift towards more selective forest management methods that partially retain deadwood on logged sites. As a result, the average amount of deadwood per hectare in Germany has substantially increased, climbing from 19.9 m³ ha^-1 yr^-1 in 2012 to 29.4 m³ ha^-1 yr^-1 in 2022.

Besides providing valuable species habitats and sequestering carbon, deadwood plays a significant role in the water cycle, by reducing surface runoff and acting as a water reservoir.

Despite its growing abundance and ecological relevance, deadwood is largely neglected in current land surface models such as in JSBACH (ICON-LAND main component), particularly with respect to its impact on hydrology and microclimates.

This omission is rooted in the historical removal of deadwood under conventional management and in limited understanding of deadwood's hydrological properties, which vary with factors such as soil characteristics, canopy closure, deadwood position and species.

Here, we present an approach to quantify and model the influence of deadwood on hydrology and microclimates, by combining experimental field measurements from Bavarian Nature Reserves and the data from the LabForest project in the University forest of the LMU in southern Germany with JSBACH outputs. We compare different methodological pathways for deriving observation-based parameterizations suitable to model integration. Preliminary results indicate that deadwood exerts measurable effects on near-surface microclimate and soil moisture dynamics, highlighting the need to explicitly represent deadwood in land surface modeling frameworks.