Long-Term Monitoring of Soil and Deadwood Water Content Across Windthrow Post-Disturbance Scenarios

Deadwood is a substantial part of a healthy forest ecosystem. Natural disturbances such as windthrow can generate large amounts of deadwood and alter forest structure, with cascading effects on ecosystem processes. To study the effect of its biological legacies on soil water retention and the microclimate is of particular interest to support future guidelines and decisions for management (forest regeneration, potential fuel load and fire susceptibility) in post-disturbance scenarios. This also includes an improved understanding of the water storage capacities and responses to precipitation of deadwood across different decay stages. Additionally, deadwood mitigates natural hazards by modulating soil water storage, thereby influencing runoff and flood peaks. Post-disturbance roughness from logs, litter, and root mats can curb erosion, shallow landslides, rockfall, and avalanches; quantifying these effects is key for integrated hazard protection.

In this case study, we take advantage of three adjacent sites (all within a radius of 1 km), ensuring comparable stand history and climatic conditions. The sites include a cleared windthrow area; a windthrow area with unaltered deadwood cover; and an intact mature forest stand. We continuously monitor soil water content across all sites, and additionally measure the water content of a representative log within the uncleared windthrow area. Using TDR sensors (Teros 10, METER Group, Pullman, WA, USA), we track long-term volumetric water content in both soil and deadwood. Soil moisture is measured at one profile per site at 10, 20, and 50 cm depth. To capture spatial variability, two additional TDR sensors were installed near each soil profile at 10 cm depth, complemented by four independently operating TDT sensors (TMS cable, TOMST s.r.o., Prague, Czech Republic) placed at greater distances. To improve the accuracy of deadwood measurements, we established a specific calibration for different decay classes. Precipitation and air temperature are recorded by a stationary weather station located in the cleared windthrow area. High-resolution UAV LiDAR flights provide the basis for analyzing the influence of micro-topography and surface roughness on water storage and deadwood volume along the slope.