Post-fire landscape evolution – insights from passive seismic monitoring of atmosphere-weathering zone coupling at the Quesenbank succession site, Harz mountains, Germany

The August 2022 forest fire event in the Harz National Park has suddenly shifted head water catchments to a new, unknown and short-lived state of equilibrium. The majority of standing bark beetle ceased trees were either burned or severely charred so that they fell in the weeks and months after the fire, giving way to the selective establishment of successive species. From studies in other fire-affected regions it was anticipated to see enhanced surface runoff and rain-driven sediment export. However, only little surface hydrophobicity was found months after fire, while measurements of diffusive fluxes out of the site are hard to constrain with typical state of the art approaches. Here, we present first results of the information that can be derived from a small seismic network in the Quesenbank site, a severely affected 12 ha patch in the Wormke headwater catchment on the southern slope of the Brocken towards the town of Schierke. In March 2024, we set up a triangular array of 4.5 Hz geophones with an aperture of about 100 m. We show successive changes in the response of soil moisture and deeper zone water dynamics to rainfall events and over multiple seasons. We use the array to detect and locate brief periods of seismic activity due to uprooting of trees and large branches falling off the dead trees, and compare the multi-seasonal evolution of event rates. We further inspect the state of coupling between atmosphere, biosphere and pedosphere by comparing meteorological time series and seismic ground response patterns.