Effects of forest harvesting operations on hydrology: Experiences from the Palatinate Forest Biosphere Reserve

Authors: TIGABU, TIBEBE - University Of California, Riverside; MULLER, EVA VERENA - Research Institute For Forest Ecology And Forestry Rhineland-Palatinate (FAWF); WAGNER, PAUL - University Of Kiel; Meles, Menberu; DAHLKE, HELEN - University Of California, Davis; SCHULER, GEBHARD - Federal Research Institute; FOHRER, NICOLA - University Of Kiel

Submitted to: Journal of Hydrology: Regional Studies
Publication Type: Review Article
Publication Acceptance Date: 3/11/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study assessed the hydrological impacts of forest harvesting in the Palatinate Forest Biosphere Reserve, focusing on soil compaction from skid trails and infrastructure pathways. The SWAT+ model simulated water flux changes across compacted skid trails (Scenarios 1) and pathways (Scenario 2) and uncompacted (Baseline) soils. To better capture groundwater-streamflow interactions, a two-layer shallow aquifer configuration was introduced, improving model accuracy. Results showed significant increases in surface runoff—74% in Scenario 1 and 125% in Scenario 2—along with a reduction in lateral flow by 14% and 26%, respectively. Steeper areas experienced more runoff, while flatter zones had greater reductions in lateral flow and percolation. These findings highlight the need to consider spatial factors and machinery type to reduce hydrological impacts during forest harvesting.

Technical Abstract: Forest harvesting significantly alters a catchment's hydrological regime due to soil compaction effects. While it is acknowledged that harvesting increases surface runoff and water yield, quantifying these effects remains challenging. This research aimed to explore how physically based hydrological models were suited for investigating the effects of soil compaction on hydrologic responses at the catchment scale. We employed a process-based SWAT+ hydrological model to assess the impact of temporary (e.g. skid trails) and more permanent timber harvest activities and infrastructure on the hydrologic response of the Palatinate Forest Biosphere Reserve in Germany. We specifically analyzed the impact of soil compaction on hydrological responses by simulating water fluxes under three scenarios: uncompacted soil as the baseline, compaction from harvest operations (Scenario 1), and compaction caused by infrastructure development (Scenario 2). Results showed substantial flux alterations under Scenarios-1 and -2 compared to the baseline. Annual average surface runoff increased by 74% and 125%, while lateral flow decreased by 14% and 26% under Scenarios-1 and -2, respectively compared to the baseline. Differences in water flux changes were noted between high and low slope areas. High slope areas exhibited larger runoff increases, while low slope areas experienced greater reductions in lateral flow and percolation. The results highlighted the need for forest harvesting strategies to account for spatial conditions and machinery types employed.