The aim of the study was evaluation of clear-cutting effect on water regime in a tree harvesting area. The results were made based on the study carried out in the Rakowski Ditch catchment, in Wielkopolska lowland in Poland. It was found that a more useful method to establish the effects of clear-cutting is to compare the groundwater level (GWL) in the post-clear- cutting area with that in a control area than to analyse the GWL changes in the same area before and after the clear-cutting. Regression analysis is a particularly useful tool in groundwater regime analyses. The results obtained in this study indicated that the groundwater regime changes in the post-clear-cutting area that were manifested as an increase in the mean GWL. The major changes in the groundwater regime after clear-cutting were observed in the minimum levels, while the lowest changes took place in the maximum GWL. The variation in GWL was higher in the period after clear-cutting than in the period before it. The analysis of linear regression of GWL in the well located in the clear-cutting area and that in the control area confirmed the change in the groundwater regime in the post-clear-cutting area. Stronger relations in the period before clear-cutting were observed.

Keywords: clear-cutting, groundwater, forest catchment, swampy habitats