Influence of forest dieback on the overland flow and isotopic composition of precipitation

Small mountain catchments in the highest part of Slovakia are undergoing significant forest changes related to windfalls and bark beetle infestations and resulting forest dieback, wood removal at some places and subsequent natural regeneration or reforestation. Natural forest changes started after 2010 also in the Jalovecký Creek catchment (The Western Mountains, area 22.2 km 2 , mean altitude 1500 m a.s.l.). Coniferous forest dominated by the Norway spruce, that used to cover 44% of catchment area consequently dries, the trees defoliate, break after some time and the natural regeneration starts. These changes affect also the hydrological cycle, e.g. interception, snow cover, water infiltration to the soil and runoff formation. We present the first results of the overland flow measurements in the alive and dead forest in summer season 2021 (June to September) and compare the isotopes of oxygen and hydrogen in precipitation and soil water. The results show that the overland flow in the forest is not uncommon, although it constitutes only several per cent of the rain. About a half of 55 rainfall events registered in the open area resulted in the overland flow in the forest (21–30 events at different sites). The overland flow represented on average 4% to 7% of the open area rainfall, but maxima for individual events exceeded 10%. Throughfall in the alive forest was isotopically heavier than the open area rainfall and dead forest throughfall. Isotopic composition of the soil water was distinctly different from precipitation until the mid-July, documenting the influence of the snowmelt water.