Background and Objectives: Mineral topsoil moisture is a very important component of the hydrological balance in forests. The moisture is closely related to the forest type, its woody species composition, stand age, and structure through interception and evapotranspiration. We aimed to investigate the topsoil moisture response to precipitation in three treatments: under young Norway spruce, white birch, and a grass-dominated treeless gap at an acidic mountain site in the Jizerské hory Mts., Czech Republic. The study was conducted in 18- to 21-year-old stands during four growing seasons. Materials and Methods: The analyzed parameters were: rainfall amounts measured by an on-site automated station, root penetration using a root auger, and soil moisture measured continuously using electric sensors, as well as derived parameters such as interception. Results and Conclusions: Even within small patches of the three treatments, soil water content was found to be higher under the gap vegetation compared to both tree species. In addition, the topsoil under spruce was significantly more saturated than under birch. The average growing-season interception capacity of birch, spruce, and the gap treatment ranged from 1.4 to 2.2 mm, 2.1 to 2.6 mm, and 1.2 to 2.2 mm, respectively. Soil moisture mostly decreased during periods of flushing and stabilized during the transitions from the growing to the dormant seasons. The seasonal effects were particularly obvious under the birch stand. The crucial factors decreasing topsoil water content under birch included both rooting depth and density, which may predispose preferential pathways for water infiltration. This validated white birch’s capability to decrease topsoil water content, which can be beneficial at secondary-waterlogged sites.

Hydromelioration networks aim to expand the vadose zones of waterlogged and peaty sites, which is expected to provide more soil space for trees’ roots, thus improving forest stand stability and production. However, the recent climate is manifested by increasing air temperatures, changed distribution of precipitation and frequent droughts. This raises the issue of the suitability of such measures. Additionally, the impacts on the ground water table (GWT) level, drainage, and forest health are disputed. This study deals with the behaviour of the shallow-aquifer GWT level in a formerly deforested headwater catchment named U Dvou louček (UDL) which had been monitored for 30 years and placed at a mountain site in north-eastern Bohemia, Czech Republic. GWT (84 m long transect with 22 probes), precipitation, throughfall, discharge, air temperatures and stand parameters were measured. Young Norway spruce stands now dominate within the UDL area. Average precipitation of the open area reached 1285 mm, and precipitation in years 2003, 2015 and 2018 was minimal (910 to 950 mm). Calibration of the GWT measurement took place in 1992–1995. After a 5-year stabilisation period in 1996–2001 with gradually falling GWT levels, following the digging of new ditches, the GWT no longer fluctuated significantly. The discharge and GWT change responses to stand growth were modest, and the impact of forest tending was limited. Lower GWTs in dry years were temporary. The inter-annual water levels in the immediate vicinity of the ditches fluctuated the least. The small-scale technical hydromelioration intervention neither had a negative impact on the GWT level, nor threatened the water supply of growing forest stands even in dry years. The results confirmed the long-term potential of such measures to improve the water regime of reforested clear cuts on waterlogged forest soils in mountains with a minimal risk of threat in warming environments.

Litter fall is an important part of nutrient cycle in forest ecosystems. Conifers are traditionally considered to be less-suitable nutrient cycling improvers and/or maintainers compared to broadleaves. Long-term observations plus information from both domestic and international publications showed an important role of conifers in process of accumulation and decomposition of the forest floor. Our results also show relations between litter fall and forest floor amounts due to thinning. From silviculture point of view, the knowledge of nutrient cycling is essential to optimize tree species composition using appropriate techniques for forest regeneration and thinning.

Clear-cutting removes a stand cover suddenly, thus impacting soil-surface conditions by the expected increase in the humus breakdown rate, due to the addition of more precipitation and solar radiation. The impacts of removing a forest were studied at a site with deep sandy soils dominated by Scots pine, where three treatments, including a stand left on site, whole-tree harvesting treatment, and stem-only harvesting treatment, were established. Clear-cut precipitation and sub-canopy throughfall were measured. The non-replicated treatments were equipped with lysimeters at depths of −10 cm and −70 cm and in addition, three exploratory wells were drilled to sample groundwater in each of the treatments. The volume and chemistry of the water samples were periodically analyzed. The mean throughfall was 84% of open-area precipitation and the pH of the water penetrating the canopy was significantly lower overall, although the subcanopy samples were only slightly more acidic. Significant differences among the treatments were shown in throughfall (total organic carbon, TOC), shallow subsurface water (pH, TOC, NO₃⁻), subsurface water at the 70-cm depth (NO₃⁻) and also groundwater (pH, TOC, NO₃⁻), where some of the differences had been observed before the stand parts were clear-cut. Limits for drinking water were exceeded in groundwater pH, as the values from both clear-cut sites fell below pH 6.5 following clear-cutting. TOC greater than 5 mg·L⁻¹ was found in the Q1-2020 samples, whereas groundwater nitrate remained low, even though the three wells differed significantly from each other. Due to the non-replicated design of the experiment, generalization of the outcomes is a matter of further research.