ABSTRACT:We documented the current typological and phytosociological characterisation of the ground vegetation as an essential component of biodiversity in 154 Czech forest monitoring plots and to describe its changes during the past 15 years in regard to the deposition and concentration of nitrogen in the soil. Plots were classified as vegetation units in accordance with the UNECE and FAO nomenclature and on the basis of their potential natural vegetation and compared in terms of the occurrence and coverage of the indicative selected nitrophilous species. In all the soil horizons tested statistically significant differences in the C/N ratio were observed between areas with and without the presence of certain selected nitrophilous species (Geranium robertianum, Impatiens parviflora, Sambucus nigra, Urtica dioica). In the areas with the presence of the Geranium robertianum and Urtica dioica species, statistically significantly higher concentrations of nitrogen were recorded in some soil horizons than in those areas with the absence of these species. The findings concerning the influence of nitrogen on nitrophilous herbaceous indicators were compared with the European results obtained in the framework of the ICP Forests international programme and with those of other foreign studies.

In recent years, the Czech part of the Silesian Beskids has been affected by strong yellowing of Norway spruce stands and gradual decline of individual trees. Similar damage has also been observed in the neighbouring parts of Poland and Slovakia. The article presents the results of an investigation in the Forest District Jablunkov – part Nýdek. To evaluate the situation, monitoring plots were established and a regional survey was carried out together with tree-ring analysis. The results show a mosaic distribution of damage in the region studied, independent of the altitude and forest type. Defoliation was lower in 20–40 years old stands. Even these young classes, however, show yellowing symptoms. The decline of stands started to be visible at the end of the 1990s; significant loss of vitality was observed in the most affected stands in 2003, after an extremely hot and dry vegetation period. Actual development of meteorological conditions plays an important role in the stand damage. Lastly, possible causes of damage and further development are discussed.

Because of climatic variability that has been increasing in last decades a higher drought risk seriously influences the forest vitality from regional to global scale. Despite there are of many studies that describe the spectral response of forest stands to the water stress, there is still a lack of information concerning the full understanding of forest reaction to the water deficiency over a longer time period. We hypothesize that the various severity and/or frequency of drought periods will result in different spectral responses of forest stands. The forest response was detected using two spectral vegetation indices (normalized difference moisture index – NDMI, wetness) which are widely used for the detection of forest health changes. These indices were calculated on the basis of Landsat (TM, ETM+ and OLI) imagery which includes 105 scenes from the 2005–2016 period. The area of our interest includes 300 forest stands (dominated with Norway spruce) in the Czech Republic, Moravia. These stands were identified as damaged by drought that occurred during the 2012–2017 period. To document the climatic water deficiency, two climatic indices were calculated (AWBPE, standardized precipitation evapotranspiration index). Despite high correlation of both spectral indices, the NDMI has high sensitivity to the drought events. However, both indices significantly decreased in reaction to the drought events. In case of the 2012 drought event the decrease was one year delayed, probably due to the lower severity of drought effect. The both groups of spectral and climatic indices bring valuable information in regard to the description and understanding of drought effect on the spruce forest stands.

As a part of International Cooperative Programme on Assessment and Monitoring of Air Pollution Effect on Forests (ICP Forests), defoliation of forest stands has been assessed in the Czech Republic since 1986. Defoliation is one of the principal parameters reflecting the health of forest stands that is assessed on monitoring plots within this programme. Monitoring plots are distributed evenly according to woodiness of the area in a regular schematic network all over the Czech Republic. Even though there has been a long-term reduction of air pollution in most European countries, forest ecosystems reflect these changes with some delay. In the Czech Republic the trend of total defoliation of coniferous and deciduous forest stands has been increasing very moderately in the last 10 years. This trend appears to be partially analogous with some neighbouring countries. Compared to the whole of Europe the trend of defoliation of broadleaves is very similar, but differences have occurred in conifers in the last 10 years. There are significant differences in defoliation levels among the particular countries; in this comparison the Czech Republic is classified as one of the worst. Differences in these levels are very evident especially among the neighbouring countries. To partly eliminate these differences, regular international calibration courses are organized.

Interception, soil moisture and soil water potential were observed in four Norway spruce stands of different age in two subsequent vegetation seasons 2017 and 2018. Vegetation season 2018 can be characterized as being abnormally hot and dry with only 66% of precipitation in comparison with normal conditions. The interception of spruce increased with the stand age and its dimensions, ranging between 16 and 48% in 2017 and in the majority of stands even increasing in 2018. The soil moisture significantly decreased during the vegetation season 2018, with soil water potential close to the permanent wilting point (–1.5 MPa) for a substantial part of the monitored period. Differences between individual stands were observed in terms of the soil water potential (SWP) development which does not follow the interception patterns suggesting that the stand transpiration is a driving factor responsible for the soil water budget. In all stands, with the exception of the oldest one, the SWP of the upper soil horizon was less than 1.5 MPa for more than 80 days. In such extreme conditions the drought would negatively influence any Norway spruce stand regardless of its age or structure.

Forest soils have a high potential to store carbon and thus mitigate climate change. The information on spatial distribution of soil organic carbon (SOC) stocks is thus very important. This study aims to analyse the importance of environmental predictors for forest SOC stock prediction at the regional and national scale in the Czech Republic. A big database of forest soil data for more than 7 000 sites was compiled from several surveys. SOC stocks were calculated from SOC content and bulk density for the topsoil mineral layer 0–30 cm. Spatial prediction models were developed separately for individual natural forest areas and for four subsets with different altitude range, using random forest method. The importance of environmental predictors in the models strongly differs between regions and altitudes. At lower altitudes, forest edaphic series and soil classes are strong predictors, while at higher altitudes the predictors related to topography become more important. The importance of soil classes depends on the pedodiversity level and on the difference in SOC stock between the classes. The contribution of forest types as predictors is limited when one (mostly coniferous) type dominates. Better prediction results can be obtained in smaller, but consistent regions, like some natural forest areas.

Soil properties and foliar chemistry of Douglas-fir stands were evaluated in four regions with historical cultivation of this introduced species in the Czech Republic. All the localities are on acidic sites with pH (KCl) ranging between 4 and 5, low in concentrations of base cations particularly at the soil depth between 10 and 40 cm and also low in phosphorus. Sufficient to increased content of nitrogen and, on the other hand, the deficiency of phosphorus, potassium and occasional deficiency of magnesium were found in foliage. Studied Douglas-fir stands are apparently proximate to the acidic limit of convenient site conditions, however, neither the foliage discoloration nor the growth suppression has been observed. Sensitive management to ensure the nutritional balance sustainability is proposed.

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