The Ore Mountains were historically one of the most polluted areas in Europe, where high sulphur dioxide concentrations and a high level of atmospheric deposition led to a vast decline in Norway spruce stands in the mountain ridge plateau. In this article, we evaluate the trends in the atmospheric deposition load, soil chemistry, tree nutrition, crown defoliation and height increment in a network of twenty research plots monitored for last thirty years in this region. The decrease in sulphur and nitrogen deposition was most pronounced at the end of 1990s. Extreme values of sulphur deposition (100-200 kg.ha-1.year-1) were recorded in throughfall under mature Norway spruce stands in the late 1970s, and after felling of the damaged stand, the deposition levels were comparable to open plot bulk deposition. Nitrogen deposition decreased more slowly compared with sulphur, and a decrease in base cation deposition was observed concurrently. The current deposition load is low and fully comparable to other mountain areas in central Europe. Accordingly, the health of young spruce stands, as assessed by defoliation and height increment, has improved and now corresponds to the Czech national average. On the other hand, no significant changes were observed in the soil chemistry, even though some of the plots were limed. Acidic or strongly acidic soil prevails, often with a deficiency of exchangeable calcium and magnesium in the mineral topsoil, as well as decreases in available phosphorus. This is reflected in the foliage chemistry, where we see an imbalance between a relatively high content of nitrogen and decreasing contents of phosphorus, potassium and calcium. Despite the observed positive trends in air quality and forest health, the nutritional imbalance on acidified soils poses a risk for the future of forest stands in the region.

This article is part of the search for alternatives to the use of pesticides (especially elicitors of resistance) within the context of integrated pest management (IPM). For this reason, resistance triggers based on potassium phosphite were used in the form of oak stem spraying. The aim of the study was to assess the influence of phosphites applied as a commercial product called Kalex. The changes in the immediate environment and the development of root systems and tree crowns (based on defoliation and health indicators) were assessed. The treatment of oak stems with potassium phosphite had no negative effects on the forest environment. The acidity (pH) of the soil did not change nor did the content of Mg and Ca. Phosphorus and potassium from the treatments were taken up by the living part of the bark and transported to the fine roots. However, some of the treatments certainly entered the soil via the logs when it rained. Thus, these elements also reached the vicinity of the roots, where they were present in larger quantities. As a result of leaf loss (defoliation), the crowns of the control trees were more thinned out than those of the trees treated with the phosphite preparation. Over several years, this led to a decrease in the health of the control trees, i.e. a change in the crown architecture (deformation due to the formation of short shoots) expressed in vitality grades. The calculated synthetic damage index (Syn), which takes into account the degree of defoliation and health, was also higher in the control trees than in the treated trees indicating the effectiveness of the treatment with the commercial product Kalex. The fine roots of the treated oaks had more favourable development parameters than the corresponding roots of the control trees especially in terms of length, number and surface area. This increased the ability of the treated oaks to take up the water needed to increase photosynthetic efficiency in order to feed the roots. However, in a situation of extreme drought in 2015 resulted in the death of the fine roots of the oaks (independent of the treatment) and continued the following year. Only in the 2017 season, when soil moisture improved significantly, did the oaks return to the state of root development before the severe drought. As a result, the percentage of dying trees in the treated tree group was statistically lower than in the control group. The treated oaks (especially those that were up to 30% defoliated) survived better during the five-year observation period (2013-2017) and were able to effectively absorb nutrients and water from the soil due to the better condition of their fine roots which was reflected in better shoot development in the crowns (assessed by defoliation, vigour and Syn-index).

An extensive discoloration (yellowing, browning), and defoliation (leaf loss) were observed in Slovak forests during the summer of 2022. These phenomena are attributed to the combination of very low atmospheric precipitation and extremely high air temperatures from June to early August. In this study, the deterioration of forest health was analysed by comparing the image classification of Sentinel-2 satellite data from the year of intense drought occur-rence, 2022, with that from a referenced year without drought occurrence, 2020. The results indicated that in 2022, the proportion of heavily damaged stands with defoliation exceeding 50% doubled, reaching 19.3% (417,000 ha), and an area of 223,000 ha experienced an increase in defoliation by 30% or more. The damage exhibited an uneven spatial distribution, with the most significant impact observed in the western and southern parts of central Slovakia, as well as partially in the southern part of eastern Slovakia. Further GIS analyses revealed that forests growing on slopes with southern aspects suffered more severe damage than with northern exposures. However, the difference between the most damaged forests with south-southeast exposure (12.2%) and the least damaged ones with north-northwest exposure (8.2%) was only 4%. The level of damage gradually decreased with increasing altitude. Nevertheless, compared to previous studies, the damage was significantly manifested even in the fourth forest vegetation zone, up to an elevation of approximately 800 m. Regarding soil texture, which influences the water regime, the damage gradually decreased with decreasing sand content, ranging from sandy soils (17.5%) to clayey soils (6.6%).