The condition was evaluated of tissues of declining young spruce stands in selected localities of the Orlické hory Mts. It refers to stands occurring in top parts affected by an air pollution disaster in the last century. Several types of damage of a different symptomatic character were distinguished. A high NO x input appears to be the risk factor of spruce dieback in the Orlické hory Mts. One of the main causes in the complex of factors is the unbalanced cause of meteorological factors during the year and unbalance in mineral nutrition. The result is decrease in lignification, imma-turity of tissues before the winter period and increased susceptibility of damaged tissues to parasites. Several potentially pathogenic species of micromycetes have been identified which can be considered to be significant pathogenic agents in case of declining spruce in the Orlické hory Mts., however, not a main cause. Fytopatologické a histologické aspekty chřadnutí smrku v Orlických horách M. ČERMÁK, M. MARTINKOVÁ, D. PALOVČÍKOVÁ, L. JANKOVSKÝ Lesnická a dřevařská fakulta, Mendelova zemědělská a lesnická univerzita v Brně, Brno, Česká republika ABSTRAKT: Hodnotili jsme stav pletiv chřadnoucích mladých smrčin na vybraných lokalitách Orlických hor. Jedná se o porosty ve vrcholových partiích, které byly postiženy imisně ekologickou kalamitou v minulém století. Bylo rozlišeno několik typů poškození s odlišným symptomatickým obrazem. Rizikovým faktorem chřadnutí smrku v Orlických horách je vysoký vstup dusíku NO x. Za jednu z hlavních příčin v komplexu faktorů je možné označit nevyrovnaný průběh meteorolo-gických prvků během roku a disbalanci minerální výživy. Důsledkem je snížená lignifikace, nevyzrálost pletiv před zimním obdobím, zvýšená vnímavost poškozených pletiv vůči parazitickým organismům. Bylo identifikováno několik potenciálně patogenních druhů mikromycet, které mohou být považovány za významný patogenní agens v případě chřadnutí smrku v Orlických horách, nikoli však za hlavní příčinu.

Mountain forests are strongly influenced by the extreme climate, short growing season and stress from environmental pollution and lower fertility of soils. The paper analyses the effect of the environment (climate and air pollutants) on the structure, production and dynamics of autochthonous spruce-beech forest stands in protected areas in the summit parts of the Orlické hory Mts., Czech Republic. The spatial pattern of tree layer was random in lower parts below the summit and aggregated under the hilltop phenomenon on an extreme edaphic site, such as aggregated horizontal structure of natural regeneration. In most cases, the relationship between the spatial pattern of tree layer and natural regeneration was significantly negative (α = 0.05) at a smaller distance (from stem to 0.6-6.1 m) except stands under the strong hilltop phenomenon (positive effect to 2.1 m). The stand density ranged from 440 to 760 trees ha -1 and the number of natural regeneration was 4 584-6 360 recruits ha -1. Dominant height decreased with increasing influence of hilltop phenomenon (P < 0.001). The volume of live trees was 239-536 m 3 ha -1. The radial growth of dominant European beech (Fagus sylvatica L.) indicated a relatively balanced long-term trend of tree-ring width in 1900-2014, but diameter increment of admixed Norway spruce (Picea abies /L./ Karst.) after 1978 significantly decreased (P < 0.001) and since 1998 radial increment in spruce distinctly increased. Radial growth of spruce was significantly negatively correlated with mean SO 2 and NO X concentrations, especially in April (P < 0.001), but there was no effect on radial growth of beech. Air pollution had a significantly higher negative effect on radial growth of spruce on the hilltop compared to the lower part of the hill. The correlation between radial increment and temperature was stronger than in precipitation for both species in mountain areas compared to lowlands. The hilltop phenomenon significantly influenced the structure of spruce-beech mountain forests. The lowest dynamics was observed in stands in middle slope parts compared to summit parts of the hill.

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The negative effect of air pollution on mountain spruce stands culminated in the 70s – 90s of the 20th century, when an extensive dieback and disturbance of stands occurred in the Krkonoše Mts., the Czech Republic. Dendrochronological analysis was used on ten permanent research plots established in 1976–1980 to document the dynamics of radial increment of Norway spruce (Picea abies [L.] Karst.). The objective was to determine the effect of SO2, NOX and O3 concentrations and precipitation and temperatures on spruce radial growth in climax forests, waterlogged forests and cultivated forests. The results document the strong depression of diameter increment in the period 1979–1991 caused by synergism of climatic extremes and high SO2 pollution in the 80s and 90s of the 20th century. After 2000 climate had prevailing effect on radial growth. Spruce increment was in positive correlation with temperature, particularly with temperature in the growing season and annual temperature of the current year. In general, temperature had a more significant effect on increment than precipitation, mainly in climax and peaty spruce stands. Diameter increment was in significant negative correlation with SO2 and NOX concentrations in all types of stands. Overall, peaty spruce stands were the most vulnerable to air pollution stress. Low radial increments were caused also by climate extremes, historically by strong frosts and winter desiccation in early spring, nowadays in time of climatic changes by extreme drought. Spruce stands have the ability of quickly responding by tree-ring width to both negative and positive impulses related with air pollution and climate.

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