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Height to crown base (HCB) of a tree is an important variable often included as a predictor in various forest models that serve as the fundamental tools for decision-making in forestry. We developed spatially explicit and spatially inexplicit mixed-effects HCB models using measurements from a total 19,404 trees of Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) on the permanent sample plots that are located across the Czech Republic. Variables describing site quality, stand density or competition, and species mixing effects were included into the HCB model with use of dominant height (HDOM), basal area of trees larger in diameters than a subject tree (BAL- spatially inexplicit measure) or Hegyi’s competition index (HCI—spatially explicit measure), and basal area proportion of a species of interest (BAPOR), respectively. The parameters describing sample plot-level random effects were included into the HCB model by applying the mixed-effects modelling approach. Among several functional forms evaluated, the logistic function was found most suited to our data. The HCB model for Norway spruce was tested against the data originated from different inventory designs, but model for European beech was tested using partitioned dataset (a part of the main dataset). The variance heteroscedasticity in the residuals was substantially reduced through inclusion of a power variance function into the HCB model. The results showed that spatially explicit model described significantly a larger part of the HCB variations [R2adj = 0.86 (spruce), 0.85 (beech)] than its spatially inexplicit counterpart [R2adj = 0.84 (spruce), 0.83 (beech)]. The HCB increased with increasing competitive interactions described by tree-centered competition measure: BAL or HCI, and species mixing effects described by BAPOR. A test of the mixed-effects HCB model with the random effects estimated using at least four trees per sample plot in the validation data confirmed that the model was precise enough for the prediction of HCB for a range of site quality, tree size, stand density, and stand structure. We therefore recommend measuring of HCB on four randomly selected trees of a species of interest on each sample plot for localizing the mixed-effects model and predicting HCB of the remaining trees on the plot. Growth simulations can be made from the data that lack the values for either crown ratio or HCB using the HCB models.

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.