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ŠUMARSKI LIST 7-8/2020 str. 31     <-- 31 -->        PDF

(Stjepanović et al., 2018), Italy (Piovesan et al., 2005) or Serbia (Stojanović et al., 2018). Favourable May temperature initiate cambium activity and radial growth can start. Contrary, below average temperature in May negatively influences tree growth and hinder cambium development which leads to narrower radial increments in particular year (Dulamsuren et al., 2016, Zimmermann et al., 2015). According to our study precipitation is less critical for beech growth at the Medvednica massif, this could be mainly because precipitation is sufficient for the growth of beech and temperature is not so high that lower amount of precipitation would lead to serious occurrences of drought, this finding is in accordance with Prislan et al. (2018) who found similar lack of response in beech in Slovenia.
Similar to other indicators of vitality such as defoliation or foliar composition, radial growth of trees is an integrative variable of tree response (Seidling et al., 2012). Studies on growth of beech show that it is strongly drought limited (Jump et al., 2006). Several authors state that tree ring width is frequently smaller during years following a severe drought (Le Dantec et al., 2000, Battaglia et al., 1998), but we found no evidence in our data that would support this. Rather, radial growth was linked solely to temperature variables, possibly revealing the shortcomings of an intensive case study in comparison with a study based on a larger number plots with diverse conditions.
The core of our interest was, however, in disentangling the relations of growth and other vitality indicators. Only a few authors report on the relationship between tree growth and defoliation, and the patterns are not always uniform (Dittmar et al., 2003, Rybníček et al., 2015). Often the studies relating crown condition and tree growth suffer from the fact that the data is provided from different groups of trees and therefore is plot-related rather than tree-related (Seidling et al., 2012). We used the same trees for tree-ring analysis and for defoliation assessments, which enabled us to make direct comparisons. Despite our sampling strategy, we did not record any significant relationship between radial growth and defoliation. This could be explained by a very narrow range of defoliation values on our plot, since several authors reported on the relationship between radial growth and defoliation but using a wide range of defoliation values in their studies. Solberg (1999) found considerable growth depressions for Norway spruce already at slight levels of defoliation, and Drobyshev et al. (2007) reported that radial increment of oaks in Sweden was highest in trees with healthy crowns. Information on the relation of radial growth and defoliation for common beech is largely missing, Seidling et al. (2012) state that increment and crown defoliation represent only partially the C allocation or C assimilation of a tree, hence a functional relationship of these parameters might not exist. However, Bréda et al. (2006) found that severe and long drought produced stress symptoms (premature leaf fall, yellowing), resulting in large number of individuals being in a weakened condition, with low radial growth. Dittmar and Elling (2007) related decreasing increment of beech in Switzerland to defoliation, suggesting that increment decline preceded crown decline. Our study, however, could not confirm this conclusion, even when taking into consideration various combinations of current and previous year observations.
 The relation of growth and tree nutrition has also been extensively studied, mostly in studies dealing with characterization of forest soil productivity or stand fertilization/liming experiments (Fox et al., 2007, Sikström, 2002) with varying results. Improved nutrition is reported to have a positive effect on tree vitality and growth in some studies (Mohamed et al., 1993, Van Praag and Weissen, 1976). Similarly, several studies (Spohn et al., 2018, Yang et al., 2016) found that beech has a high metabolic flexibility to cope with low soil P stocks by growth adjustment. However we can expect long-term negative effects of prolonged drought (enhanced vulnerability to stresses, reduced growth) on beech trees, as the effects of low P are similar to drought-induced decreased stomatal conductance (Zavišić and Polle, 2018). Nys (1989) found that the addition of CaCO3 had a positive effect on the nutrition, defoliation and increment of beech in the French Ardennes. While liming in Belgian Ardennes improved foliar Ca and Mg status of beech trees and significantly limited the decline in crown condition triggered by the summer drought in 2003, it had no effect on basal area increment (Jonard et al., 2010). Compared to fertilization experiments, the analysis of naturally occurring mineral foliar concentrations is more demanding in that the differences in nutrient status are smaller and more difficult to detect. In our study K concentrations correlated to residual tree ring chronology, although this relation was not particularly strong. It is unlikely that this is due to any direct negative K effect on growth, but rather shows the elevated uptake of K and restricted uptake of Ca in hot and dry years. This is important because Ca has a direct influence on the capacity of plants to regulate the intensity of transpiration (Berkowitz, 1998) and tree water deficits can reduce radial growth as well as bud production (Bréda et al., 2006). Therefore, although we could not relate radial growth to precipitation directly, there is some evidence of indirect linkages of nutrition, growth and defoliation patterns.
In this study, we were able to determine that high maximum temperature variables of current year early spring and summer months, as well as previous year summer months caused an increase of defoliation. Low precipitation during