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ŠUMARSKI LIST 7-8/2020 str. 23     <-- 23 -->        PDF

Meteorological data – Meteorološki podaci
We used climate data from E-OBS gridded dataset (Haylock et al., 2008). Values were extracted using R statistical environment (R Core Team, 2016) with “raster” (Hijmans, 2016) and “rgdal” (Bivand et al., 2017) packages. From the daily dataset we calculated mean monthly temperature (mt), mean monthly minimum temperature (min_m), mean monthly maximum temperature (max_m), absolute monthly minimum temperature (min_a), absolute monthly maximum temperature (max_a), and monthly sum of precipitation (pr). Furthermore, we calculated the quantile range of the central 90% region (0.95–0.05 quantile) of monthly maximum and minimum temperatures (max_Q and min_Q) to investigate the influence of extreme temperature variability on vitality indicators, our assumption being that increased variability of monthly extreme temperatures induces physiological stress that can be detected through vitality indicators. This dataset was also used to generate Standardised Precipitation Index (SPI) and self-calibrating Palmer drought severity index (scPDSI), which are standard indices for quantifying and reporting meteorological drought. Standardised Precipitation Index (McKee et al., 1993) was calculated for the period 1951-2008 on a time scale of three months. To calculate SPI and scPDSI we used R programming environment and package “SPEI” (Beguería and Vicente-Serrano, 2017) and “scPDSI” (Ruida et al., 2018), respectively. Values of SPI above 2 indicate extremely wet conditions, under -2 extremely dry conditions, and normal conditions range from 0.99 to -0.99. Values of scPDSI lower than - 1 indicate moderate drought while values lower than -2 indicate severe drought.
Defoliation assessment – Procjena osutosti
Defoliation of sample beech trees on the plot was assessed annually according to the ICP Forests Manual (Eichhorn et al., 2016) in the period 1996-2007. The same two observers performed assessments in late August/early September. Each year 45 trees were assessed but only 29 beech trees that were assessed every year in this period were used in the sample.
Sampling and chemical analysis of foliage – Uzorkovanje i kemijska analiza biljnog materijala
Each year the same five trees were sampled from 1997 to 2007. Samples were taken from the upper third of the crown in mid-September. Collected samples were combined in the laboratory based on equal dry mass. Samples of foliage (100 leaves per sample) were dried at 105 °C, ground and analysed for total nitrogen (N) content at Leco CNS 2000 analyser (ISO-13878, 1998). The analysis of other elements content required sample drying, grinding and wet digestion. Phosphorus (P) was determined on UV/VIS spectrophotometer PE Lambda 1A, potassium (K) on flame photometer Eppendorf and calcium (Ca) and magnesium (Mg) by atomic absorption spectroscopy on Perkin-Elmer Aanalyst 700 (Rautio et al., 2016).
The established procedure for the interpretation of foliar analysis is based on the comparison of element concentrations with limit values as according to Raitio (1993). For evaluation of foliar nutrient concentrations, we compared them to the critical values statistically derived from van den Burg’s literature compilation which are close to a general optimum range, indicating health and intact resistance mechanisms of these tree species (Mellert and Göttlein, 2012).
Tree-ring measurements – Izmjera širine godova
We collected cores from all 29 beech trees that were assessed for defoliation in autumn 2007 (last fully formed ring was in 2007). Each core was mounted and sanded to a high polish