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ŠUMARSKI LIST 7-8/2022 str. 40     <-- 40 -->        PDF

two needle traits contributed to the separation of the populations Zlatar and Dubočica. The highest mean values of the same needle traits contributed to the separation of the populations Tara and Osogovo, as well as the CMD values that were considerably higher than in the other populations (364 and 298; respectively). The NL vector was the shortest, which indicated that it was poorly described by the first two principal components and had less effect on population separation compared to the other two morphological needle traits (Figure 3).
Three clusters could be observed according to the agglomerative hierarchical clustering (AHC) analysis of the morphological needles traits of 16 silver fir populations (with a dendrogram cut at 0.076 Euclidean distances) (Figure 4). One cluster consisted of the two groups of populations: Stara planina, Goč, Osogovo and Tara (with NL > 2.67 cm, lower IDM values < 50 and higher values of CMD), and Hajla, Kovač, Kopaonik, Golija and Javor (NL > 2.50 cm, the indices did not stand out in values compared to other populations). Dubočica population had the lowest mean values (for example NL = 2.08 cm, NW = 0.15 cm and NT = 0.03 cm) of the analyzed traits, although none of the climatic factors differed significantly relative to the other populations. Other populations formed the third cluster with two subclusters according to the NL values: Pohorje, Lisina, Pirin, Zlatar, Romanija and Rila populations had less values (NL < 2.50 cm and CMD values < 72, and IDM values > 63) compared to the populations from the other cluster (Figure 4). Optimal classification of the analyzed populations into homogeneous groups - clusters was obtained on the basis of the large differences between (75.64%) and within (24.36%) homogeneous groups.
Tree populations continuously face new and rapidly changing selective pressures, such are more frequent extreme droughts that threaten the conservation of forest ecosystems (Lindner et al. 2010; Griesbauer et al. 2021). Since the global warming has caused water shortages and high temperatures in recent decades, the genetic diversity remains one of the most important factors that contribute to species adaptability (Thompson et al. 2009; Sánchez-Velásquez et al. 2021). Forest degradation leads to a reduction in population size that may lead to a reduction in genetic diversity in the next generation (Leimu et al. 2006). Reduction of forest areas, caused by drought, happens more often at the southern borders than in the center of the species distribution according to the biogeographic distribution scale (Hampe and Petit 2005; Jump et al. 2009). Numerous studies of interpopulation and intrapopulation (genetic) variability enable the understanding of differential responses of tree populations to drought stress (Allen et al. 2010).