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Shen, M., S. Piao, N. Cong, G. Zhang, I.A. Jassens, 2015: Precipitation impacts on vegetation spring phenology on the Tibetan Plateau. Glob. Chang. Biol., 21(10): 3647-3656.
Sogaard, G., O. Johnsen, J. Nilsen, O. Junttila, 2008: Climatic control of bud burst in young seedlings of nine provenances of Norway spruce. Tree Physiol., 28: 311-320.
Stener, L.G., 2013: Clonal differences in susceptibility to the dieback of Fraxinus excelsior L. In southern Sweden. Scandinavian Journal of Forest Research, 28, 3: 205-216.
Temunović, M., 2013: Utjecaj ekoloških čimbenika na genetičku varijabilnost poljskog jasena (Fraxinus angustifolia Vahl, Oleaceae), Disertacija, Prirodoslovno-matematički fakultet, ­Zagreb.
Narrow-leaved ash (Fraxinus angustifolia Vahl) is a hygrophilic and predominantly thermophilic tree species that favours deep, clayed and moist soils exposed to occasional seasonal flooding. The largest complexes of narrow-leaved ash (80 %) are located along the Sava river. In the context of global climate change, it is important to know the composition and structure of genetic variability, particularly in terms of adaptive potential such as growth, survival and leaf phenology. The goal of research was to analyze the beginning of the leaf unfolding phase (L2 phase), the duration of leaf development (L2 – L6) and the impact of atmospheric parameters on the beginning of leaf unfolding, as well as to determine intrapopulation and interpopulation variability and the existence of ecotypic forms in relation to the beginning of leaf unfolding. Phenological characteristics of leaf phenology of narrow-leaved ash were monitored in the clonal seed orchard of Nova Gradiška in the course of three years of research (2012, 2014 and 2015). Monitoring included 42 clones originating from three populations (Jasenovac, Novska and Stara Gradiška). Every clone was represented with four ramets each (in total 168 plants). Leaf development was divided into six phenophases (figure 2, table 1); the analysis focused exclusively on Phase L2 (beginning of leaf unfolding). The average number of days from January 1st to the beginning of leaf unfolding was 98 days in 2012, 93 days in 2014, and 103 days in 2015 (figure 3, table 2). The average number of days required for leaf development amounted to 27 days in 2012, 26 days in 2014 and 20 days during 2015. Based on phenological results throughout the three years of study, the clones were divided into two ecotypic forms (early and late) with regard to the beginning of flushing (figure 5, table 4). The justification of division into two forms was statistically confirmed (table 3). The average values of the number of days for early ecotypic forms ranged from 90 to 101 days, and for late forms from 99 to 107 days. Along with temperature requirements as the most crucial activating factor in the manifestation of leaf pheno­logy, researche also confirmed high correlation between cumulative values of precipitation quantity (from December 1st to the beginning of Phase L2) and the beginning of leaf unfolding in narrow-leaved ash (r=0,93). Statistically significant differences were found between all the studied clones, and so were for intrapopulation variability for the beginning of leaf unfolding; however, no statistically significant differences were found between the studied populations (table 3). Intraclonal values of the coefficient of variability (CV %) for the property of leaf unfolding decreased with the age of the experiment and on average amounted to 15.22 % at age 2 + 8 years, 13.46 % at age 2 + 10 years, and 7.8 % at age of 2 + 11 years, indicating higher stability and uniformity of phenological characteristics among the ramets as their age increased (figure 4). The affiliation of the clones to ecotypic forms did not coincide with their geographic origin, which additionally confirmed important intrapopulation variability of narrow-leaved ash.
KEY WORDS: narrow-leaved ash, leaf unfolding, precipitation, intrapopulation and interpopulation variabi­lity, intraclonal variability, early and late ecotypic forms