Variability and Relationship Between Phenological and Morphological Traits in Early and Late Pedunculate Oak

Variability and relationship between phenological traits and leaf, acorn, and tree size morphometric traits were examined in early and late bud-flushing groups of the pedunculate oak population in the vicinity of Sremska Mitrovica, Serbia. According to the obtained three-year results, there were no significant differences in tree size and leaf morphometric characteristics between the early and late group. The effect of trees within phenological groups was statistically significant and considerable, especially in leaf blade width (lbw) and leaf area (la). Acorn length (acl) and acorn index (acinx) were significantly influenced by phenological group, achieving moderate contribution of phenological group to the total variation. There was a clear effect of phenological group on variation of examined phenological traits. The effect of year of monitoring on the same traits was not significant, but there was a clear effect of interaction between phenological group and year, especially in case of traits describing the period from bud swelling until the emergence of wrinkled leaves (f12a), unfolded leaves (f12b), and fully developed leaves (f12g) and their ratio with the period from 8 March until the emergence of wrinkled leaves: f12b/f02a and f12g/f02a ratio. Earlier phenology in warmer years is clearer in the early bud-flushing group than in the late one. Periods between different bud swelling and f12a, f12b, and f12g phenological phases were significantly shorter in 2017 (with a warm April) than in 2015 (with moderate temperatures in March and April) in the early group, but significantly longer in the late group. Examined traits were classified in six groups based on their factorial loadings with the first six principal components rotated by Varimax method, revealing strict distinction between traits by their original nature. In that sense, all examined groups of traits could be considered as informative in variability studies of pedunculate oak. The tree size traits (tree height and diameter at breast height) formed the separate, fifth group, suggesting no close relationship of these traits with any other examined characteristic. Both cluster analysis and PCA suggest distinct classification by trees' phenology, but also considerable differences by the second principal component which is closely related to leaf size characteristics. The research should be continued on variability between populations and progenies, especially with respect to phenological and acorn morphometric traits. Understanding the phenological variations between early and late oaks could be essential for designing robust forest adaptation management strategies.