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|ŠUMARSKI LIST 9-10/2015 str. 29 <-- 29 --> PDF|
Spreading more up to north in relation to other European species of elm trees, the wych elm (Ulmus glabra Huds.) is a very valuable, noble hardwood species, taxonomically determined within Ulmaceae family. Given the optimal habitat conditions, U. glabra is related to the hill and mountain areas, so that it occures at sites up to 1500 meters above sea level. From phytosociological point of view, it is a typical member of the zonal, mesophilic and rarely of the thermophilic beech forests, likewise it is a characteristic species in azonal communities of Tilio platyphylli-Acerion pseudoplatani alliance.
The devastation of the natural habitat, stimulated by conversion of forest into agricultural land, as well as the sudden change of climate parameters through the process of global warming, pose a great threat to the stability of elm genetic resources. In the last hundred years elms have been faced with the Dutch elm disease pandemics, which resulted in mass yellowing of adult trees of all indigenous European elm species, especially U. glabra and U. minor. Consequently, emphasis of contemporary elm research is on quantification of genetic variability of natural elm populations and selection of hardy trees, in order to develop basis for the Dutch elm disease tolerant clones production.
It should be stressed that in Croatia, the wych elm has not been subject to scientific studies to date. In this research inter-population and intra-population morphological variability of foliar traits in natural populations of the wych elm from Mountainous Region of Croatia has been determined.
Material for the morphometric analysis was collected in four natural populations in the Mountanious Region of Croatia (Figure 1). Each population was represented by 5 trees and each tree by 30 healthy and undamaged leaves, collected from short fertile shoots of the outer, light-exposed part of tree top. The leaves were scanned and measured by the Image J programme. Ten foliar traits were defined and measured altogether (Figure 2).
The measured morphological traits were shown through descriptive statistical parameters. For determining the intra-population and inter-population variability, the univariate analysis of variance was used. For determining similarities or differences of analyzed populations on the basis of measured morphological leaf traits, multivariate statistical method – cluster analysis was used. These statistical analyses were conducted using the statistical programme STATISTICA 8.0
The results of the descriptive statistical analysis are given in Table 1, by population. According to the analysis of variance, trees within populations differ significantly on all analysed traits (Table 2). Populations differed significantly for variables: PMPW, AI, BL, LA, OL. Correspondingly to Fischer LSD-tests, all observed populations, except Delnice – Vrbovsko and Delnice – Otočac, showed significant differentiation for leaf area (LA) trait. Significant difference in blade length (BL) was confirmed for Vrbovsko – Gospić and Otočac – Gospić population pairs (Table 3). According to partitioning of variance, differences among trees in a single population accounted for the most of variability determined, while the remaining component, the amount of variation attributable to differences among populations proved to be considerably smaller (Table 4). UPGMA dendrogram elucidated that according to the researched leaf traits the most similar populations were Delnice and Vrbovsko, followed by population Otočac. These three populations formed a cluster, succeeded by the most distant population Gospić (Figure 3). The southernmost and geographically most distant population Gospić was morphologically significantly different from the other three populations, that was particulary observable in relation to Delnice and Vrbovsko population.
Differentiation of population Gospić and its formation of a separate cluster with regard to other populations, can be explained by specificity of incidence of U. glabra on this site. Wych elm trees from Gospić population grow in beech forests with deadnettle association (Lamio orvalae-Fagetum sylvaticae / Horvat 1938 / Borhidi 1963), while the plant material from populations Delnice, Vrbovsko and Otočac was sampled from trees growing in beech-fir forests (Omphalodo-Fagetum /Tregubov 1957 corr. Puncer 1980 / Marinček et al. 1993). Environmental and climatic parameters of these two communities differ considerably, therefore the separation of Gospić population can be clarified through ecological and geographical principle.
By means of conducted research, which is also the first study of U. glabra in Croatia, intra-population and inter-population morphological variability of leaf traits in Mountainous Region of Croatia is quantified. This study represents an initial groundwork for further research and encourages analytical approach to U. glabra vulnerability issues, that will eventually result in setting up of guidelines aiming to protect natural wych elm populations in Croatia.
KEY WORDS: Ulmus glabra Huds., variability, leaf morphology, Mountainous Region of Croatia