Petrokas, R. and Baliuckas, V. 2014. Morphological Intergradation of Native Elm Species Is Shown by Site-specific Parameters. Baltic Forestry 20(2): 238-247

As a consequence of the fragmentation and small size of populations caused by the destruction of their native habitats, elms are getting endangered in Lithuania. The aim of the study was to learn about the native elm species, Ulmus glabra Hudson and Ulmus minor Miller, and their hybrid, Ulmus × hollandica Mill., based on the research of site-specific parameters of canopy overlap, soil properties, and herb layer characteristics at the contact zones, where it may become increasingly difficult to differentiate pure forms from the hybrids. Conceivably, the morphological intergradation of native elm species can be related to the natural gradients of moisture, pH, and nutrients as well as North-South and up-down oriented parameters of canopy overlap of elms with surrounding woody species. Elm habitats were studied to establish a predictive model for the presence of the hybrids and species in the very few contact zones existing in Lithuania. Quick, Unbiased, Efficient Statistical Tree method (QUEST) was used to select predictors from the sixty eight site-specific parameters. In conclusion, the morphological intergradation of native elm species in the contact zones is shown by differences in soil type, canopy overlap and herbal cover.

Key words: Ulmus minor, Ulmus glabra, Ulmus × hollandica, morphological intergradation, soil type, herbal cover, canopy overlap, contact zone