Climate warming caused changes in the bud swelling phenophase of introduced conifer species, considering the aspect of hardiness zones in their natural habitats.
Background. Changing climatic conditions cause changes in tree phenology, which is important for the survival of species and their spread in local ecosystems. This study concentrated on long-term (1957-2016 or 1980-2016) observations of 11 conifer species introduced to Lithuania with the aim to evaluate the response of their bud swelling phenophase to climate warming, considering the hardiness zones of their natural habitats. Materials and Methods. Sequences of the start date of the bud swelling phenophase of 11 introduced conifer species (Abies veitchii, Larix decidua, L. kaempferi, L. laricina, L. × marschlinsii, L. sibirica, L. sukaczewii, Picea mariana, Pinus mugo, Taxus baccata and Thuja occidentalis) were analysed. Data were collected from the paper archives of Kaunas Botanical Garden of Vytautas Magnus University (VMU). Sequences of bud swelling start dates were transformed into sequences of number of days from the beginning of the year. Results. Results indicated an advance of the bud swelling phenophase of ten conifer species introduced to Lithuania (the speed of changes varied from -0.10 to -0.98 days/year in the 1980-2016 period) and a delay of Larix sukaczewii (respectively, +0.12 days/year) of the bud swelling phenophase, mainly influenced by the March temperature. Conclusions. The connection between the observed conifer species hardiness zone of the natural habitat and the reaction of the bud swelling phenophase to climate warming could be observed only when species from one genus were compared. To confirm this phenomenon, a research on a larger amount of introduced species with wider habitat hardiness zone options is needed in future.