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Pedunculate oak ( Quercus robur L.) is a long-lived species that dominates the extra–zonal natural forests in the steppe landscape of southeastern Ukraine. Although Q. robur is considered to be one of the most important species in European dendrochronology, it has received little attention in the steppe zone because of its scarcity in the often-degraded steppe forests. Nevertheless, a small and unique patch of old-growth oak exists within the boundary of Donetsk, a large industrial center in Eastern Europe. This forest is a remnant of an ancient wood and includes several dozen old-age trees that can contribute to filling some of the spatial gaps in pedunculate oak dendrochronology in Eastern Europe. In this study, we aim to determine the effect of climatic variables on pedunculate oak growth in the steppe zone, and to estimate the longevity of this species in the heterogeneous conditions of an urban forest. A total of 20 trees were cored for this study, varying in age from 55 to 254. The resulting tree-ring chronology correlates strongly with local precipitation in spring and summer, and with local temperature in April, June and July. Moving correlation analysis indicates a shift over the last 80 years in the relationship between oak growth and late winter and early spring temperatures, as well as between oak growth and precipitation in February and August. These findings imply that warming has caused both an advance in oak phenology and changes in the climatic conditions in early spring. [ABSTRACT FROM AUTHOR]

[Display omitted] • Four bioclimatic clusters determine black locust distribution in Europe. • The eastern cluster overlaps with climatically suitable area in current and future distribution. • The black locust highlighted spatially and temporally variable climate sensitivity. • The plasticity in secondary growth may increase the black locust's invasive potential. As a consequence of native tree species decline and distribution range contraction in Europe, acclimation of the non-native tree species at the edge of their distribution is gaining importance. Although non-native tree species may provide sustainable ecosystem services, as a potentially invasive species they may be a threat to local ecosystems as well. In Europe, black locust (Robinia pseudoacacia) a non-native species, seems to meet the condition of acclimation as a multi-generational process. The acclimatization, however, may have consequences not only for growth performance but also for the species' invasive potential. This study investigates the spatiotemporal pattern of secondary growth and climate sensitivity among six black locust stands along continentality gradient in Eastern Europe with the respect to bioclimatic conditions of the species distribution in Europe. Despite comparable bioclimatic conditions, climate sensitivity of black locust stands is highly variable, both temporally and spatially. The winter and spring temperatures are a key climatic driver of the growth pattern in southern and western Poland. Growth response to previous winter and current summer precipitation distinguished stands in western and eastern Poland. A significant increase in the mean annual temperature during the last 70 years likely triggered temporal instability of the black locusts' climate signal. In general, drought conditions were found to be the main limiting factor at the edge sites within the black locust gradient. Thus, the climate sensitivity of black locust stands reflects rather site-specific microclimatic conditions then bioclimatically-based clustering pattern. Despite climate-related limiting factors, black locust seems to be characterized by high potential for acclimatization to Eastern European climatic conditions, suggesting high invasive potential. Thus, the replacement of native species by black locust or the conversion of local habitats into monocultures for biomass production should not be recommended, while species management should follow proactive measures to reduce the risk of uncontrolled spread of the species. Divergent growth reaction of black locust stands implies high plasticity of secondary growth and thus high probability of acclimatization to future climate. Given the expected range expansion to the East in Europe, we call for expanding dendroclimatic studies to the areas of future species expansion in order to test its climatic and edaphic limitations. This seems to be crucial for formulating non-native species management strategies in line with sustainable forestry, preventing the uncontrolled expansion of the species that threatens vulnerable habitats. [ABSTRACT FROM AUTHOR]

Climate change is altering forest ecosystems worldwide, particularly in steppe landscapes, where the rare tree communities are challenged with steadily increasing droughts. In the steppe of Eastern Europe, amid dry conditions, Quercus robur occupies mostly riverine habitats and ravines. Here we study the climate sensitivity and drought vulnerability of a Q. robur population located at the rear edge of the species range, in the steppe of Ukraine. The population occupies two adjacent but clearly contrasting in their microclimatic conditions sites: a river floodplain and a steep-sloping river bank. We develop tree earlywood, latewood, and total ring width site-level chronologies and evaluate their relationship with regional climate variables and the local river's water level using response function analysis. We find that trees growing in the floodplain and at the steep river bank have exhibited slightly different growth patterns. The trees at the flooded site have benefited from water proximity, which facilitated their earlywood growth. These trees have responded positively to the current May and previous September precipitation and previous and current May temperatures. At the non-flooded site, the trees have experienced warm temperatures and the lack of precipitation in June. The extreme drought episodes have triggered a decrease in the latewood and total ring width in trees from both sites. We established that oak growth in the floodplain had been depressed by an unknown stressor around 1900, therefore limiting our ability to identify the more beneficial steppe habitat for Q. robur conclusively. Nevertheless, our results provide a dendrochronological evidence of Q. robur survival in a dry steppe environment and lend new insights into local microclimatic factors contributing to it. [ABSTRACT FROM AUTHOR]