Key European tree species are expected to contract their ranges under changing climate, thus there is a need to assess range shifts for other native tree species that could fill their forest niche. Recent studies have focused on economically important species, revealing a wide range of shifts in their distribution worldwide and highlighting several pathways for potential future changes. We aimed to quantify changes in projected ranges and threat levels by the years 2041-60 and 2061-80, for 20 European temperate forest tree species under four climate change scenarios. We compared ten standard stock tree species with ten alternative stock species, that are less frequent and less preferred by managers. We combined distribution data from several sources for each tree species and developed species distribution models using MaxEnt and seven bioclimatic variables. We applied these models to projections of future climate from four global circulation models, under four Shared Socioeconomic Pathways and for near and middle terms: 2041-60 and 2061-80. We also assessed the relationships between predicted range contraction and their functional traits. Analysis of MaxEnt models divided the studied tree species into three groups: non-threatened (Sorbus torminalis, Ulmus minor, Tilia platyphyllos, Acer pseudoplatanus, Prunus avium, and Carpinus betulus), partially threatened (U. laevis, Betula pendula, Quercus robur, Q. petraea, A. platanoides, Fagus sylvatica, Fraxinus excelsior, T. cordata, Alnus glutinosa, and U. glabra), and the most threatened (Abies alba, Larix decidua, Picea abies, and Pinus sylvestris). For the last group, almost half of the range contraction will occur earlier (2041-2060) compared to our previous predictions (2061-2080). The proportion of range contraction decreased with increasing specific leaf area, leaf area, leaf nitrogen content, seed mass, and specific stem density while it increased with increasing height. Our study provides novel predictions of shifts in climatic optima under the most recent climate change scenarios, which would be useful for evidence-based conservation and management of European forests. The near-term predicted threats to the main standard stock tree species call for intensified preparation for incoming changes. We recommend splitting the silvicultural risks over a wider range of tree species, also including alternative stock species.

Invasive tree species decrease ecosystem resilience with negative impacts on natural regeneration. The influence of alien tree species on ecosystems is unevenly recognized and does not always account for different habitat specificity. We assessed the impacts of the three most frequent invasive tree species in European forests: Prunus serotina Ehrh., Quercus rubra L., and Robinia pseudoacacia L. on natural regeneration diversity, species composition, and density. We hypothesized that invaded forest types, in comparison with non-invaded, will differ in terms of species composition, will have lower taxonomic, functional, and phylogenetic diversity of natural regeneration, and will have lower densities of native tree species. We used a set of 189 study plots (200 m²) in a systematic design, established in various forest types in Wielkopolski National Park (West Poland). We analyzed impacts of forest type, accounting for soil C:N ratio, soil pH, and light availability on natural regeneration (woody species up to 0.5 m height) species composition, diversity, and density. We found an overlap of species composition among invaded and non-invaded forests and low impacts of invasive species on taxonomic diversity and functional richness. We found no impacts on phylogenetic diversity and other functional diversity components. In contrast, we found that the natural regeneration of forest-forming tree species reached lower densities in invaded than non-invaded forest types. However, sub-canopy and shrub species reached higher densities in invaded than non-invaded forest types. We confirmed that invasive tree species affect natural regeneration by decreasing the regeneration density of native tree species (in eight of nine tree species studied), species composition homogenization, and supporting natural regeneration of sub-canopy and shrub species. Therefore, the restoration of invaded forests requires eradication of invasive tree species to decrease propagule pressure and to stop decreases in the abundance of native tree species’ natural regeneration.

We assessed drivers of ecological success along resource availability gradients for three invasive woody species: Prunus serotina Ehrh., Quercus rubra L. and Robinia pseudoacacia L. We aimed to check how much of invasion success, measured by invader biomass, is explained by propagule pressure and plant community invasibility. Using 3 years of observations from 372 study plots (100 m² each) in temperate forests of Wielkopolski National Park (Poland) we investigated the hierarchy of predictors and partial dependencies using the random forest method. Our study indicated that propagule pressure explained more variance in success of invaders than invasibility—describing availability of resources and competitors in understory vegetation. We also found different responses of seedlings and saplings, connected with dependence on stored carbohydrates, which decreased seedling responses to resource availability gradients. However, resource availability (light and leaf litter predictors) had greater influence than predictors describing understory vegetation. Based on importance and response strength the species studied may be arranged by decreasing requirements for soil fertility and acidity: P. serotina < Q. rubra < R. pseudoacacia, whereas for light requirements and competition vulnerability the order is: P. serotina > Q. rubra > R. pseudoacacia. However, low light requirements of R. pseudoacacia may be biased by high proportion of sprouts supplied by parental trees. Results provide guidelines for effective management of invasive woody species in forest ecosystems and describe complex interactions between factors studied on ecological success of invaders.