Annabel J. Porte

This study evaluates changes in the sensitivity of radial growth of Quercus robur to water balance, assessed using the Standardized Precipitation Evapotranspiration Index (SPEI), in stands located within the Supiy River valley (Kyiv Region, Ukraine) in relation to the dam destruction in 1941 and the subsequent construction of a drainage network in the floodplain. Two valley stands were investigated: Tashan Park (TAS), situated downstream of the former dam site, and Zgurivka Dendropark (ZGU), located upstream. Two extra-valley sites, Bykivnia Forest (BYK) and Feofaniya Park (FEO), were used as the regional reference (REF) sites. The study period was divided into two intervals: before hydrological alterations (1910–1940) and after the completion of major drainage works (1962–2015); 1941–1961 were excluded from the analysis. Statistical modeling revealed a pronounced shift in moisture sensitivity of Q. robur within the Supiy valley: at TAS, the previously negative relationship between growth and March SPEI3 became positive after 1961, while the positive relationship with July SPEI3 observed before 1941 shifted to negative. In contrast, ZGU exhibited only weak changes in sensitivity, and the regional reference chronology (REF) maintained a consistently positive response to SPEI throughout the study period. These findings indicate a localized shift in hydroclimatic controls on tree growth within the river valley, particularly downstream of the dam site. The complex interaction of hydrological alterations, water management practices, small-stream regulation, and ongoing climate change complicates the prediction of ecological consequences of dam destruction and drainage works without empirical evidence from comparable settings.

Black locust (Robinia pseudocacacia) is a widely planted tree for wood production; however, it is a very problematic invasive species through Europe. At local scale, this tree is able to invades adjacent ecosystems owing to its strong ability of asexual reproduction through root suckers. Due to this phenomenon, the role of sexual reproduction has been quite neglected at local scale. Here, we propose a double approach (i) to evaluate the ability of the species to develop under forest cover using French national forest inventory data (ii) to quantify the role of sexual and asexual reproduction at local scale using a simple visual assessment method. We evidenced that juvenile black locust regenerates in broadleaved forests where R. pseudoacacia did not contribute to the adult canopy; moreover, a significant higher presence in riparian forests relatively to non-riparian ones was demonstrated using national forest inventory data. Regeneration from sexual reproduction mode significantly contributes to local scale invasion (38% of the up-rooted juvenile plants) with a significantly higher ratio of sexual reproduction within oak dominated forests compared to pine dominated ones. We conclude that black locust forestry should consider that both reproduction modes contribute to the species natural regeneration and that both modes can occur under both coniferous and broadleaved forest cover. Thus, we propose to set up safety buffers around sensitive ecosystems such as natural reserves or riparian areas, to maintain black locust cultivation while minimising undesired invasions in natural areas.

Aim: Tree mortality is increasing world‐wide, leading to changes in forest composition and altering global biodiversity. Nonetheless, owing to the multifaceted stochastic nature of tree mortality, large‐scale spatial patterns of mortality across species ranges and their underlying drivers remain difficult to understand. Our main goal was to describe the geographical patterns and drivers of the occurrence of mortality (presence of a mortality event) and the intensity of tree mortality (amount of mortality related to that mortality event) in Europe. We hypothesized that the occurrence of mortality represents background mortality and is higher in the margin than in core populations, whereas the intensity of mortality could have a more even distribution according to the spatial and temporal stochasticity of die‐off events.Location: Europe (Spain, France, Germany, Belgium, Sweden and Finland).Major taxa studied: More than 1.5 million trees belonging to 20 major forest tree species.Methods: We developed binomial and truncated negative binomial models to tease apart the occurrence and intensity of tree mortality in National Forest Inventory plots at the range‐wide scale. The occurrence of mortality indicated that at least one tree had died in the plot, whereas the intensity of mortality referred to the number of dead trees per plot.Results: The highest occurrence of mortality was found in peripheral regions and the climatic trailing edge linked with drought, whereas the intensity of mortality was driven by competition, drought and high temperatures and was scattered uniformly across species ranges.Main conclusions: We show that tree background mortality, but not die‐off, is generally higher in the trailing‐edge populations. It remains to be explored whether other demographic traits, such as growth, reproduction and regeneration, also decrease at the trailing edge of European tree populations.

Aim Tree mortality is increasing worldwide, leading to changes in forest composition and altering global biodiversity. Yet, due to the multi-faceted stochastic nature of tree mortality, large-scale spatial patterns of mortality across species ranges and their underlying drivers remain difficult to understand. Our main goal is to describe the geographical patterns and drivers of the occurrence and intensity of tree mortality in Europe. We hypothesize that the occurrence of mortality represents background mortality and is higher in the margin than the core populations, whereas the intensity of mortality could have a more even distribution according to the spatial and temporal stochasticity of die-off events. Location Europe (Spain, France, Germany, Belgium, Sweden and Finland) Time period 1981 to 2014. Major taxa studied More than 1.5 million trees belonging to 20 major forest tree species Methods We develop hurdle models to tease apart the occurrence and intensity of tree mortality in National Forest Inventory plots at range-wide scale. The occurrence of mortality indicates that at least one tree has died in the plot and the intensity of mortality refers to the number of trees dead per plot. Results The highest mortality occurrence was found in peripheral regions and the climatic trailing edge linked with drought, whereas the intensity of mortality was driven by competition, drought and high temperatures and was uniformly scattered across species ranges. Main conclusions Our findings provide a new perspective in our understanding of tree mortality across species ranges. We show that tree background mortality but not die-off is generally higher in the trailing edge populations, but whether other demographic traits such as growth, reproduction and regeneration would also decrease at the trailing edge of European tree populations needs to be explored.