Declining Radial Growth in Major Western Carpathian Tree Species: Insights from Three Decades of Temperate Forest Monitoring.

This study investigates the radial growth response of five key European forest tree species, i.e., Fagus sylvatica, Picea abies, Abies alba, Quercus petraea, and Pinus sylvestris, to dry years in the West Carpathians, Slovakia. Utilizing data from ICP Forests Level I plots, we identified species-specific growth declines, particularly in Pinus sylvestris and Fagus sylvatica, with milder radial growth declines for Quercus petraea and Picea abies. Abies alba exhibited a growth peak in the mid-2000s, followed by a decline in the end of the observed period. Elevation emerged as the only significant environmental predictor, explaining 3.5% of growth variability during dry periods, suggesting a potential mitigating effect. The scope of this study was limited by the complex interplay of ecological factors that influence tree growth, which vary across the ICP Forests Level I monitoring sites. Nonetheless, our findings enhance the understanding of species-specific growth responses and offer insights for the climate-smart management of temperate forests under changing conditions.

Empirical and process-based models predict enhanced beech growth in European mountains under climate change scenarios: A multimodel approach.

Process-based models and empirical modelling techniques are frequently used to (i) explore the sensitivity of tree growth to environmental variables, and (ii) predict the future growth of trees and forest stands under climate change scenarios. However, modelling approaches substantially influence predictions of the sensitivity of trees to environmental factors. Here, we used tree-ring width (TRW) data from 1630 beech trees from a network of 70 plots established across European mountains to build empirical predictive growth models using various modelling approaches. In addition, we used 3-PG and Biome-BGCMuSo process-based models to compare growth predictions with derived empirical models. Results revealed similar prediction errors (RMSE) across models ranging between 3.71 and 7.54 cm2 of basal area increment (BAI). The models explained most of the variability in BAI ranging from 54 % to 87 %. Selected explanatory variables (despite being statistically highly significant) and the pattern of the growth sensitivity differed between models substantially. We identified only five factors with the same effect and the same sensitivity pattern in all empirical models: tree DBH, competition index, elevation, Gini index of DBH, and soil silt content. However, the sensitivity to most of the climate variables was low and inconsistent among the empirical models. Both empirical and process-based models suggest that beech in European mountains will, on average, likely experience better growth conditions under both 4.5 and 8.5 RCP scenarios. The process-based models indicated that beech may grow better across European mountains by 1.05 to 1.4 times in warmer conditions. The empirical models identified several drivers of tree growth that are not included in the current process-based models (e.g., different nutrients) but may have a substantial effect on final results, particularly if they are limiting factors. Hence, future development of process-based models may build upon our findings to increase their ability to correctly capture ecosystem dynamics.

Climate warming induced synchronous growth decline in Norway spruce populations across biogeographical gradients since 2000.

Covering large parts of Europe, Norway spruce (Picea abies L Karst.) plays an important role in the adaptation strategy of forest services to future climate change. Although dendroecology can provide valuable information on the past relationships between tree growth and climate, most previous studies were biased towards species-specific distribution limits, where old individuals grow slowly under extreme conditions. In the present study, we investigated the growth variability and climate sensitivity of 2851 Norway spruce trees along longitudinal (E 12-26°), latitudinal (N 45-51°), and elevation (118-1591 m a.s.l.) gradients in central-eastern Europe. We reveal that summer weather significantly affects the radial growth of spruce trees, but the effects strongly vary along biogeographical gradients. Extreme summer heatwaves in 2000 and 2003 reduced the growth rates by 10-35%, most pronounced in the southern Carpathians. In contrast to the population in the Czech Republic, climate warming induced a synchronous decline in the growth rates across biogeographical gradients in the Carpathian arc. By demonstrating the increased vulnerability of Norway spruce under warmer climate conditions, we recommended that the forest services and conservation managers replace or admix monocultures of this species with more drought-resilient mixtures including fir, beech and other broadleaved species.