Forest growth in Europe shows diverging large regional trends

Abstract

Forests cover about one-third of Europe’s surface and their growth is essential for climate protection through carbon sequestration and many other economic, environmental, and sociocultural ecosystem services. However, reports on how climate change affects forest growth are contradictory, even for same regions. We used 415 unique long-term experiments including 642 plots across Europe covering seven tree species and surveys from 1878 to 2016, and showed that on average forest growth strongly accelerated since the earliest surveys. Based on a subset of 189 plots in Scots pine (the most widespread tree species in Europe) and high-resolution climate data, we identified clear large-regional differences; growth is strongly increasing in Northern Europe and decreasing in the Southwest. A less pronounced increase, which is probably not mainly driven by climate, prevails on large areas of Western, Central and Eastern Europe. The identified regional growth trends suggest adaptive management on regional level for achieving climate-smart forests.

Major tree species of Central European forests differ in their proportion of positive, negative, and nonstationary growth trends

“…Conversely, the majority of sites displayed stationary or nonstationary positive growth trends. These results support other evidence regarding increasing productivity of Central European forests, benefiting from rising temperatures, prolonged growing seasons, and stable or increasing availability of resources such as CO 2 and N (Buras & Menzel, 2019; Gao et al., 2022; Oulehle et al., 2022; Pretzsch et al., 2023; Trotsiuk et al., 2020). Notably, the prevalence of stationary positive trends was predominantly detected at higher elevations, while lowland areas indicated a growing proportion of steadily declining trends, probably due to increasing drought frequency (Dubrovsky et al., 2009; Trnka et al., 2011).…”

“…Climate change is expected to significantly impact Central European forests, leading to growth declines in drought‐limited areas (lowlands) and growth stimulation in temperature‐limited (i.e., montane) regions (Trotsiuk et al., 2020). However, growth trends have been observed to vary across species and regions even recently (Girardin et al., 2016; Pretzsch et al., 2023), highlighting the need for systematic evaluation. To identify and quantify these changes, we investigated the growth trends of the most common tree species in European temperate forests: Norway spruce, European beech, Scots pine, silver fir, pedunculate oak and sessile oak.…”

Stand age diversity and climate change affects forests’ resilience and stability, although unevenly

“…Recent studies confirm our results, finding lower relative increment gains for the conifer species Norway spruce and Scots pine (18 and 35%) compared to the deciduous species as European beech and sessile/common oak (75 and 46%) (Pretzsch et al, 2023). Many model simulations have failed to replicate this phenomenon.…”

Turning point in forest productivity revealed from 40 years of national forest inventory data

“…Studies on forest productivity trends and drivers mostly focus on a limited number of tree species within defined regions in simple stand structure and composition (see Boisvenue and Running 2006 or Kahle et al 2008 for reviews) in order to explicitly control for confounding factors in observational settings and to pinpoint trends to given tree species, usually of economic interest or with widespread distributions. While this approach has been successful in revealing environmental- and climate-driven trends (Charru et al 2017, Ols et al 2020, Pretzsch et al 2023) it lacks systemasticity regarding the tree species, stands and regions considered (but see Henttonen et al 2017). Furthermore, this approach of focusing on a limited set of tree species-regions couples limits the climatic gradients considered, potentially reducing the power of detecting climatic drivers behind the trends identified.…”

“…Furthermore, this approach of focusing on a limited set of tree species-regions couples limits the climatic gradients considered, potentially reducing the power of detecting climatic drivers behind the trends identified. At the other extreme, large-scale studies usually do not assess regional trend divergence with few exceptions such as Wang et al 2023 in Canada or Pretzsch et al 2023 in Europe. In the context of adapting forest management regimes to climate change, policy-makers and forest managers need systematic assessment of forest productivity trends and their drivers for a large number of species and over broad ecological gradients.…”