• Energy Research

AbstractExtreme droughts are expected to increase in frequency and severity in many regions of the world, threatening multiple ecosystem services provided by forests. Effective strategies to adapt forests to such droughts require comprehensive information on the effects and importance of the factors influencing forest resistance and resilience. We used a unique combination of inventory and dendrochronological data from a long‐term (>30 years) silvicultural experiment in mixed silver fir and Norway spruce mountain forests along a temperature and precipitation gradient in southwestern Germany. We aimed at examining the mechanisms and forest stand characteristics underpinning the resistance and resilience to past mild and severe droughts. We found that (i) fir benefited from mild droughts and showed higher resistance (i.e., lower growth loss during drought) and resilience (i.e., faster return to pre‐drought growth levels) than spruce to all droughts; (ii) species identity determined mild drought responses while species interactions and management‐related factors strongly influenced the responses to severe droughts; (iii) intraspecific and interspecific interactions had contrasting effects on the two species, with spruce being less resistant to severe droughts when exposed to interaction with fir and beech; (iv) higher values of residual stand basal area following thinning were associated with lower resistance and resilience to severe droughts; and (v) larger trees were resilient to mild drought events but highly vulnerable to severe droughts. Our study provides an analytical approach for examining the effects of different factors on individual tree‐ and stand‐level drought response. The forests investigated here were to a certain extent resilient to mild droughts, and even benefited from such conditions, but were strongly affected by severe droughts. Lastly, negative effects of severe droughts can be reduced through modifying species composition, tree size distribution and stand density in mixed silver fir‐Norway spruce forests.

This RESONATE policy brief informs about the escalating risks that climate-driven disturbances pose to Europe’s forests. Extreme weather events become more frequent and severe. This challenges the resilience of forests, with disturbances like fires, bark beetles, and droughts increasing in intensity. The brief underscores the need for adaptive management strategies to address novel disturbance regimes and ensure long-term forest resilience. Key findings include that the frequency of natural disturbances and their interactions is growing, which can intensify the impacts on forests. For example, bark beetle outbreaks often follow droughts, and wildfires can exacerbate the damage from previous storms. With disturbances predicted to increase up to threefold by the end of the century, proactive forest management is crucial. Strategies such as increasing tree species diversity, fostering mixed forest stands, and mimicking natural disturbances through prescribed burns can enhance forest resilience and biodiversity. The brief also emphasizes the importance of supporting forest owners through policy tools like financial assistance and improved regulations, as well as providing guidance on adaptive forest management. By integrating climate change adaptation into forest planning, Europe should work towards safeguarding its forests against the escalating threats of disturbance, ensuring their stability and productivity in the future. Reference: Lindner, M., Seidl, R., Grünig, M., Bauhus, J., Willig, J., Hlásny, T., Nabuurs, G.-J., Patacca, M., Peltoniemi, M., Espelta, J. M., Picos, J., Hoeben, A. D., Cantarello, E., & Schifferdecker, G. (2025). Policy Brief: Managing Forest Disturbances in a Changing Climate. EFI. https://doi.org/10.36333/rs9

Abstract Purpose of Review Forests support most global terrestrial biodiversity and contribute to the livelihood of billions of people, but these and other benefits are in jeopardy due to global change. This leads to questions, such as how to address the challenges of global change in forest management, given the lack of knowledge and deep uncertainty about future developments. In addition, many of the impediments to implement adaptation strategies are unknown. Recent Findings Here, we present an overview of results from a global survey of 754 forestry professionals (370 researchers and educators, 227 practicing foresters, 37 policymakers, 64 administrators, and 56 with other or unspecified roles) from 61 countries across 6 continents who were interested in global change issues. These professionals were asked about their opinion regarding three different adaptation strategies: resist, adapt, and transform. Most respondents agreed that the majority of global change factors will negatively influence the ability of forests to provide desired ecosystem services. Similarly, they agreed about major challenges when implementing adaptation strategies and specifically whether our current knowledge base is sufficient. These concerns were not limited to ecological aspects, but respondents also highlighted the need for a better appreciation of social/political and economic barriers, especially regarding transformation strategies. In addition, the response patterns, including differences due to economic status, highlight the importance of developing and evaluating adaptation strategies in a local social–ecological context. Summary Our study demonstrates a widespread perception on the part of forestry professionals around the world, especially among researchers and practitioners, that many global change factors will affect sustainable forest management negatively, resulting in the need for active silvicultural adaption. The results also suggest potential barriers to different adaptation strategies, particularly a relative lack of information and social acceptance for transform strategies. Further, this study highlights the importance of social and political factors and the need to understand the general public’s values regarding adaptation strategies as well as how the influence of public opinion is perceived by forest managers.

AbstractPlant diversity effects on community productivity often increase over time. Whether the strengthening of diversity effects is caused by temporal shifts in species-level overyielding (i.e., higher species-level productivity in diverse communities compared with monocultures) remains unclear. Here, using data from 65 grassland and forest biodiversity experiments, we show that the temporal strength of diversity effects at the community scale is underpinned by temporal changes in the species that yield. These temporal trends of species-level overyielding are shaped by plant ecological strategies, which can be quantitatively delimited by functional traits. In grasslands, the temporal strengthening of biodiversity effects on community productivity was associated with increasing biomass overyielding of resource-conservative species increasing over time, and with overyielding of species characterized by fast resource acquisition either decreasing or increasing. In forests, temporal trends in species overyielding differ when considering above- versus belowground resource acquisition strategies. Overyielding in stem growth decreased for species with high light capture capacity but increased for those with high soil resource acquisition capacity. Our results imply that a diversity of species with different, and potentially complementary, ecological strategies is beneficial for maintaining community productivity over time in both grassland and forest ecosystems.

Abstract Over-aged coppice forests (older than 40 years) occur all over Europe as a result of the abandonment of traditional harvesting practices during the last 60–100 years. With the increasing demand for bioenergy, there is renewed interest in coppicing, which typically aims at maximizing biomass production. For the sustainable management of these forests, accurate estimates of their biomass potential are needed. Therefore biomass equations for the two most common tree species traditionally managed in Central European coppice systems were developed in this study. In total, 24 oak ( Quercus petraea ) and 24 hornbeam ( Carpinus betulus ) trees from two different, aged coppice stands in Rhineland-Palatinate (southwest Germany) were felled and separated into various biomass compartments which were directly weighed in the field. From every compartment, samples were taken to the laboratory to determine wood density and water content. Based on dendrometric parameters (diameter at breast height (dbh)) and compartment dry mass, allometric equations were developed. Power functions provided the best fits for relationships between dbh and biomass in tree compartments and whole trees ( R 2 = 0.97 and 0.92 for oak and hornbeam, respectively). These allometric equations for oak differ considerably from those developed for trees grown in high forests, pointing to the need to use equations that are specific to silvicultural systems, in this case for aged coppice forests.

AbstractUnprecedented tree dieback across Central Europe caused by recent global change‐type drought events highlights the need for a better mechanistic understanding of drought‐induced tree mortality. Although numerous physiological risk factors have been identified, the importance of two principal mechanisms, hydraulic failure and carbon starvation, is still debated. It further remains largely unresolved how the local neighborhood composition affects individual mortality risk. We studied 9435 young trees of 12 temperate species planted in a diversity experiment in 2013 to assess how hydraulic traits, carbon dynamics, pest infestation, tree height and neighborhood competition influence individual mortality risk. Following the most extreme global change‐type drought since record in 2018, one third of these trees died. Across species, hydraulic safety margins (HSMs) were negatively and a shift towards a higher sugar fraction in the non‐structural carbohydrate (NSC) pool positively associated with mortality risk. Moreover, trees infested by bark beetles had a higher mortality risk, and taller trees a lower mortality risk. Most neighborhood interactions were beneficial, although neighborhood effects were highly species‐specific. Species that suffered more from drought, especially Larix spp. and Betula spp., tended to increase the survival probability of their neighbors and vice versa. While severe tissue dehydration marks the final stage of drought‐induced tree mortality, we show that hydraulic failure is interrelated with a series of other, mutually inclusive processes. These include shifts in NSC pools driven by osmotic adjustment and/or starch depletion as well as pest infestation and are modulated by the size and species identity of a tree and its neighbors. A more holistic view that accounts for multiple causes of drought‐induced tree mortality is required to improve predictions of trends in global forest dynamics and to identify mutually beneficial species combinations.