Abstract
Key messageClimate-warming related replacement of beech by oak forests in the course of natural forest succession or silvicultural decisions may considerably reduce ecosystem carbon storage of central European woodlands.ContextClimate warming may change the carbon (C) storage in forest biomass and soil through future shifts in tree species composition. With a projected warming by 2–3 K over the twenty-first century, silvicultural adaptation measures and natural succession might lead to the replacement of European beech forests by thermophilic oak forests in drought- and heat-affected regions of central and south-eastern Europe, but the consequences for ecosystem C storage of this species shift are not clear.AimsTo quantify the change in C storage in biomass and soil with a shift from beech (Fagus sylvatica) to oak forest (Quercus petraea, Q. frainetto, Q. cerris), we measured the aboveground biomass (AGC) and soil C pools (SOC).MethodsAGC pools and SOC stocks to − 100 cm depth were calculated from forest inventory and volume-related SOC content data for beech, mixed beech-oak and oak forests in three transects in the natural beech-oak ecotone of western Romania, where beech occurs at its heat- and drought-induced distribution limit.ResultsFrom the cooler, more humid beech forests to the warmer, more xeric oak forests, which are 1–2 K warmer, AGC and SOC pools decreased by about 22% (40 Mg C ha−1) and 20% (17 Mg C ha−1), respectively. The likely main drivers are indirect temperature effects acting through tree species and management in the case of AGC, but direct temperature effects for SOC.ConclusionIf drought- and heat-affected beech forests in Central Europe are replaced by thermophilic oak forests in future, this will lead to carbon losses of ~ 50–60 Mg ha−1, thus reducing ecosystem carbon storage substantially.
Highlights
Climate warming-related heat waves and droughts have the potential to destabilise temperate forests, as became visible in the extraordinary heat and drought of the summers 2018 and 2019 in Central Europe
The difference in aboveground biomass carbon (AGC) between beech forests and oak, mixed oak-beech- and linden-dominated forests was found in all three transects (Fig. 7, in the Appendix), whereas the trend to higher Soil organic carbon (SOC) contents in the beech forests was only observed in transects B and C (Fig. 8, in the Appendix)
Given that the current climate in the studied oak forest zone in western Romania is about 2.5 °K warmer than in the beechdominated submontane belt in southern Germany (Walentowski et al, 2017), we use our findings in a space-for-time substitution approach to predict that natural succession driven by a temperature increase by 2–3 °K would transform large parts of the southern German beech forests in oak-dominated communities with higher drought and heat tolerance
Summary
Climate warming-related heat waves and droughts have the potential to destabilise temperate forests, as became visible in the extraordinary heat and drought of the summers 2018 and 2019 in Central Europe. With the recent increase in summer temperatures, VPD and the frequency of heat waves (Barriopedro et al, 2011; Schär et al, 2004), and regionally decreasing summer precipitation (Caloiero et al, 2018; Schönwiese and Janoschitz, 2008) , it is predicted that the climate will become less favourable for beech in southern and south-eastern Europe and in parts of its Central European distribution range (Dolos et al, 2016; Garamszegi et al, 2020; Mette et al, 2013; Walthert et al, 2020). Modelling results based on tree species’ climate envelopes and additional information on the species’ site requirements predict for the warmer and drier lowlands and lower montane elevations of Central Europe a shift from beech forest to more drought-tolerant, thermophilic forest communities with oak and hornbeam in the course of climate warming in the twenty-first century (Fischer et al, 2019)
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