Interplay of species mixture, climate change, and management regimes on carbon stocks and sinks in a Mediterranean beech forest

Abstract

Beech (Fagus sylvatica L.) is the most widespread species in the Apennines, but at the same time it is susceptible to climatic stress. Forestry should strive to increase the adaptability of beech forests to climate variations, and thus maintain or improve the ecosystem services they provide. Here we analysed the role of forest management and climate on the potential of beech forests for climate change mitigation. In the Tuscan-Emilian Apennine National Park (PNATE), we compared five different management types (coppice, stored coppice, high forest, mix with broadleaves, mix with silver fir) in their ability to store carbon under different climate change scenarios and management intensities. We collected tree and stand data in 57 forest plots, estimated the current carbon stocks and sinks, assessed expected changes in the species distribution under climate change scenarios by environmental niche modelling, and projected the future growth of forests using the 3-PGmix forest growth model. Carbon sinks are higher in beech forests mixed with broadleaves than in pure beech coppice or stored coppice (+25 % and +40 %, respectively), suggesting a positive effect of mixtures on the forest’s ability to mitigate climate change. Distribution models predict a significant reduction in the species' range at lower elevations in the near future, suggesting that PNATE could serve as a climate refugium within the Apennines. Growth simulations revealed that species complementarity (mix with broadleaf or fir) increases carbon stocks and sinks, as long as harvest stays at intermediate intensities. Beech in mix with fir showed higher average delta carbon stocks (as difference between carbon stocks at the beginning of the simulation and after 80 years; > 98–317 %) and carbon sink (> 38–330 %) compared to pure beech management under all climate scenarios. Climate change scenario SSP 1–2.6 results in an average increase of carbon stocks and sink across management and intensities, while SSP 3–7.0 implies a decrease for all treatments, except for the mix with silver fir that shows a remarkable increase. Active coppice is the management where biomass carbon sink is less sensitive to an increase of management intensity (-0.5 % and 7.8 %). Our findings underline the crucial role of beech forest management in locally optimising carbon uptake, underlying the positive effect of mix with fir and other broadleaves. We therefore recommend an informed and adaptive forest management approach that considers harvest intensity, species mixture, and ongoing climate change to effectively maintain resilient and functional forests through a mosaic of different forest management approaches.