Effect of mixture and management of a Southern European beech forest on carbon stocks and sinks

Beech forests in Italy represent 10% of the country's forest area and are hotspots of carbon storage. In the central-northern Apennines, where 61% of Italian beech coppice forest area is found, improved management practices can increase the territory's economic value through the generation of voluntary carbon credits. However, the effect of management models (coppice, high forest, coppice left to natural evolution from more than 60 years) and degree of mixture (with other broadleaves at lower elevations or with silver fir at higher ones) on carbon stocks and sinks are poorly understood. We analysed the effect of species mixture and management on carbon stocks and sinks of beech forests in the Appennino Tosco Emiliano National Park. We sampled 60 beech forest plots (12 for each mixture or management treatment) and implemented allometry-based biomass estimates, dendrochronological analysis of tree cores, and CHN analysis of soil. Generalized Linear Models were used to analyse the results while controlling for environmental variables' effects. Mixture or management had limited influence on soil carbon stocks. On the contrary, mixture and management strongly affected biomass stocks: model results show abandoned beech coppice mixed with broadleaves having the highest stock (1150 Mg CO2eq. ha-1), followed by monospecific old coppice (900 Mg CO2eq. ha-1). Unexpectedly, old coppice also shows the highest carbon sink (14 Mg CO2eq. ha-1 yr-1), while high forest the lowest (10 Mg CO2eq. ha-1 yr-1). These results show that rewilding of coppice forest can be an interesting management option when the objective is to increase the carbon stocks and sinks, also due the co-benefits in terms of structural complexity and biodiversity. However, the long time required for the natural transition of coppice to high forest could slow down these effects. Also, they question the practice of active conversion into high forest: in case of climate change mitigation, tree density reduction might be counterproductive. Promoting forest mixture with broadleaf species can be beneficial for carbon stocks. These results, however, do not consider the climate induced stresses (e.g. droughts, wildfires). A long term modelling work with different climatic scenarios is needed to better define the best management practices for beech forests in Italy.