Gross primary productivity, tree growth and carbon reserve under climate change: the modelling case study of a dieback Quercus forest in San Paolo Albanese (Pollino National Park)

The interplay between gross primary productivity and plant growth under the impact of summer drought events is mediated by the tree carbon reserves. To investigate how plant carbon reserves might buffer drought impacts or if the plant is at risk of carbon starvation continuous experimental data of both carbon fluxes and different storages under multiple conditions would be required. Conversely mathematical models, while they are a simple representation of the complex processes involved, they can still provide qualitative explanations. We thus run the process-based forest model 3D-CMCC-FEM at the experimental site of San Paolo Albanese, located in the Pollino National Park in the Basilicata region. The stand is an old forest of Quercus frainetto Ten. that was affected by crown damage and tree decline, similarly to other areas in the region, which have been affected by severe drought-induced forest diebacks since 2000. We simulated the stand carbon cycle dynamics and the model performance was evaluated over the period 2000-2018. Using tree ring data the model was adjusted to fit the interannual variability of the basal area increment. We then set up a modeling framework to run the model under different climate change scenarios and initial stand conditions. We used this case study as the first step to investigate the covariation of plant gross primary productivity, growth and carbon reserves under drought related stressors.