Assessing most relevant factors to simulate urrent annual increments of beech forests in Italy

Recent papers have demonstrated the applicability of a calibrated bio-geochemicalmodel – BIOME-BGC - for estimating current annual increments (CAIs) ofMediterranean forests. In this study, the above model is applied to assess thegross primary production (GPP) of nine beech forest sites in Italy using a previouslyproduced data set of meteorological data over a ten-year period (1999-2008). The obtained GPP estimates are integrated with relevant autotrophicrespiration and allocation to obtain forest net primary production (NPP) averagesfor the same forests. The simulations are performed assuming differentlevels of ecosystem disequilibrium, i.e., progressively taking into account theeffects of specific site history in terms of woody biomass removal and standaging. The NPP estimates, converted into CAIs by means of specific coefficients,are validated through comparison with data derived from tree growthmeasurements. Results indicate that the modeling of quasi-equilibrium conditionstends to produce overestimated CAI values, particularly for not fullystocked, old stands. The inclusion of information on existing biomass leads to apartial improvement, while optimal results are obtained when information onecosystem development phase is considered. The implications of using differentNPP estimation methods are finally discussed in the perspective of assessingthe forest carbon budget on a national basis.