Remote sensing and bio-geochemical modeling of forest carbon storage in Spain

This study simulates annual net primary production (NPP) of forests over peninsular Spainduring the years 2005-2012. The modeling strategy consists of a linked production eciency modelbased on the Monteith approach and the bio-geochemical model Biome-BGC. Recently produceddatabases and data layers over the study area including meteorological daily series, ecophysiologicalparameters, and maps containing information about forest type, rooting depth, and growing stockvolume (GSV), were employed. The models, which simulate forest processes assuming equilibriumconditions, were previously optimized for the study area. The production eciency model was usedto estimate daily gross primary production (GPP), while Biome-BGC was used to simulate growth(RG) and maintenance (RM) respirations. To account for actual forest conditions, GPP, RG, and RMwere corrected using the ratio of the remotely-sensed derived actual to potential GSV as an indicatorof the actual state of forests. The obtained results were evaluated against current annual incrementobservations from the Third Spanish Forest Inventory. Coecients of determination ranged from0.46 to 0.74 depending on the forest type. A simplified dataset was produced by applying regularincrements in air temperature and reductions in precipitation to the original 2005-2012 daily serieswith the goal of covering the range of variation of the climate projections corresponding to thedierent climate change scenarios reported in the literature. The modified meteorological series wereused to simulate new GPP, RG, and RM through Biome-BGC and corrected using GSV. Precipitationwas confirmed as the main limiting factor in the study area. In the regions where precipitation wasalready a limiting factor during 2005-2012, both the increment in air temperature and the reductionin precipitation contributed to a reduction of NPP. In the regions where precipitation was not alimiting factor during 2005-2012, the increment in air temperature led to an increment of NPP. Thisstudy is therefore relevant to characterize the growth of Spanish forests both in current and expectedclimate conditions.