Modeling the ecohydrological processes in the Landes de Gascogne, SW France

In this study, we simulated the ecohydrological processes of a landscape that comprises of managed maritime pine stands and crops, in a spatially explicit manner. We used various spatio-temporal datasets to run the STEPS model that describes ecophysiological, biogeochemicaland hydrological processes in a tightly coupled manner. The simulated gross primary productivity (GPP) and evapotranspiration (ET) showed large spatial variability over this landscape owing to the heterogeneities in landcover, soil texture, topography and soil hydrology. Croplands exhibited higher magnitudes of GPP (200–2500 gCm⁻² yr⁻¹) and ET fluxes (150–800 mm yr⁻¹) in comparison to other landcover types. Maize (C4) is generally cultivated in this landscape that is managed in terms of optimal availability of water and nutrients. The spatial variability was huge in the croplands due to the presence of fallow vs. cultivated lands. The maritime pine stands also showed considerable spatial variability in GPP (426 to 1320 gCm⁻² yr⁻¹) and ET (234 to 570 mm yr⁻¹) because of their stand ages (and the LAI) and depending on the nature of their understory species compositions. It was found that the understory contributions to the stand scale annual GPP and annual ET as much as 27% and 34%, respectively. The comparison of the simulated daily values with the measurements taken at the LeBray eddy covariance site (a maritime pine stand) revealed that the model performance were reasonable for both GPP (R2= 0.92, RMSE= 0.77 gC m⁻² day⁻¹) and ET (r2=0.81, RMSE= 0.52 mm day⁻¹). The seasonal patterns of ET fluxes were more dynamic than GPP due to the presence of distinct subcomponent processes that were uniquely governed by environmental factors.