Simulating carbon and water cycles of larch forests in East Asia by the BIOME-BGC model with AsiaFlux data

[摘要] Larch forests are widely distributed across many cool-temperate and borealregions, and they are expected to play an important role in global carbonand water cycles. Model parameterizations for larch forests still containlarge uncertainties owing to a lack of validation. In this study, aprocess-based terrestrial biosphere model, BIOME-BGC, was tested for larchforests at six AsiaFlux sites and used to identify important environmentalfactors that affect the carbon and water cycles at both temporal and spatialscales.

The model simulation performed with the default deciduous conifer parametersproduced results that had large differences from the observed net ecosystemexchange (NEE), gross primary productivity (GPP), ecosystem respiration(RE), and evapotranspiration (ET). Therefore, we adjusted several modelparameters in order to reproduce the observed rates of carbon and watercycle processes. This model calibration, performed using the AsiaFlux data,substantially improved the model performance. The simulated annual GPP, RE,NEE, and ET from the calibrated model were highly consistent with observedvalues.

The observed and simulated GPP and RE across the six sites were positivelycorrelated with the annual mean air temperature and annual totalprecipitation. On the other hand, the simulated carbon budget was partlyexplained by the stand disturbance history in addition to the climate. Thesensitivity study indicated that spring warming enhanced the carbon sink,whereas summer warming decreased it across the larch forests. The summerradiation was the most important factor that controlled the carbon fluxes inthe temperate site, but the VPD and water conditions were the limitingfactors in the boreal sites. One model parameter, the allocation ratio ofcarbon between belowground and aboveground, was site-specific, and it wasnegatively correlated with the annual climate of annual mean air temperatureand total precipitation. Although this study substantially improved themodel performance, the uncertainties that remained in terms of thesensitivity to water conditions should be examined in ongoing and long-termobservations.

[学科分类] 地球化学与岩石