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

Abstract

Abstract. Larch forests are widely distributed across many cool-temperate and boreal regions, and they are expected to play an important role in global carbon and water cycles. Model parameterizations for larch forests still contain large uncertainties owing to a lack of validation. In this study, a process-based terrestrial biosphere model, BIOME-BGC, was tested for larch forests at six AsiaFlux sites and used to identify important environmental factors that affect the carbon and water cycles at both temporal and spatial scales.The model simulation performed with the default deciduous conifer parameters produced results that had large differences from the observed net ecosystem exchange (NEE), gross primary productivity (GPP), ecosystem respiration (RE), and evapotranspiration (ET). Therefore, we adjusted several model parameters in order to reproduce the observed rates of carbon and water cycle 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 observed values.The observed and simulated GPP and RE across the six sites were positively correlated with the annual mean air temCorrespondence to: M. Ueyama (miyabi-flux@muh.biglobe.ne.jp) perature and annual total precipitation. On the other hand, the simulated carbon budget was partly explained by the stand disturbance history in addition to the climate. The sensitivity study indicated that spring warming enhanced the carbon sink, whereas summer warming decreased it across the larch forests. The summer radiation was the most important factor that controlled the carbon fluxes in the temperate site, but the VPD and water conditions were the limiting factors in the boreal sites. One model parameter, the allocation ratio of carbon between belowground and aboveground, was site-specific, and it was negatively correlated with the annual climate of annual mean air temperature and total precipitation. Although this study substantially improved the model performance, the uncertainties that remained in terms of the sensitivity to water conditions should be examined in ongoing and long-term observations.

The impact of climate variation and disturbances on the carbon balance of forests in Hokkaido, Japan

“…The correlations of daily and monthly NEP were lower than those of GPP and RE (Table S2 in the Supplement), as reported in previous studies (Ichii et al, , 2013Ueyama et al, 2010). NEP represents the small difference between large gross fluxes such as GPP and RE.…”

“…This is likely because Ueyama et al (2010) added biases for each season, whereas our data included a year of severe drought in 1984 (694 mm), which had the lowest precipitation in 6 decades. This is likely to be the reason why we, but not Ueyama et al (2010), noted a critical effect of precipitation on carbon balance.…”

Spatial and seasonal variations of CO2flux and photosynthetic and respiratory parameters of larch forests in East Asia

“…Although the annual GPP and RE increased with the stand age at the first stage of the stand development (< 50 years old), these tended to decrease with the stand age (Fig. 7); therefore, the disturbance history may partly affect the relationship of NEE to temperature or LAI, as suggested by processbased ecosystem model studies (Ueyama et al 2010;Ichii et al 2013). However, the effects of other environmental factors are included in this apparent relationship, and it is difficult to distinguish these effects in our bulk analyses; thus, the age or management effect must be clarified by the comparison among different-aged forest stands under similar environments in future studies.…”

“…forests are characterized by their deciduous habit, a trait that allows them to endure the extremely cold and dry winters across high latitudes of Eurasia, including the Siberian taiga (Gower and Richards 1990). These forests are considered to have a strong influence on the terrestrial carbon and energy cycles, because of their vast area and the potentially large carbon stocks in their peat soils in the permafrost (Schulze et al 1999;Dolman et al 2004;Ueyama et al 2010). Siberian forests constitute 20% of the world's forested area (Dolman et al 2004), and larch forests cover 37% (Abaimov et al 1998), 70% (Gunin et al 1999) and 13.6% (Jiang and Zhou 2002) of forested areas in Russia, Mongolia and China, respectively.…”

Multi-model analysis of terrestrial carbon cycles in Japan: limitations and implications of model calibration using eddy flux observations

“…As stated before, previous model intercomparison projects generally lacked detailed model calibration and evaluation using observations, resulting in errors in the simulations. Owing to the recent increase in the availability of relevant data (Baldocchi, 2008), model improvements have been carried out using eddy flux data, and the impact on the model simulations was evaluated on a global scale (Friend et al, 2007;Stokli et al, 2008), as well as on a regional scale (Ueyama et al, 2010). Since the differences among multi-models should be reduced by the constraints from the observed data, potential differences should be evaluated after each model has been calibrated based on observations.…”