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 temperature 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.
Highlights
The northern high latitude region is currently undergoing rapid and drastic warming (IPCC, 2007); the air temperatures in Eastern Siberia have risen by 7 ◦C in winter and 1– 2 ◦C in annual basis during the past few decades (Dolman et al, 2008)
For the plantation disturbance of Tomakomai site (TMK) and Laoshan site (LSH), we assumed that the amount of vegetation planted was 30% of the dynamic equilibrium of the vegetation, and the rest was removed from the sites; the leaf and fine root C and N pools were included in the fine litter pool
The peaks of gross primary productivity (GPP) and RE were generally underestimated for TMK, SKT, and YLF and overestimated for Neleger site (NEL) and Tura site (TUR), the seasonality, such as the onset and offset of the growing season, was generally reproduced
Summary
The northern high latitude region is currently undergoing rapid and drastic warming (IPCC, 2007); the air temperatures in Eastern Siberia have risen by 7 ◦C in winter and 1– 2 ◦C in annual basis during the past few decades (Dolman et al, 2008). These measurements have revealed the important processes that determine the carbon and water cycles in larch forests, such as the environmental factors that control evapotranspiration (Ohta et al, 2008) and carbon flux (Hollinger et al, 1998; Wang et al, 2005; Li et al, 2005; Hirata et al, 2007; Nakai et al, 2008), and the role of stand disturbance (Machimura et al, 2007) Since these analyses are site-specific, we need to analyze them at multiple site scales to clarify how the carbon and water fluxes are spatially distributed, how the responses to the environmental conditions differ spatially, and how terrestrial biosphere models perform in simulating carbon and water dynamics. Our specific objectives are to (1) improve the model performance by using the observed flux data; (2) clarify the environmental factors, including climate and stand disturbance, that control the carbon and water fluxes across the larch forests in East Asia; and (3) examine the response of the carbon budget to changes in seasonal weather patterns
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