Simulation Of Carbon Dynamics In A Natural Secondary Forest In Northeast China Using IBIS

Many ecosystem models have been developed for simulating water and carbon exchanges between the atmosphere and terrestrial ecosystems, which have the potential to underpin our interpretation of regional CO₂ source-sink patterns. The Integrated Biosphere Simulator (IBIS) simulates carbon, water, energy fluxes with four sub-modules by integration of bio-physical, physiological and ecological processes. This study was conducted for exploring the ability of the IBIS for forests in regional scale in Maoershan, Northeast China. The carbon fluxes of six forest types were simulated and validated. The forests were Mongolian oak (Quercus mongolica Fisch.), aspen-birch (Populous davidiana Dode and Betula platyphylla Suk.), mixed deciduous (no dominant tree species), hardwood (dominated by Fraxinus mandshurica Rupr., Juglans mandshurica Maxim., and Phellodendron amurense Rupr.) forests, Korean pine (Pinus koraiensis Sieb.et Zucc.) and Dahurian larch (Larix gmelinii Rupr.) plantations. Some concluding remarks were given:(1) The IBIS successfully simulated the seasonality and annual sum of total soil respiration (R_s) and the rhizospheric respiration component (R_a) in 2004-2005 for all the six forest ecosystems. However, the model did not fully catch the seasonality of the heterotrophic component of soil respiration, especially for the pine plantation, aspen-birch and mixed deciduous forests. Although the heterotrophic simulation did not substantially influenced total soil respiration, the biases in some periods limited the prediction of the model.(2) The simulated gross (GPP) and net primary (NPP) and ecosystem (NEP) productivity was reasonable. The GPP ranged from 10 to 11.5 t C ha^-1 yr^-1, with small difference between forest types. However, the NPP of larch plantation was highest (about 7 t C ha^-1 yr^-1), other forests were all less than 5 t C ha^-1 yr^-1. The model might underestimate the NPP of the four broadleaved forests. The average carbon use efficiency (CUE) was 0.41 (±0.12) (SD), ranged from 0.33 for hardwood broadleaved forest to 0.64 for larch plantation. The CUEs of the four broadleaved forests were lower than the average of the same biome, which suggested the potential underestimation of NPP of natural forest. The NEP ranged from 0.89 for hardwood broadleaved forest to 4.61 t C ha^-1 yr^-1 for larch plantation, with an average of 2.18 t C ha^-1 yr^-1, which indicated the six forests behaved as moderate carbon sinks.This studies modified and validated IBIS in various forest ecosystems in Maoershan, and lays a foundation for the further modification and application of the model in Northeast China.