| Forest ecosystem is a large carbon sink and plays an important role in land carbon cycle. The small change of forest photosynthesis and respiration may produce large change of CO2concentration in the atmosphere. Therefore, it is very important to estimate the distribution of forest carbon sources or sinks quantitatively. We need to establish and use more reliable, more suitable and simpler carbon cycling model to estimate forest carbon flux. So far, there are twenty kinds of carbon cycling models, such as IBIS, Biome-BGC, SiB3, BEPS, CASA, LPA and so on. However, these models does not either include the effects of human activity and landcover change on forest carbon cycle or take into account of forest age when calculating NPP. These models simulate forest carbon dynamics in short-term scale. In this study, long-term scale carbon cycling model, InTEC model, was chosen to simulate the distribution of northeast forest carbon sources and sinks. The InTEC model is a process-based boiogeochemical model to simulate C, N, water flux and the interactions between them. It includes the influences from climate, atmospheric composition, and disturbance regimes and simulates the responses of forste cabon and water cycle to these factors.Northeast forest annual NPP, NBP during1901-2009and their temporal and spatial variations were estimated using biogeochemical InTEC model, driven by remotely-sensed vegetation types, climate, forest age, leaf area index, and soil data. The relationship between NPP and forest age was modified in this study to suit northeast forest. We also analysed the sensitivity of the biogeochemical parameters in InTEC model and optimized these parameters according to the results of sensitivity analysis in order to accurately estimate forest carbon dynamics. At last, the effects of non-disturbance (climate, atmospheric CO2concentration, and N deposition) and disturbance (fire, insect, and harvest) factors on forest carbon sources and sinks estimation were analysed quantitatively.The detail contributions and conclusions were as followed:1. It is the first time to simulate the relationship between NPP and age for northeast forest tree species in this study to fill the blank of the northeast forest-related research, which verify the previous research in the United States and Canada, and provide important basic data for the carbon cycle model in the northeast forest applications2. Climate change, CO2fertilization, nitrogen deposition and disturbance caused the increases of annual northeast forest NPP. NPP value was higher in DaXing’an Mountains and Changbai Mountain, followed by Xiaoxing’an Mountain.3. Forest NBP became a source and reduced to-140gC·m-2·a-1in1920because of disturbances. In recent years, the northeast forest NBP began to increase. Forest in DaXing’an Mountains and Changbai Mountain has higher NBP and carbon sequestration ability, followed by that in Xiaoxing’an Mountain.4. Sources and sinks of soil carbon pool depend mainly on the history disturbances and atmospheric temperature and precipitation changes. Northeast forest soil is a huge carbon sink.5. Atmospheric CO2concentration has positive impact on forest NPP, NBP. Changes in atmospheric N deposition make forest NPP increase6gC·m-2·a-1during109years, NBP remains basically unchanged.6. Non-disturbance factor has the positive effect on forest NPP. Forest total NPP increases17%due to non-disturbance influence. Only considering the impact of disturbance, northeast forest total NBP has a little increase, with the value of0.8gC·m-2·a-1. Therefore, ignoring disturbance effects, non-disturbance factor has a little impact on the carbon sequestration for forest ecosystem. Carbon sequestration of forest ecosystem can be enhanced by proper disturbance.7. Only considering the impact of disturbance, northeast forest NPP, NBP all increase. If the disturbance effects are omitted, NBP estimation will decrease of60%. Therefore, an appropriate disturbance has a positive impact on the carbon sequestration for forest ecosystem. |
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