NPP And Carbon Storage In Subtropical Forest, Eastern China

The carbon cycle of terrestrial ecosystems plays a key role in regulating CO₂ concentration in the atmosphere. Thus, enhancing carbon storage in terrestrial ecosystems, and especially in forests, will be a key factor in the maintenance of the atmosphere's carbon balance. Forest is the main terrestrial carbon pool, and one of most important ecosystems in carbon cycle. Accurate assessment of forest carbon storage and carbon balance is a key factor of estimating future atmospheric CO2 concentrations.Forests in Zhejiang have thousand years of disturbing history, especially serious damage after war and in 1958. They represent most of the forest of China. Since China began reform and open, Zhejiang's economic and social had rapid develop speed, thus total economic production of the province is at the fourth position of China. The rapid development of industrialization and economic effectively accelerate the urban sprawl process. While large areas of cropland were transformed to urban areas, rural forests restore as rural population falling down. Zhejiang's economic development and ecological restoration are at the front throughout the country. The study on its forest ecological benefit and urbanization effect on regional carbon storage, would give a model for the future development of provinces and cities in the central and western of China.Ecological service forest (ESF) is established to maintain ecological processes and protect the environment. We sampled 149 stands from 5 to 50 years old, covering 101,800 km₂, in Zhejiang Province, in China's eastern subtropical zone. The samples included four types of ESF: evergreen broad-leaved forest (ESF-EF), coniferous and broad-leaved mixed forest (ESF-MF), pine (Pinus massoniana) forest (ESF-PF), and Chinese fir (Cunninghamia lanceolata) forest (ESF-CF). Based on the data from field investigations in Zhejiang (1999-2000), we estimated biomass, litterfall production, NPP and carbon storage in Zhejiang. We also used estimated results to exam TRIPLEX model, then synthesized model and remote sense to assess the urbanization effect on regional NPP using Great Hangzhou Area (GHA) for example. The main results are summarized as follows:1) The mean values of biomass in evergreen broad-leaved forest, coniferous and broad-leaved mixed forest, pine forest, and Chinese fir forest were 89.19, 70.06, 51.25, and 54.15 t ha^-1, respectively. The NPP for the four types of ESF ranged from 4.41 to 8.35 t ha^-1 year^-1.2) Overall, biomass, litter production, NPP, and carbon density were all significantly lower in pine forest and Chinese fir forest than in evergreen broad-leaved forest, whereas the values for the coniferous and broad-leaved mixed forest were intermediate.3) Four main forest types in have subtropical forest larger difference at NEP. This shows that the evergreen broad-leaved forest have greater potential for carbon sink. By comparing the main forest types in the region, we found that promoting succession process will maximize young or disturbed forests in the subtropical region of China to increase carbon storage in future (the highest growth of 42.49%), and become larger carbon sink. Next 50 years, it will be an important stage for enlarge carbon sink in Zhejiang Province. We provided data to correct carbon source/sink data of China, and also filled the gaps at north latitude between 25 and 30 degrees. Through the measurement of underground productivity and heterotrophic respiration in the field, we can further estimate subtropical forest carbon balance accurately, to examine the hypothesis that high-latitude forest may be an important carbon sink.4) The results show that simulated density, H, DBH, litter pool, aboveground and total biomass are consistent with observed data collected through Zhejiang Province, suggesting that the TRIPLEX1.0 model is capable in simulating forest growth and biomass dynamics of subtropical forest ecosystems. The independent validations obtained by utilizing TRIPLEX1.0 demonstrate that the model offers competency while providing confidence when applying its ability to extrapolate outcomes at regional scales and its ability to withstand rigorous testing for simulating carbon storage in subtropical forest ecosystems.5) We used GHA for example to study urbanization effect on NPP. The urban areas in GHA sprawl rapidly between 1975 and 2003; total area of rural forests increased significantly; cropland areas decrease quickly; water areas remain stable. The NPP of urban area decline was not obvious from 1975 to 1990, but it dropped by 50 g m^-2 yr^-1 from 1990 to 2003. Since 1975, NPP of GHA has average annual growth rate of 1.22% in 28 years. This shows that urbanization did not reduce but increased GHA regional NPP, and implied that urbanization has offset effect on regional vegetation.6) Carbon densities for the four types of ESF were lower than the mean values for China, especially coniferous forest (25.6 and 26.8 tC ha^-1), because the ESFs are relatively young in Zhejiang. If these plantations and secondary forests are restored to mature forest, they would attract a lot of CO₂, then ESFs in Zhejiang still have great potential on accumulation of carbon.Due to the complexity of mechanisms and the universality of fields in carbon cycle and carbon balance, there are still many problems need further study and discussion: Sources of error and uncertainty analysis, vegetation and soil carbon sinks, and scaling. In order to be more accurate in estimation, we need to sample within the whole province including all forests randomly, to combine with soil respiration and heterorespiration, then can calculate carbon balance of the whole ecosystem and evaluate the benefit of carbon source and sink. What's more, based on the current parameters of models and simulation data of local climate in the future 100a from IPCC, we can predict local carbon storage and flux in the future, and scale to larger region. These results suggest that the evergreen broad-leaved forest has great potential for offsetting CO₂ emissions, and that promoting succession from coniferous forests to evergreen broad-leaved forest can enhance carbon sinks in the forests of subtropical China. To improve carbon storage, the current management approach for ecological service forest should be reformed to accelerate the succession of coniferous forest into evergreen broad-leaved forest, thereby increasing the productivity of existing ecological service forest.