森林生态系统碳平衡估测方法及其研究进展

综述了全球范围内森林生态系统碳平衡估测的 2种主要方法 ,即测定表面通量的微气象学方法 (涡相关法 )和生物量清单统计方法。指出了每种方法的优缺点及综合运用各种方法的重要性。简要介绍了应用上述方法对森林生态系统碳平衡研究的进展情况 ,并对今后森林生态系统碳平衡研究的发展趋势进行了探讨。

SUMMARY OF ESTIMATION METHODS AND RESEARCH ADVANCES OF THE CARBON BALANCE OF FOREST ECOSYSTEMS

Forests are major reserves for terrestrial carbon and major components of global primary productivity. The carbon balance of forests is very important for global change in the future. In this paper, two main methods to estimate the carbon balance of forest ecosystems were introduced. The two principal approaches are micrometeorological measurements of surface fluxes and biomass inventories. The methodological problems of each approach and the significance of combination of the two methods were also pointed out. Advance of the research work and the development trend of the study on the carbon balance of forest ecosystem were summarized. Eddy covariance is a micrometeorological technique relying on directly measuring the turbulent transport of CO_2 above a forest canopy. Applying eddy covariance techniques, several flux observation networks, such as EuroFlux in Europe, AmeriFlux in North and South America, MedeFlu in Mediterranean, Oz Net in Australia and AsiaFlux in Japan, have been set up to seek for the carbon cycle mechanism in terrestrial ecosystems and the carbon flow among carbon pools. Many field measurements have subsequently been made. The advantage of eddy covariance technique is that it can provide the data bases of carbon and energy fluxes of inter- and intro-annual variability on a large regional scale. Although eddy covariance has been used in estimating the bulk photosynthesis and respiration of forest sites, there is still uncertainty, much of which has focused on the night-time flux. Beside, there are few observation sites in the word and the data from each site is recorded separately, which restricts the study of the forest carbon balance on a global scale. So the network should be extended. The second main method used to estimate the carbon balance of forest is biomass inventory. Measurements of the diameter at breast height of trees can be converted to estimates of living, above-ground biomass using empirical allometric relations determined for each tree species. This method has been very popular and has a long history. Many countries have forest inventory data. Forest inventory has been made five times in China since 1949. The advantage of forest inventories is that they are direct, fairly unambiguous and technologically simple. The main disadvantages of biomass inventories are they are frequently incomplete and provide only intermittent records of the carbon stocks, which may not capture the effects of seasonal and inter-annual changes. In addition, one main uncertainty factor for estimating forest carbon balance is soil carbon stocks, which have been estimated very roughly or bypassed in many studies, because they are very difficult to test. Forest ecosystems are immensely complex dynamic systems. As shown earlier, each method of estimating carbon balance of forest ecosystem has both advantages and disadvantages. So a combination of a few kinds of techniques and methods, such as forest inventory, micrometeorological approaches, chlorophyll index and others, can provide new insight into the above-ground and below-ground flows of carbon. In addition, different groups of scientists work at different sites with different methods, and some of them are not concrete. International communication and cooperation is very important.