关键词: 桉树, 森林资源清查, 地理分布, 森林生产力, 碳储量, 碳汇能力

Abstract:

Objective: It is important to study the resource changes, productivity and carbon sink capacity of Eucalyptus plantation forests in China during 1973—2018, with a view to revealing the soil fertility depletion of Eucalyptus plantation forests, objectively evaluating the contribution of Eucalyptus plantation forests to increasing timber supply and enhancing forest carbon sink capacity in China, and providing a scientific basis for formulating sustainable management policies. Method: In this study, we collected the sample plot data from 9 national forest inventories(NFIs) during 1973—2018, China forest-land database map in 2003 and 2016, as well as climate and elevation data, and analyzed the dynamic changes in the spatial distribution of Eucalyptus plantation forests and continuously tracked the changes of Eucalyptus in fixed sample plots, and quantitatively evaluated Eucalyptus in China based on the accumulation data of eucalyptus fixed sample plots for 5 periods of 25 years(from 1994 to 2018). The productivity, carbon accumulation capacity, and abandonment rate of Eucalyptus in China were quantitatively evaluated based on the accumulation of Eucalyptus in fixed sample plots for five periods of 25 years. Result: The results showed that regions with annual mean air temperature of 19-21 ℃, annual precipitation of 1 400-1 600 mm, and elevation of 0-300 m above sea level suit the growth of Eucalyptus plantations best. The average annual productivity of Eucalyptus trees nationwide generally ranges from 4.14 to 8.57 m³·hm^?2a^?1, which is higher in four provinces of Hainan, Guangdong, Guangxi, and Fujian, with 2-3-year-old Eucalyptus forests approaching 40 m³·hm^?2a^?1; according to the 9th inventory (2014—2018) data, the average annual carbon sequestration per hectare of Eucalyptus was 5.29 t·hm^?2a^?1, which was 2.95 and 2.18 times higher than that of fast-growing tree species, horsetail pine and fir plantations in the same region. Despite the low harvesting age of Eucalyptus and the fact that 46% of the harvesting volume is used for paper production, 54% of the harvesting volume is still in the form of panels for long-term carbon sequestration, and the carbon sink function is still strong. Eucalyptus is an important timber species, and while the area of Eucalyptus accounts for 6.85% of the country's plantation forest, the annual timber harvest accounts for more than 17.96% of the country's plantation forest harvest; among them, Guangdong and Guangxi account for 30.32% and 34.91% of their plantation forest area, while the harvest accounts for 66.29% and 49.97% respectively. However, Eucalyptus grow vigorously and consume large amounts of land power. The abandonment rate of the original Eucalyptus plantation area is about 25% or more every 5 years, and the cumulative abandonment rates at 10 and 20 years are close to 50% and 75%, respectively, with the risk of serious decline in land power and difficulty in reforestation after long-term continuous planting. Conclusion: Through measures such as controlling the continuous management cycle of Eucalyptus plantations, carrying out reasonable crop rotation and improving scientific management, the abandoned land can still be replanted. The area of Eucalyptus plantations replanted within 20 years accounts for less than 20% of their abandoned areas, and less than 30% within 50 years, indicating that there is still potential to increase the replanting rate. Therefore, sustainable management of Eucalyptus plantation forests in China should be strengthened to maintain soil fertility and make greater contributions to securing China's timber supply, protecting natural forest resources, enhancing forest carbon sequestration capacity and mitigating climate change.

Key words: Eucalyptus plantations, national forest inventory (NFI), geographical distribution, forest productivity, carbon storage, carbon sink capacity