4.3 Carbon sequestration potential of grassland restoration in Horqin sandy land
Desertification expanded from near-zero levels during the 19th century to reach 50.198 km² by 2000, which amounts to 47.6% of the total land area of Horqin (Zhao et al. 2009). Desertification affects the storage of C greatly; for example, Zhou et al. (2008) calculated that a total of 107.53 Mt of C was lost because of the desertification of the Horqin sandy lands during the 20th century. As a result of various efforts at restoring these lands, the desertified area decreased from 48.5% of total land area in 1975 to 47.5% (50.147 km²) in 2000. These efforts include afforestation of active sand dunes and banning grazing.
Li et al. (2013) found that SOC to a depth of 100 cm increased by 205 kg ha−1 every year over 28 years of afforestation with Mongolian pine, and Hu et al. (2008) found that C stock of the total ecosystem increased following the afforestation of grassland, above-ground stocks by 2.75 Mg ha−1 a year in the poplar plantations and by 1.06 Mg ha−1 a year in the Mongolian pine plantations. Li et al. (2013) estimated that if 30% of the severely desertified land (290.61 ha) were to be afforested with Mongolian pine, the C sequestered to a depth of 100 cm could reach 3.01 Mt after 38 years and that the ecosystem biomass could reach 4.48 Mt.
As to the present study, a conservative estimate puts the ecosystem C pools, after more than 20 years, at 104.29 t/ha in FG, 102.96 t/ha in MG, 92.24 t/ha in UG, and 24.48 t/ha in CK. Compared to CK, the amounts increased significantly over time, the total pools in any of the three treatments being, on average, four times those in the untreated control, particularly in soil and in the trees. The differences between the three treatments were probably due to the treatments themselves, and also due to the species, the extent of disturbance, and management practices in the past (zheng et al. 2008, Bisbing et al. 2010). These grasslands thus have a considerable potential to sequester C, as was also shown by Jones and Donnelly (2004) and He et al. (2008).
Controlling desertification requires re-establishment of vegetation cover, conservation of soil and water, enhancement of soil quality, and increased biomass production (Lal 2001). Different management practices that enhance or weaken C storage in the Horqin grasslands have significant implications for the global C budget, because the grasslands of northern China form a significant proportion of the Eurasian continent (Ojima et al. 1993).