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).