2.1 Study area
From southwest to northeast on the MP, the pattern of vegetation cover
grades from desert to grassland to forest, and the plateau shows
dramatic spatial and temporal variations in land cover (Liu, 1993).
According to the Global Aridity Index dataset, which is based on UNEP’s
(1997) aridity degree classification, the MP can be divided into an arid
area (including an extremely arid area), a semi-arid area, and a semi
humid area (including a humid area). The desert, grassland, and forest
are located mainly in the arid, semi-arid, and semi humid areas,
respectively (Miao et al., 2014). Although climate change, especially
precipitation changes, have affected the boundaries of these climate
zones to some extent (Jeong et al., 2011; Sternberg et al., 2015), they
have remained relatively stable on the whole. Here, we divided the MP
into three subregions, namely desert, grassland, and forest, in
reference to the UNEP (1997) aridity degree divisions. The distribution
of land cover is shown in Figure 1.
The desert subregion (DSR) is located in the southwest of the MP and has
an annual mean precipitation of <200 mm. The main land cover
is bare land and sparse vegetation (65%) and grassland (32%). The
grassland subregion (GSR) is located in the central and northern
portions of the plateau, and receives annual precipitation of between
200 and 400 mm. This is a subregion of the Eurasian grassland, which is
one of the largest grassland ecosystems in the world (Batima and
Dagvadorj, 2000). The main land cover is grassland (90%) and farmland
(4%). The forest subregion (FSR) receives annual precipitation of
approximately 400 mm, and the forest landscape is fragmented across this
region (Bohannon, 2008). The main land cover in this region is grassland
(41%), forest (34%), and farmland (18%).