4.2 Discussion of different vegetation types
Here, we compared vegetation restoration and degradation on the MP, and
found that the relative intensity of vegetation change in the three
subregions was: FSR > GSR > DSR. For
comparison, we considered changes in different types of vegetation cover
from previous research over the same time period. Research that focused
on the grassland and forest regions of East Asia showed that the mean
value of carbon use efficiency (CUE) was grassland >
farmland > forest > shrub during the period
2000–2013 in China (Liu et al., 2019). That is, the highest CUE was
found in grassland, and the increase of CUE was caused mainly by
increases in precipitation, while increases in temperature inhibited the
vegetation CUE. Liu et al. (2020) studied the response of the NDVI on
different types of vegetation cover influenced by climate change on the
Loess Plateau of China. Their results showed that the NDVI of different
vegetation covers does not correspond to the size of the occupied area,
and that the increasing trend of the NDVI in the forested areas was
greater than that in the grassland areas (the grass area is larger than
forested area), which is similar to the conclusion of this study.
Other spatiotemporal studies reported different results. De et al.
(2013) described the relationship between vegetation and climate over
the period between 1981 and 2008 based on meteorological indicators, and
found that climate can explain nearly 54% of vegetation change.
The impact of vegetation change on climate is concentrated mainly in
areas of desertification and surrounding areas. Charney (1977, 2006)
explored the possible impact of vegetation dynamics on climate, and
pointed out that desertification increases the surface albedo, reduces
the soil moisture content, and reduces the surface roughness. This leads
to reduced precipitation, which would be followed by deterioration of
the vegetation and soil. Vegetation recovery becomes more difficult
under these conditions (Nicholson et al., 1988), and these impacts can
then extend to the surrounding areas (Xue, 1993, 1996). The expansion of
a desert region may strengthen regional climate change, aggravating land
degradation. Grassland has a greater ecological elasticity to climate
change compared with desert areas (John et al., 2013). Peng et al.
(2012) proposed that, compared with forest ecosystems in humid areas,
grassland ecosystems in semi-arid and arid areas are more sensitive to
drought. Desert grassland is more sensitive to drought compared with
typical grassland and meadow grassland (Bailing et al., 2018).
Therefore, there may be a negative feedback relationship between
vegetation change and climate in desert areas. Here, we observed that
the DSR has the slowest observed vegetation restoration.
Bao et al. (2015) studied vegetation dynamics and its response to
regional climate change in Mongolia, and showed that continuous warming
is likely to be the main factor driving the reversal of the NDVI trend.
Furthermore, climate-related vegetation reduction and related potential
desertification may aggravate other environmental problems in East Asia
(e.g., sandstorms).
The vegetation restoration associated with human activity in the desert
is inseparable from vegetation restoration measures and projects
formulated by local governments. We list the policy measures and their
impacts on regional vegetation restoration after 2000 in Table 4.
Therefore, we conclude that the desert is the region of the MP most in
need of vegetation restoration, although it is also currently the area
with the slowest rate of vegetation restoration. Restoration of desert
areas is effective, and the desert should be a high priority area for
improving vegetation restoration.
5 Conclusions
Our evaluation of vegetation dynamics and the associated driving factors
across the MP and its subregions has revealed the following. The
proportion of each subregion that experienced vegetation restoration
during the study period was greatest in the FSR, followed by the GSR,
with the DSR showing the least restoration. From the perspective of
driving factors, overall, climate change was conducive to vegetation
restoration, whereas the amounts of vegetation restoration and
degradation caused by human activity were relatively similar. From the
regional perspective, the extent of restoration caused by climate change
in the FSR and GSR was far greater than that caused by human activity,
but in the DSR, restoration by human activity exceeded that related to
climate change. Restoration in the DSR was slower than that in the FSR
and GSR. As a result, the DSR should be a priority area for policy and
investment. Human activity was the main driving force behind vegetation
restoration in the DSR, and thus the restoration effect of human
activity is still effective in this region. China’s government should
use “the Belt and Road Initiative” (Liu, 2015) to cooperate and
establish links with Mongolia and other countries to assist
desertification control and curb regional land degradation.
Acknowledgments: This research was supported by National Key
R&D Program of China (No. 2018YFC0806900).
Conflicts of Interest: The authors declare no conflict of
interests.