Scale Measurement and Threshold Optimization for Implementation of the “Returning Farmland to Forests or Grass” Policy: Based on the Dual Perspectives of Human and Nature
Authors: Wang Jing , Liu Jun , Yang Na 
Published: January 2024

Land degradation is the most serious environmental issue globally, which
is associated with human activities and climate change. Quantified
information on land degradation and restoration is required to support
the development of policies for sustainable ecosystem management and
socioeconomic development. The arid and semiarid zones of China (ASZC)
have experienced significant land degradation, and multiple ecological
projects have implemented to address the issue. Among them, The
Returning Farmland to Forests or Grass (RFFG) is a major ecological
project in China. It is intended to protect and improve the ecological
environment and achieve sustainable development. Since 2002, the country
has incorporated the county economies, which are key components of the
national economy, into the reform system. This paper uses 342 counties
(districts) of the Loess Plateau as the basic research unit to more
comprehensively evaluate the effect of the RFFG. Based on meteorological
and socioeconomic data from 2000 to 2019, fractional vegetation cover
(FVC) was derived from the MODIS normal difference vegetation index
using threshold regression models in two dimensions, namely the
population level of urbanization (PLU) and the standardized
precipitation evapotranspiration index (SPEI). Using the FVC, we
demonstrate the ecological restoration effects of implementing the
“RFFG” on the Loess Plateau. We performed scale measurement and
studied methods to optimize the implementation of this policy on the
Loess Plateau, via empirical analysis of threshold effects and optimal
thresholds of the PLU and SPEI. The findings are as follows: In terms of
PLU, the rapid development of the population level of urbanization in 55
of the 342 counties (districts) in the Loess Plateau (PLU more than
76.41%) seriously hinders the implementation of the RFFG. The 12
counties (districts) are further effective in ecological projects in the
Loess Plateau. The priority development area applied (PLU does not
exceed 18.12%). Only 27 counties (districts) in the region have
achieved the FVC optimal value, and the growth space of FVC in Qinghai
and Ningxia is close to 100%, followed by Gansu and Shanxi. The
optimized area of the Loess Plateau is as high as 64.748 million hm2,
covering the whole region (98.51% of the area). In terms of SPEI, the
ecological project in the Loess Plateau is expected to be further
effectively implemented in 29 counties (districts) that tend to turn
mild drought to extreme drought, and the implementation of the RFFG has
been strongly inhibited by 37 counties (districts) (which tends to the
evolution of moderate flooding to extreme flooding). The 202 counties
(districts) in the region achieved the FVC optimal value, and the FVC
growth areas in Gansu, Ningxia, and Shanxi were relatively large. The
optimized area can reach 31.235 million hm2, accounting for 47.52% of
the total area of the Loess Plateau. The empirical results of the two
threshold regression models show that the effect of SPEI on the FVC is
weaker than that of PLU, and the effect of flooding on the FVC is more
significant than that of drought, which is concentrated in the central
Loess Plateau. Furthermore, the implementation of the “RFFG” has
promoted the coordinated development of PLU and FVC, and SPEI and FVC.