Global Extent of Land Degradation and Its Human Dimension - Principles of Sustainable Soil Management in Agroecosystems - page 215

tural intensification since its actions could directly lead to land degradation or
improvement.
9.4.1 a grIcuLturaL I ntenSIfIcatIon
Agricultural intensification—quantity of fertilizer applied per hectare—is positively
associated with the NDVI at a global level. This is not surprising since agricultural
intensification increases yield, thereby reducing the need for agricultural expansion.
Accordingly, Bai et al. (2008) also observed that cropland and rangelands, respec-
tively, accounted for 18% and 43% of the 16% of global land area where the NDVI
increased. In SSA where fertilizer application is the lowest, agricultural intensifica-
tion did not have a significant effect on the NDVI. In the Middle East and North
Africa (MENA), agricultural intensification was negatively correlated with the
NDVI. This result could be due to the fact that fertilizer is not a big driver of the
NDVI in the hyperarid region—where water is the driver of the NDVI.
9.4.2 p opuLatIon d enSIty
At a global level, there was positive but nonsignificant relationship between change
in population density and the NDVI ( Table 9.3 ). This is consistent with Bai (2008)
who observed a positive correlation between global level population density and the
NDVI. The same pattern is observed in East Asia and MENA regions. These results
demonstrate that it is possible to achieve sustainable land management even in areas
with high population density. This has been achieved in China and India—the first
and second most populous countries in the world. As Tiffen et al. (1994) demon-
strated in their work in Kenya—“more people less erosion”—this is achievable even
in low income countries, but certain conditions are required. Boyd and Slaymaker
(2000) show that access to markets contributed to the “more people less erosion”
case in Kenya. In South Asia and SSA, where intensity of poverty is high, change in
population density is negatively related with change in the NDVI. This is consistent
with past studies, which have shown land degradation to be positively correlated with
population density (e.g., Greperrud 1995; WCED 1987). This further demonstrates
that the impact of population density on land degradation is dependent on other con-
ditioning factors (Bosio et al. 2008)—including those discussed below.
9.4.3 e conomIc g rowth (gdp)
Consistent with the EKC, Table 9.3 shows the increase in national level GDP at
a global level; EU, Latin American countries (LAC), and MENA are first associ-
ated with a decrease in the NDVI, but later both increase after reaching a thresh-
old. However, given that forest extent in EU and North America* decreased in the
nineteenth century and recovered in the twentieth century (Meyfroidt and Lambin
2011), the forest transition observed in EU in the reference period (1981-2006) is a
* As noted earlier, North America was not included in the regression because the region has only a few
countries.