Environmental Engineering Reference
In-Depth Information
arable land every calendar year—range from less than 1 (in Canada or on the U.S.
northern Great Plains, where some i elds are fallowed and the rest are planted only
once a year) to about 1.2 (China's current national average, rel ecting northern
single-cropping and southern multicropping) to more than 2 (in the most produc-
tive coastal and interior provinces of South China, where triple-cropping is not
uncommon).
The total numbers of domestic animals that relied solely or largely on grazing
eventually became too large to be supported by seasonal or year-round productivity
of natural grasslands. As a result, the conversion of natural ecosystems to heavily
grazed pastures has affected not only many grassy ecosystems but has been a major
reason for tropical deforestation (particularly in many countries of Central America
and in Brazil) and for the destruction of wetlands. According to the FAO, in the
year 2000 the global area of permanent meadows and pastures was, at about 3.35
Gha, more than twice as large as the total area of agricultural land (FAO 2011f).
Europe was the only continent where the reverse was true: its pastures occupy an
area equal to only about 60% of its i elds and orchards. In contrast, Asia's pastures
cover twice the area of the continent's i elds and plantations.
But a recent global account that was also based on inventory data came up with
only 3.15 Gha of pastures, and its adjustment on the basis of satellite imagery
resulted in an even smaller area of just 2.8 Gha (Ramankutty et al. 2008), while the
History Database of the Global Environment lists 3.43 Gha (HYDE 2011). The
FAO/HYDE total means that permanent pastures are the largest area of natural
ecosystems that has been modii ed in various degrees by human actions. Croplands
are next, and tree plantations and actively managed forests come third, with the
total about 650 Mha (Noble and Dirzo 1997), followed by impervious surface areas.
The FAO's land-use and land-cover statistics have been generally accepted as the
most consistent and most reliable global compilation for the post-World War II
period. Their main categories related to food production now list the following
areas: total agricultural land, arable land, land devoted to permanent crops, irrigated
land, fallow land, and permanent meadows and pastures.
Data are available online for all countries and as various regional groupings and
global totals since 1961 and in print since 1947, with many data gaps in the earliest
years. The information in the FAO's database relies on the ofi cial submissions of
member countries and, when these are not available, on the best estimates prepared
in the organization's headquarters in Rome. Either sourcing can be problematic,
as some countries have supplied deliberate misinformation and as the internal esti-
mates are often based on the best available but unreliable and dated information.
