Agriculture Reference
In-Depth Information
3.1 NEOTROPICAL SAVANNAS AND THE CERRADO
Savannas are major land ecosystems comprising a global extent that has been esti-
mated to vary between 15 and 37 million (M) km 2 (House and Hall 2001). This
broad range of area reflects the difficulties in defining what exactly is a savanna veg-
etation, not only due to its wide variability in plant diversity and degree of tree cov-
erage but also because savannic areas shift considerably in decadal time frames due
to changes in regional rainfall and land use. In the context of this article, a savanna
is defined as a biome in which different combinations of grass, shrub, and tree strata
occur, either as a roughly homogeneous mix in the same area or as a dominantly
grassy landscape where shrubs and trees are sparse, or concentrated on patches or
drainageways. Savannas occur in large areas in Africa and the Americas, but also in
Southeast Asia and Australia. The word “neotropical” is traditionally used to refer to
the tropics of the “New World,” especially South America. Neotropical savannas dif-
fer considerably from their African counterparts, more notably by a relatively more
humid climate, high plant, and animal biodiversity (Grace et al. 2006) but paucity
of large terrestrial animals, and a sparser human occupation (House and Hall 2001;
Romero-Ruiz et al. 2012).
Neotropical savannas are estimated to cover 2.69 M km 2 , which can be broadly
divided into two major areas and a group of much smaller, isolated occurrences
(Rippstein et al. 2001). These two main savannas consist of the Cerrado of central
Brazil and the Llanos of Venezuela and Colombia, comprising, respectively, 76%
and 17% of the total neotropical savanna area. The remaining 7% consists of smaller
formations in the Caribbean, Central America, Amazon basin, and other regions of
South America. These isolated savannas evolved under disparate environmental set-
tings, and most do not support intensive agriculture presently and are sparsely stud-
ied. For example, the savannas of the inner Amazon basin are so remote and poorly
known that earlier aerial images of them were interpreted as clear-felled areas. On
the other hand, the Llanos (from the Spanish word for “plains”) of the Orinoco basin
has for centuries been used as natural pastures, the only land use compatible with the
low-fertility, poorly drained soils and the excessive rain in some areas. Pioneering
centers for agriculture research, such as Centro Internacional de Agricultura Tropical
(CIAT), were established in the region and have done extensive research to study the
Llanos environment and stimulate crop production. However, significant infrastruc-
ture improvements have only recently been established to support oil production and
also intensive annual cropping (Rippstein et al. 2001). As much as 14% of Colombian
flooded savannas were converted to croplands, exotic pastures, and oil palm ( Elaeis
guineensis Jacq.) plantations between 1990 and 2010, and 70% of the eastern Llanos
is expected to be converted to agriculture in the near future (Romero-Ruiz et al.
2012). Despite recent developments and a solid base of scientific research, the full
agricultural potential of the region is yet to be realized, and the predominant land use
is still low-density cattle ranching (Rondón et al. 2006).
In contrast, the Brazilian Cerrado (also known as Cerrados ) covers a contiguous
land area of 2.04 M km 2 ( Figure 3.1 ), an area slightly larger than that of Mexico. It
is the most important savanna ecosystem for agriculture in the world not only due to
its areal extent, favorable climate and soil but also because of recent state-induced
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