Agriculture Reference
In-Depth Information
of total genera and species it is the most common sub-family. Although some of these
Caatinga legumes are found in neighbouring vegetation and a few are pan-tropical,
more than 50% are endemic to the region. There is also a high level of endemism in the
Cerrados, although not all data are available. There are few data on the effectiveness
of nodules in the Caatinga, except for some
Mimosa
and
Chamaecrista
species that were
studied by Sprent et al. (1996) and E.K. James et al. (unpublished data) as described
for the Cerrados in Section 2.2.2. However, the annual rainfall in Caatinga is less that
in the Cerrados (300-1000 mm). Endemic species are found in a variety of soils, from
rich calcareous areas to sand dunes. There is no obvious pattern of legume distribution
among these types. However, there are better possibilities for estimating nitrogen fix-
ation in this area by the
15
N method, as the soil nitrogen has a higher content of this
isotope (R.M. Boddey, personal communication; Unkovich et al., 2008). This suggests
that nitrogen cycling in at least some areas of the Caatinga may differ from that in some
areas of the Cerrados. How or whether this is relevant to nitrogen fixation is not yet
clear.
2.3.2 Other areas
The situation in the SDTF of Peru (another biodiversity hot spot) is broadly similar
across sub-families (Table 2.2B), although the total number of taxa is smaller (Linares-
Palomino, 2006). There are, however, differences in the genera, with, for example
Chamaecrista
having only one species in Peru, but
Inga
(Mimosoideae), a genus absent
from Caatinga, having seven.
2.4 Rain forests
Rain forests are usually associated with the Amazon, tropical Africa and Asia, but
are also found elsewhere. Before dealing with the tropical ones, the South American
Atlantic forest and temperate rain forests will be considered.
2.4.1 Atlantic forest
This is a 1,233,875-km
2
biodiversity hot spot extending down the Atlantic coast of
Brazil from Rio Grande do Norte, to Rio Grande do Sul. It has two parallel parts, the
coastal, lowland region and the inland montane and 'Campo Rupestre' region, which
extends to Paraguay. It merges with the SDTF region of Brazil, discussed earlier, with
which it has many genera and species in common. Again, legumes form the dominant
family, with
Inga
being among the most numerous in terms of species. This large genus
extends throughout the neotropics and has shown rapid recent speciation (Richardson
et al., 2001), a topic that will be covered in Chapter 3. Like the Cerrado and Caatinga
regions, it has been decimated by agriculture, this time mainly for sugar cane and
coffee growing. The complex nature of the Atlantic forest and its overlap with other
regions such as the Caatinga are discussed by Oliveira-Filho et al. (2006). This paper
also has appendices with extensive lists of tree species.
