Conversion of native vegetation, here referred to as deforestation,
has altered at least 697,770 km2 (10%) of
the basin, mostly due to expansion of agriculture and
cattle ranching in the southeastern “arc of deforestation”
(Figure 1; Eva et al. 2004). Deforestation in the uplands
increases water runoff and stream discharge through decreased
evapotranspiration (Hayhoe et al. 2011) and al-ters the morphological and biogeochemical conditions of
freshwater ecosystems through soil erosion and increased
export of terrestrial sediments into streams (Neill et al.
2001). These local processes can have profound effects
at regional scales. For example, deforestation of %50%
of the Tocantins and Araguaia basins (Figure 1) has increased
year-round water discharge by 25% and shifted
the flood pulse by one month in those rivers (Costa 2004;
Coe et al. 2009).
In floodplains, deforestation reduces the abundance
and diversity of highly productive plant communities that
sustain abundant animal populations (e.g., fishes; Melack
& Forsberg 2001). In the Lower Amazon, 56% of the
mainstem floodplain was deforested between 1970 and
2008, mostly for cattle ranching (Figure 1; Ren´o et al.
2011). In the riparian zones of small streams and rivers,
deforestation can lower water quality, increase water
temperature, and alter biotic assemblage composition and
production through increased sediments and removal of
structures that provide habitat for aquatic biota (Williams
et al. 1997; Neill et al. 2001). However, there are no
basin-wide data on the extent of riparian or floodplain
deforestation.