446 Richard T. Corlett and Richard B. Primack
Even in so-called “selective logging,” the pro-
cess of finding, cutting, preparing, and extracting
rainforest logs can be devastating (Nepstadet al.
1999), yet most wildlife can survive one cycle
of selective logging (Johns 1997, Fimbelet al.
2001). However, the loss of trees is a lesser impact
than the construction of roads and other infras-
tructure. Improved access brings in hunters and
encourages recurrent cycles of logging. Landless
farmers often move into the area and remove the
remaining trees for agriculture. Recently logged
forests are also far more likely to burn than those
that have not been logged or were loggedlong ago
(Siegertet al. 2001).
Hunting
Rising human populations, the wide availabil-
ity of guns, and improved transport systems
connecting hunters to regional markets have
transformed subsistence hunting of rainforest
wildlife into a commercial enterprise (Robinson
and Bennett 2000, Milner-Gulland and Bennett
2003, Walshet al. 2003, Corlett 2007). The
bushmeat trade, and more local hunting for tra-
ditional medicine (e.g., Nijman 2005) and the pet
trade (e.g., Wrightet al. 2001, Duarte-Quiroga
and Estrada 2003, Raselimanana 2003), threat-
ens vertebrates throughout the tropics. Hunting
of forest vertebrates not only affects the survival
of the harvested species, but also disrupts the
web of interactions that maintains forest diver-
sity, including seed dispersal (particularly of large
seeds), seed predation, browsing of seedlings, and
predation (Wright 2003).
Fire
Undisturbed rainforests do not normally burn
except under extreme drought conditions
(Whitmore 1998). Rainforest fires became more
common over the last 25 years due to forest
fragmentation, logging, and increased ignition
sources (Barlow and Peres 2004). Farmers com-
monly use fire for clearing rainforest and pre-
venting regrowth, but these fires are difficult to
control. Uncontrolled fires burned an estimated
50–60 million ha of forest in Southeast Asia and
the Neotropics during unusually dry conditions
caused by the 1997–1998 El Niño event (Nepstad
et al. 2004). The open canopy and abundant fuel
supply in loggedforests make them particularly
vulnerable to fire (Siegertet al. 2001). Forest
fragments are also vulnerable because structural
changes at the edges increase available fuel, while
exposure to wind and sunlight reduces humidity
(Laurance 2004). Single fires lead to positive feed-
backs by further increasing fuel load and canopy
openness (Cochraneet al. 1999). The result is a
landscape that becomes vulnerable to fire after
weeks, rather than months, without rain.DeforestationRainforests potentially can recover from log-
ging, hunting, and single fires, but few rainforest
species can survive complete removal of the for-
est (Figure 26.2). Generalizing about the causes
of rainforest conversion is impossible, given the
variety of human systems in the tropics, but glob-
ally, most rainforest destruction still results from
small-scale crop cultivation by poor farmers, typi-
cally migrants from other rural areas in the same
country. Large farms and cattle ranches on the
forest frontier are often formed by consolidat-
ing smaller plots opened up by the first settlers,
although direct clearance by large landowners
and commercial interests is the major cause of
conversion in some areas. Small-scale shifting cul-
tivation is the primary cause of deforestation in
Central Africa (Zhanget al. 2005). Cattle ranch-
ing has been most important in tropical America
(Fearnside 2005), while tree plantations (oil palm,
rubber trees, cacao, etc.) cause most deforesta-
tion in Southeast Asia (Barberet al. 2002, Curran
et al. 2004). In Brazil, mechanized soybean cul-
tivation is an expanding threat in the Amazon
region (Fearnside 2001, 2002, but see also Brown
et al. 2005).
Deforestationratesvarygreatlybothwithinand
between regions (Table 26.1), changing rapidly
in response to factors such as El Niño, local
and global economies, and political events in
individual countries. Satellite imagery showed
that approximately 58,000 km^2 per year (0.5%)