Tropical Forest Community Ecology

Tropical Rainforest Conservation 447

Figure 26.2 Agriculture is a major

contributor to rainforest destruction.

In this case, indigenous people in the

Brazilian Amazon have cut down trees

and burned them in preparation for

planting their crops. Here a local chief

stands in front of land that has been

cleared (photograph courtesy of Milla

Jung).

of the 11.5 million km^2 of humid tropical for-
est observed in 1990 were cleared from 1990
to 1997 (Achardet al. 2002, Mayauxet al.
2005). Another 23,000 km^2 annually (0.2%)
were degraded to an extent that was visible in
satellite images. Rates of both loss and degra-
dation were twice as high in Asia (including
New Guinea) as in Africa, with tropical Amer-
ica showing the lowest overall rates of both.
These averages, however, masked huge differences
withinregions,withdeforestation“hotspots”such
as Acre in Brazilian Amazonia, parts of Madagas-
car, and central Sumatra experiencing deforesta-
tion of more than 4% per year. Note also that
the 1990–1997 period of this study omits the
1997–1998 El Niño Southern Oscillation (ENSO)
event, during which huge areas of forest were
burned.

Invasive species

Invasive species are most obviously a threat on

oceanic islands such as Hawai’i, where exotic

species of all types are a huge problem (Loope

et al. 2001). Continental rainforests have proven

much more resistant (Teoet al. 2003, Denslow

and DeWalt Chapter 24, this volume), but increas-

ing numbers of cases exist where species from

one continent have invaded disturbed and frag-

mented rainforests on other continents. Old

World honeybees in the Amazonian rainforest

(Roubik 2000), feral pigs in Australia and New

Guinea (Heise-Pavlov and Heise-Pavlov 2003),

and neotropical pioneer plants in Old World forests

(Peters2001,Struhsakeret al.2005)arejustthree

examples.

Global climatic and atmospheric

change

Abundant evidence exists that climate changes

are affecting biological communities in the north-

ern temperate zone (Parmesan 2007), but the

evidence from the tropics is less clear. Empiri-

cal evidence suggests increased tree turnover in

Amazonian forests in the last two decades, but

there is currently no consensus on the driver(s)

of these changes (Lewiset al.2006). Global cli-

mate models predict changes in temperature and

water balance in the tropics over the next cen-

tury that will subject many species to conditions

outside the range of tolerance that their current

distributions indicate (e.g., Meynecke 2004, Miles

et al. 2004). In most areas, the direct impact of

these changes will probably be dwarfed by interac-

tions with other human impacts (Corlett 2003). In

particular, any increase in the frequency and/or

intensity of dry periods would accelerate the

synergy between logging, drought, agricultural

clearance, and fires (Laurance 2004).

MANY RAINFORESTS

There are five main rainforest regions in the world,

each with its own level of threat from human

activities.