From the perspective of climate change and the
global carbon cycle, agroforestry is attractive for at
least 2 reasons. The first is that the tree component
fixes and stores carbon from the atmosphere. Because
trees are perennial plants they can function as active
carbon sinks for periods of many years; trees continue
to store carbon until they are cut or die. As much as
500 to 600 million ha of tropical land may be suitable
for agroforestry (Houghton et al. 1991), although practices
could probably be established on only about
160 million ha by the middle of the next century
(Trexler & Haugen 1991). A second interest in agroforestry
is its apparent potential to reduce the need to
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CLIIMATE RESEARCH SPECIAL: TERRESTRIAL MANAGEMENT
clear new forest land for agriculture by providing an
alternative to shifting cultivation (Nair & Fernandes
1984, Winterbottom & Hazelwood 1987, Sanchez et al.
1990, Wiersum 1990, Andrasko et al. 1991). Current
estimates are that 1 to 2 Gt of carbon are released
to the atmosphere annually due to deforestation
(Houghton 1991). This is not all the result of clearing
for agriculture, but a significant portion is. As many as
300 million people are dependent on some form of
shifting cultivation, and they account for about 60 % of
all forest clearing (Myers 1991).