A small fraction of the plant diversity of the original forest may be present
in crop fields because some forest trees are preserved by shifting cultivation
farmers. Their wood may be too hard to be cut using traditional tools (e.g.,
Samanea dinklageiand Lophira alatain Africa, Koompassiaspp. in Southeast
Asia, Dipteryx panamensisin Mesoamerica). Their crown may produce a very
light shade and therefore not hinder the crop growing beneath (e.g., Piptade-
niastrum africanumin Africa). Another, more compelling reason is that these
trees are the source of important products for purposes such as construction,
food, and medicine, or they have strong cultural values. Among the trees
spared for food, Coula edulis(nuts), Garcinia kola(nuts), Irvingia gabonensis
(fruits), and Ricinodendron heudelotii(fruits) are examples of species common
in forest fallows throughout humid lowland Africa. Another interesting exam-
ple is Sterculia rhinopetala.The Ntumu in southern Cameroon preserve this
species because the fruits are considered to attract small antelopes, a favorite
game animal in the region (Carrière 1999). Among the forest tree species nur-
tured by the Krissa of Papua New Guinea, 9 percent are retained because when
in flower or fruit they attract a range of game animals and birds and are con-
sequently used by hunters as hides to ambush game (Kocher-Schmid 2001).
In Southeast Asia, Koompassiaspp. trees are preserved not only because of the
hardness of their wood but also because they are a favorite place for bees to
establish their hives (Mabberley 1987; Prebble et al. 1999).
Switching the focus to the neotropics, Unruh (1988) recorded a number
of valuable primary forest plants conserved by shifting cultivation agricultur-
ists on farms in Peruvian Amazonia. Brazil nut (Bertholletia excelsa) is a prime
example of a primary forest tree species conserved because of its high value
(backed up in Brazil by a law that prohibits the cutting of this species). The
low density of B. excelsatrees in most Amazonian primary forest (Shanley et
al. 1998) may mean that trees are not abundant on farms, although they are
certainly present on many (A. da Silva Dias, pers. comm., 2001). Peña-Claros
(2001) suggests that B. excelsamay be just as abundant in anthropogenic habi-
tats as in primary forest in the southwest Amazon, or more so, because of a
combination of tree conservation by farmers and successful regeneration
caused by the light-demanding nature of this species. B. excelsais suitable for
planting in fallows and actively used agricultural habitats, although this prac-
tice is not common (Peña-Claros 2001).
The planting of trees by farmers seems related more to complex agroforests
(see Chapter 10, this volume) than to classic shifting cultivation. Limits are
not always clear, however, and the Krissa people in Papua New Guinea prac-
tice a form of shifting cultivation focusing on woody species, nurturing or
planting trees (Gnetum gnemon) and palms (Areca catechu, Cocos nucifera,
Metroxylon sagu) as major crops in their shifting cultivation gardens. A cursory
count in a Krissa garden revealed 11 different trees, two palms and two bam-
boo species planted, and seven tree and two palms nurtured from the
- The Biodiversity and Conservation Potential of Shifting Cultivation Landscapes 169