et al. 1988; Fuhr 1999; White 1994). Even in the secondary forest that is
sometimes derived from fallow, the long period of vegetation dominance by
long-lived pioneer tree species, with a low representation of forest-dependent
species caused by factors discussed earlier, ensures that recovery of the compo-
sitional characteristics of mature forests probably will take centuries even if
forest-dependent species are colonizing the site, which they may not be
(White 1994; Finegan 1996; Fuhr 1999). Shade and root competition from
pioneer trees undoubtedly slow the increase of species richness and diversity.
In Africa, Leroy-Deval (1973) and Kahn (1978) have shown that Macaranga
huriifolia (a short-lived pioneer species) and Aucoumea klaineana (a long-lived
pioneer species) established root grafts early in succession, increasing the com-
petitive power of the species and allowing the establishment of pure stands.
Despite low species richness in the early stages of fallow development,
shifting cultivation landscapes may be quite diverse when the species of fallows
of different ages are added up. For example, Christanty et al. (1986) reported
that the kebun-talun system of Java contained 112 plant species, largely
because of a long period of perennial production in a managed fallow. It is also
obvious that species richness in fallows increases dramatically in comparison
with that of crop fields. Hart (1980) and Ewel (1986) have suggested that such
systems may be designed as analogs of natural forest systems in that they tend
to mimic successional stages of the forest in structure and presumably in func-
tion. On the other hand, the increasing tendency to fallow invasion by highly
dominant species such as Chromolaena odorata (discussed earlier) is a tendency
toward further reductions in the plant species diversity of fallows.
From this subsection and those preceding, it is clear that the contribution
of fallows to the recovery of local-scale (alpha) diversity of vegetation, and the
compositional characteristics of primary forest, is small. This is because of the
shortness of fallow periods and the dominance of the vegetation by resprouts
and, in relation to regeneration from seed, by widespread short-lived pioneer
tree species. Plant diversity of fallow landscapes may be high, on the other
hand, although it does seem very unlikely that species numbers increase with
area at the same rate as in primary vegetation. The number of forest-dependent
species present in landscapes seems likely to depend principally on the area of
remnant primary forest.
Animal Biodiversity of Fallows in Shifting Cultivation
Shifting cultivation landscapes are a spatially and temporally heterogeneous
habitat for vertebrates, to a degree that is undoubtedly influenced by the scales
at which different species perceive such environmental variation. As in the case
of plant species and communities, research on vertebrates has focused on vari-
ations of species diversity and composition between different habitat types in
the landscape. Researchers have sought to relate this variation to factors such
- The Biodiversity and Conservation Potential of Shifting Cultivation Landscapes 173