Box 8.2. Main Features of Community-Level Biodiversity
in Shifting Cultivation Landscapes
- Cultivated plants belong mainly to a few species, but crop fields may
harbor important agrobiodiversity at the genetic level whose creation
and maintenance are little understood.
•Weed communities sometimes are quite diverse and potentially valu-
able for medicines and food and perhaps for some aspects of ecosys-
tem function but have low intrinsic conservation value.
•Weeds such as Chromolaena odoratamay become dominant and
inhibit successional change for many years. - Forest tree species are among the trees conserved by farmers but usu-
ally belong to the small subset of species that have some kind of value
to farmers. - The fallow plant community is dominated by species with high resprout-
ing capacity and pioneers with precocious fruiting and functioning
seed dispersal mechanisms. - Although fallow plant communities change over time, their species rich-
ness and diversity, as well as their representation of forest-dependent
species, remain low in comparison with original forest.
•A trend toward shorter fallows further limits potential for biodiversity
recovery in patches. - Fallow and secondary forest communities are not a stage in the recovery
of original forest but are entirely new, anthropogenic vegetation types. - The number of vertebrate species that make exclusive use of single
habitat patches probably is limited because of the small size of such
patches, so their community characteristics must be characterized and
understood at the landscape scale (see Box 8.1).
•Crop fields, fallows, and secondary forest patches nevertheless are used
by many forest vertebrates (with some more frequently observed in such
patches than in mature forest) and species of disturbed habitats. - The diversity of observed vertebrate assemblages or particular compo-
nents of them may be the same as, lower than, or higher than in mature
forest, depending on factors such as surrounding vegetation. - The composition of vertebrate assemblages is more sharply differenti-
ated between patch types than richness and diversity; declines in some
bird guilds and increases in others are predictable, for example, when
comparing mature forest with fallow and secondary vegetation. - The diversity and composition of observed vertebrate assemblages
often change over time. - Compositional changes are linked to variation in factors such as habi-
tat structure, food availability and foraging behavior, microclimate,
and hunting pressure. - Overall, the prevailing short fallows greatly limit the potential for bio-
diversity recovery, and especially mature forest attributes, in most
patches in the landscape.