A landscape is defined in this book as a mosaic of ecosystems or habitats,
present over a kilometer-wide area. Landscapes are composed of individual
elements (e.g., forests, agricultural or agroforestry plots, wooded corridors, or
pasture areas) that in turn make up the patches, corridors, and matrix ele-
ments of the landscape (Forman 1995). Landscapes are also characterized by
their relief, including hills, plateaus, and valleys, which influence the flow and
distribution of energy and matter and biotic processes (Sanderson and Harris
2000). In many tropical landscapes, the presence of agroforestry systems (e.g.,
shaded tree crops, fallow areas, or crop and pasture areas with trees) influences
ecological processes and characteristics such as the presence and dispersal of
fauna and flora, water and nutrient flows, microclimate, and disease and pest
dynamics within the landscape. Such landscapes are appropriately called agro-
forestry landscapes, reflecting the common view in landscape ecology, conser-
vation biology, and agroforestry that certain important effects of agroforestry
on biodiversity conservation, water and nutrient cycling, and soil conservation
cannot be fully appreciated by merely looking at the individual plot or system
because their most significant impacts may occur at the landscape scale. Fur-
thermore, a given agroforestry system does not exist in isolation in that farm-
ers may manage forest gardens or shaded tree crop plantations together with
shifting cultivation plots, irrigated rice fields, or pastures, which therefore
occur together in the same landscape and jointly determine its properties.
What agroforestry means and how agroforestry practices influence the
structure and composition of tropical landscapes are best illustrated with some
examples (note that an agroforestry practice or system is not synonymous with
an agroforest, which includes the most complex, forest-like types of agro-
forestry systems). Tropical smallholder farmers often grow staple food crops
such as upland rice, maize, and cassava in slash-and-burn systems in rotation
with natural tree fallows, which may vary in length from a few years to several
decades. This shifting cultivation (or swidden agriculture), which results in a
mosaic of crop fields and plots with secondary forest or savanna regrowth in
the landscape, is one of the oldest and most extensive forms of agroforestry,
although it has often been excluded from the concept of agroforestry on the
faulty assumption that all shifting cultivation is unsustainable or inefficient as
a land management strategy. Several specific agroforestry practices have
evolved in different tropical regions from their common origin in shifting cul-
tivation. In the West African savanna, for example, it is common for farmers
to retain useful trees (which may also be difficult to fell and resistant to fire)
when preparing a plot for cropping, thereby creating parklike landscapes of
scattered trees between crop fields and rangelands that are typical of this
region (Figure I.1; Boffa 1999). In the lowlands of Sumatra and Kalimantan
(Indonesia), smallholder farmers have modified the traditional crop-fallow
rotation by introducing rubber trees into their cropping systems together with
annual and short-lived perennial crops. Through a prolonged fallow cycle of
Introduction: Agroforestry in Biodiversity Conservation in Tropical Landscapes 3