resources, often leads to exploitive rather than sustainable use. Poverty, war,
and social inequality generate environmental degradation, which further
drives socioeconomic crises in a continuous feedback loop. These underlying
drivers of environmental degradation and biodiversity loss must be addressed
for successful conservation of tropical ecosystems.
Threats to Tropical Forest Ecosystems
Environmental degradation is driven by several major threats, including habi-
tat loss and fragmentation, exploitation, pollution, introductions of nonnative
species, and human-induced global change. For tropical ecosystems, land use
is ranked as the major driver affecting these regions for the next 100 years (Sala
et al. 2000). In this section we briefly review these threats and point to the
potential role of agroforestry that will be discussed in more detail in subse-
quent chapters.
Habitat Fragmentation
Although human presence affects landscape biodiversity in many ways, one of
the most visible and widespread effects is habitat fragmentation (Gascon et al.
2003). Because of the dynamic nature of landscapes, fragmentation alters the
behavior of natural interactions within the landscape and the functioning of
the entire landscape. For example, the species composition and diversity of a
tropical landscape differ near a treefall as compared with a dense canopy.
However, the temporal recovery of treefalls over an entire tropical landscape
results in areas at all stages of natural forest growth. These areas provide a vary-
ing but consistent species composition and diversity for the entire landscape.
Conversely, in fragmented landscapes, the number of areas at different stages
of forest growth is lower, and the average functioning of the landscape
becomes less predictable. If a substantial portion of a tropical landscape under-
goes deforestation, the ecological function of the fragmented landscape can be
permanently altered from its natural state. These changes in the biodiversity
and integrity of fragmented landscapes argue in favor of the construction of
conservation corridors, where biodiversity-friendly land uses such as agro-
forestry can be integrated with fragments of natural habitat in interconnected
networks that help restore functional aspects of the landscape.
Fragmentation alters not only the functioning of the landscape but also the
behavior and dynamics of populations in the fragmented system (Bierregaard
et al. 2001; Chapter 2, this volume). The response of populations to landscape
changes often is very negative. If no patches exist that are habitable for a par-
ticular population, then that population is likely to be lost. Forest fragmenta-
tion can result in species population survival or extinction, depending on
many factors such as how easily the species can disperse between forest patches
- Biodiversity Conservation in Deforested and Fragmented Tropical Landscapes 19