in air, land, and water (Garstang et al. 1996; Tilman 1999; Tilman et al.
2001). This has caused direct and indirect effects on global climate and bio-
geochemical cycling that, without abatement, will lead to a drastically altered
environment.
The threat of human-induced climate change to the planet is well docu-
mented: global average surface temperatures have increased by approximately
0.6°C since the end of the nineteenth century (Houghton et al. 2001). Green-
house gas emissions are still accelerating, and we need to keep the remaining
forests intact to mitigate CO 2 release. Indeed, tropical deforestation releases
about 2 Giga-tons (Gt) of carbon per year; in the 1980s this was estimated to
make up 25 percent of carbon emissions from human activity (FAO 2001).
Shukla et al. (1990) simulated the hydrological cycle over Amazonia and
found that rapid deforestation could result in a longer dry season. This disrup-
tion in precipitation patterns would have widespread ecological implications,
such as increases in fire frequencies and disruption of the life cycles of pollina-
tion vectors. So severe are the potential changes that if large areas of Amazon
tropical forests are destroyed, they may not return (Shukla et al. 1990).
The protection of tropical ecosystems is a cornerstone of global climate
change solutions. The effect of human-induced climate change on biodiversity
will be profound. Species ranges will track climatic patterns, including tem-
perature and precipitation patterns. The heterogeneous nature of climate
change over time and space makes it difficult to predict the effects on local or
even regional scales. In general, in the warming climate species ranges will
independently shift toward the poles and upwards in altitude, although there
is no general linear pattern (Peters 1991). Protected areas must not only serve
the flora and fauna within their borders but also permit natural migrations
and climate-induced range shifts. The surrounding matrix will be a key to mit-
igating biodiversity losses from global climate change as landscapes undergo
rapid temporal changes. Protecting biodiversity cannot be achieved on static
spatial scales, and matrix areas must be used to conserve biodiversity. Agro-
forestry practices may help to create a permeable matrix that allows such
migrations (Chapter 20, this volume) and may also make a certain contribu-
tion in reducing carbon emissions after forest conversion. Practices such as
riparian strips and contour plantings may also help to reduce nutrient and sed-
iment losses from agricultural lands and thereby limit the effects of agriculture
on biogeochemical cycling.
Conservation Strategies
Recent scientific knowledge about how the tropical rainforests are affected by
fragmentation, logging, road building, and encroaching agricultural frontiers
suggests that much of the resulting ecological degradation (postfragmenta-
tion) can be accounted for by just a few factors. These factors include the size
22 I. Conservation Biology and Landscape Ecology in the Tropics