Genetic Resources in Agroecosystems - Agroecology: The Ecology of Sustainable Food Systems - page 192

FIGURE 14.6 Genetically engineered cotton in California's Central Valley. A few transgenic varieties account for a large
percentage of the state's crop.

long-term sustainability by reducing genetic diversity at
many levels, making domesticated species more vulner-
able to pests, diseases, and environmental changes, and
increasing the dependence of cropping and livestock pro-
duction systems on human intervention and external
inputs (Figure 14.6).

nents of diversity are independent, they combine to create
nine different facets of agrobiodiversity, from food diver-
sity worldwide to the genetic diversity of a crop variety
on a particular farm. These facets of agrobiodiversity,
somewhat simplified, are shown in Table 14.2.
As a result of the ways that conventional agriculture
has been exploiting the genetic resources at its disposal
over the last century or so, agrobiodiversity is being lost
in all nine ways. These trends of loss are also shown in
Table 14.2.
There is no shortage of evidence that agrobiodiversity
is declining at every geographic scale and every genetic
level. This decline is seen in two interrelated ways: fewer
and more uniform varieties and breeds are in widespread
use, and more varieties and breeds are disappearing from
use and being lost altogether. Here are a few telling facts:

14.3.2 L OSS OF G ENETIC D IVERSITY

Genetic diversity in agriculture, or agrobiodiversity , mat-
ters in two ways: in the differences among organisms —
what can be called diversity's genetic component — and
in how these differences are arrayed spatially in actual
on-the-ground use — what we can term the geographic
component of diversity (Brookfield, 2001). And for each
component, diversity matters at three distinct scales.
Geographically, diversity is important at a worldwide
scale, a regional or national scale, and a farm scale. Genet-
ically, we can focus on the diversity of food types, the
diversity within a species, or the diversity that exists
within a particular breed or variety. Since these compo-

• There are perhaps as many as 300,000 edible

plant species on earth, but now more than 60%
of the world's dietary energy comes from just
four of these plant species — wheat, rice,