| Abstract: |
| Agroforestry can provide agricultural products while partially maintaining the
ecological services provided by forests. Because agroforestry systems contain many
natural species, its proponents often stress that agroforestry can make vital contributions
to the preservation of biodiversity. This is generally not the case, however, at least not
for the parts of global biodiversity most under threat. Four reasons are discussed why
agroforestry and other ‘conserve through use’ strategies cannot be a full substitute for
the setting aside of substantial areas with an uncompromised conservation status.
First, species sensitive to human activity, because they are exploited commercially
or merely sensitive to human disturbance, cannot be maintained this way. Second,
several wild animals are pests in agroforestry, and will tend to be eliminated, even
though they could in principle live in agroforests. These two effects together imply that
a predictable portion of the species of old-growth forests will not survive in agroforestry
landscapes. The presence of a trade-off between exploitation and biodiversity implies
that only unexploited old-growth forests guarantee the full preservation of biodiversity.
Given the constraint of sufficient agricultural production, we should therefore favor a
segregation of functions at the landscape level from the perspective of biodiversity
preservation.
A third problem is that biodiversity is best maintained in large wildlands rather
than in isolated fragments, as a result of immediate and subsequent gradual species loss in these fragments (‘relaxation’). In order to maintain sufficient overall agricultural
production, the remaining areas will have to be used intensively, leaving a role for
agroforestry in biodiversity preservation only in ecologically sensitive sites. Moreover,
agroforests are an exponent of fragmented landscapes and do not contribute to reducing
fragmentation. Encouraging agroforestry in practice will often result in increased
fragmentation. Fragmentation also implies that agroforests, where they are stable, will
tend to lose many of the species they currently harbor.
Finally, because agroforests are often a transient phase in the developmental
sequence and tend to be replaced by more intensive land uses, their ability to contribute
to biodiversity perpetuation is limited. Overall, then, agroforestry will make only a
limited contribution to biodiversity preservation, and may in fact adversely affect it if it
competes with wildlands for space in the landscape. |
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