Rehabilitation and Restoration Of Degraded Forests (PDF) - IUCN

Chapter 6: Approaches at the site level
colonists or at least reduce the extent to which they will be inhibited
from colonizing (see line A in Figure 5). A more modest number of
species and individuals means the process of colonization and canopy
closure will take longer (line B). This means the site will be exposed to
a longer period of risk from disturbances such as wildfires or grazing
that will return it once again to its degraded state. Sites which are left
to recover unaided are exposed to this risk for an even longer time
period (line C). In some situations the magnitude of the risk from
disturbances such as fire may mean that recovery will never occur.
Figure 5. Rate of recovery of biodiversity
Biodiversity
100%
Full restoration
Time
Safety threshold
The rate of recovery depends on the resources devoted to restoration. When large
numbers of species are planted and substantial resources are applied (A) the rate of
recovery towards the original degree of biodiversity may be rapid as additional
species colonise from outside. With fewer species and more limited resources (B)
there is more time before the system crosses a “safety threshold” (i.e. when the canopy
closes), leaving the site exposed to risks of further disturbances such as fires or
grazing. If the site is left to recover unaided (C) there is an even higher degree of
risk and it may or may not recover.
6.3.6 Ecological “surprises”
In many cases things don’t happen as planned. Direct seeding may fail
because predators harvest all the seed. Successions may become
dominated by a small number of aggressive species causing competitive
A
B
C
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