Environmental Engineering Reference
In-Depth Information
then fertilizing seedlings may increase growth rates,
although the effect of fertilizer on seedling growth is
mixed (Carpenter et al . 2004 ; Zanini & Ganade 2005 ).
If herbivory is high, then it may be necessary to take
actions, such as fencing, to protect seedlings from
mammalian herbivory (Holl & Quiros - Nietzen 1999 )
or use fungicides on leaf cutter ant colonies to control
ant herbivory (Nepstad et al . 1990 ). Such maintenance
efforts necessarily increase costs and can also have
negative side effects, so they should be carefully tai-
lored to site conditions. For example, widespread use of
fertilizers may inhibit succession by encouraging the
establishment and growth of weedy species (Harcombe
1977), and herbicides can reduce natural regeneration
by forest species (Griscom et al . 2009 ).
by bats, but their effi cacy in increasing seed dispersal
in open pastures and their effect on seedling establish-
ment have yet to be demonstrated.
A number of studies have also demonstrated that
piles of branches and logs serve as perching structures
and shelter for a number of bird species, while reduc-
ing light levels and temperatures at the soil surface,
and providing safe sites for woody seedling establish-
ment (Peterson & Haines 2000). In one study in Ven-
ezuela, artifi cially created piles of logs resulted in
higher woody seedling establishment during the fi rst
year following pasture abandonment (Uhl et al . 1982 ).
This promising technique for facilitating recovery
should be tested more widely.
9.5 PAYING FOR TROPICAL
RESTORATION
9.4.2
Encouraging seed dispersal
Given that tropical forest recovery is often dispersal
limited, another potential means for facilitating recov-
ery, particularly in pastures lacking remnant trees, is
the use of artifi cial structures, such as perches for birds,
to enhance seed dispersal by frugivores. If such struc-
tures are successful in attracting animals into aban-
doned agricultural lands, then this approach would
seem promising. Not surprisingly, however, such efforts
have met with mixed results, since tropical forest trees
can be both dispersal and establishment limited, and
perches only serve to overcome dispersal limitation.
Several studies have investigated the use of bird-
perching structures, which generally consist of
branches or posts 2-5 m tall with a perching structure
on the top (Holl 1998; Shiels & Walker 2003). In all
these studies, a variety of fruit-eating birds were
observed on perches, and seed rain under perches was
higher than in areas without perches, but well below
the number in forest and under remnant trees. Most
seeds falling below perches were from ruderal species
that are widespread in active agricultural land or
pioneer species. The few studies that have measured
seedling establishment below perches, however, have
only found higher establishment of seedlings where
pasture grasses were cleared or competition with other
vegetation was minimal (Miriti 1998; Shiels & Walker
2003), suggesting that perching structures will only
serve to facilitate recovery if barriers to establishment
are low. Kelm et al . (2008) have suggested that bat
boxes may serve as a strategy to increase seed dispersal
Given the large areas of land that have been deforested
in the tropics and the competing need to provide for
human livelihoods, a major question is how to pay for
restoring tropical forests, particularly given that most
are located in countries with relatively low per capita
income. In addition to the costs of active restoration
strategies, removing lands from agriculture or other
uses for tropical forest restoration necessarily means a
loss of income to people in these regions, particularly
in areas that are particularly good for farming or have
high value for resource extraction. Therefore, for forest
conservation and restoration to succeed over the long
term, they must be balanced with production systems
carried out in other areas (e.g. for agriculture and
timber). Additionally, landowners and other relevant
stakeholders must be compensated for foregone
income on lands where direct use is restricted. Fortu-
nately, there are some promising approaches for paying
for these costs.
First, given the increasing recognition of the need to
restore natural capital to improve the fl ows of eco-
system goods and services that forests provide, both
locally and globally (Aronson et al . 2007a ), there are
increasing numbers of programmes worldwide, and
specifi cally in tropical forests, that fi nancially compen-
sate land owners for maintaining and restoring water-
sheds that provide these services (Wunder 2007). The
effi cacy of these programmes has been variable and,
particularly with respect to tropical forest restoration,
has generally not been well evaluated to date (Wunder
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