Environmental Engineering Reference
In-Depth Information
taxa (Pausas
et al
. 2006). In fact, these birds act as
ecosystem engineers
,
sensu
Jones
et al
. (1994) . Fur-
thermore, the perch tree may also create a favourable
microsite for germination and survival. Dead trees may
also be used by birds as caches (e.g. for acorns). These
bird-mediated facilitation processes inspired a restora-
tion technique based on providing bird perches (dead
trees and artifi cial woody structures) in old-fi eld sites
to accelerate colonization rates and ecosystem restora-
tion. Although being an attractive and inexpensive
technique to help succession, it has seldom been
applied to Mediterranean ecosystems and most exam-
ples come from tropical forest ecosystem restoration
projects (see Chapter 9). In many areas of extensive
old - fi elds, where there is generally a very low seed
availability of late-successional species, this technique
could be especially appropriate.
mowing, fi re and solarization), chemical control with
herbicides, and biological control by insects or other
herbivores. Some techniques that have been effective in
MCRs are reviewed here.
Often, the extent of invasion is too large for mechan-
ical and chemical control to be effective across large
and complex landscapes. In these cases, efforts have
focused on isolated populations or preserves that are
particularly threatened by alien invasives, as in the
case of the riparian tree and shrub invader
Tamarix
ramosissima
in California. This tenacious species has
been
eradicated
by hand control and herbicide in
defi ned stands, but introduced
Tamarix
still dominates
the riparian zone of thousands of kilometers of rivers
in the western United States. Following careful testing,
a host - specifi c biocontrol beetle,
Diorhabda elongata
,
from Eurasia, has recently been released, and is now
beginning to show good results in efforts to control
Tamarix
across large areas (Ehleringer
et al
. 2009 ).
Where normal riparian hydrologic regimes still exist,
native riparian trees are recolonizing and the abun-
dance of the invasive
Tamarix
is declining.
Invasive species can be more readily controlled if
they have not invaded at high density. In the Azores,
that have woodlands of Mediterranean origin but
an oceanic climate, low-density invasive trees were
removed with cutting and herbicide from a laurel
forest, followed by successful establishment of planted
native trees (Heleno
et al
. 2010 ). The moist climate
likely promoted establishment, as seedlings in a
summer-dry Mediterranean climate may suffer higher
mortality. Alien trees also re-established from seed in
this experiment, but in a real restoration situation
would need to be controlled by future treatment. Native
11.2.4 Principles of control for invasive
alien plants in MCRs
The principal goal of restoration after invasive species
control is to create a stable stand of native vegetation
that is resistant to further invasion (D'Antonio &
Chambers 2006; see Chapter 20). The degree of
success of this undertaking depends upon the extent
and density of the invasion, the extent to which soil
and ecosystem characteristics have been altered, life
histories of
invasive
and
native plant species
and
interactions among these characteristics (Table 11.3).
Invasive plant species include all life forms from herbs
to shrubs and trees, and the range of techniques to
control them includes mechanical removal (cutting,
Table 11.3
Probability of restoration success after the invasion of alien species based on
invasive species characteristics.
Invasive species characteristic
Probability of restoration success
Higher
Lower
Extent of invasion
Small
Large
Control technique
Biological control
Mechanical or chemical
Plant size
Large (woody)
Small (herbaceous)
Density of invasion
Sparse
Dense
Recolonization ability
Low
High
Seed bank longevity
Short-lived
Long-lived
Seed bank density
Sparse
Dense
Soil and ecosystem feedback
Minor
Major
