Biology Reference
In-Depth Information
respectively (Sand and Manley 1990; Dodd 2004), where the target plants did
not usually occupy inaccessible sites (cf.
M. calvescens
in French Polynesia,
Meyer and Florence 1996).
4.
The target species' seed bank should be short-lived
. Duration of resurveys of sites
after all visible plants have been removed relates directly to the longevity of the
target species' seed bank (Groves and Panetta 2002). The proverbial ideal target
species has a short seed bank life (e.g., < three years), and several successive
annual searches of once infested sites could remove any remaining individuals.
This species attribute relates directly to Item 7 below. As a corollary, eradication
is strongly hampered, even rendered problematic, if the species routinely persists
through vegetative propagation, i.e., adventitious roots and stems, rhizomes, or
stolons. Consequently, eradication of
E. crassipes
or
Polygonum cuspidatum
(Japanese knotweed) would be exceedingly difficult because both species pro-
duce seeds and readily propagate vegetatively (Barrett 1980; Palmer 1994).
5.
Likelihood of eradication is inversely proportional to the size of the occupied new
range and the number of locations
(Groves and Panetta 2002). The close, inverse
relationship between eradication success and the extent of an invasive species is so
strong as to persuade some that it is essentially an inviolate principal (Rejmánek
and Pitcairn 2002; Groves and Panetta 2002; Panetta and Timmins 2004). And
clearly, the bulk of plant eradications have occurred for species with very limited
distribution in their new range (Groves and Panetta 2002; Mack and Lonsdale
2002). But the on-going
S. asiatica
eradication program as well as the earlier
Barberry Eradication Campaign illustrate that while admittedly more difficult,
eradication or near eradication can be achieved if key components of the eradica-
tion strategy are scrupulously followed.
6.
Emphasis should be directed first at the invasion's outlying nascent foci
. The
initial remediation to environmental damage is often directed at the largest, most
conspicuous source of the hazard, e.g. so-called Superfund sites of pollutants in
the US (Cannon 2007). However, this approach fails in eliminating the hazard of
a plant invasion because plants, unlike pollutants, perpetuate themselves.
Furthermore, small, outlier populations are more likely to contribute recruits to
previously unoccupied new range than plants within a large focus of the invasion
(Moody and Mack 1988). As a result, destroying these outlying populations
before they become new sites of plant dispersal is essential. Awareness of this
eradication principle is apparent in the US Witchweed Eradication Campaign
(Eplee 1979, 1981). In effect, the barberry campaign also emphasized the
destruction of outlier foci: clear attention was paid to all plants, regardless of
their local abundance (Kempton 1921).
7.
Resurvey of all searched sites for remaining individuals must be diligent and
prolonged
. No matter how conspicuous the target species, all plants will not be
initially detected. Furthermore, resurveys are mandatory to detect plants that
emerged postsurvey (Mack and Lonsdale 2002 and references therein). Given
the unlikelihood of detecting immigrants immediately upon their entry into the
new range, a seed bank will have already been established by the time eradica-
tion is initiated.
