Biology Reference
In-Depth Information
known or suspected damaging species (FAO 2000; Shine et al. 2005), some
unwanted nonnative species always gain entry. Postentry detection and some pre-
scription of response then become the inevitable second line of defense against
these immigrant species (Wittenberg and Cock 2005).
Postentry response falls into two categories (aside from an ignominious third
option, “do nothing”): control (i.e., curtail, contain, minimize, or otherwise limit)
the alien species or eradicate it. Eradication refers to the complete destruction of all
individuals (sensu Simberloff 2003a) and properly expresses a permanency of
action that control does not achieve. For IAS or potentially invasive species, eradi-
cation involves the complete elimination of the species in a new range. This action
is valued second only to the prevention of the alien species' entry through quarantine
as an effective deterrent (Mack et al. 2000). Eradication does not of course preclude
future reentry of the unwanted species (Simberloff 2003a and references therein),
but it does mean that any new arrivals will not supplement (numerically, spatially,
or genetically) an existing population.
Here we review and evaluate the record for eradication, as opposed to control or
no-control, of alien plant species' postentry into a new range, regardless of whether
this effort is initiated at the point of entry (the proverbial “beachhead”) or much
later in the plant invasion. The frequency of survey and the recent justified empha-
sis on early detection of the potential invader (Harris et al. 2001; Westbrooks 2004)
are not per se objects of our review, although the speed and thoroughness with
which any immigrant species is detected in a new range directly affects the likeli-
hood of success of any eradication effort (Mack and Lonsdale 2002). Rather, we
investigate here evidence for the feasibility of eradication. Much is at stake in this
debate: the tide of immigrant species is increasing worldwide (U.S. Congress,
Office of Technology Assessment 1993; Levine and D'Antonio 2003), adding to
the worldwide pool of invasive and incipient invasive species. Making correct deci-
sions on when eradication is feasible, as opposed to control, will largely affect the
diversity, scope, and impact of plant invasions throughout the twenty-first century
and beyond.
Informed opinion on plant eradication stretches along a continuum from infea-
sible to feasible with each opinion couched in provisos based on the species' traits
and environmental circumstances in the new range (Groves and Panetta 2002). For
example, Rejmánek and Pitcairn (2002) examined the outcome of eradication
projects for 18 species in California. They found that eradication was often success-
ful where the new range was <1 ha; a sharply lower success rate was recorded as
the size of the treated area and number of foci increased. Although they apparently
did not examine data for any campaigns that involved new ranges much larger than
1,000ha, they concluded that eradication for plant infestations that occupy
>1,000 ha “is very unlikely.” Panetta and Timmins (2004) basically agree with this
conclusion and propose “the 1,000ha rule” based on this California study, even
though Rejmánek and Pitcairin (2002) did not assign the term “rule” to their con-
clusion. Given that the California eradications occurred mainly in agricultural set-
tings, Panetta and Timmins are even less optimistic for successful eradications in
natural ecosystems. In these cases, they reason that the effective areas for eradication
