Biology Reference
In-Depth Information
ease of cultivation, and any other purportedly beneficial aspects. Detrimental fea-
tures, such as the potential for the species to become invasive or a source of fuel for
wild fires, have often been ignored (Lonsdale 1994).
Western Australia contains immense treeless areas that have been long viewed
as potential grazing land for livestock. The region's aridity not only sets a limitation
on forage production but also exacerbates soil salinity (Burvill 1979). The impetus
has been clear for graziers to foster species (native or introduced) that are palatable
and grow vigorously on these salt-laden soils. This need was thought to have been
met in part by Kochia (
Bassia scoparia
), a Eurasian chenopodiaceous shrub. Seeds
of the shrub were introduced in 1990 onto 52 properties in Western Australia. Signs
appeared within a year that the introduction was going awry when a landowner
noticed
B. scoparia
seedlings becoming established well beyond the point of
Kochia's introduction. By 1993 the shrub was behaving clearly as an incipient
invader: dead Kochia formed seed-laden tumbleweeds, and these blew across the
treeless landscape, spreading numerous seeds (Randall 2001).
An eradication program rapidly took form after the landowner's report. Further
introductions were halted within 12 months, thanks to the state and national funding that
was sustained throughout the eradication campaign. Even with such swift action,
B.
scoparia
eventually occupied 2,281 ha; most of this area occurred as two parcels (140
and 1,000 ha) (Dodd 2004). Eradication site-by-site with herbicides, mechanical
removal, and intense sheep grazing proved effective, and sites were resurveyed yearly.
A site was considered Kochia-free if no plants were detected for three consecutive years
after the last plant had been eliminated. Despite the shrub's conspicuous features and a
short-lived seed bank (coupled with sustained, diligent plant removal), some plants
were detected as much as seven years after initiation of the eradication campaign. By
2004, Western Australia was, however, considered free of Kochia (Dodd 2004).
This eradication project was successful through the remarkable confluence of
events, species' traits, and circumstances. First and foremost, the problem was rap-
idly reported to government authorities by a conscientious landowner. Consequently,
the problem was detected before Kochia had dispersed to thousands of widely sepa-
rated sites, and luckily fences minimized the dead, seed-laden tumbleweeds from
spreading without constraint (Dodd and Randall 2002). Furthermore, adult Kochia
are large and readily detected, and the shrub's seed bank is long-lived (Dodd 2004).
Moreover, the authorities were able to take prompt action without the need to
search for public funds for eradication. And finally, the public was alerted by the
press to Kochia's threat (Randall 2001).
3.6 A Warning Unheeded: The Failure to Eradicate
Miconia
calvescens
in Hawai'i
The Hawaiian Islands are simultaneously among the most remote and most invaded
landmasses. The Islands' long involvement as a way station for oceangoing ships
and its eager colonization by the US (Daws 1968) has produced a naturalized flora
