Environmental Engineering Reference
In-Depth Information
invasive plants since 1903. In Australia, funds for biological control have come
from the public and private sectors. h e analysis involved 29 projects and 14 of
these returned a net positive benefi t. h e main fi ndings were that a national invest-
ment of AU$4.3 million/year has provided an average return of AU$95.3 million/
year (Page and Lacey 2006). h ese authors highlight the fact that social and envir-
onmental benefi ts have rarely been quantifi ed in the studies and yet it is known
that many projects have had a positive impact in one or both. An example of the
economic return of one of these Australian projects is given in Box 6.2. It has been
written many times that one of the advantages of classical biological control is that
benefi ts accrue year after year, with no need for further investment. h e economic
benefi ts certainly show that initial investments have in general been worth making
even though the success rate with biological control is very low.
Box 6.2
Economics of the biological control of the rubber vine in Australia
Rubber vine (
Cryptostegia grandifl ora
) is native to Madagascar and is a scrambling
shrub used as an ornamental. It grows well in semi-arid tropical watercourses and
is tolerant of a wide range of soil types. The plant was introduced into Queensland,
Australia in the 1860s to cover old coal tips but became naturalized and by 1944
had infested 1200ha. The rubber vine smothers tall trees and pastures and forms
impenetrable thickets (Figs. 6.1 and 6.2). By 1973 the plant had become a serious
invader of riparian vegetation, fl oodplains, and natural eucalyptus woodlands. By
the early 1970s it was estimated to be spreading at 1-3%/year and by 1989 there
were about 120,000ha of dense infestations. It was also estimated that the poten-
tial distribution of the plant in northern Australia could be 32,000-160,000km
2
.
Rubber vine reduces grazing in pasture areas, restricts access to water, and is also
toxic to livestock. The cost to the cattle industry in 2001 was estimated to be
AU$18.3 million. But rubber vine also has a major impact on native plant com-
munities. In about the late 1980s, rubber vine was reported to threaten: four
vulnerable animal species; 13 plant communities; one Ramsar site; 13 important
wetlands; and 48 reserves.
On this basis a biological control was undertaken and host-specifi c agents
from the native range of rubber vine introduced. A moth (
Euclasta whalleyi
) was
released in 1988-91 and a rust fungus (
Maravalia cryptostegiae
) in 1995-97. Both
agents established and spread well, the rust being the more effective agent as the
moth is now affected by parasitism. Rubber vine populations had decreased by
25-65% 4 years after the release of the fungus and the agent also prevents recol-
onization. At the same time, pod numbers were reduced by 85%, leaf cover by
73%, and fl ower production by 48%. Overall (using 2004-05 AU$ values), the
rubber vine biological control project cost AU$3.6 million and this provided
a net value by 2004/05 of AU$232.5 million, providing a benefi t:cost ratio of
108:1. This did not include the benefi ts to the environment such as the reduced
threat to native plant communities (Page and Lacey 2006).
