Agriculture Reference
In-Depth Information
Box 12.2 (
cont.
)
generally promotes the invasion process but close-interval repeat fires are often
sufficient to reduce resprouting capacity and eliminate the seedbank, thus
locally extirpating this shrub (Swezy & Odion
1998
; Odion & Haubensak
2002
; Alexander & D'Antonio
2003
). This treatment appears to be sufficient
for sustainable control of this target species although such close-interval fires
inevitably favor alien grasses and forbs (Jacobsen
et al.
2004
; Keeley
2006a
)
and are not an appropriate management strategy for shrubland ecosystems.
South African fynbos is heavily invaded by postfire seeding shrubs from
Australia such as
Hakea sericea
and fire alone will only act to spread this
invasive. Effective control has been achieved by first cutting, drying and
burning; however, this management results in much greater fire intensities
and reduced native regeneration (Richardson & van Wilgen
1986
). For this
and other woody species, fire alone does not seem to be sufficient to eliminate
invasion of fynbos (Holmes
et al.
2000
). There has been considerable study
focused on restoration of invaded lands by the removal of infestations of
invasive trees. A variety of approaches have been used including burning
standing vegetation, felling and burning the dead fuels, and felling followed
by removal of most dead fuels to reduce fire intensity, as well as biocontrol
agents (Holmes
et al.
2000
; Pretorius
et al.
2008
; Richardson & Kluge
2008
;
Roura-Pascual
et al.
2009
). Burning standing vegetation is often not successful
because of seed released from woody cones and subsequent postfire seedling
establishment. While felling and burning kills seedlings and thus reduces the
density of invasive plants, the high fire intensities involved may have detrimen-
tal effects on native species. Felling and brush removal followed by fire has
shown good success but is expensive. A clear benefit of removing invasive
shrubs and trees, however, has been shown in increased water supply in natural
watersheds (Le Maitre
et al.
2002
; Gorgens & van Wilgen
2004
).
Fire is frequently advocated as a control method for many herbaceous alien
species. One example of the pitfalls in using prescription burning is in the
application of spring burning to control yellow starthistle (
Centaurea
solstitialis
L.). This European pest is established in parts of western North
America and particularly noxious because it greatly alters livestock range
conditions. Short-term reductions in this species can be achieved with repeated
burning. However, this thistle has a relatively long-lived seedbank, and longer-
term study shows that it re-establishes once burning is halted (
Fig. B12.2.2
).
Clearly, prescribed burning provides only temporary reduction and does not
lead to sustainable control of this alien; and may exacerbate the alien situation
(Keeley
2006a
).
This outcome should not be surprising since most alien herbs are opportun-
istic species that capitalize on disturbance. Prescription burning is a non-
specific eradication method that affects both the target species and potential
Continued
