Literature review: Impact of Chilean needle grass ... - Weeds Australia

vegetation by fire, so as to render the new year’s growth serviceable”. Great fires across the pampas were reported in 1853
(Soriano et al. 1992).
The fire history of Southern Brazil is “poorly known” but palynological studies indicate that fires were rare before c. 7400 years
ago and then became frequent, possibly as a result of deliberate burning for hunting (Overbeck and Pfadenhauer 2007 p. 28). In
southern Brazilian grasslands, where N. neesiana is native, fire became more frequent from the beginning of the Holocene,
proabably as a result of the advent of human populations, and currently grazed native grasslands are burned approximely
biannually, usually in August (Overbeck et al. 2007). Most of the grassland species of southern Brazil “seem to be adapted to
frequent ... burning” (Overbeck et al. 2007 p. 107).
Honaine et al. (2009) stated that winter burning, along with grazing, in the flechillar community of the Tandilia Range of Buenos
Aires province, in which N. neesiana is a major component, led to the dominance of Achillea millefolium L. and Carduus
acanthoides L. (Asteraceae). Historical observations suggest that fire occurred at intervals of 5 years in the stipoid dominated
savannah grasslands of the more arid Caldenal, to the south and west of the Pampean region, before the introduction of livestock
(Fernández et al. 2009).
Bourdôt (1989) noted that in New Zealand “regular burning promotes the grass” and that after fire “tussocks quickly begin to reestablish
from clandestine seeds present in old tiller bases”. Liebert (1996 p. 15, quoting Craig Bay on the plant’s behaviour at
Organ Pipes National Park, Victoria) stated that it is “usually the first grass to resprout after fire”. Stewart (1996) recorded that
dense N. neesiana quickly regained high cover after a wildfire at Broadmeadows Valley Park, Victoria, in December 1994,
reaching 50% cover after approximately 6 months and 70% cover after 7 months, and reaching a height of over 50 cms after 11
months. Kirkpatrick et al. (1995 p. 35) considered that it “generally ... recovers more quickly than other species” and is “as well
adapted to fire as the native dominant” T. triandra (op. cit. p. 82). However the precise timing of fire in relation to rainfall likely
has a large influence on which plant species recover first.
Young seedlings and small plants are possibly killed by fire, but larger plants lose most of their above-ground biomass and
resprout from protected buds. In the classification used by Overbeck and Pfadenhauer (2007) the seedlings are “non-sprouters”,
while tussucks are fire “resistors”, retaining some dead stem biomass after burning. The above-ground meristems are protected
by the densely packed basal leaf sheaths (Overbeck and Pfadenhauer 2007), some of which burn, but many of which resist
burning because of their high moisture content and tight packing and merely char on the outside. Thus, older tussocks are best
adapted to frequent burns.
Britt (2001) found that burning, after application of 1 litre of methylated spirits to square metre areas surrounded by a metal
frame, eradicated adult plants in an infested pasture. Hocking (2005b) reported on small scale experimental burning of thickets at
the Iramoo native grassland, Victoria, in late spring and summer 2002. Both early and late spring burning resulted in less than
10% of mature tussocks resprouting after the autumn break, much lower than unburnt treatments, a reduction of more than 75%
in mature tussocks, but an increase in the number of small tussocks and very immature tussocks, likely resulting from
fragmentation of what had previously been large plants. Late spring burning removed all viable seed from the site, reduced seed
production in the subsequent fruiting period by c. 50% and appeared not to lead to any major seedling recruitment, up to and
including the following spring. Early spring fire had no effect on subsequent seed production.
As with other grasses, the specific effects of fires are likely to be dependent on the intensity, severity and precise timing of the
fire. Seed that has found its way into the soil is likely to survive, presumably in a similar way to that of Austrostipa.
Other disturbances
Weed invasion of natural communities is often facilitated by disturbance, and the more frequent, intense or prolonged that
disturbance the greater the invasion is likely to be (Fox and Fox 1986, Carr et al. 1992, D’Antonio et al. 1999). According to
Weber (2003 p. 280) in a survey of environmental weeds of the world, based on a very limited literature review, N. neesiana
“invades mainly degraded and disturbed plant communities”. Bartley et al. (1990), commenting on the situation in Victoria,
wrote that “prior disturbance does not appear to be necessary for invasion” for N. neesiana invasion of native grasslands. This
was echoed by Kirkpatrick et al. (1995 p. 35), who nevertheless added that “its spread is certainly facilitated by soil
disturbance”. According to Slay (2002a p. 4) N. neesiana “evolved under conditions of low disturbance”, however Gardener
(Gardener 1998, Gardener et al. 1996, 1999, 2003b) found that N. neesiana seeds only germinate on bare ground, in gaps or
areas bared by herbicides and other disturbances, and that seedlings only survive in bare areas. The plant survives well in the Rio
de Plata grasslands where trampling by cattle “is the main anthropic disturbance” (Soriano et al. 1992). Bedggood and Moerkerk
(2002) recorded regrowth of N. neesiana in wheel tracks after treatment of infestations with glyphosate using vehicle mounted
wick wipers. Liebert (1996) recommended the avoidance of unnecessary soil disturbance to minimalise N. neesiana invasion.
Bruce (2001) attempted to determine the importance of different types of disturbance in determining the level of N. neesiana
infestation in native grasslands in the ACT. She assessed the current extent of four ‘disturbance types’ on a four point scale from
absent (0) to high (5): bare ground, other exotic weed populations, soil disturbance (earthworks, erosion, cultivation, animal
diggings etc.) and the amount of refuse dumping (garden waste, soil, rubbish). The literature contains numerous mentions of the
importance of ‘bare ground’ to enable seedling establishment. The usual meaning appears to be soil lacking other vascular plants
above ground and devoid of litter. Bruce (2001) found that N. neesiana had wide levels of abundance, from absent to dominant,
where bare ground was present at low and medium levels. It had the largest range of abundances (0-5) at high weed levels, and
the lowest (0-3) at low weed levels (perhaps suggesting that N. neesiana facilitates invasional meltdown). The single site with no
soil disturbance had occasional patches of the weed, sites with low soil disturbance had a range of infestation levels (0-5) and
sites with medium soil disturbance were overall more highly invaded (1-5). No sites had high soil disturbance. Infestation levels
varied widely for all levels of dumping, but N. neesiana was observed to have established and be spreading from scattered piles
of lawn clippings at one site.
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