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

In comparison to annual grasses, perennial grasses have relatively low seedling vigour and slow early growth (Evans and Young
1972). The outcome of competition between perennial grass species is therefore highly dependent on the timing of germination
and differential rates of early growth.
Impacts on animals
Invasive grasses may provide or fail to provide resources for a wide range of other organisms. They are used by birds in nest
construction e.g. Nassella trichotoma by Yellow-rumped Thornbill Acanthiza chrysorrhoa (Quoy and Gaimard) (Peters 2000).
Naturalised grasses provide food for various animals. Many birds eat the seeds of exotic grasses in Australia, including the
Stubble Quail Coturnix pectoralis Gould and Plains Wanderer Pedionomus torquatus Gould in native grasslands (Loyn and
French 1991). Most cockatoos and parrots consume exotic grass seeds and some species have become largely dependent on the
resource, paticularly in cereal growing areas (Cole 1975, Loyn and French 1991, Barker and Vestjens 1989). In Victoria
kangaroos eat and disperse the seed of Aira elegantissima Schur, Briza minor L., Hordeum marinum Huds., Lolium rigidum
Gaudin and Vulpia bromoides, while feral horses and sambar eat and disperse the seed of Anthoxanthum odoratum and Holcus
lanatus L. (Carr 1993).
Significant negative impacts on native fauna appear to be commonplace where extensive, dense infestations of exotic grasses
occur, but have rarely been investigated in any detail in Australia. Compared to habitats dominated by native grasses,
monocultures of invasive Bothriochloa species in central Texas have been found to have reduced rodent species richness and in
Kansas had significantly reduced bird species richness, and reduced abundance and biomass of arthropods (Schmidt et al. 2008).
The suppression of native psammophilous grasses by invasive Cynodon dactylon (L.) Pers. in Germany has impacted on the
native leafhopper fauna of these grasses, and two exotic leafhoppers associated with C. dactylon now occur (Biedermann et al.
2005). The advent of New World-Old World hybrid Spartina in Europe appears to have resulted in the establishment of an
American planthopper that attacks the European native Spartina maritima (Curtis) Fern. (Biedermann et al. 2005).
Some recorded negative impacts on fauna in Australia include those of Aleman Grass Echinocloa polystachya (Kunth) A.S.
Hitchc., and Olive Hymenachne Hymenachne amplexicaulis (Rudge) Nees, which “can choke out waterways used by ... pygmy
geese” (Vidler 2004, citing Garnett 2003). In Queensland, Brachiaria mutica Para grass and H.amplexicaulis are a threat to the
Jabiru Ephippiorhynchus asiasticus Latham (Vidler 2004 citing Williams pers. comm.). Briza maxima L., is considered a threat
to the Eltham Copper butterfly Paralucia pyrodiscus lucida Crosby (Vidler 2004 citing DPI/DSE 2003b).
Hydrology
Invasive grasses can modify hydrological cycles in a range of simple and complex ways. They can modify the rate and timing of
evapotranspiration, infiltration and overland flow of water, and of the nutrients, minerals and soil particles in the water (Levine
et al. 2003, Grice 2004).
Alterations of soil water usage, in total, seasonally and at different levels in the soil may occur. Replacement of native summergrowing
grasses with annual spring-growing grasses results in wetter autumn soils, higher water tables and increased drainage
flows (Sinclair 2002). Replacement of deep-rooted perennials by shallow rooted annuals may reduce water use and concentrate
water use to a particular season (Levine et al. 2003). In Californian native grassland, annual grasses reduced the reproduction
and seedling growth of native perennial Poaceae through competition for soil moisture (Lenz et al. 2003). Absence of summer
growth due to prior depletion of soil water may also result in higher erosion during intense summer rainfall events (Sinclair
2002). Markedly increased rates of soil drying by high densities of the annual invasive Bromus tectorum adversely affect
seedlings of a native perennial grass when the two were germinated simultaneously (Evans and Young 1972).
Disturbance regimes
Exotic grasses can change the nature and timing of disturbances through feedback effects (Woods 1997). Alterations to fire
regimes and the frequency and intensity of flooding, erosion or herbivory may occur.
The most dramatic and best documented of feedback disturbance effects involve increases in fire (D’Antonio and Vitousek 1992,
Woods 1997, Mack and D’Antonio 1998, Levine et al. 2003, Vidler 2004). Changes to evapotranspiration may lead to altered
soil and vegetation dryness patterns, while changes in timing and density of biomass production can alter the fuel load and its
temporal and spatial (vertical and areal) distribution (including continuity and curing rates), leading to changes in the the
frequency, severity and timing of fires. Grass invasions commonly result in increased grass biomass production (Rossiter et al.
2006). Grass leaves have a high surface area: volume ratio and grasses commonly accumulate large amounts of dead biomass
(Mack and D’Antonio 1998) with some species producing much more poorly biodegradable, inflammable bulk than others. But
in most cases where increased biomass production occurs, the specific reasons are unknown (Levine et al. 2003). More frequent
and hotter fires result in higher rates of nutrient loss and alterations in microclimate, and may stymie succession processes; thus
altered fire regimes can result in major shifts in the composition and functioning of ecosystems, including dramatic alterations to
biodiversity. In northern Australia, Gamba grass, Andropogon gayanus (Kunth), a South African species, produces up to seven
times as much fuel as native grasses, resulting in a fire regime that is more frequent and much more intense (Rossiter et al. 2003,
Ferdinands et al. 2006). If the changed fire regime leads to greater abundance of the responsible grass a ‘grass-fire cycle’ is
initiated that reinforces the impact of the invasion (D’Antonio and Vitousek 1992, Hobbs and Heunneke 1992). Invasion by A.
gayanus has led to reduced tree cover in open woodlands by this mechanism (Ferdinands et al. 2006).
Mission grass Pennisetum polystachion (L.) Schultes and buffel grass Cenchrus ciliaris L., two other high biomass invasive
species in northern Australia also effect fire regimes (Rossiter et al. 2003, Grice 2004). Fire enhances growth of C. ciliaris which
in turn enables more intense fires (Puckey and Albrecht 2004). A large range of short lived native grasses and forbs disappear
when the density of C. ciliaris reaches a certain threshold. The number of native ground cover species declines significantly,
there is very little germination of native seed and total invertebrate diversity and abundance of most inverterate groups is reduced
(Puckey and Albrecht 2004). It is a specifically identified as a threat to the skipper butterfly Croitana aestiva E.D.Edwards
(Vidler 2004 citing Wilson and Pavey 2002). Increased cover of C. ciliaris has been correlated with a decline in the numbers of
Carnaby’s skink Cryptoblephrus carnabyi and delicate mouse Pseuodmys delicatulus in central Queensland (Puckey and
Albrecht 2004 - see their references). C. ciliaris cultivar populations have low genetic diversity because of the dominance of
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