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

(Chan 1980). The region also contains large areas of native pasture and secondary grasslands (Sharp and Shorthouse 1996, ACT
Government 2005).
Despite the relatively high altitude of these tablelands grasslands, their vascular plant composition is more similar to the
grasslands of the Victorian Volcanic Plains than to alpine grasslands (Lunt et al. 1998). T. triandra, Austrodanthonia auriculata,
A. caespitosa, A. carphoides, A. laevis, Austrostipa bigeniculata, A. scabra, Bothrichloa macra, Poa labillardieri and P.
sieberiana are generally the dominant native grasses (Sharp 1997). B. macra was dominant in some areas in the late 1970s
(Groves 1979). Areas of the Monaro tablelands not dominated by Poa sieberiana were probably dominated by T. triandra, which
was largely replaced under bovid grazing by less palatable Austrostipa spp. from the mid 1840s (Kirkpatrick et al. 1995). Similar
to other areas, pasture improvement intensified dramatically from the 1940s, resulting in widespread losses of native grasslands
or major modification of their components and structure, including massive incursions of weeds (Keith 2004). Exotic plants have
been reported to comprise 29% of the Monaro grassland vascular flora (Kirkpatrick et al. 1995). Unlike the Victorian Volcanic
Plains, rocks are not a common feature (Melbourne 1993, Kukolic 1994).
Kirkpatrick et al. (1995) briefly described the following lowland grassland communities in the region: 1. Poa labillardieri –
Austrostipa – Bothrichloa macra Monaro Basalt Grassland, a widespread, dense-tussock formation on clays in the ACT and
NSW; 2. Poa sieberiana – Carex appressa – Juncus Monaro Grassland, probably best thought of a highland community; 3.
Austrostipa scabra – Enneapogon nigricans Monaro Grassland, a mid-dense tussock grassland found mainly on upper slopes and
ridges; 4. Themeda triandra – Poa sieberiana – Bulbine bulbosa Monaro Grassland, found on valley floors or slopes with a
southerly aspect; 5. Themeda triandra – Eryngium ovinum – Carex inversa Canberra Grassland, largely confined to the ACT in
valleys on limestone;
Sharp (1997) provided an analysis of the floristic associations present in the ACT (Table 14) and previous floristic
classifications. The Austrodanthonia association occurred on sites subject to historical levels of moderate to high disturbance on
well drained clay soils with low nutrient levels, and had the largest areas of bare ground. A wet Themeda association occurred in
areas with moderate to high historical disturbance regimes, on poorly drained (seasonally wet) sites with higher soil P and acidity
levels. A dry Themeda assocation occurred on well drained sites with low levels of disturbance, and had high litter cover of c.
40% and low soil P (7.9 ppm). About 70% of vascular plant species present were forbs, with Asteraceae an important component
(Sharp and Shorthouse 1996). No community had consistently higher exotic richness, but the wet Themeda association had the
highest exotic cover in spring, and the dry Themeda association the lowest (Table 14).
Table 14. Floristic characteristics of natural grassland floristic associations in the ACT from a survey of 39 sites (Sharp 1997).
Association Mean spp. richness (per 10 m 2 ) Mean spp. richness (sites) % exotic cover
Native Exotic Total Native Exotic Total (spring)
Austrodanthonia 24.7 12.4 37.1 33.2 21.7 54.9 32.8
Wet Themeda 25.3 13.7 39.0 36.3 23.2 59.5 35.5
Dry Themeda 21.8 8.6 30.4 41.8 23.6 65.4 11.1
Remnant grassland on the Southern Tablelands is highly fragmented and adequate reservation was considered unlikely to be
achievable (Sattler and Creighton 2002). Remaining remnants are in various states of degradation and exist in a matrix of exotic
pasture (Keith 2004). Approximately 5% of the original 20,000 ha of grasslands in the ACT were in more of less natural
condition (florisitically and structurally intact, with low weed cover) in 1996, with an additional 550 ha of low quality grassland
(Sharp and Shorthouse 1996, Sharp 1997). Sharp and Shorthouse (1996) provided a map of the pre-European distribution and
remaining remnants and estimated that c. 70% of the grasslands identified in the late 1970s had subsequently been destroyed by
urban development, conversion to pasture or invasion by exotic plants. Less than 3% of the pre-European area remained in
reasonable condition by 2005, reduced from 11% of the region pre-1750 to about 1% in 2000 (ACT Government 2005). Most
had been destroyed by intensive agriculture and urban growth, and existing remnants were threatened by inappropriate
management. Remaining sites were mostly