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

Much less is known about the conservation status of plants at the intraspecific level. Groves and Whalley (2002) emphasised the
need to conserve the widespread intraspecific variation in Australian grasses (polyploid complexes, ploidy levels, breeding
systems). T. triandra for example, is widely variable, consisting of a polyploid complex, mainly of diploid and tetraploid
populations in southern Australia (Hayman 1960) and different populations have varying flowering responses to photoperiod and
temperature (Groves 1975).
Many of the rare and endangered plants have become scarce as a result of the same processes that have led to the loss and
degradation of grassland communities. Continuous livestock grazing is considered to be a major cause of decline of such species
as Swainsona recta A.T. Lee and S. plagiotropis F. Muell. (Fabaceae), Rutidosis leptorhynchoides, Senecio macrocarpus
(Asteraceae) and Thesium australe R.Br. (Santalaceae), and, except for S. plagiotropis and T. australe, fire is probably, or should
be, important in maitaining their habitat. Competition in dense T. triandra swards affects S. recta, R. leptorhynchoides, S.
macrocarpus and T. australe (Scarlett and Parsons 1993). Colobanthus curtisiae J.G. West and Stakhousia gunnii Schltdl.
disappear from grasslands when the perennial grass sward covers all the bare ground (Kirkpatrick 2007). Rutidosis
leptorhynchoides survived in areas subject to frequent fires, but disappeared from two railway reserves in the Melbourne area
when regular burning ceased in the 1980s (Kirkpatrick et al. 1995). Three sites where it existed, at Canberra, Queanbeyan and
near Melbourne, were allowed to be developed on the condition that populations were transplanted, but the transplanting failed
(Kirkpatrick et al. 1995). Morgan (1995b) considered it was restricted to remnant grasslands never subjected to grazing,
ploughing and fertiliser application. Senecio behrianus Sond. and F. Muell. was formerly known from the Western District of
Victoria and the Northern Plains and was apparently restricted to heavy clay, winter-wet soils (Walsh 1999). The one known site
where it continued to exist appeared to have once been Eucalyptus camaldulensis woodland but was highly modified and
difficult to botanically categorise (Scarlett and Parsons 1993).
Taxa endangered in the Riverina include two chenopods, Maireana cheelii (R.H. Anderson) Paul G. Wilson and Sclerolaena
napiformis Paul G. Wilson, along with several from other families that are also found in the more mesic grasslands (Kirkpatrick
et al. (1995).
Senecio georgianus DC “known ... probably from grassland” (Kirkpatrick et al. 1995 p 30) was recorded from Lake Omeo and
the Macalister River in Victoria and from Western Australia, South Australia and Tasmania (Walsh 1999) but is now extinct
(Walsh and Stajsic 2007). Stemmacantha australis (Gaudich.) Dittrich, the only Australian native thistle, known in Victoria from
Lake Omeo and Murrindal, “probably” from grasslands, is now extinct in Victoria (Jeanes 1999b p. 677) and NSW, but survives
in Queensland (Kirkpatrick et al. 1995).
Diuris fragrantissima, Sunshine Diuris or Fragrant Doubletail (Orchidaceae) is endemic to Victoria (Walsh and Stajsic 2007), in
particular to an area with a 25 km radius now part of western urban Melbourne (Smith et al. 2009). It and was “once widespread
on the Keilor Plains” (SGAP 1991 p. 206), and was so common at the time of European settlement that it was referred to as
‘Snow-in-the-Paddocks’ (Webster et al. 2004). It is now “exceedingly rare, restricted to remnant dry grassland on the basalt
plains near Sunshine” (Entwisle 1994 p. 858) at two sites – a railway reserve at Tottenham and Laverton North Grassland where
it has been planted (Webster et al. 2004, Smith et al. 2009). The site at Sunshine/Tottenham has few remaining plants, and the
plantings at Laverton North have progressively declined and not resulted in a viable population (Smith et al. 2009). N. neesiana
is a “very serious” direct threat to the small population at the Tottenham site, and the immediate surrounding area is extensively
invaded (Webster et al. 2004).
The threatened Curly Sedge, Carex tasmanica Kuk grows in wetlands and at grassland edges, often in areas too wet to support
tussock grassland (Morcom 2004). In Victoria it was known to exist at only nine sites, “in remnant grasslands” (Morcom 2004).
Leucochrysum albicans has no persistent seed bank, but disperses widely on the wind, and in part of its range is dependent on
heavy sheep grazing to create patches of bare ground every few years in which seedlings can establish (Kirkpatrick 2007).
Many of the rare and endangered forbs produce large amounts of seed and are long-lived, and some reproduce vegetatively, but
recruitment of new individuals is usually rare, for reasons that are poorly understood (Robinson 2005). Rare and threatened
vascular plants of grasslands often survive in areas with ususual disturbance regimes, which also usually favour weeds and few
other natives, so tend to be degraded, and to be assigned little conservation value (Kirkpatrick et al. 1995, Kirkpatrick 2007).
These species usually have poor competitive abilities and are disturbance-dependent (Kirkpatrick 2007). Robinson (2003 2005)
demonstrated that many species that recruit poorly in grassland remnants lack specialised germination requirements and can be
propagated and grown relatively easily under nursery conditions, but that a range of Apiaceae, Fabaceae, Ranunculaceae and
some Asteraceae do have specialised requirements such as cold stratification and after-ripening requirements that may rarely be
met in the wild.
Factors that are probably important in limiting forb recruitment include the presence of weeds, particularly Nassella spp.,
herbivory by exotic invertebrates, grazing by livestock and rabbits, and the loss of small-scale soil disturbance formerly achieved
by native vertebrates (Robinson 2003 2005). Reynolds (2006) demonstrated that soil digging is indeed an important factor,
critical for recruitment of several species. Soil disturbance may have a significant role in increasing seed contact with the soil or
actual seed burial, or may be more important in enabling penetration of the radical (Robinson 2005). Iincreased survival and
flowering of Diuris fragrantissima established using soil digging might be due to enhanced functioning of its fungal symbiont
due to improved aeration (Smith et al. 2009). The scale and intensity of the disturbance is of obvious importance in determining
the effects on competitors, nutrient levels and other factors.
Ecological history
The pre-European disturbance regimes of temperate Australian grasslands are poorly understood (McIntyre and Lavorel 2007).
Fire is universally recognised as an important factor, both pre-aboriginal and ‘managed’ aborignal burning (Kershaw et al. 1994,
Hope 1994, Kershaw et al. 2000 ). Marsupial grazing must have had a large influence: Australian grasslands are presumed to
have once been grazed by a now extinct marsupial megafauna, and known to have been occupied by numerous smaller
herbivorous mammals, most of which are now extinct or have relictual distributions. Climatic variation has also been important
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