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

Willis (1964) considered that the flora of the Volcanic Plains to have the fewest species of higher plants of all the major
vegetation provinces in Victoria (543 spp.), similarly for mosses (c. 85 spp.), lichens and fungi, but probably not for terrestrial
and aquatic algae. This “floristic deficiency” (Willis 1964 p. 397) was not, in his opinion, due to degradation. McDougall (1987)
calculated that the Melbourne area T. triandra grasslands had a total of 183 indigenous vascular species. Of the 108 taxa detected
by Stuwe and Parsons (1977) in 59 remnants across the plains, 39 were exotics of which 52% were annuals, whereas annuals
comprised only 10% of the native species and 76% of the annuals were alien species, while of the 151 species at Evans St.,
Sunbury, grassland 101 were native and 50 exotic.
The Keilor Plains (Little, Werribee and Maribyrnong River catchments, along with some creeks that enter the lower Yarra River)
at the eastern end of the Volcanic Plains is a rainshadow area with grasslands containing a larger component of ‘dry country’
species, typically found in the Northern Plains (Sutton 1916-1917, Lunt et al. 1998). The Keilor Plains and the plains between
Geelong and Cressy “are and always have been open, dry tussock grassland, without any arboreal growth or even tall shrubs”
(Willis 1964 p. 398 – except the Banksia (see above)) and with floristic and numerical dominance of Poaceae and Asteraceae,
which together comprise nearly one quarter of the vascular plant species (Willis 1964). At least 40 species of native grass and
about 150 other native plants are found on the Keilor Plains (Scarlett et al. 1992). These grasslands are also characterised by the
absence of perennial plants that are obligate seed regenerators (Lunt and Morgan 2002). They are notable for the large areas of
‘bare’ ground between the plants (‘intertussock spaces’) (Willis 1964),75-80% of the areas at Derrimut treated by by annual or
biennial burning or grazing and 85-97% at Laverton North (Henderson 1999), but this space disappears as the grassland ages and
the biomass of the dominant grass increases, leading to loss of the intertussock species, through shading, increased seed
predation, etc. (Lunt and Morgan 2002). Frequent destruction or natural sparseness of the grass canopy is needed to maintain
floristic diversity (Lunt and Morgan 2002).
Stuwe and Parsons (1977) sampled 59 remnants in 1976 with wide variation in climate, substrate and position in the landscape,
and found remarkable uniformity in floristic composition, which was most affected by the current management regime. Railway
sites, burnt annually, usually in late spring and often with slow, patchy fires had significantly greater mean species richness, with
abundant intertussock space. Roadsides, once commonly grazed, but then “virtually unmanaged” (Stuwe and Parsons 1977 p.
473) generally were depauperate, with dense, litter-rich T. triandra stands and no bare ground. Pastures grazed by sheep, cattle
and horses contained open, species poor vegetation. Morgan (1998c) examined five grasslands on the volcanic plains and found
that vascular plant richness varied more between sites than within them, i.e. sites were internally homogeneous.
Most of the flora commences growing from dormant buds after soaking rains in late autumn or winter, blooms in spring (October
and November), sheds seeds in summer (December and January) and dies back to dormant buds with very limited growth in the
driest period of the year (December to April) (Willis 1964, Lunt and Morgan 2002).
By the mid 1970s only remnants remained, the richest and least weed-infested being along railway lines, managed by annual
burning, with roadsides, largely unmanaged or burnt annually or less frequently by local fire brigades, and native pastures having
lower plant diversity, the former dense and the latter relatively open (Stuwe and Parsons1977, Morgan 1998c). By the 1990s
most intact T. triandra grasslands on the Victorian volcanic plains were no longer grazed or were subjected to minimal vertebrate
grazing (Morgan 1998c 1998d) but the largest remnants had been degraded by long-term livestock grazing, generally contained
few rare species, had low native plant diversity and in some instances a weed dominated soil seed bank (Lunt 1990b 1990c).
Over 95% of all native vegetation on the Victorian Volcanic Plain has been cleared (Sattler and Creighton 2002). According to
Sattler and Creighton (2002) 78 Ecological Vegetation Classes (EVCs) have been mapped in the region, 15% of which are
probably extinct and 78% threatened. Barlow and Ross stated that 48 EVC occurred on the Volcanic Plain, as determined by
direct observation or modelling. According to Dahlhaus et al. (2003 citing Ross et al. 2002) 115 EVCs, including mosaics and
complexes occur in the region. Plains Grassland and Grassy Woodlands originally occupied three quarters of the region and only
about 1% remains, much of it degraded (Sattler and Creighton 2002). Nature conservation reserves occupy approximately 1.3%
of the region and contain approximately 40% of the EVCs, and biodiversity conservation is heavily reliant on private land, road
and rail reserves and other public land (Sattler and Creighton 2002).
Barlow and Ross (2001) cautioned that the several attempts to determine the area of grasslands currently existing in the region
were beset with methodological problems, including the difficulty of identification where vegetation was highly altered. Using
DNRE (1997) data, they concluded that grassland complexes had been reduced to an area of 1671 ha by 1997, an estimated 0.2%
of the pre-1750 extent. But a more complete estimate was suggested to be 5000-6000 ha, or 0.6-0.7%. In the early 1990s
possibly