Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
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Foreman (1997) investigated the effects <strong>of</strong> livestock grazing, cultivation and burning on a long-grazed species-rich remnant.<br />
Only the diminuitive annual species were not grazed and they increased in abundance under grazing by exploiting the increased<br />
gaps. Cultivation increased the abundance and species richness <strong>of</strong> exotic species, and the abundance <strong>of</strong> some native annuals<br />
(probably because they had a soil seed bank). Fire reduced the abundance <strong>of</strong> exotics, particularly annuals, presumably by<br />
destroying surface seeds. He also found that drought had a very significant effect on the flora, causing a substantial drop in<br />
above-ground species richness and abundance, and that native annuals were more abundant when winter rainfall was high.<br />
Irrigated agriculture is the major landuse in the Riverina and salinity is a widespread problem, while other threats include<br />
cultivation, irrigation, inappropriate grazing and fire regimes, weed invasion, feral animals and increased fertiliser use (DNRE<br />
1997).<br />
The Northern Plains Grasslands are listed as a threatened community under the Flora and Fauna Guarantee Act. (Department <strong>of</strong><br />
Sustainability and Environment 2009a). Terrick Terrick National Park near Mitiamo, a former grazing property, is the largest<br />
and most important conserved remnant <strong>of</strong> this ecosystem in Victoria (Lunt et al. 1998).<br />
Victorian Basalt Plains Grasslands<br />
The <strong>grass</strong>lands <strong>of</strong> the Victorian basalt plains were a very large area <strong>of</strong> <strong>grass</strong>land at the time <strong>of</strong> European settlement (Tables 11<br />
and 12). The <strong>grass</strong>y ecosystems <strong>of</strong> the plains extended from Melbourne to Hamilton (Stuwe and Parsons 1977) or to “beyond the<br />
South <strong>Australia</strong>n border, broken only in a few places by deeply dissected ranges” (McDougall 1987 p. 17), at altitudes from less<br />
than 100 m to over 600 m (Stuwe and Parsons 1977). The Volcanic Plains as a land unit occupies c. 22,000 km 2 <strong>of</strong> which about<br />
37% or 8,260 km 2 (or over 10,000 km 2 according to Williams 2007) was occupied by <strong>grass</strong>land complexes and most <strong>of</strong> the<br />
remainder by <strong>grass</strong>y woodland (28%) and herb-rich woodland (14%) complexes (DNRE 1997, Barlow and Ross 2001).<br />
Numerous other vegetation types occurred, including wetland, forest and swamp scrub, forming a complex mosaic, in which,<br />
judging by the maps <strong>of</strong> early surveyors, “treeless areas occurred as discrete ‘openings’ in the landscape”, which they identifed as<br />
“Plains” (Barlow and Ross 2001 p. 26).<br />
The majority <strong>of</strong> the Victorian Volcanic Plains terrain is composed <strong>of</strong> Newer Volcanics, a series <strong>of</strong> lava flows and tuff plains with<br />
extinct volcanic cones (commonly scoria cones but also lava domes) aged from 46 million years ago, peaking at about 2.4<br />
million years and ceasing about 7,000 years ago, i.e. Middle Pliocene to recent (Hills 1967, Dahlhaus et al. 2003), although<br />
radiocarbon evidence indicates that the most recent volcanic activity was >20,000 years ago (Rosegren 1999). The most recent<br />
lava flows are represented by stony rises <strong>of</strong> ropy lava (Hills 1967). Smaller volcanoes, such as Mt Cottrell, produced the majority<br />
<strong>of</strong> the geological material, mostly highly fluid, basalt lava, that spred in thin sheets 20-200 cm thick, with overlapping flows to<br />
60 m thick in some areas (Rosengren 1999). Eruptions were infrequent and there was little pyroclastic material and ash in most<br />
areas, so vegetation would have survived widely beyond the edges <strong>of</strong> the lava flows (Rosengren 1999).<br />
Despite common parent materials, the soils are highly variable, ranging from gradational clayey chocolate soils and kraznozems<br />
on the younger basalts, to coarsely structured duplex soils on the older rocks (Dahlhaus et al. 2003). Much <strong>of</strong> the lava plains was<br />
“originally rough and stony, resulting in an irregular topography with many small depressions” (McDougall 1987). In areas that<br />
have not been worked, there is still abundant surface rock (Hills 1967), and in areas with developed soils, basalt corestones<br />
(‘floaters’) are common at the surface. Much <strong>of</strong> the rock in developed areas has been cleared, and many kilometres <strong>of</strong> dry stone<br />
walls were built (Patton 1935). The rock is fine-grained, blue-grey in colour and not very hard (Patton 1935) and underlying rock<br />
is very close to the surface in many areas (Sutton 1916-1917). The development <strong>of</strong> watercourses is generally poor, with lava<br />
flows <strong>of</strong>ten resulting in blockages and substantial areas <strong>of</strong> internal drainage to ephemeral wetlands, swamps and lakes (Dahlhaus<br />
et al. 2003), many <strong>of</strong> which have been drained (McDougall 1987) Waterlogging is widespread (Dahlhaus et al. 2003), partly<br />
because the soils are so shallow (Patton 1935), but much <strong>of</strong> the area is well drained due to strong fracturing <strong>of</strong> the underlying<br />
rocks (McDougall 1987).<br />
The eastern areas are Miocene to recent lava plains, with two dominant soil types, formed in situ: grey cracking clays, Northcote<br />
classification Ug 5.2, and hard alkaline red soils Northcote classification Dr 2.13, ranging in surface texture from sandy loam to<br />
clay, but mostly clay loams or light clays, and in colour from black to grey, brown and reddish brown (Stuwe and Parsons 1977).<br />
Patton (1935) thought the darker soils characteristic <strong>of</strong> more low-lying areas, the colour attributable to leaching or organic matter<br />
from upslope, and considered that soils higher up the slope had lower clay content. The clays have a high water-holding capacity<br />
(45% according to Patton 1935) and high shrink:swell ratio so become waterlogged with poor aeration in winter and deeply<br />
cracked in summer (Stuwe and Parsons 1977). With a moisture content <strong>of</strong> 19%, the soil is “definitely sticky” (Patton 1945 p.<br />
185). Patton (1935) provided a generalised soil pr<strong>of</strong>ile <strong>of</strong> a red-brown earth on the Keilor Plains and noted that the B horizon,<br />
extending from c. 40-85 cm depth, is not generally penetrated by roots and rests directly upon bedrock. It contains abundant<br />
calcium carbonate giving it a white colour. “Most <strong>of</strong> the richest aricultural and pastoral land in the Western District is composed<br />
<strong>of</strong> ... recent tuffs” (Hills 1967). For <strong>Australia</strong>n soils, the clays are relatively nutrient rich, particularly in phosphorus (Barlow and<br />
Ross 2001).<br />
The Victorian Volcanic Plain has average annual rainfalls <strong>of</strong> 500-700 mm (Dahlhaus et al. 2003) and western Victorian<br />
<strong>grass</strong>lands between 450-850 mm (Jones 1999b) , with some areas in the east in rain shadow (between Melton and Werribee)<br />
receiving slightly less (Dahlhaus et al. 2003), the areas between Anakie and Melbourne with a range <strong>of</strong> c. 400-600 mm<br />
(McDougall 1987), and areas at higher altitude receiving up to 1000 mm, and is evenly distributed throughout the year (Stuwe<br />
and Parsons 1977) or with a late winter peak (Jones 1999b). Eight major droughts occurred in the eastern area between 1887 and<br />
1987 (McDougall 1987). Average monthly temperatures are 7-20ºC (Jones 1999b). February is hottest, with maxima sometimes<br />
exceeding 40ºC and annual frost days in the eastern area range from 16 to 53 (McDougall 1987). Evaporation is very high in the<br />
summer (December to February). The precipitation to evaporation ratio appears to have fallen over the last 100 years, so the area<br />
seems to be drying (Dahlhaus et al. 2003). Much <strong>of</strong> the western area is severely affected by rising water tables and dryland<br />
salinity, predicted to dramatically worsen (Dahlhaus et al. 2003). Mean daily minimum and maximum temperatures are 5-12ºC<br />
in July and 12-26ºC in January (Stuwe and Parsons 1977).<br />
Victorian western plains <strong>grass</strong>lands a result <strong>of</strong> both soil and climate factors, not aboriginal burning (Cook and Yugovic 2003).<br />
Treelessness is explained by seasonal aridity,cold temperature and heavier clay soils (Willis 1964 p. 398). Fires and ash falls<br />
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