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

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