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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Based on a study <strong>of</strong> a three Asteraceae in New England Tablelands <strong>grass</strong>lands, a rare native Microseris sp., a rare to common<br />
native Cymbonotus lawsonianus Gaudich. and an abundant exotic Hypochoeris radicata L., McIntyre (1995) argued that many<br />
native <strong>grass</strong>land forbs must have highly specific ecological requirements for regeneration that are rarely being met under current<br />
mangement regimes, and that many <strong>of</strong> these requirements might possibly be met by the types <strong>of</strong> exogenous disturbances <strong>of</strong>ten<br />
considered to be harmful management practices. For example, a suite <strong>of</strong> endangered <strong>grass</strong>land forbs appear to require soil<br />
disturbance, although the general result <strong>of</strong> soil disturbance is a decline <strong>of</strong> rare native species and enhanced cover <strong>of</strong> exotics<br />
(McIntyre 1995). This apparent paradox may be best resolved by determination <strong>of</strong> the type and nature <strong>of</strong> ‘natural’, endogenous<br />
<strong>grass</strong>land disturbances that have been lost, or now occur in few areas or at a different frequency (e.g. soil disturbance by<br />
marsupial foraging or burrowing), and by more detailed examination <strong>of</strong> processes and disturbances that occur in a range <strong>of</strong><br />
marginal habitats in which rare and uncommon species persist or from which they have disappeared.<br />
Morgan (1998) investigated germination responses <strong>of</strong> many <strong>of</strong> the forbs, none <strong>of</strong> which are promoted by darkness (i.e. seed<br />
burial) (Groves and Whalley 2002).<br />
Robinson (2003) compared the survival <strong>of</strong> planted seedlings <strong>of</strong> Podolepis sp. 1 and Bulbine semibarbata in disturbed and<br />
undisturbed soil <strong>of</strong> a Victorian basalt plains <strong>grass</strong>land. Much greater survival <strong>of</strong> seedlings occurred on the disturbed soil. In the<br />
same <strong>grass</strong>land, Reynolds (2006) compared the establishment <strong>of</strong> seedlings <strong>of</strong> five native forb species (Podolepis sp. 1, Ptilotus<br />
spathulatus, Velleia paradoxa, Rutidosis leptorhynchoides and Pycnosurus chrysanthes) after surface sowing <strong>of</strong> seed and<br />
planting <strong>of</strong> seedlings on disturbed and undisturbed soil. Plots were treated with mowing, raking, repeated herbicide treatments<br />
over a period <strong>of</strong> a few months and fire to remove all above ground plant biomass prior to sowing. The disturbed soil was dug<br />
with a spade to a depth <strong>of</strong> at least 20-30 cm. Six months after sowing the proportion <strong>of</strong> seed that produced established seedlings<br />
on undisturbed soil did not exceed 2%, while in disturbed soil the proportion that established was 2-65%. Four species grown on<br />
disturbed soil flowered, but all seedlings on undisturbed soil remained very small. Mortality <strong>of</strong> seedlings after six months was<br />
greater on undisturbed soil (54% survival) than disturbed soil (80%) and significantly different for three <strong>of</strong> the four species for<br />
which there was adequate data. All species grew significantly taller and wider in disturbed soil. Soil digging created an<br />
abundance <strong>of</strong> suitable microsites for seed germination, whereas the smooth compacted surface <strong>of</strong> the undisturbed soil provided<br />
very few. Seedlings <strong>of</strong> exotic weeds originating in the soil seed bank had to be continuously removed from the disturbed plots<br />
during the period <strong>of</strong> the study but no data about them was provided. Reynolds concluded that the germination <strong>of</strong> both native<br />
forbs and exotic weeds would be promoted by such soil disturbance.<br />
Soil disturbance affects the population dynamics <strong>of</strong> the native forbs in a range <strong>of</strong> ways that remain poorly understood. Soil<br />
disturbances increase seed incorporation into the soil, which advantages some species and not others. Lunt (1995a) found that<br />
buried seed had significantly greater survival than unburied seed for three <strong>of</strong> the species he tested. Some species exhibited major<br />
differences in the timing <strong>of</strong> germination between buried and surface seeds, while others did not.<br />
Particular disturbances or disturbance regimes always favour a subset <strong>of</strong> native species and disadvantage some species. A<br />
changed disturbance regime is small remnants normally results in the disappearance <strong>of</strong> some species which are unable to<br />
recolonise because <strong>of</strong> the now highly fragmented geographical distribution <strong>of</strong> remnants (Kirkpatrick et al. 1995).<br />
A vegetation assessment protocol that enables the classification <strong>of</strong> native <strong>grass</strong>lands on the basis <strong>of</strong> their botanical signficance<br />
has been devised for use in the <strong>Australia</strong>n Capital Territory (Sharp 2006). A <strong>grass</strong>land is characterised as native if >50% cover<br />
consists <strong>of</strong> native species. The botanical significance rating (BSR) depends on the level <strong>of</strong> vascular plant species richness (very<br />
low, low, moderate, high, very high) and the presence <strong>of</strong> very common, relatively common, less common and uncommon native<br />
species, which in turn are very tolerant, moderately tolerant, sensitive or highly sensitive to anthropogenic disturbances.<br />
Grasslands with the highest BSR have several to many representatives from each <strong>of</strong> these native species groups including the<br />
most disturbance-sensitive taxa. The systems has been used for conservation planning in the ACT.<br />
Non-vascular plants and fungi<br />
Bryophyta (mosses), Hepatophyta (liverworts) and Anthocerophyta (hornworts), collectively known as bryophytes (Meagher and<br />
Fuhrer 2003) provide another component <strong>of</strong> biodiversity in south-eastern temperate <strong>grass</strong>lands. Bryophytes <strong>of</strong> <strong>Australia</strong>n native<br />
<strong>grass</strong>lands are relatively poorly studied, e.g. Meagher and Fuhrer (2003) provided lists <strong>of</strong> genera for numerous habitats and<br />
vegetation formations, but not for native <strong>grass</strong>lands. The bryophytes along with lichens (symbiotic associations <strong>of</strong> algae or<br />
cyanobacteria with fungi) and algae, collectively known as cryptogams, are found on exposed rock surfaces but are more<br />
prevalent on the soil surface, forming what is known as the ‘cryptogam crust’ (Scarlett 1994), or where lichens are largely<br />
lacking, the ‘bryophytic mat’ Morgan 2004). This acts to restrict soil erosion and increase water infiltration (Lunt et al. 1998 p.<br />
11). Many <strong>of</strong> the lichens fix atmospheric N (Lunt et al. 1998) and biological soil crusts also contribute significantly to C fixation<br />
(Morgan 2004). The lichen crust reportedly becomes apparent after the inter-tussock forbs die back (Kirkpatrick et al. 1995).<br />
Effects <strong>of</strong> the soil crust on shed seed and seedling germination differ between plant species (Morgan 2004). It can provide “a<br />
foothold for germinating seedlings” (Lunt et al. 1998 p. 11) but commonly restricts seedling establishment by limiting contact <strong>of</strong><br />
the radicle with mineral soil (Mack 1989).<br />
Cryptogam diversity in native <strong>grass</strong>lands has rarely been studied, but where it has, it has it has been found to be highly variable,<br />
e.g. there were at least 32 species at Evans St., Sunbury, but only 3 at Derrimut (Morgan and Rollason 1995) perhaps in part due<br />
to the ‘overdominance’ <strong>of</strong> T. triandra at the latter site (Lunt 1990a) and its long history <strong>of</strong> grazing. Soils crusts are poorly<br />
developed also at other previously grazed <strong>grass</strong>lands – Organ Pipes National Park and Laverton North Grassland Reserve<br />
(Scarlett 1994). Willis (1964) found a total <strong>of</strong> about 85 species in the Victorian basalt plains flora, markedly less than in non<strong>grass</strong>land<br />
areas <strong>of</strong> the State. Scarlett (1994) found that railway reserve <strong>grass</strong>lands were dominated by mosses and liverworts,<br />
rather than lichens. Morgan (2004) surveyed six T. triandra <strong>grass</strong>land remnants on the Victorian volcanic plains and found a<br />
total <strong>of</strong> 19 mosses and 8 liverworts <strong>of</strong> which 9 were present only at single sites. The richest site has 10 mosses and 7 liverworts<br />
in 150 m 2 , the poorest had 6 mosses and 3 liverworts in the same area. Again lichens were uncommon.<br />
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