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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In the southern Brazilian campos <strong>of</strong> Rio Grande do Sul, N. neesiana occurs along with a wide range <strong>of</strong> both C 3 and C 4 <strong>grass</strong>es<br />
including Aristida spp., Paspalum spp., Piptochaetium spp. and other Nassella spp. (Overbeck et al. 2007).<br />
On Tenerife, Canary Islands, N. neesiana occurs in environments characteristic <strong>of</strong> the Bidenti pilosae-Ageratinetum<br />
adenophorae community, especially in areas cleared <strong>of</strong> vegetation along margins <strong>of</strong> roads and gutters and is especially prevalent<br />
relatively humid areas in gorge bottom inhabited by such species as Myrica faya and Salix canariensis (Martín Osorio et al.<br />
2000). The vegetation invaded was characterised in detail by Martín Osorio et al. (2000) (see Table 3).<br />
In Villa Ada, Rome, Italy, it has ‘colonised some hectares <strong>of</strong> hedges and lawns’ and it is found in <strong>grass</strong>y areas in Italy generally<br />
(Moraldo 1986 p. 217).<br />
These records in the native and invaded habitats indicate that N. neesiana coexists with a diverse array <strong>of</strong> other dominant and<br />
subsidiary <strong>grass</strong>es and a wide variety <strong>of</strong> forbs in natural <strong>grass</strong>lands but is rarely associated with trees and shrubs.<br />
In southern New South Wales N. neeisana forms dense monocultures that can dominate pastures (Verbeek 2006). In New<br />
Zealand pastures, dense clumps <strong>of</strong> N. neesiana also exclude other pasture species (Bourdôt and Ryde 1986) and replace more<br />
desirable <strong>grass</strong>es, particularly Lolium perenne (Bourdôt and Hurrell 1989b). Bourdôt and Hurrell (1989b) sprayed out a dense<br />
infestation <strong>of</strong> N. neesiana on low-fertility soil, rotary hoed the area and sowed plots <strong>of</strong> Lolium perenne, Dactylis glomerata<br />
L.and Phalaris aquatica. Plots were fertilised with superphosphate and lime or unfertilsed, and N. neesiana germinated<br />
uniformly across the area. 13 months later, N. neesiana ground cover in unsown areas was greatest in fertilised plots (69%) than<br />
unfertilised (53%) and its dry mass production in fertilised plots was also greater (3.43 t/ha vs. 2.72 t/ha). In Lolium plots N.<br />
neesiana cover was only 1% in fertilised plots and 11% in unfertilised plots. In Phalaris plots N. neesiana cover was<br />
approximately equal in fertilised and unfertilised treatments. In Dactylis plots N. neesiana cover was much higher in unfertilised<br />
plots (39%) than fertilised plots (19%). Plots were fertilsed again in year two. Over three years the dry mass <strong>of</strong> N. neesiana in<br />
both fertilised and unfertilised unsown plots as a proportion <strong>of</strong> total dry mass in the plot fell significantly from c. 95% to c. 75%,<br />
the balance being “litter and other species”, but mainly litter. In competition with the other <strong>grass</strong>es, dry mass production <strong>of</strong> N.<br />
neesiana as a proportion <strong>of</strong> total plot biomass was greatest with Phalaris. N. neesiana was less productive in competition with all<br />
three pasture <strong>grass</strong>es in fertilised plots, with the effect most pronounced for Lolium and least with Phalaris. Seeding <strong>of</strong><br />
N.neesiana was considerably reduced in the sown plots compared to the unsown and most reduced in competition with Dactylis.<br />
In unfertilised plots with Lolium, N. neesiana became the dominant biomass component after three years, with Dactylis remained<br />
at a constant proportion over the period and with Phalaris declined as a proportion <strong>of</strong> total biomass. Fertiliser treatment induced<br />
temporal stability in terms <strong>of</strong> the proportion <strong>of</strong> contributions <strong>of</strong> the sown <strong>grass</strong>es and N. neesiana to total biomass production. In<br />
conditions <strong>of</strong> low fertility S.neesiana appeared to suppress Lolium, but under high fertility the dominance was reversed. S.<br />
neesiana was considered to be a stress-tolerant competitor, “evolved under conditions <strong>of</strong> low disturbance but moderate-severe<br />
stress from low soil moisture and probably low fertility” (Bourdôt and Hurrell 1989b p. 324).<br />
During the early period <strong>of</strong> invasion at Derrimut Grassland, Victoria, N. neesiana occurred occasionally in a Vulpia association<br />
<strong>of</strong>ten with Austrostipa bigeniculata, along drainage lines and in areas ploughed during the 19th century or subsequently heavily<br />
grazed (Lunt 1990a). This formation was considered to be occupying areas probably previously dominated by T. triandra.<br />
N. neesiana has poor competitive abilities with <strong>grass</strong>es and clovers that respond to high soil fertility (Connor et al. 1993, Liebert<br />
1996). Vigorous pastures can resist invasion including Phalaris, although Phalaris pastures are sometimes invaded (Bedggood<br />
and Moerkerk 2002). Grech (2007a 2007b) found little difference between Phalaris aquatica and N. neesiana responses to<br />
increased phosphorus. Lunt and Morgan (2000) found a negative relationship between T. trianda and N. neesiana at Derrimut<br />
Grassland Reserve which indicates that this competitive summer-growing C 4 <strong>grass</strong> can resist invasion. There is evidence for<br />
similar resistance to N. trichotoma by T. triandra (Hocking 1998) and Bothriochloa macra (Steud.) S.T. Blake when maintained<br />
in a healthy condition (Michalk et al. 1999), but distribution surveys suggest no such resistance is provided by C 3 wintergrowing<br />
native <strong>grass</strong>es (Badgery et al. 2002). N. neesiana is reported to have “choked out” N. trichotoma in trial plots (Hunt<br />
1996, McLaren et al. 1998) and to have invaded infestations <strong>of</strong> this <strong>grass</strong> (Liebert 1996 citing David Boyle). Bruce (2001)<br />
compared the level <strong>of</strong> N. neesiana invasion to the “botanical significance” rating <strong>of</strong> 39 <strong>grass</strong>land sites in the ACT and found no<br />
clear trends,both rich and poor sites having both zero and high level infestations.<br />
Such data indicate that N. neesiana can be excluded from vegetation that is dominated by healthy growth <strong>of</strong> other perennial<br />
<strong>grass</strong>es. Management practices that reduce competition by other plants, such as slashing <strong>of</strong> N. neesiana on roadsides, might<br />
therefore be counterproductive (Bedggood and Moerkerk 2002).<br />
Herbivory<br />
Grasses have coevolved with large grazing mammals and have a wide array <strong>of</strong> adaptations to grazing. One <strong>of</strong> the most important<br />
is the presence <strong>of</strong> intercalary meristems at the base <strong>of</strong> the leaves, rather than on the plant apices, a defence that probably played<br />
an important role in the evolution <strong>of</strong> the family (Stebbins 1986) and enable a plant to more readily regenerate after it is grazed.<br />
As in some other <strong>grass</strong>es (de Triquell 1986), the presence <strong>of</strong> multiple inflorescences on the panicle <strong>of</strong> N. neesiana allows the first<br />
developed, upper panicle to be sacrificed to herbivores, while the inflorescences closer to the ground and concealed beneath leaf<br />
sheaths, remain protected. The basal cleistogenes <strong>of</strong> N. neesiana are well protected from grazing mammals and develop even<br />
under conditions <strong>of</strong> heavy grazing (Dyksterhuis 1945, Gardener and Sindel 1998). N. neesiana thus has major advantages<br />
compared to <strong>Australia</strong>n native <strong>grass</strong>es which lack cleistogenes.<br />
Little information appears to be available about the native mammalian herbivores that utilise or once utilised N. neesiana in<br />
South America. Before human occupation the pampean region was occupied by“outlandish humpless camels and giant flightless<br />
birds” (Crosby 1986 p. 159). Large grazing animals went extinct at about the same time as indigenous human occupation <strong>of</strong> the<br />
southern Brazilian <strong>grass</strong>lands in the early-mid Holocene (Overbeck et al. 2007). According to Overbeck and Pfadenhauer (2007)<br />
large native herbivores became extinct in the pampas c. 8000 years ago, at the end <strong>of</strong> the last glacial period. The Pleistocene<br />
megafauna and other large grazing mammals through Argentina, Uruguay and southern Brazil included such species as Toxodon<br />
platensis (Notoungulata), Glyptodon spp., Megatherium, Pampatherium sp., Stegomastodon platensis (Xenarthra), Equus sp.and<br />
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