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

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