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

In Australia the altitudinal range is from near sea level (e.g. in the Altona area near Melbourne) to c. 1200-1400 m at Guyra on
the Northern Tablelands of NSW (Gardener et al. 2005). In the Sydney region it is found from 0-600 m (Benson and McDougall
2005).
Climate
Stipeae are generally classic xeromorphs or mesic, Austrostipa aristiglumis (F.Muell.) S.W.L. Jacobs and J. Everett and
Trikeraia being exceptions (Arriaga and Jacobs 2006). In south-eastern South America members of the tribe increase with
increasing latitude, being absent in the megathermic zones, a major vegetation component in mesothermic zones and dominant in
Patagonia (Perelman et al. 2001). Indeed, increases of c. 15 to 23% in the average relative cover of Stipeae compared to other
grass tribes has been measured across the narrow latitudinal range (c. 35-38°) of the Flooding Pampa, in Argentina (Perelman et
al. 2001). The distribution of particular Stipeae, including several Nassella species, in this region shows strong latitudinal
correlations, with a group including N. hyalina and N. charruana found only in the north, and others found only in the south
(Perelman et al. 2001).
N. neesiana is unusual in that it has a very wide climatic tolerance. It has invaded areas outside the climatic range it occupies in
South America (Gardener 1998). The stronghold of N. neesiana, the pampas region, has warm, often humid summers, mild,
usually drier winters with temperatures uncommonly below freezing, annual rainfall of 600-1000 mm, and little drought (Mack
1989). In the pampas, “grass is driven out only where water is very abundant in the soil, as ... along the banks of rivers ... the
climate is a perfect grassland-climate, with ... rainfall not more than moderate but well distributed ... humid, moderately warm
vegetative season [and] strong winds ... with moderate atmospheric humidity ... hostile indeed to woodland” (Schimper 1903 p.
459). Summer rainfall is prevalent in eastern South America south of 30° including Rio Grande do Sul, eastern Uruguay and
Argentina (Schimper 1903). Restricted occurences in southern Brazil, where the grasslands are considered to be relicts of drier,
cooler conditions, may be determined by the more subtropical, humid climate (Overbeck and Pfadenhauer 2007). N. neesiana is
one of the dominant grasses in La Plata district of Buenos Aires where the climate is warm temperate and humid, with a mean
annual temperature of 16.5 ºC and mean annual rainfall of 992 mm (Cabrera 1949). It occurs across the Flooding Pampa of
north-eastern Argentina which has annual rainfalls of 850-900 mm, average annual temperatures of 13.8-15.9°C and average
minimum temperatures in July of 1.8-6°C (Perelman et al. 2001). It is a major grass in the Tandilia Range of south-east Buenos
Aires province where the annual rainfall is about 800 mm and the mean monthly temperatures for the coldest and warmest
months are 13 and 23°C (Honaine et al. 2009), and in parts of south-west Buenos Aires Province, where the climate is humid
temperate with a mean annual temperature of 14.5ºC and annual average rainfall of 850 mm (Amiotti et al. 2007). It occurs in
the littoral areas and lower parts of the La Plata basin where the climate lacks a marked dry season (Schimper 1903). Large tracts
of northern Argentina, the base of the Andes and the Provinces of Entre Rios and Corrientes have annual rainfall of 1000-1200
mm (Schimper 2003) and in those areas N. neesiana loses its dominance in grassland to species better adapted to a wetter, more
subtropical climate (Soriano et al. 1992). In Uruguay N. neesiana is supposedly “resistant to adverse climates” (Gardener et al.
1996b p. 3, citing Rosengurtt et al. 1970). In the Pampean province of southern Brazil the annual rainfall is in the range of c.
1200-1600 mm and mean annual temperatures are 13-17°C (Overbeck et al. 2007). On the Juan Fernández Islands of Chile it
grows in dry or humid areas (Baeza et al. 2007).
In continental South America as a whole N. neesiana is found in the 500-1500 mm annual rainfall zones, with some extreme
outliers, and its northern distribution is “limited by lack of low winter temperatures necessary for vernalization” (Gardener et al.
1996b), so is restricted to higher altitudes in the tropics. It occurs in southern Chile near Valdiva where the average annual
rainfall exceeds 2600 mm and maximum/minimum temperatures are 22.8/11.1 in January and 11.1/5.0ºC in July (Gardener et al.
1996b). Similar seasonal temperatures occur in montane-alpine areas of south-eastern Australia, although few such areas have
rainfall exceeding 1600 mm. It occurs in areas of far north-east Argentina near Posadas, where the rainfall was over 1900 mm
per annum, with January and July maximum/minimum temperatures of 33.2/21.8ºC and 21.9/11.4ºC (Gardener et al. 1996b).
The closest approximations to such a climate in Australia occur in the wet tropics. In western Argentina it occurs at Medoza,
where the climate is very dry (223 mm) with January/July maximum/minimum temperatures of 32.0/19.4ºC and 14.7/2.4ºC
(Gardener et al. 1996b), similar to some arid areas of inland southern Australia. In arid regions of South America it may only
occur where the microclimate is more mesic, e.g. along rivers (Gardener et al. 1996b).
In South Africa N. neesiana has been recorded in temperate summer rainfall areas (Wells et al. 1986). The climate parameters of
one of its stronghold areas in New Zealand are an annual average rainfall of 650-900 mm, warm summers with frequent droughts
and moderate winters, conditions said to be very similar to the climate in its Argentinian range (Bourdôt and Hurrell 1989a). The
900 mm isohyet has been quoted as a limiting factor in north-facing hill slopes in the Hawkes Bay area of New Zealand (Slay
2002) where its potential range was considered to be “northerly facing hill country in low to medium rainfall (700-900 mm)”
(Slay 2001 p. 5).
In south eastern Australia N. neesiana occurs primarily in areas with 500-800 mm average annual rainfall (Muyt 2001) in a range
of climates including the warm wet summer/cold dry winter of the Northern Tablelands of NSW, and hot dry summer/cold wet
winter of southern Victoria (Gardener et al. 1999). In the Sydney region it is found in areas with 700-1000 mm mean annual
rainfall (Benson and McDougall 2005).
N. neesiana appears to be well adapted to seasonal dryness (Bourdôt and Hurrell 1987b) and is drought tolerant (Muyt 2001,
McLaren et al. 2002b, Slay 2002c, Storrie and Lowien 2003). Tsvelev (1977 p. 2) thought that the small chromosomes and small
pollen grains (general stipoid characters), lemma and palea structure protecting the flowers, a dense clumping habit and the
presence of intravaginal shoots (as in N. neesiana) all indicated specialisation for xerophytic climates. Slay (2002a p. 10) thought
that the bare ground resulting from drought was “the catalyst for seedling establishment”.
Fire
Fire is a feature of the campos and pampas grasslands of South America, but as in other areas of the world, the ancient and pre-
European fire regimes are poorly understood. Darwin (1845 p. 114) reported that the plains from Bahía Blanca to Buenos Aires
were commonly deliberately burnt, “chiefly for improving the pasture”: “it seems necessary to remove the superfluous
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