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seed heads

Natural populations

Themeda triandra (syn. T. australis) dominates many grassy woodlands and tropical savannahs in both Australia and Africa. The grass was probably the original dominant of all Australian grasslands [38]. As one of Australia’s most widespread species, adapted to environments from the arid interior to the alps, there is probably more than one genetic race [38]. However, no significant variation has been distinguished in its natural range to classify formally. While abundant in the south it is probably of tropical origin, reflected in the fact that it withstands grazing better in summer-rainfall areas than it does further south [40]. The grass tolerates a range of soil types and conditions including low levels of salinity [6]. It has a low to moderate frost tolerance and a high drought tolerance [38]. Formally known as Themeda australis, African populations of this grass are now recognised as being conspecific [40]. Note that the National Herbarium of New South Wales still refers to this species as T. australis [43].

Flowering and seeds

A summer growing C4 grass, the flowering and seeding period is in summer; awned caryopsis. It is a warm season grass (C4) with an optimum temperature for growth of 25-35 degrees [40]. With the covering structure removed from the caryopsis (ie grass fruiting body) and alternating temperature conditions of 35 degrees day and 20 degree night temperature, high rates of germination are recorded [90]. However germination variability is reported by some.  It has been found that approximately 2/3 of seed collected from one inflorescence can be infertile and difficult to distinguish from fertile seed as both turn brown and hold on to their awns; generally fertile seed is larger [48].  No significant response to fire (heat) and smoke treatments [75]. Seed set occurs primarily in mid-summer but germination does not occur until spring when soil moisture is high and soil temperatures are above 20 degrees [78]. Germination may benefit from a 6-12 month after ripening period at ambient temperatures and when it is sown with awns better results are achieved [pers. comm. Paul Gibson-Roy, Grassy Groundcover Project].

Cultivation and uses

It is an excellent fodder grass though becoming coarser with maturity and will disappear if it is grazed continuously [18] and under conditions of increased fertility [38, 60]. The presence of kangaroo grass on creek margins and on alluvial plains indicates excellent condition [18].  It is thought that it was more widespread but being highly palatable and not resistant to heavy grazing it has become rare in the central and north-west regions of Western Australia [18].

To maintain kangaroo grass pastures, they should be stocked at low stocking rates (1 DSE/ha in run country) or spelled at regular intervals [60].  Themeda triandra has moderate production (t/ha), digestibility of 54 – 75 per cent and crude protein of 5 – 17 per cent [60]. It is not of marked value in pastures in the Central Australia where it occurs sporadically, where though palatable, mature plants are neglected [35]. 

A deep rooted perennial tussock grass, Themeda can be eliminated under moderate and particularly under heavy grazing in grassy woodland [77]. Without disturbance, Themeda increases in dominance [77]. The practice of burning grazing land (in spring) favours Themeda grass [40]. In an undisturbed sward (10 years since fire or grazing) in southern Victoria, tussocks were fewer and were poorly rooted compared to Themeda tussocks in a frequently burnt area, and litter levels were greater minimising seedling recruitment [78]. If conditions continue (e.g. ongoing fire exclusion) it leads to the death of many tussocks [78].

Key descriptors:

Climate parameters
Mean annual rainfall: 100-2700 mm
Rainfall distribution pattern: summer, uniform or winter
Mean annual temperature: 12-23 °C
Mean max. temperature of the hottest month: 17-39 °C
Mean min. temperature of the coldest month: -2-21 °C
Frosts (approx. no. per year): greater than 20
Frost intensity: light to moderate (0 to -5°C)
Altitude: 0-1300 metres
Tolerance of extremes in climate
Drought: known to be tolerant of protracted droughts
Fire: regenerates foliage after damaging fire
Frost: tolerates frosts in the 0° to -5°C range
Wind: tolerates salt-laden coastal winds
Soil factors
Texture: clay loam, cracking clays, light to medium clay (35-50% clay), loam, sandy loam, sandy clay loam or sand
Soil pH reaction: acidic (less than 6.5)
Drainage: well-drained
Salinity: non-saline
Biological traits under cultivation
Habit: evergreen groundcover
Longevity: short-lived less than 15 years
Growth rate: fast
Root system: shallow and spreading
Windbreak potential: tolerates salty coastal winds
Shade tolerance: grows best in full sunlight or tolerates partial shade

References

[6] Beilby G, Shoebridge B, Carland F, Dennis C, Jackson A (2006) Salt Tolerant Plants of the Western District Ramsar Lakes. GreeningAustralia Victoria and the Australian Plants Society Colac Otway Group.

[18] Mitchell A, Wilcox D (1994) Arid shrubland plants of Western Australia. University of Western Australia Press, Perth.

[35] Lazarides M (1970) Grasses of Central Australia. Australian National University Press, Canberra.

[38] Mitchell M, Miller M (1990) The identification of some common native grasses in Victoria - a set of compilation notes. Rutherglen Research Institute, Victoria.

[40] Forbes SJ, Cade JW, Lamp CA (2001) Grasses of Temperate Australia - a field guide. Bloomings Books, Melbourne.

[43] National Herbarium of New South Wales (2008) PlantNET - Flora of New South Wales. (Online resource) http://plantnet.rbgsyd.nsw.gov.au/floraonline.htm (Accessed: February 2008)

[48] Australian National Botanic Gardens and National Herbarium (2008) Growing Australian Plants. (Online Resource) http://www.cpbr.gov.au/gnp/index.html (Accessed: February 2008)

[60] Australian Government (2005) Grazing Native Pastures in Tasmania : managing kangaroo grass pastures. Land Water and Wool Australia fact sheet. (Online Resource) http://products.landwaterwool.gov.au/matrix/pdf/PF050865.pdf (Accessed: December 2007)

[75] Clarke S, French K (2005) Germination response to heat and smoke of 22 Poaceae species from grassy woodlands. Australian Journal of Botany 53, 445-454.

[77] Fensham RJ (1998) The grassy vegetation of the Darling Downs, south-eastern Queensland, Australia : Floristics and Grazing Effects. Biological Conservation, Vol. 84, No. 3, pp 301- 310.

[78] Morgan JW, Lunt ID (1999) Effects of time-since-fire on the tussock dynamics of a dominant grass (Themeda triandra) in a temperate Australian grassland. Biological Conservation 88, pp 379-386.

[90] Flynn S, Turner RM, Dickie JB (2004) Seed Information Database (Release 7.0, October 2006). (Online database) http://www.kew.org/data/sid/ (Accessed: July 2007).

Internet links

Australian National Botanic Gardens – Growing Australian Plants: http://www.anbg.gov.au/gnp/interns-2004/themeda-triandra.html

FloraBase Western Australia Flora Online – species description & distribution: http://florabase.calm.wa.gov.au/browse/profile/673

South Australia Flora Online – species description & distribution: http://www.flora.sa.gov.au/cgi-bin/texhtml.cgi?form=speciesfacts&family=Gramineae&genus=Themeda&species=triandra

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