Invasive grasses and conservation of natural ecosystems

Bob Congdon and his students are studying the ecology of invasive exotic grasses and the native plant communities with which they interact, in order to better understand how we can manage these communities to conserve native species.

Para grass (Urochloa mutica) is an introduced pasture species from Africa which is invading tropical wetlands and conservation reserves in coastal north Queensland. Sarah Swan compared the germination and growth of this species with the rare native grass Paspalidium udum, especially to determine the likely effects of management regimes such as burning, grazing and water level manipulation on the two species. Smoke and heat significantly increased germination of Para grass seed, with no effect on P. udum. Clipping (simulated grazing) of plants promoted tiller production in Para grass, but it declined in P. udum. Potential palatability (higher protein, lower lignin) of P.udum was also better. Para grass also survived increasing water levels better than P. udum. Consequently, the use of fire, grazing or water level manipulation to control Para grass is likely to be detrimental to the vulnerable P. udum, where it occurs.

Guinea grass (Megathyrsus maximus) is also an introduced pasture grass from Africa. It grows well on the margins of wetlands, but also spreads into native woodlands. Bree Clouten is studying the ecology of Guinea grass and several native grasses. She found there was little difference in viability and germinability of Guinea grass seed compared to Kangaroo grass, Black Spear grass and Giant Spear grass. Aged seed of the 3 native species gave higher germination, but this was not the case for Guinea grass. Germination of all species was not improved when exposed to a heat shock, similar to what they would experience in a moderate to intense fire. Germination of the two Spear grass species improved on exposure to smoke but Guinea grass did not. This study suggests that the success of Guinea grass is not due to features of germination, but probably more due to the comparatively large numbers of seed produced, and the vigour of the mature plants when competing with native grasses. Further field studies are examining the timing and amount of seed produced by these grasses, and the impact of swards of Guinea grass on abundance of native species under different management regimes (herbicide, grazing, grazing followed by fire, slashing and mowing).

Contact name: Robert.Congdon@jcu.edu.au