Can competition from Themeda triandra inhibit invasion by the perennial exotic grass Nassella neesiana in native grasslands?
Ian D. LuntA and John W. MorganB
A The Johnstone Centre, Charles Sturt University and CRC for Weed Management Systems, PO Box 789 Albury, New South Wales 2640, Australia.
B School of Botany, LaTrobe University, Bundoora, Victoria 3083, Australia.
Change in the distribution of the perennial, exotic Chilean needle grass, Nassella neesiana (Trin. & Rupr.) Barkworth, was documented over a 10-year interval in a temperate grassland reserve dominated by kangaroo grass, Themeda triandra Forsskal, in western Melbourne, Victoria. Nassella neesiana increased from 16% of quadrats in 1986 to 42% in 1996. There was a significant negative association between T. triandra cover in 1986 and the number of quadrats in each cover class which were invaded by N. neesiana in 1986 (P <0.05) and 1996 (P <0.01). Comparatively few quadrats with more than 50% T. triandra cover were invaded by N. neesiana. Furthermore, there was a significant negative rank correlation between N. neesiana cover in 1996 and T. triandra cover in 1986 or 1996 (P <0.05) for those quadrats where N. neesiana occurred in 1996.
The expansion of N. neesiana cover in each quadrat was also significantly negatively correlated with T. triandra cover in 1986 (P = 0.001). Where N. neesiana did invade areas which supported dense T. triandra in 1986, only small stands generally developed. The present extent of T. triandra and N. neesiana in the reserve is a function of past land use; areas most heavily disturbed in the past (by ploughing last century and grazing) were the most prone to N. neesiana invasion. It is concluded that competition from dense swards of T. triandra may play a valuable role in slowing (but not necessarily preventing) invasion by N. neesiana in temperate grassland reserves.
Plant Protection Quarterly (2000) 15 (3) 92-94.