Allocasuarina (Casuarinaceae) Invasion of an Unburnt Coastal Woodland at Ocean Grove, Victoria: Structural Changes 1971–1996

Abstract

Changes in vegetation structure in a long-unburnt (> 115 years) woodland at Ocean Grove, Victoria, were assessed by comparing density data collected in 1971 by Withers and Ashton (1977) with comparable data from 1996. The changes in structure outlined by Withers and Ashton (1977) continued to operate over the 25 year period, namely, a dramatic increase in the density of Allocasuarina littoralis (Salisb.) L.A.S.Johnson, and a continued decline in the once-dominant eucalypts, especially Eucalyptus ovata Labill. The density of A. littoralis increased from 911 trees ha^–1 in 1971 to 3565 trees ha^–1 in 1996. Most of the surviving E. ovata displayed extensive crown dieback, and appear likely to die in the near future. Many eucalypt seedlings which were planted into burnt and unburnt experimental plots in 1971 were still alive in 1996, but most were less than 0.5 m tall and suppressed by tall regrowth of A. littoralis and Acacia pycnantha Benth. In the continued absence of fire and other disturbances, it is predicted that A. littoralis will continue to dominate the reserve, leading to further declines in eucalypts. It appears unlikely that a single fire will prevent A. littoralis dominance, and frequent burning at short intervals may be required to reinstate an open woodland structure.