Vegetation change over 50 years in eucalypt forest on north stradbroke island

Abstract

Detailed vegetation surveys on North Stradbroke Island (known by Traditional Owners as Minjerribah) by University of Queensland botanists in 1967 provided a rare and valuable opportunity to assess vegetation composition and structure changes over the last 50 years. The eucalypt forest assessed is dominated by scribbly gum (Eucalyptus racemosa), representing Regional Ecosystem 12.2.6. It is the most widespread forest on the island and is also abundant on Moreton and Fraser Islands, as well as the Cooloola Coast, so that this evaluation is relevant to a broad area. At the forest site, located south of Brown Lake, a previously continuous ground cover of kangaroo grass (Themeda triandra) has all but disappeared, while other herbaceous plants and species richness have declined. Large shrub and small tree densities have dramatically increased, particularly Allocasuarina littoralis and Leptospermum trinervium. Eucalypt crowns have been damaged and several trees are dead. The forest south of Brown Lake was burnt by intense fires in 1965 and 1995, but was not burnt in the extensive January 2014 wildfire. The study site may have experienced other fires which have not been documented, but was long unburnt by the time of the 2016 survey. We suggest that the dramatic loss of grass and herb cover, shrub and small tree thickening, plus crown damage, resulted from irregular, high-intensity fires. The re-establishment of regular, low-to moderate-intensity fires during periods of good soil moisture is likely to reduce crown damage, maintain shrubs at a healthy density and promote native grasses.