Tasmania's giant eucalypts: discovery, documentation, macroecology and conservation status of the world's largest angiosperms

Context: Tasmania is the epicentre of the tallest and most massive angiosperms on Earth. Aims: To survey Tasmania's tallest and most massive (large trunk volume) trees. Methods: LiDAR and satellite imagery identified areas with very tall trees. Field surveys recorded the geolocation, height, diameter and condition of exceptionally large individuals, and effects of recent fires. Key results: Giant trees occur in a band between dry forests and temperate rainforests, with the largest trees in areas with 1000-1500 mm rainfall and 8-12°C mean annual temperature. We documented 18 trees taller than 90 m, and 32 trees with trunk volume of >250 m³. Trunk volume was better correlated with diameter at 10-m height than at breast height, owing to irregularities near the base of large trees. The tallest tree was measured to be 99.6 m tall (now 96 m tall), and the most massive tree had a trunk volume of 460 m³. Most of the largest and tallest trees in Tasmania were Eucalyptus regnans, but occasional individuals of Eucalyptus globulus, E. obliqua and E. tasmaniensis were also over 85 m tall or had a trunk volume of >280 m³. Post-fire surveys highlighted vulnerability of giant Eucalyptus trees to fire, with 60% of the largest known trees killed by fire since 2004. Conclusions: The giant trees of Tasmania are of global significance, but vulnerable to a warming, drying climate and associated increase in fire activity. Implications: We outline steps for the conservation of giant trees, a task made urgent by climate change.