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.