Eucalyptus regnans (Mountain Ash) is a species of eucalypt native to southeastern Australia. Reaching heights in excess of 90 m, it is recognised as the tallest of all flowering plants. It is currently surpassed in height by only two species of conifer, Sequoia sempervirens (Coast Redwood) and Pseudotsuga menziesii (Douglas-fir), which can be found in the temperate forests along the northwestern coast of North America.
In physical appearance, a mature forest of mountain ash is an imposing sight, with giant straight trunks, creamy-white to pale green or grey, rising 30–60 m above a wet sclerophyll or rainforest understorey. The tree has a 5–10 m stocking of fibrous brown bark at its often buttressed base; then the smooth cream to light grey gum-type bark above extends to the upper branches. Sometimes the first branches will not appear for 60 m up the trunk, and they are often draped with long peeled strips of annually shed bark. Because the leaves hang vertically, the tree crown may appear unduly small in proportion to the size of the trunk, especially to a viewer directly below the crown. Source
In Out of Control: the tragedy of Tasmania’s forests (2007), Richard Flanagan claims that over 85% of Tasmania’s old-growth regnans forests are gone, and it is estimated that fewer than 13,000 hectares of these extraordinary trees remain in their old-growth form. In Tasmania’s Styx Valley, the world’s last (and tallest) great unprotected stands of old-growth Eucalyptus regnans are being reduced to piles of smouldering ash.
While many species of eucalyptus recover from severe bushfires through epicormic growth mechanisms, stands of E. regnans are highly susceptible to destruction by intense crown fire because of their dependence on total regrowth from seed. Fortunately, the natural habitat of E. regnans is the areas of Australia with the highest and most reliable rainfall, which are inherently less prone to catastrophic fires than other forested areas. All of Victoria’s 15 tallest trees grow in designated water catchments enclosed within the Wallaby Creek headwaters of Kinglake National Park and the O’Shannassy region of the Yarra Ranges National Park, which are completely protected from logging (but not from bushfire). Some publicly accessible protected tall stands can be found in the Otway Ranges (top – Turtons Track), Dandenong Ranges (centre – Olinda Falls), and the Strzelecki Ranges (bottom – Mt Worth).