The legend of the world’s tallest tree is said to have been measured by a Tasmanian forester, only after having cut it down and stepping out his paces along the fallen tree trunk. Whatever the height, it didn’t make the official record books.
With more refined (and much less damaging) techniques used to measure tree heights, the official tallest tree is a Coast Redwood (Sequoia sempervirens), named Hyperion, growing at 116 metres tall in California. Australia can, however, boast the tallest living hardwood species; a Mountain Ash (Eucalyptus regnans) of Tasmania, measured at 99.82 metres in 2014.
A stand of large Mountain Ash is a very impressive sight, but their towering stature is not their only claim to fame, with their ecological function in wet forests every bit as important. Mountain Ash grows in high rainfall, mountainous areas of Tasmania and Victoria, including areas in the Otway Ranges where yearly rainfall reliably exceeds 1000mm.
Mountain Ash typically grow in pure stands, forming tall-open forests, their canopies protecting a species-rich ferny understory from the scorching summer sun. In lower rainfall area on poorer soils, stands of Mountain Ash may be restricted to sheltered valleys or along watercourses. Such is the case at the Wilderlands project site of Crowes Lookout, near Lavers Hill. Here, other tall eucalypts can be found growing with Mountain Ash, namely Messmate Stringybark (E. obliqua), Mountain Grey-gum (E. cypellocarpa), and Southern Blue-gum (E. globulus). In fact, some of the biggest trees in Victoria are a hybrid between Mountain Ash and Messmate Stringybark, known as Otway Messmate when found in the Otway Ranges.
Many arboreal (tree dwelling) animals benefit from the Mountain Ash forests, including the endangered Leadbeater’s Possum, Victoria’s faunal emblem. Australia’s largest owl, the Powerful Owl, hunts through the Mountain Ash forests and may use large tree hollows formed by limbs hit by lightning or torn away in high winds. At Crowes Lookout and within pockets across the Otway Ranges, the Yellow-bellied Glider uses Mountain Ash as its playground and feeding-ground. This large glider can move between tall trees with ease, gliding on skin stretched between its legs. With their sharp teeth, they carve V-notches into the smooth trunks, causing the tree to ‘bleed’ sap that provides a nutritious feed.
The latin regnare, from which the botanical name Eucalyptus regnans is derived, means “to rule” – and it does just that. The trunk of a mature Mountain Ash forms a massive buttress at its base that may reach up to 5 metres in diameter. The well-known Ada Tree near the town of Warburton, east of Melbourne is a whopping 15 metres in circumference and thought to be between 300 and 350 years old.
A number of historical events have diminished our impressive Mountain Ash stands across Victoria and Tasmania, the most significant of those being clear felling for timber used in building, furniture, and joinery. For this reason, there are very few examples left of massive specimens like the Ada Tree.
Mountain Ash forests are also susceptible to wildfires, with complete canopy scorch resulting in tree death, as the species is unable to resprout from epicormic (stem) shoots, unlike many other eucalypt species. In preparation for times like this, Mountain Ash hold tightly to seed within their protective fruits (nuts), releasing billions of seed across the forest floor following a wildfire. Germination and regrowth of Mountain Ash is spectacular, often described as a ‘wheat-field’ of jam-packed seedlings. As the seedlings grow, competing with each other for light, moisture, and nutrients, the stems are naturally thinned.
Over the course of the next 200-300 years, the thinning of trees continues, until a mature stand of ‘giants’ may include only ten to twenty trees per hectare. A dense forest canopy is formed by upper-, mid-, and lower-storey trees, shrubs and ferns, creating a very sheltered, moist environment, even during the summer period, thus affording greater protection from wildfire. Eventually, in the absence of intense wildfire, mature Mountain Ash may die of old age, their bodies returning nutrients to the soil and making way for a new rainforest dominated by Beech (Nothofagus cunninghamii) and Blackwood (Acacia melanoxylon). Should wildfire find its way into the rainforest, perhaps during severe drought, the entire cycle begins again, with Mountain Ash seedlings returning.
The majority of large Mountain Ash in Victoria today are trees that began growing as seedlings following the wildfires of 1926 (Black Sunday) and 1939 (Black Friday) and have since escaped the chainsaw or a subsequent wildfire. Our conservation areas on public and private land are vital for the recovery of Mountain Ash forests and their potential transition to rainforest ecosystems.
Your support of the Wilderlands project at Crowes Lookout, ensures long-term survival of our forest giants in the Otway Ranges – giving hope that in another 100 years, our grandchildren and great-grandchildren will be able to witness the impressive display of a stand of trees growing 100 metres tall and 5 metres across.
Chris Lindorff, Wilderlands Chief Ecologist, is an experienced ecologist and land manager with a degree in Science, and Forest Science, from University of Melbourne.