Mountain ash

Appearance

''Eucalyptus regnans'' is a broad-leaved, evergreen tree that typically grows to a height of 70–114 m but does not form a lignotuber. The crown is open and small in relation to the size of the rest of the tree. The trunk is straight with smooth, cream-coloured, greyish or brown back with a stocking of more or less fibrous or flaky bark that extends up to 5–20 m at the base. The trunk typically reaches a diameter of 2.5 m at breast height . Young plants and coppice regrowth have glossy green, egg-shaped leaves that are held horizontally, 55–120 mm long and 22–50 mm wide and petiolate. Adult leaves are arranged alternately along the stems, the same shade of glossy green on both sides, lance-shaped to broadly lance-shaped or sickle-shaped, 90–230 mm long and 15–50 mm wide, tapering to a reddish petiole 8–25 mm long. The upper and lower surfaces of the leaves are dotted with numerous tiny, circular or irregularly-shaped oil glands. Secondary leaf veins arise at an acute angle from the midvein and tertiary venation is sparse.

The flower buds are arranged in leaf axils in groups of between nine and fifteen on one or two unbranched peduncles 4–14 mm long, the individual buds on pedicels 3–7 mm long. Mature buds are oval, 4–7 mm long and 2–4 mm wide with a rounded operculum. Flowering occurs from March to May and the flowers are white. The fruit is a woody, cup-shaped or conical capsule 5–8 mm long and 4–7 mm wide on a pedicel 1–7 mm long and usually with three valves near the level of the rim. The seeds are pyramid-shaped, 1.5–3 mm long with the hilum at the end.

Seedlings have kidney shaped cotyledons, and the first two to three pairs of leaves are arranged in opposite pairs along the stem, then alternate.

Distribution

''Eucalyptus regnans'' occurs across a 700 km by 500 km region in the southern Australian states of Victoria and Tasmania. The species grows mostly in cool, mountainous areas that receive rainfall over 1,000 millimetres per year. ''E. regnans'' reaches its highest elevations of about 1,100 metres ASL on the Errinundra Plateau in north-eastern Victoria, and its lowest elevations near sea-level in some southern parts of its Tasmanian distribution.

In Victoria, stands of tall trees are found in the Otway, Dandenong, Yarra and Strzelecki ranges as well as Mount Disappointment and East Gippsland. However, the distribution is much reduced. Most of the ''E. regnans'' forest across Gippsland was cleared for farmland between 1860 and 1880, and in the Otway Ranges between 1880 and 1900, while severe bushfires hit in 1851, 1898 and 1939. In Tasmania, ''E. regnans'' is found in the Huon and Derwent River valleys in the southeast of the state.

In the Otways, the species is found in wet forest in pure stands or growing in association with mountain grey gum , messmate and Victorian blue gum . Other trees it grows with include manna gum , shining gum , myrtle beech and silver wattle The mountain ash-dominated forest can be interspersed with rainforest understory, with such species as southern sassafras , celery-top pine , leatherwood and horizontal . The mountain ash is most suited to deep friable clay loam soils, often of volcanic origin; in areas of poorer soils, it can be confined to watercourses and valleys.

Status

''E. regnans'' forests are particularly susceptible to destruction by bushfire, and, to a lesser extent, timber harvesting.

Opposition to logging of wet forests by clearfelling has grown very strong in recent years . It is a controversial debate with strong opinions both for and against timber harvesting.

Several applications have been made to Victoria's Flora and Fauna Guarantee Scientific Advisory Committee to list mountain ash forests as an endangered vegetation community. The committee rejected an application in 2017 as being ineligible and that it did not satisfy at least one criterion set out in the Flora and Fauna Guarantee Act 1988 and its Regulations of 2011. The assessment criteria included, was there a demonstrated state of decline, has there been a reduction in distribution or has vegetation community altered markedly.


Studies conducted by Murray Cunningham and David Ashton found that the re-growth habit of ''Eucalyptus regnans'' requires high light conditions, and the high nutrients contained in the ash layer. These conditions are found typically following a high intensity wildfire, which are an infrequent, yet periodic feature of mountain ash forests. For this reason clearfelling – with the complete removal of all trees, followed by a high intensity fire and seeding – is used by the timber industry and forest scientists to ensure regeneration of harvested areas because it mimics the conditions found after high intensity wildfire.

Melbourne's forested water catchment areas, which provides water requiring little treatment, are composed of large areas ''E. regnans'' forest. The management of 157,000 hectares of Melbourne’s forested water catchments were vested in the Melbourne and Metropolitan Board of Works in 1891 with a closed catchment policy where timber harvesting and public access was not permitted. These areas are now included in the Yarra Ranges National Park. There has been a long running political campaign to add more areas to create the Great Forest National Park.

Water yields from catchments fall significantly for 20 to 40 years if trees are killed by bushfire or timber harvesting. The MMBW began research into forest cover on water supplies as early as 1948. In the early 1960s they set up a new series of paired catchment experiments in wet mountain forests near Healesville to measure the long term impacts of timber harvesting and bushfire on water quality and quantity. It took another 10 years for the results to emerge more clearly. It was found that while timber harvesting had an impact, the most dramatic threat to stream flows remained catastrophic bushfires like those on Black Friday in 1939 or Black Saturday in 2009.

In 2018, some researchers concluded that Mountain Ash forests in Victoria represent a collapsing ecosystems. They coined the term 'hidden collapse' meaning an ecosystems that give a superficial appearance of being intact but has lost key elements. At their research sites they found that between 1997 and 2011, up to 50% of large old-cavity trees had been lost and there had also been a significant decline in the numbers of tree dwelling marsupials such possums and gliders and birds. They identified fast and slow drivers of change: fire, logging and climate change and indicated that Mountain Ash forests would be replaced with Acacia-dominated woodlands.

Habitat

''Eucalyptus regnans'' occurs across a 700 km by 500 km region in the southern Australian states of Victoria and Tasmania. The species grows mostly in cool, mountainous areas that receive rainfall over 1,000 millimetres per year. ''E. regnans'' reaches its highest elevations of about 1,100 metres ASL on the Errinundra Plateau in north-eastern Victoria, and its lowest elevations near sea-level in some southern parts of its Tasmanian distribution.

In Victoria, stands of tall trees are found in the Otway, Dandenong, Yarra and Strzelecki ranges as well as Mount Disappointment and East Gippsland. However, the distribution is much reduced. Most of the ''E. regnans'' forest across Gippsland was cleared for farmland between 1860 and 1880, and in the Otway Ranges between 1880 and 1900, while severe bushfires hit in 1851, 1898 and 1939. In Tasmania, ''E. regnans'' is found in the Huon and Derwent River valleys in the southeast of the state.

In the Otways, the species is found in wet forest in pure stands or growing in association with mountain grey gum , messmate and Victorian blue gum . Other trees it grows with include manna gum , shining gum , myrtle beech and silver wattle The mountain ash-dominated forest can be interspersed with rainforest understory, with such species as southern sassafras , celery-top pine , leatherwood and horizontal . The mountain ash is most suited to deep friable clay loam soils, often of volcanic origin; in areas of poorer soils, it can be confined to watercourses and valleys.

Uses

''Eucalyptus regnans'' is valued for its timber, and has been harvested in very large quantities. Aside from being logged in its natural range, it is grown in plantations in New Zealand and Chile, and to a limited extent, in South Africa and Zimbabwe. Primary uses are sawlogging and woodchipping. It was a major source of newsprint in the 20th century. Much of the present woodchip harvest is exported to Japan. While the area of natural stands with large old trees is rapidly decreasing, substantial areas of regrowth exist and it is increasingly grown in plantations, the long, straight, fast growing trunks being much more commercially valuable than the old growth timber.

It is a medium weight timber and rather coarse in texture. Gum veins are common. The wood is easy to work and the grain is straight with long, clear sections without knots. The wood works reasonably well for steam-bending.
Primary uses for sawn wood are furniture, flooring , panelling, veneer, plywood, window frames, and general construction. The wood has sometimes been used for wood wool and cooperage. However, the wood needs steam reconditioning for high value applications, due to a tendency to collapse on drying. This wood is highly regarded by builders, furniture makers and architects.

Cultural

''Eucalyptus regnans'' is too large for the majority of gardens, but may be suitable for parks. Propagation is from seed, with the best germination rates being obtained by refrigerating for three weeks before sowing. Seed may be stored for several years if refrigerated and kept dry. Seedlings are grown in containers but are more prone to damping off than other eucalypts; they are highly susceptible to ''Phytophthora cinnamomi'' and ''P. nicotianae'' Young plants are generally planted out once they are 8 or 9 months old. These are at risk of being eaten by grazing rabbits, wallabies and possums, which can destroy young plantations in severe cases.

American horticulturist and entrepreneur Ellwood Cooper noted its rapid growth but demanding soil requirements in his 1876 work ''Forest Culture and Eucalyptus Trees''. ''Eucalyptus regnans'' requires fertile soil with good drainage and annual rainfall of 1,000 millimetres spread over the year, and has poor tolerance to temperatures below −7 °C or drought.

Outside Australia, plantations have been successfully established in New Zealand, South Africa, Kenya, and Tanzania.