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How old are ‘old growth’ eucalypts?

How long can they live?

What is the origin of rainforests that support an overstory of widely-spaced massive old growth eucalypts?

I began to ask these questions in the 1970s when I first became acquainted with giant old trees in Tasmanian mixed rain- and eucalypt forests, whilst making comparisons to similar giants in the Karri and Tingle forests of my childhood in the SW of Western Australia (WA). I saw these questions as pivotal to the issues of conservation of old growth forests generally, and especially the Tasmanian cool temperate mixed forests. Over the following years, I became familiar with similar mixed forests in East Gippsland as well as warm temperate and subtropical analogues further up the east coast in NSW and into Queensland.

The age of trees

The answers I got from foresters, conservationists and scientists were in alignment and initially I accepted this orthodoxy.

The answer to the first question is mostly in the eye of the beholder. Back in the 70s, it was usually a pre-European tree over 200 years old. More recently in our local Wombat Forest some of the magnificent examples of husbanded regrowth from the gold era devastation of the forest 130 years ago (and that survived the second rape of the Wombat in the Kennett government era) are called ‘old growth’. I suppose it is all relative to what else is left.

I have surprised landholders many times by suggesting a very large eucalypt specimen that they assumed was pre-European in age, was more likely to be a post-settlement regrowth tree with ideal growing conditions. Tree workers in Melbourne suburbs removing large eucalypts from the 1970s planting fad occasionally report dealing with trees more than 1m in diameter. Overseas, eucalypts are known for their extremely fast growth and, despite the ravages of hundreds of species of insects that feed on them in Australia, our regrowth trees can do the same in the right conditions.

The answer to the second question seemed decidedly unsatisfactory to me. In the process of exploring that question, I came to my own novel answer to my third question. The fast grown and not very durable Ash group eucalypts of Tassie and the east coast states and the analogous Karri (Eucalyptus diversicolor) in WA were assumed to live for 200-300 years before crown breakage, fire damage, internal decay, termites and fungi got the better of them. Because these species have thin bark with weak capacity for epicormic recovery from bushfire, and little or no ability to coppice from the stump, regeneration of these very tall (60-100m) wet sclerophyll forests was assumed to be only through seed regeneration onto a sterile ash bed following catastrophic fire that killed most, if not all, the previous trees. In the absence of fire, progressive decay of the giants leads to a successional process to more slow-growing but dense understory species that don’t need fire to regenerate. In Tasmania and many parts of the east coast, a variety of species form a closed canopy ‘rainforest’ of lower stature than the giant eucalypts. In extensive swathes of Victoria, especially in the central highlands, Blackwood (Acacia melanoxylon), shrubs and ferns fill the niche while in the Karri forests of WA, forest-form tea trees and shrubs do the same.

In the drier forests and woodlands, slower growing and more durable wood trees, such as Box and Ironbark in the east, and Jarrah, Tuart and Wandoo in the west, are generally smaller but assumed to live longer, as well as having the capacity to coppice from stumps that might push the age to well over 500 years. In most trees, girth and degree of buttressing at the base are indicative of great age. Red Gums (E. camaldulensis) of great girth are often assumed to be some of our oldest trees, being relatively durable and growing in environments not so subject to catastrophic hot bushfires. Our local Guilford ‘Big Tree’ is variously estimated as being between 500 and 1000 years old. I say estimated, but these figures are simply guesses based on assumptions. Of course we can count the rings of a cut tree section or even a fine core taken from a living tree but typically old eucalypts are rotten or hollow from fire inside. Even more confusingly, eucalypts are opportunists with growth pulses in response to some of the most erratic climates on earth. Deciding what is an annual ring and what are extra rings is problematic to say the least and dendrochronologists have avoided the issue by concentrating their limited research time and budgets on conifers such as Tasmanian Huon Pine (Lagarostrobos franklinii) or Callitris pine species in inland areas of the eastern states.

I don’t know if the overlapping climatic record of the last 11,000 years from durable logs recovered from the Pieman River gorge on the west coast of Tasmania is still the oldest tree ring climate record in the world, but that study certainly highlighted what we can learn from old trees and wood before it decays.

Knowing the age of our most ancient trees is arguably the most important question in understanding what our forests can teach us. Old trees are our living connection to the past and guides to how we might husband forests of the future.

A bit of background

This essay, like my koala and wombat essays, is the first written record of my theories about our most fought-over forests. I came to these theories in the 1970s and put them verbally to friends, colleagues and, on occasions, foresters and researchers closer to the scientific fields in question. While my knowledge of wildlife ecology behind the previous two essays is sketchy to say the least, I have the opposite problem in relation to southern Australian tall wet forests: I know so much that I don’t know what to include to help explain the context without boring the lay reader, nor what to leave out to get to the nub of the issue to convince experts in the field to take seriously and further investigate my hypotheses (unless of course the orthodoxies I am challenging have since been overturned).

In any case, like the koala and wombat essays, this longer one is a recording of ideas and stories from the past, gleaned through my own observations, discussions with knowledgeable folk and readings of both lay and scientific literature back in the days when these issues were more in the forefront of my thinking.

In 1973 I read Routley and Routley’s The Fight for the Forests, an academic appraisal of the conservation vs timber production issue in the tall wet forests of the South West and South East of the continent as well as Tasmania. The previous year, activists living close to the front line of industrial forestry in northern Tasmania published a brilliantly crafted A4 pamphlet ‘Woodchip Laughs at you! all the way to the bank’. During a plant collection expedition with Bill Mollison in 1975 I met some of the activists involved, who were also founders of the Teapot commune in Jackeys Marsh. Two years later I moved to Jackeys Marsh to deepen my skills in self-reliant bush living, reading landscape and ecological hunting.

In 1979 I moved to the far south coast of NSW to help my mother establish her bush homestead at Wyndham (documented in Permaculture in the Bush). Over the next few years I had a role in starting the Towamba Valley Catchment Protection Association and contributing to forest camps organised by Concerned Residents of East Gippsland across the NSW/Vic border in Bonang/Goongerah area.

While living in Jackeys Marsh, I developed an alternative theory of forest regeneration to explain the structure of some of the most iconic and fought-over tall wet forests. These ‘mixed forests’ consisted of an overstory of massive eucalypts, typically E. regnans and similar Ash group eucalypts, sometimes well in excess of 60 meters tall and sometimes more than two metres in diameter over a dense, closed canopy of rainforest species up to 30 or more metres tall. These rainforest species were typically dominated by Myrtle Beech (Nothofagus cunninghamii) but included Sassafras, Celery Top Pine, King Billy Pine and many small trees and large shrubs over a ground cover of diverse species of ferns, mosses and liverworts. The conventional understanding of the mixed forest as a successional stage between wet sclerophyll eucalypt and rainforest made a lot of sense to me. As the giants age, decay and fall, without fire to favour the seed regeneration of the eucalypt, rainforest species take over and permanently lock out the eucalypts: a classic case of ecological succession!

Foresters saw these mixed forests as senescent where the total volume of harvestable wood was declining and that they were ripe for harvesting followed by a (very hot) regeneration burn to achieve fantastic vigorous and fast-growing regrowth eucalypts that could reach sawlog size in less than a human lifetime, guaranteeing an abundant supply of long, straight, fault-free construction hardwood for future generations. To let such forests senesce and succeed to rainforest was a waste that would radically reduce current and future wood supply.

Conservationists saw these forests as the most diverse of our rainforests. Overstory trees provided massive eco-structures, complete with diverse and large elevated habitat hollows and nectar-rich flowers, over a rainforest of great diversity with a moisture-holding forest floor providing unrivalled catchment water holding and purifying services. They argued that all of the mixed forests should be conserved.

In Jackeys Marsh I lived, gardened, hunted and cut wood in a patchwork of abandoned farmland and regrowth ash type forests of E. regnans, E. delegatensis and obliqua, E. viminalis and E. ovata, rainforests dominated by Myrtle Beech as well as lowland and subalpine versions of the mixed forests. I found circumstantial evidence that the mixed forests could be their own system, capable of maintaining a wide spaced upper canopy of eucalypts and a dense lower canopy of rainforest species that could reproduce itself over time without the need for a catastrophic wildfire, which is assumed necessary for eucalypt regeneration in these wet climates.

The orthodox understanding of wet sclerophyll eucalypt regeneration

While regeneration of eucalypts in drier forests is more complex, foresters mostly assume that in the wetter forests new trees only arise from a post-fire seedbed, or radical disturbance by flood, landslip or earth moving that exposes mineral rather than organic soil. In the rich forest compost, the growth of ferns and other luxuriant plants can smother light-demanding eucalypts while the tiny eucalypt seeds are easily consumed by ants or succumb to damping off (a common fungal disease). To the average person, it seems strange that the forest giants need either subsoil or fire ash to establish and that compost-rich soil prevents regeneration.

In mature wet sclerophyll forests with annual rainfall over 1000mm, the forests are generally too moist to burn but in bad drought years fires can occur and they are generally very hot. The thinner bark of Ash and similar wet forest eucalypts combined with a lack of epicormic or basal resprouting, means the trees all die. Intact seed capsules on the fire-killed giants open, shedding the fine seed on the sterile but fertile ash bed. Along with activated wattle seeds stored in the soil and other fast growing pioneer shrubs, the fire results in an incredibly dense stand of trees, more like a giant wheat field than a forest. Savage competition results in death and decay of weaker stems. Some eucalypts maintain their heads in the sun over the wattles, which are somewhat more shade tolerant, while the quick growing pioneer shrubs such as Cassinia and other daisy bushes soon die out and are replaced by more slowly-establishing shade tolerant shrubs such as Coprosma and ferns.

Evidence against the orthodoxy

Living in Jackeys Marsh, I came to comprehend the growth rate of Silver Wattle, the predominant nitrogen-fixing pioneer. To my amazement, the twenty metre tall dead and dying wattles that I cut for my firewood supply were only twenty years old with very large and countable seasonal rings. In places, these wattle stands had a well-established understory of young Myrtle Beech and other rainforest trees, supporting the idea that where the soil moisture and fertility was right, Silver Wattle was the pioneer for rainforest without any eucalypts. Disturbance, whether by fire or otherwise, produced another crop of wattles from the hard, long-lived seeds in the soil, and so back to rainforest.

On sunnier less moist sites, logging and/or fire resulted in the pattern described above where the eucalypts stayed ahead of the wattles and formed a tall, close-spaced stand of competing spar trees that slowly thinned through competition. Trees of great height result but ongoing competition restricts the growth of the girth as the forest matures. All foresters understand how thinning is the essential prerequisite to get fat trees suitable for sawlogs, and in nature I think it is a similar process over a longer timescale. To get the huge girth we see in the mixed forests, steady competition might not be enough. Disease might take out some trees, but in Ash type forest, fungi such as Armillaria often kill a patch rather than thin the forest. Wind might fell some but it more typically causes a domino effect. Like lodging of grain in a field, forests succumb to windthrow in a swathe.

In Jackeys Marsh I found what appeared to me might be the answer: an old logging coup from the 1960s where large stumps greater than 1.5m diameter showed the past presence of widely spaced forest giants, but all I could see was a dense tall stand of wattle and myrtle beech. Looking closer I found a spindly eucalypt that had been strong enough to keep ahead of the wattles. The next eucalypt was more than 40m away rather than the 40cm it would have been in a typical post-logging stand of eucalypts. Just as I surmised, the densely-shading wattle killed off any eucalypts in the sites with the best growing conditions. On intermediate sites I surmised that a widely spaced stand of eucalypts would allow early invasion by rainforest trees to recreate the mixed forest from its disturbance phase rather than waiting hundreds of years for the eucalypt canopy to thin through aging and collapse.

Returning to Jackeys Marsh in 1979 from time in New Zealand I took the advice of my mentor, Haikai Tane, to get a camera to record my reading landscape. Permaculture enthusiast and camera technician Bruce Hedge provided me with my Olympus OM1. The Kodachrome slide of that dense regrowth stand where I first worked out the natural process for radical thinning of eucalypts became one of my selected set to inspire students on permaculture design courses in the art of reading landscape.

Another observation supported the possibility that eucalypts may be able to regenerate in these wet forests without fire, logging or other radical disturbance. When a large Ash eucalypt blows down, it generally throws up a large fan of spreading roots and associated subsoil. Little grows on some of these, but on others, I found eucalypt spars with a broad and spreading root system forming a buttressed base to stabilise the flag top growing in the lightwell created by the fallen giant. Might individual tree replacement be another way in which the eucalypt overstory could be sustained through incremental single tree replacement? The problem with this idea is that an uneven aged stand would be created, but most wet forest eucalypts stands are assumed to be the same age, even if diameter differences are quite substantial. But if the trees could live 500 to 1000 years, the very rare replacement tree reaching full height and more than 1m diameter in a perfect sheltered lightwell in 200 years might not be noticed. Without accurate measure of tree age, my guess seems as good as the most qualified forester or ecologist.

Gippsland

In 1980 and 81 I was involved with colleague Peter Brew in planning sites for the forest camps of The Concerned Citizens of East Gippsland, which aimed to bring together foresters, ecologists activists and local residents to better understand the diverse and special forests of east Gippsland, especially around Errinundra Plateau. In Victoria it is only on the Errinundra Plateau of far east Gippsland that you find extensive mixed forest away from watercourses similar to the Tasmanian mixed forests.

At the first of those gatherings I met David Cameron, the Victorian government rainforest ecologist who was in the frontline of deciding what constituted rainforest to be protected from the impact of eucalypt logging. Exploring the forests with an expert was a treat, and I learnt so much to complement and challenge my own learnings about similar forests, mostly in Tasmania.

But I think it was on the second camp the following year I remember David being puzzled by a forest which was a pure stand of silver wattle. He speculated on various successional processes that could have eliminated both eucalypts and rainforest trees. I said I was familiar with many such stands in Tasmania and suggested that it was an old rainforest site where the wattles grew fast enough to shade out regenerating eucalypts.

David was sceptical of my suggestion since there were no rainforest trees regenerating. I remember the group we were with stopping to have a cuppa, sitting on a log more than half a metre in diameter. Curious, I took my pocket knife to the moss-covered rotten wood to expose a clean surface hoping it might be a rainforest species that could support my hypothesis. I found medullary ray wood characteristic of northern hemisphere oaks, Australian casuarinas and proteaceous trees such as silky oak. There was only one candidate species in that part of Victoria with medullary ray wood: Gippsland Waratah (Telopea oreades). This is a close relative of the NSW floral emblem, which grows as a spindly shrub and understory tree, typically less than 20 cm diameter. We were sitting on a waratah log that suggested the rainforest that preceded the wattle stand was of greater age and grandeur than anything existing today. David remained sceptical but I felt my greater experience in the Tasmanian mixed forests had given me an edge over David in trying to piece together the much more fragmentary rainforest ecology of Victoria.

Back to Jackeys Marsh

In January 1983 I was back in Tasmania and contributing to sessions at the Jackeys Marsh Forest Festival. There were plans for three walks: one by a local forester focusing on the logging history; one by a rainforest ecologist from Smithton, Bob Mesibov; and one run by me, as an ex-resident Marshian, on the human ecology and landuse history of the Marsh. We decided to join forces and run a tour where participants could learn from our exchanges. In having more local knowledge, I suggested a route from the valley floor festival site up the footslopes of Quamby Bluff to an extensive and mature unlogged mixed forest below the subalpine scree slopes.

Early into the walk we came across a large Manna Gum, nearly 2m diameter, which the forester suggested was probably over 250 years old and perhaps not taken by the loggers because they figured it was hollow. I asked: if a 2m diameter tree was about 250 years old then how old would a 4m diameter tree be, given the slowing of growth with old age? My interlocutor suggested 4m diameter might be possible in rare circumstances but ages much beyond 250 years are unlikely. I replied that there are a lot of stumps greater than 2m in the Marsh and quite a few up to 4m diameter and, that according to local old timers, some of the largest timber cut in northern Tasmania came out of Jackeys Marsh.

A little further up the track we came across a huge stump 4m diameter at the level the loggers had cut the tree above the buttresses more than 6m above ground level. I said nothing.

Later that year, when visiting the Cumberland Junction tree reserve in Victoria where the interpretive sign suggested the 1.5 to 2m diameter trees were ‘overmature’, I remember being scathing of the sign and in awe of the trees. A staircase of side branches from epicormic regrowth were, in 1982, only just outgrowing the fire-killed dead tops, some of which were broken off at what I estimated to be one metre diameter more than 60m above me. I noted the trees were not buttressed at all, rising vertically from the soil, suggesting they were in their prime when nearly killed by the Black Friday bushfires of 1939. Surely, I thought, the damage and resulting decay would ensure they would never reach their potential for much greater girth and buttressing. Historic photos from the nineteenth century show families living in massive buttressed hollow trees that would be at least three times the age of these giants.

My other memory of the forest tour at Jackeys Marsh was resting in the magnificent pure stand of wide-spaced Myrtle Beech explaining my theory about the mixed eucalypt rainforests. I remember Bob Mesibov exclaiming: did I realise that I was challenging the accepted successional process from wet sclerophyll to rainforest?

A bushfire, apparently lit by local rednecks to scare the greenies, turned into a huge saga that occupied me with high altitude firefighting for the next week, including saving Warners Track from destruction, but that is another story.

Subtropical forests

Mixed forests in the subtropics provide the odd data point that supports my case about tree age. In 1979, Terania Creek in the Nightcap Ranges of NSW was a small but pivotal milestone in the fight for the forests, which influenced and inspired later activism in the southern forests. The NSW Forestry Department had already protected some rainforests from logging but regarded these forests with overstory Brush Box (Lophostemon confertus) as ripe for sawlog supply to local mills. The back-to-the-land settler activists of the region organised a pioneering example of non-violent direct action that had the foresters, timber men and politicians scratching their heads and backing down. Brush Box is a close relative of eucalypts that appears to have a relationship as shelterwood over rainforest, similar to the southern forests, even if the subtropical rainforests are far more species- and structurally-diverse with epiphytes, vines and strangler figs all adding to palms and many different trees.

I am less familiar with the regeneration process for Brush Box but I had the idea that it might be halfway between the (so called) fire-only regeneration process of the Ash eucalypts and the emergent overstory of the subtropical and tropical rainforest conifers further north in Queensland (such as Hoop, Bunya and Kauri Pine). I heard a story that after Terania Creek forest was saved, someone asked CSRIO scientists to investigate, measure or guess (I don’t know) the age of the 1 to 2 m diameter overstory trees, and the figure I remember being told was 1000-1200 years. Can anyone confirm or refute that figure and its validity? In defence of the forestry orthodox view, we should not jump to the conclusion that similar ages must apply to faster growing and much less durable southern Ash eucalypt species.

Celery Top Pine tabletop

Perhaps the strongest evidence for my hypothesis came after the festival and firefighting when visiting Donoghue Benson, an old friend and neighbour in Bill Mollison’s network, on the footslopes of Mt Wellington, Hobart. I wanted to buy some Tasmanian Celery Top Pine (Phyllocladus aspeniifolius) to take back to Melbourne to make a dining table for my beloved, Su Dennett. Donoghue had a stack of rough sawn Celery Top that he was happy to pass onto me. I put it through his thicknesser to skip dress it prior to racking for further drying before dressing by hand over the next year.

I previously had experience building with Celery Top salvaged by the Mountain River sawmill. The miller, whose name I forget, had a ‘Minor Species’ salvage licence from the Tasmanian Forestry Commission. This allowed him to extract rainforest species sawlogs from clearfell logging coups in SE Tasmanian mixed forests after the big sawmills and export pulp contractors had extracted the Ash eucalypts but before the massive volume of slash debris was burnt on the forest floor to create a seedbed for eucalypt regeneration. The foresters aimed to burn the following summer, leaving little time for salvage of Celery Top and other rainforest species. The Mountain River miller was running a public campaign to have more time to salvage trees while the foresters worried about fern and other regrowth making the coups too wet to get a good burn through both green and wet rotten logs up to a metre or more in size.

The miller had CSIRO scientists age the salvaged Celery Top logs that were in his yard (the same timber as in my table). This isn’t hard to do: sand a log section, polish and count the rings, if necessary with a magnifying glass (or these days using a high resolution digital photograph). The scientist confirmed the Celery Top logs less than a metre in diameter were from trees 750 to 800 years old. What a waste to burn such precious timber that, in its better knot-free grades, is almost as good a boat building timber as the even slower growing and related Tasmanian conifer Huon Pine.

So what has that dining table got to do with my forest thesis? Celery Top, like all the southern conifers, is easily killed by fire and, remembering that mild fires are impossible in these tall wet mixed forests, there couldn’t have been a fire in that forest of any sort for at least 800 years. So the overstory eucalypts were also at least 800 years old and/or there must be some mechanism (such as my single tree replacement hypothesis) by which eucalypts can renew themselves without the aid of fire.

The rings in the Celery Top pines don’t lie about their age so either:

1. the severe fire or similar massive site disturbance requirement theory for wet forest eucalypt regeneration collapses or
2. the current understanding about the potential age of the world’s largest flowering plants (the supposedly 200-year-old Ash trees) needs to be revised 4-fold older than currently thought.

Checkmate! Unless some forester or ecologist can show how I am conclusively wrong, I think it’s about time forest scientists in this country go back to first principles in understanding our remaining old growth wet forest giants, which are mostly in national parks and reserves (without needing to cut down any more of them). And aren’t we all at least curious about the age of the local ancients that witnessed generations of indigenous culture and husbandry before the arrival of white people, perhaps less than half their lives ago? And what do we need to understand and do with the current regrowth forest that we are responsible for to ensure that some of those youthful trees might still be here toward the end of the current millennium?

David Holmgren
Melliodora
Winter, 2024