Big old trees: life cycles, time scales, meaning and growth

A compelling look at our beloved trees and the need to act now to save Victoria's mountain ash forests and the life they support. 

This is an article from our member-only magazine, habitat. To receive habitat and enjoy more stories like this, become an ACF member today. 

There is a great big gum tree in the front garden of my childhood home. I don’t know what species it is, but when I hear or read the word ‘tree’, it is the image that comes to mind. I know this tree intimately.

The base is wide and buttressed. The branches are long, pale and perfectly spaced for climbing and it’s home to possums, birds and cicadas. It is a totally inappropriate tree for the location, but over time, against the odds, it has thrived and today it stands majestic and tall.

I have loved this tree my whole life.

Planted just four or five decades ago, it is now the tallest tree in the street. As a kid I thought it was the tallest tree in the world.

Trees are synonymous with life on the Australian continent.

They vary in form from the huge single-stemmed Stringybarks of south-eastern Australia, to the spindly multi-trunk Mulga of the Australian outback. They inhabit virtually every terrestrial ecosystem from the muddy seashores of the tropical north to the frozen mountaintops of temperate Tasmania. Some are ubiquitous, like the River Red Gum, which grows in every mainland state, while others are seldom seen, like the Wollemi Pine, restricted to a few remote gorges deep in the Blue Mountains.

The tallest tree in Australia, in fact the tallest flowering plant in the world, is the Mountain Ash Eucalyptus Regnans. From a seed measuring just a few millimetres in length, sprouts a mature tree that grows to nearly 100 metres. This miraculous feat of nature requires just the right mix of conditions: soil, slope, rainfall, temperature and fire frequency. But, most importantly, the full life cycle of this extraordinary tree takes time. Lots of it. 

Mountain Ash live for four or five hundred years and won’t form hollows for at least their first century.

Some trees exist on similar time scales to our own. The apricot tree my cousin planted just five years ago in his backyard provides him with enough fruit this summer to make his belly ache. For a pulp plantation manager, 20 or so years is all the time it takes to grow a profitable crop.

Yet many trees exist on timescales far beyond our lifetimes. Mountain Ash live for four or five hundred years and won’t form hollows for at least their first century. River Red Gums can live for up to a thousand years. There are specimens surviving in the MCG car park that bear the scars of bark shields and canoes carved by people of the Kulin Nation in times long ago. 

Trees change shape and meaning as they grow. From tiny seeds, to striving saplings, old-growth giants and scarred old stumps —the form of trees, and what we value about them, shifts and varies over time. As an archetype, the tree is a near universal symbol of life. In religion, philosophy, mythology and epistemology, for thousands of years the tree has come to represent nature, growth, knowledge and unity.

But different trees can mean different things to different people, at different times. To the wildlife biologist, an old hollow-bearing tree is critical habitat for an endangered species. To the wood-worker, a single tree can provide beautiful timber to make valuable hand-made furniture. 

To the bushwalker, fallen branches mean a heat-giving fire on a cold night out. To the industrialist, a forest is just feedstock for manufacturing. To the carbon farmer, a tree is more valuable left standing. To the water catchment manager, a forest is a giant sponge. To the young child growing up in the suburbs, a tall tree in the front garden is an adventure that never grows old.

Planted just four or five decades ago, it is now the tallest tree in the street. As a kid I thought it was the tallest tree in the world.

For centuries, a great old Mountain Ash forest cloaked the peaks and valleys of the Kulin Nation, along the Great Dividing Range in the area we now call Victoria’s Central Highlands. Today, just one per cent of that Mountain Ash ecosystem is classified as ‘old growth’.

Devastating bushfires of increasing frequency and intensity and more than a hundred and fifty years of logging have taken a tremendous toll. With global warming now amplifying those pressures, the entire Mountain Ash ecosystem has been listed as critically endangered and at risk of ecological collapse. What remains of that great old forest is now young and highly fragmented; made up in large part of 70- to 80-year-old trees —regrowth from the devastating 1939 bushfires.

These forests are virtually the only habitat of Victoria’s faunal emblem, the critically endangered Leadbeater’s Possum, which has suffered an 80 per cent reduction in population since the 1980s, when a relentless program of clear fell logging took hold in these forests.

Left to grow, these 70- to 80-year-old trees will become the hollow-bearing old growth forest of the future —the critical habitat the Leadbeater’s and other threatened species need to survive.

However these ageing trees, growing straight and tall, are also highly sought after by the timber industry and account for nearly 90 per cent of the trees that are logged in Victoria. Considering all we now know about the vulnerability of wildlife to extinction, it is incredible that we are still making low value paper and wooden products from high conservation value forests.

I have no doubt we will look back on this time and wonder what on earth were our leaders thinking when they allowed these precious forests to be felled when they should have been left to grow.

The Victorian Premier, Daniel Andrews, is perhaps the last Victorian leader with the opportunity to change the course of history and save the State’s faunal emblem from extinction and the Mountain Ash ecosystem from collapse. To do so, he must act urgently to create the Great Forest National Park, which will restore, protect and connect the great Mountain Ash forests. But he needs to hear from people like you and me —people who value nature deeply. He needs to hear loud and clear that the time for change has come.

We must leave the Premier with no doubt that protecting forests and wildlife is the right thing to do —that our magnificent Mountain Ash trees need time to grow old.