eucalypt

Magic amidst a multitude of stems

Victoria's box-ironbark forests are magic. Whatever time of year you visit, their beauty is evident. The rugged, gnarled trunks of the ironbarks stand black as if they’ve clung to their night-time colour scheme despite the breaking of day. Up close, the black bark is crisscrossed by deep fissures, forming a net whose depths are the colour of rich amber and give the sense that the trees are bursting with warmth. The other eucalypts are more demure. From the pale grey, elephant skin-like bark of the Grey Box to the shaggy mess of bark cloaking a Red Stringybark, each adds its own immutable stamp on the box-ironbark forest identity. Above, the foliage hangs grey-green as if a thick mist has descended on the forest. The calls of woodland birds ring out, and, at certain times of the year, the forest floor and understory is awash with floral splendour. There is no choice but to be spellbound.

The different bark characteristics of the dominant eucalypts (left to right: Red Ironbark, Grey Box, and Red Stringybark) give the box-ironbark forests an unmistakeable character.  Image: Rowan Mott

The different bark characteristics of the dominant eucalypts (left to right: Red Ironbark, Grey Box, and Red Stringybark) give the box-ironbark forests an unmistakeable character. Image: Rowan Mott

When gold was found in central Victoria in the middle of the 1800s, miners soon flocked to box-ironbark country. They, like me, quickly saw how special these forests are. However, the value they saw was in the versatility of the timber. It made for ideal stays to bolster mine shafts deep underground; it was perfectly suited for use as railway sleepers in the burgeoning rail network freighting gold across the state. And, as hinted by the warm colour in the fissures of the bark, it burned with a long and lovely heat in campfires and cooking stoves. The rapidly growing population also increased demand for food and many of the grassy box-ironbark woodlands on fertile soils were soon replaced by agricultural enterprises to supply this demand. In the years that followed the discovery of gold, mining boomed and the magnificent box-ironbark forests were felled. 

Miners quickly descended on (and under) Victoria’s box-ironbark country during the middle of the 1800s following the discovery of gold. Evidence of their activity can still be readily seen today.  Image: Rowan Mott

Miners quickly descended on (and under) Victoria’s box-ironbark country during the middle of the 1800s following the discovery of gold. Evidence of their activity can still be readily seen today. Image: Rowan Mott

I started this article by spruiking the magic of today's box-ironbark forests, and they are indeed magical. The box-ironbark forests we are fortunate to have today rekindled themselves from ruin like a magical phoenix rising from the ashes - a small, irrevocably damaged phoenix. When the gold rush began to ebb, disused mine sites began to regain their tree cover. However, box-ironbark forests never returned to their full extent. In fact, only 17% of their former area is forest today. Unlike the gold mining boom, agriculture and settlements have relinquished little of their hold over box-ironbark country with the passing of time. 

In parallel with the huge reduction in forest, a quick walk through one of Victoria’s box-ironbark forests today reveals other, more subtle legacies left by the gold rush. Most of the trees now standing have regrown from the base of the cut stump of their predecessor, and this regrowth has resulted in a forest made up of trees with multiple, thin stems. Gone are the immense forest giants of previous centuries, and their loss has seen the depletion of many habitat features relied upon by the wildlife that calls these forests home.

Many of the trees in today’s box-ironbark forests have re-grown from the base of a cut stump. This typically results in a multi-stemmed growth form.  Image: Rowan Mott

Many of the trees in today’s box-ironbark forests have re-grown from the base of a cut stump. This typically results in a multi-stemmed growth form. Image: Rowan Mott

Tree hollows used by large birds and arboreal mammals are now scarce, and nectar – a key food source for many birds in these forests – formerly produced in copious quantities by the forest giants is now supplied in inferior volumes by their multi-stemmed counterparts. Furthermore, the larger trees would have produced more and larger fallen timber than today’s smaller trees, and thus species that use fallen timber for den sites (e.g. the Yellow-footed Antechinus) and foraging (e.g. the Hooded Robin) likely suffer as a result.

Species that depend on large tree hollows, such as the Barking Owl, are threatened by the lack of large trees in present day box-ironbark forests. The thin, multi-stemmed growth form of most of the trees simply cannot provide enough of this vital habitat feature.  Image: Rowan Mott

Species that depend on large tree hollows, such as the Barking Owl, are threatened by the lack of large trees in present day box-ironbark forests. The thin, multi-stemmed growth form of most of the trees simply cannot provide enough of this vital habitat feature. Image: Rowan Mott

Species that forage on the ground among fallen timber, such as the Hooded Robin, are declining in Victoria. The loss of large, old trees, which contribute disproportionally to the amount of fallen timber, is likely a contributing factor in their decline.  Image: Rowan Mott

Species that forage on the ground among fallen timber, such as the Hooded Robin, are declining in Victoria. The loss of large, old trees, which contribute disproportionally to the amount of fallen timber, is likely a contributing factor in their decline. Image: Rowan Mott

As time passes, it is possible to see the slow succession as the forest crawls towards its former glory. Tree stems growing from the base of a dead and decaying stump are often weak, and it is not uncommon to see one or more stems of a multi-stemmed tree lying on the forest floor, having split from the stump. Similarly, the dead stump lacks bark, which usually provides the tree with a protective shield from fire. Fire in a box-ironbark forest, even a low intensity fuel reduction burn, will often result in many multi-stemmed trees collapsing because they are burnt out from the base once fire enters the exposed stump.

And so, as the number of stems slowly decreases, the growth rate of those that remain increases because they no longer experience as much competition for resources, such as light, nutrients and water. The transition of our box-ironbark forests to their original state is glacially slow, but I am hopeful that one day these forests will once again be dominated by trees of a behemoth size.

It is not uncommon to see one or more stems lying on the ground after their weak attachment to the stump from which they were regenerating gives way.  Image: Rowan Mott

It is not uncommon to see one or more stems lying on the ground after their weak attachment to the stump from which they were regenerating gives way. Image: Rowan Mott

Fire can more easily burn a dead and decaying stump than a live, bark-covered tree. Trees that have resprouted from the base of a cut stump are often more susceptible to fire than free-standing trees because they are readily burnt out at the base.  Image: Rowan Mott

Fire can more easily burn a dead and decaying stump than a live, bark-covered tree. Trees that have resprouted from the base of a cut stump are often more susceptible to fire than free-standing trees because they are readily burnt out at the base. Image: Rowan Mott

If you were to take a large diamond and hit it with an even larger hammer until the diamond shattered into many tiny fragments, would you then throw the diamond fragments away? Of course you wouldn’t; they’re still diamonds after all! Victoria’s box-ironbark forests have been shattered by the hammer of the gold rush and agriculture, but they remain incredibly valuable. Their worth cannot be understated for declining species such as the Squirrel Glider, Woodland Blind Snake and Regent Honeyeater, for which box-ironbark forests represent their core habitat. Far from diminishing the magic of box-ironbark forests, their history of degradation in the last two centuries and the resilience they have shown is even more reason to celebrate them. 


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Rowan Mott

Rowan is a Monash University PhD graduate and now works there as an ecologist. His research interests are broad, spanning seabird foraging ecology to plant invasions. When not in his office, he will most likely be in a woodland with binoculars around his neck and camera in hand.

You can find him on Twitter at @roamingmoth


Banner image courtesy of Rowan Mott.

It’s a long way to the top and every stratum plays a role

The wet forests east of Melbourne are home to the tallest flowering plant on earth, the mountain ash. Reaching heights of over 90 metres, they dwarf many of the other plants growing alongside them. Being tall gives mountain ash first use of the sunlight that falls on the forest. This is an important advantage because energy harnessed from sunlight is what almost all plants use to fuel their growth. Closer to ground level, smaller plants have to contend with less and less light, as foliage above casts them into shadow. This has resulted in adaptations including large leaves that are rich with the light-harvesting pigment chlorophyll to maximise the amount of light captured. You may be able to see this for yourself because these leaves are usually a darker green colour. Other plants invest very little energy in woody tissue and have adapted to become climbers instead. These species piggyback on other plants to get their leaves as high as possible at the lowest cost.

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  Many species, such as this swamp wallaby, live in the ground layer. Despite the tangled nature of the understory vegetation, the animals that inhabit this layer have little trouble moving through it. Photo: Rowan Mott. 

Many species, such as this swamp wallaby, live in the ground layer. Despite the tangled nature of the understory vegetation, the animals that inhabit this layer have little trouble moving through it. Photo: Rowan Mott. 

There is a paradigm that habitat diversity begets biodiversity. The many ways that different plants compete for available light open up opportunities for a diversity of animals. At ground level, the vegetation is often dense and impenetrable to people. Yet, many species of birds move through the tangle of leaves and twigs with ease, and swamp wallabies crash through with little problem. Some birds, such as the superb lyrebird and Bassian thrush, pass their days almost exclusively searching through leaf litter on the forest floor. Amongst the decaying leaves, their favoured invertebrate prey items are readily found.

Slightly higher above ground, small birds such as brown thornbills and eastern yellow robins inhabit low shrubs such as kangaroo apple and snowy daisy bush. However, brown thornbills and eastern yellow robins use very different foraging strategies. The latter sit and wait on an exposed perch, darting down to the forest floor to snatch insects as they emerge from the cover of the leaf litter, whereas small parties of brown thornbills actively move through the shrub layer gleaning small insects from the foliage.

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  The eastern yellow robin is a denizen of the lower stratum where it can be found clinging to a vertical trunk, or perched on an exposed branch, waiting to spot an invertebrate among the leaf litter. Photo: Rowan Mott. 

The eastern yellow robin is a denizen of the lower stratum where it can be found clinging to a vertical trunk, or perched on an exposed branch, waiting to spot an invertebrate among the leaf litter. Photo: Rowan Mott. 

Above the layer of soft tree ferns and into the forest midstorey, a new suite of birds replaces those found in lower strata. Here, tall shrubs and small trees including hazel pomaderris and silver wattle provide habitat for grey fantails, golden whistlers and Lewin’s honeyeaters. This layer is also frequented by white-throated and red-browed treecreepers as they hop upwards on the trunks of even taller trees. Once again, these species each have a specialist foraging strategy. Grey fantails sally insects while in flight, whereas golden whistlers pick their insect prey from leaves and bark. Contrary to what is suggested by its name, the Lewin’s honeyeater eats mainly fruits, but it does feed on nectar from time to time and also includes insects in its diet. The two species of treecreeper probe in crevices and under loose bark on trunks and branches, hoping to find spiders and other small invertebrates.  

High up in the canopy there is more freedom to move, and this is the domain of large-bodied species such as crimson rosellas, pied currawongs, and powerful owls, but there are also smaller species such as white-naped honeyeaters and spotted pardalotes. Often, the species inhabiting this stratum are predators, nectarivores or lerp specialists. This is also the layer where arboreal mammals such as greater gliders can be found.

Except for locations where people feed crimson rosellas, this species is usually found in the canopy where they feed on eucalypt seeds and a range of other foods. Photo: Rowan Mott. 

Except for locations where people feed crimson rosellas, this species is usually found in the canopy where they feed on eucalypt seeds and a range of other foods. Photo: Rowan Mott. 

All of this diversity is made possible because of the exceptional height of mountain ash trees. This allows many distinct vegetation strata to occur, which in turn support distinct assemblages of animals. When walking along a forest path, it is easy to get caught up in your immediate surroundings. However, by taking the time to look up and down, you may be lucky enough to see a wealth of life that would have otherwise gone unnoticed. It can also be good to take a little bit of extra time where the trail is flanked by steeply sloping terrain. Here, the forest below may offer the chance to glimpse canopy-dwelling species closer to eye-level, giving the illusion that you are high amongst the mountain ash. 


Rowan Mott

Rowan is a PhD student studying seabird ecology. When he's not thinking about the ocean he likes to think about woodland birds. 

Check him out on Twitter at @roamingmoth