Tree care for the land custodian – less is more

Cassian Humphreys considers conservation arboriculture for tree care and land care in general.

I’m always being drawn to ideas to help sell arboriculture, in concept as well as in service. I’m working on a brochure for homeowners and private land custodians, as I recognise that many top end projects are grass roots.

I recognise many homeowners have a great love of their gardens and take great pride in caring for their properties. Winning these kinds of clients leads to top-end work and great repeat business. In this issue I’m writing for those who seek resilience, sustainability, or sovereignty on their own turf – I’m discussing tree care for the land custodian.

A veteranised ancient Marri Gum – Corymbia calophylla – located on the Brockman Highway WA, heading to Augusta, with a 2.2m stem diameter. I’d suggest this tree is at the end of the second third of its lifespan, roughly 180 years old. It would’ve been seedling in or around 1840. It’s a living monument to our Aussie past. The wildlife habitat provided by trees like this cannot be replicated by humanity, but can be easily supported by us via proactive tree care.


What is arboriculture? ‘Arbor’ is Latin for tree,and involves the culture of trees. ‘Arborist’ – a shortened version of ‘arboriculturist’ – is a term that best defines the industryled practitioners and enthusiasts, as opposed to the professional, or those who call themselves arboriculturists. Most arborists prune, lop (look at Wikipedia’s definition), fell, and process trees into mulch, and this is contrary to the intention/meaning of ‘arboriculture’. The profession is driven by an industry prerogative which is more about tree removal, machinery sales, economics, and compliance than it is tree care. The top end 5%-10% of the arboricultural profession is science-focussed and very passionate about tree care for the land custodian.


So why conservation arboriculture? Conservation we are largely familiar with. This series is being developed in support of tree-custodians – that’s tree/homeowners and professionals alike. Or, those individuals who can discern for themselves (with only a gentle nudge), the silent lore of nature and natural systems. I believe many land custodians have the capacity for great conservation arboriculture with only a little good education. In the previous issue I introduced the term ‘naturaculture’, arboriculture aligned with nature intelligence. Not everyone gets arboriculture, but deep down we all get naturaculture – the culture of nature is at the seat of our consciousness, biology, and part of our DNA.

The way we care for gardens, our bodies, diet, health, animals, and the land is personal. For those of us switched on by nature, we need to see and understand her graces for ourselves, as opposed to being told. Impacts on our, and nature’s, resilience are the norm. We only need to look at tree longevity to see this. With our current lifestyles, we all support reduced tree-life expectancy in the order of decades. Most urban and rural trees currently live only a third of their actual lifespans. Imagine if we humans all died at ages 25-30? This issue also impacts on the wildlife dependent on habitat hollows in trees. The significant lack of old-age class trees is a reflection on just how much forest clearing historically occurred Downunder.


Conservation arboriculture is being born out of the tree-care movement.

In the face of climate change I see this as the next level in resilient towns and cities, with the targeted 60 per cent minimum for green city or town cover to achieve sustainability.

A Bridgetown veteranised ancient Jarrah Gum – Eucalyptus marginata. this tree is an Alpha which has had its crown naturally supressed by nature. This tree looks like it’s been lopped, but not so. The taper from the trunk to outer canopy is true, the only wounding in this tree is from dieback.
Optimum taper, squatness, and structure in the tree’s upper crown.


Marri gum, before and after (right) a preliminary prune on a Marri Gum. The prune was to reduce elongation and set up the branch for subordination, while sustaining photosynthetic capacity. With most cuts ranging from 2.5cm to 4cm, with one cut at 6cm. The goal being to keep cuts small, while reducing overall lever arm/end load weight. A volume reduction that reduces 5% in overall height and spread actually removes 30% in volume. In this example removing approximately 150 kilos at the limb’s periphery (ref: dotted line), involved the lifting of the whole limb by 20-40cm, validated by viewing the closure of the gap (dotted circle), with foliage now touching foliage.
The image to the right shows another neighbouring Marri gum. The dotted lines show the kinds of elongations that cause tension failures in this species. Though I have no problem with large-diameter fractured stubs (micro-bat habitat), for the sake of tree longevity and reduced risk I prefer smaller diameter cuts in the outer canopy. This prevents larger-diameter failure (and therefore risk) in storm events.

Here are some arboricultural tree terms with explanations:
• Ancient – a tree in the prime of its life, usually in the last one-third of its lifespan
• Veteran – a tree of any age which has had its body impacted by an event (ie storm damage or development). An ancient tree can also be a veteran
• Alpha – Latin for ‘number one’, this is a tree which has been trained for resilience and longevity. The 1 in 10,000 trees, alphas may be reflective of a species, a genus (group of species) or an individual specimen. This is a natural phenomenon caused by the pruning of terminal buds. In nature and cities this is created by wind, frost, drought, wildlife, bus pruning (caused by repetitious bud-strike on trees overhanging bus lanes), and arboriculturists. We humans can help train trees to stand up to storm events and to be naturally resilient. ‘Stormproofing’ is a term I love to use, though in nature there are no absolutes. Yet alpha-trained trees perform far better than their wild-forest cousins when it comes to storm events
• Tree health care – often known in arboricultural circles as ‘plant health care’. It’s one thing to have ancient, veteran, and alpha trees in our gardens, it’s another to have healthy trees. Tree health is insurance against tree failure. Like healthy humans, healthy trees are naturally resilient to disease and breakage. Tree diseases like Phytophthora, Phellinus, Chrysoporthe, Marri Canker, Canker Syndrome, and the new kid on the block, Polyphagous Shot-hole Borer (a symbiotic relationship with Fusarium fungi) are common across Australia. Healthy trees are resilient, while stressed or ‘sick’ trees are not. Insuring tree health is all about sustaining healthy biologically diverse soils, supported by air, water, carbon and soil microbiology.

The great love of the modern arborist, sensitive reduction (increasing limb diameter in proportion to length) buys decades of extra years for a limb or tree, yet adds to, rather than subtracts from form. Personally I see great value in these long pendulous hanging branches on Marri Gum, exceptional wind dampers.

The pump

I’ve been in Bridgetown, WA, expanding on my relationship with trees Downunder, and one of the great things I’ve witnessed in southwest WA is natural rewilding of roadside verges adjacent to state forest and national parks. As a result of people pressure and herbicide application adjacent to urban and rural land, weeds are better supported than native plant regeneration.

To give perspective, including climbing and pruning, the above operation took 2.5 hours (often reflective of a minimum call out rate). Based on the cheaper end of professional-arborist rates with relevant insurances, equipment and so forth, that would cost $875 (less GST). Done on a five-yearly cycle, while retaining a functional limb and tree, this is reasonable – especially considering the environmental benefits that such a tree presents.

Complete removal of a large limb such as this is known to significantly reduce tree lifespan, as well as biomechanically setup a tree for upper crown failure.

With consideration of the tree as a pump, the father of arboriculture, Dr. Alex Shigo, was the first to make such reference. Trees, in fact most living plants including weeds, fix nutrients in soils. This they do by harvesting atmospheric elements like carbon, oxygen, nitrogen, water and so forth, and building them into their bodies. Via exchange, being eaten and decomposition, plants then make inorganic elements available to all other life forms in organic form.

Next time I’ll discuss tree health care by attending to the bottom end of the pump.

Evidence of wound-scribing by parrots, this I have been documenting on the east-coast going back 15 years, these bird targeted limbs and forks are set up for habitat with repetitious wounding. The problem for trees/tree managers is the causation of tension/branch break-out failure. Even more reason for volume reductions, that reduce failure, whilst sustaining habitation.

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