Conservation-arboriculture: delivering nature’s essentials

Conservation-arboriculture is essential to tree health. Cassian Humphreys pays tribute to microbiologists.

l don’t recall getting significant feedback during my 23-year career as an arboricultural writer. I’ve had the odd nod and thank-you, but largely straight silence – until some particularly constructive feedback on my August/ September 2023 piece Plant Health Care – the ®evolution.

Thanks to this recent feedback I’m expanding on the tree-health-care topic. With plant health care (PHC) we are ensuring our city trees enjoy a greater surface area for nutrientabsorbing roots, nutrient absorption, and the rhizosphere, involving multiple oxygenated/hydrated pathways into compacted/deficient soils.

The best professional advice I ever had from anyone in vegetation management came from a botanist who directed me to ‘study the nutrient-cycle’.

In the beginning

My history in what I call ‘holistic arboriculture’ goes back to Merrist-Wood (1990-92), talk of mycorrhizae, then Shigo and that classic ’97 AAA article Troubles in the Rhizosphere. In 1998 I did a Totally Wild television episode on ‘tree doctoring’ a schoolground Brisbane fig tree. It simply involved adding air, water, carbon, and associate plants.

Active experimentation, founded on a horticultural background, led to my early creativity in the field.

l started cultivating what I named ‘nutrient beds’ (which, when activated with fungi, also became a nutrient sponge) and ‘plant systems’ (the plant component of an ecosystem), utilising the bare bones of nature – ripped rawtimber as edging, composted mulches, harvesting inoculum from Bush Turkey mounds, and introducing the native rainforest fungi Phallus rubicundus. As Phallus rubicundus turns mulch to humus it supplies carbon to the microorganisms that help release the macroand micro-nutrients.

On top of that I was making vertical fissures in soils to help with aeration, water distribution and mycelial propagation.

Answering a need

Due to the lack of explanation in support of conservation and plant health care, I co-created the terms ‘oasification’ and ‘desertification’. Where on-point words are missing, new words can help us understand concepts and ideas. The concept of ‘oasifying’ the land in support of trees is the whole point of tree health care and the PHC movement.

Mycelial mass harvested in composted Acacia leaf, twig, and wood-chip from a client’s 3″ chipping machine. Image: Cassian Humphreys

Brown-rot decayed wood sample, with cellulose digested this material is brittle like coal, natures-biochar, habitat for microbes while holding air. Image: Cassian Humphreys

Holistic health

Like holistic health care of humans, holistic health care of trees is based on natural precedent. All biological life is driven by the nutrient cycle, or in the case of land plants (as the pump), the interfaces between the atmosphere and the rhizosphere. In the case of animals and humans – that interface is our stomach-lining. Sunlight, air, water, and biologically active carbon are essentials for trees. Associated plant microbiology looks after the details, including the timing and supply of nutrients. This is validated by study of soil-food-web science and the leading educational microbiologists.

Application of the essentials (carbon with probiotics) in soils is the heart of plant health care. To be holistic we just need to mirror nature’s detail. This is impossible if we only reference the man-made big-pharma model. Fertilisers, herbicides, fungicides and so forth make up a suite of products that are about longevity of industry over longevity of biology. This study reflects a conservation arb approach to achieve plant health care.

Sunlight is a given, adding air, water, and bio-carbon in soils requires greater detail to get right. Detail and holistic arboriculture go hand in hand. When we mimic nature’s processes the detail is taken care of by Mother Nature.

However, detail is also about application. When it comes to the nutrient cycle, as with arb operational safety, we need to be concerned about human shortcuts – such as using static piles of green, chipped vegetation. To best support nature’s cycle we must mirror the nutrient cycle, which, via natural succession, processes vegetation minus the photosynthates, or sugars. In nature the parts (leaves, twigs, and limbs) and processes draw the sugars out prior to shedding, to then be broken down via the microbiology.

The same applies to us. Hence the benefit in eating probiotic-rich foods such as sauerkraut and kimchi. Eating excess sugar kills our gut-health.

A nutrient bed and plant system, collectively a man-made reflection of a forest-ecosystem, also creating an exclusion zone over the treated TPZ of an ancient veteran Ficus (SRZ-TPZ with aerated vertical-fissures). Comprised of chocolate-gold harvested from an abandoned bush-turkey-mound, covered with forest-blend-mulch, and capped/edged with processed palm logs (another resource for absorbing-root extension). Planted out with Dietes and Bromeliad species (client selection). Image: Cassian Humphreys

Artificial is not natural

What trees need for longevity is inherent to the natural cycle. This isn’t supported by manmade, containerised products. As soon as biology is packaged or compartmentalised from nature for any length of time it dies or goes dormant. Compost tea is a classic example. If microbiology in solution isn’t kept aerated it changes from being compost-tea to being a stagnant bacterial soup. A simple rule of thumb is if it either stinks or smells inert, it’s not much use to woody plants that need soils or solutions (think of aerated springwater) lower in bacteria.

With harvested green mulch this must be cold-processed, or temperature controlled, via regular turning and irrigation.

On a slope, a swale nutrient bed and trench garden, constructed out of Forest Red Gum/Silky oak. The plant-system is comprised of Dianella caerulea, Lomandra histerix and Breynia oblongifolia, with an aerated trench filled with biochar and chocolate-gold compost, capped with harvested bamboo leaves (for sun reflection) and rocks/logs for Bush Turkey mitigation. This system was set up for deep irrigation/flood mitigation and water retention. Multiple swale/trench gardens are the best option for steep slopes subject to surface water run-off. The deep roots of the Lomandra will hold the system together even after the logs decompose. Image: Cassian Humphreys


When considering air in soils, one word is key – friability.

All arboriculturists need to understand the meaning of this word intimately, and to be able to recognise healthy, friable soil by the senses. We should never plant trees in ‘dirt’ (structureless, biologically inert soil) without at least treating it at the planting stage. For best practice it’s better to treat damaged soils beforehand. Leaving desertified soils to go fallow and grow weeds is a first simple step in holistic arboriculture and in conservation.

Treatment of a highly stressed Psychotria daphnoides with oasification. Biological desertification in soils is caused by a lack of any of the essentials: air, water, biocarbon. The first stage in soil restoration is to open up compacted ground via fissures, achieved by hand forking the soil at its simplest.Image: Cassian Humphreys

The right balance

To know what makes a healthy soil or compost, the best place to learn is in nature’s ecosystems, where shed vegetation builds up.

l covered my sources in the first part of my 2022 article on land care. Australia was known to the First Nations people and the European biologists as being a land of friable soils. Until we learn how to restore soil friability by adding air, water, and biology, I maintain we’re unable to practice arboriculture. This also applies to water retention and enabling natural propagation of beneficial fungi in soils (like Trichoderma). We need sufficient soil/ oxygen and soil/water. The balance of air/ water/carbon supports the activation of the microbiology responsible for nutrient assimilation and disease suppression.

Understanding this is why Shigo documented the tree as a living pump, the symbolic logo for modern arboriculture.

Conservation arb, holistic arb or plant health care, along with crown volume reductions for crown subordination, is proactive arboriculture at its best.

The next step in the process of oasification is to add water. Regardless of the water source it must be free of excess mineral or chemical additives (an issue with bore and town water). This is why I use charcoal-filter cartridges. The aerated and hydrated soil fluffs up when subject to fissuring. Image: Cassian Humphreys
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