Though it’s been over three years since I have written for Australian Arbor Age magazine, this article comes straight on the back of my last three-part article that served as an introduction to Conservation Arboriculture.
My whole career has been a steady progression down this path, where I see all trees and their byproducts(when processed correctly) as benefits for the living biological computer that is planet earth. This work is my view on trees through cultural practise as a professional contractual and consulting conservation arborist. This two-part article is a reflection on recent arboricultural projects of mine, carried out with my current professional circle – Treepeeps (run by Mandy Blyss and Tony Aitkenhead) working the Scenic Rim to Greater Brisbane in S.E. Queensland. This article starts with a recent Arb report on the retention of a veteran tree with RNE and flows into a 5 per cent crown reduction as a means to reduce load on a mechanically constrained gum over a Mount Tamborine cabin.
Flooded Gum Assessment
Following a request from the VACC Parks, Gardens and Cemeteries Coordinator to assess a Flooded Gum tree in the centre of Oswald Park, on behalf of Treepeeps Pty Ltd, I carried out a site/tree assessment on March 14, 2019.
The Rathdowney Flooded Gum tree is a local wet sclerophyll woodland species, located close to the centre of Oswald Park beside a footbridge on the edge of a gully.
The Flooded Gum stands at approximately 20m tall with an approximate crown spread of 8m. The stem diameter (at chest height) is 1m and the trunk flare diameter (at ground level) is around 1.2m. This tree is made up of a single main stem, has an asymmetric crown (trunk, branches and canopy) and is approximately aged 30-40 years.
A question has been raised in relation to the trees condition with the long term in mind, the symptoms that bought this tree into consideration involves an extensive lesion on its main stem extending into a lateral branch, exposed desiccated sapwood, early signs of hollowing and effected wound margins.
Evidence of genus, species and health The Flooded Gum – Eucalyptus grandis has fair vitality (historically good), this is evidenced by foliage, leaf size, leaf colour, bark colour and past wound wood generation.
Evidence of Crown Structure (relating to biomechanical assessment) The body language of the Flooded gum indicates stress levels impacting on vitality, this is visible in recent wound wood production surrounding pruning cuts, is also evidenced by a history of past and recent (still green) limb failure. Study of a failed limb (present at the time of assessment) revealed wood embrittlement indicative of dehydration/drought stress.
Observations / Discussion
In a past local consulting role for Toowoomba Regional Council (TRC) in 2015/16, I was involved with the risk management of Gum trees with exactly the same symptoms. Over the period of several months I gathered extensive data on Gum trees with similar failures and identical lesion symptoms.
In my experience these kinds of wounds/lesions are caused by local Parrots (Galah’s and Rainbow Lorikeets) seeking to create habitation. The birds scribe the outer bark of branch forks into the sapwood with their beaks and return to the same forks to scribe the generating wound wood. This has the effect of perpetuating the injury enabling sustained wood exposure akin to a perennial canker. In fact my research (I assessed over 100 mature Gum trees in association with the TRC project), revealed that the Birds and Canker decay organisms are working together to propagate these injuries.
I first became aware of this issue whilst assessing trees for Arborist Bernard Keays of pre-amalgamation Moreton Bay Shire Council and for Energex in 2007. Prior to this time I did not see these symptoms (as an active tree climbing arborist in S.E. Queensland 1991-2004 I was in a position to) and believe that the issue of wound scribing of branch fork unions has occurred since then because of habitat loss caused by decades of development and loss of habitat trees for the birds.
Coming back to the Rathdowney Flooded Gum – Parrot/canker damage is well recognised with study of the recent limb failure captured for this report. Study of page 8 of the linked report (refer to: https://bit.ly/2YcJIX2) reveals very similar symptoms to the symptoms posed by the Flooded Gum limb failure (Fig. 8-10).
Those symptoms being a lesion from parrot wound scribing, the failure leaving a branch stub (also noted on our Flooded gum), wood embrittlement from dehydration/oxidised tissues and part cross grain shearing and delamination – creating a tear. Though based on study of the failure and consideration of the site/ recent climate I also maintain the tree was drought stressed at the time of failure (another failure criterion).
There is also the site/site history to consider, the tree is located on the top of an embankment with a footpath running through its root zone, the construction of the bridge and footpath may well have originally occurred before the tree was established, though high density human traffic around the trees root zone coupled with lawn maintenance machinery is a sustained load on any top soil (Fig. 3-4). Also with the sustained removal of leaf litter and the inability of the soil profile to cycle humus this is an added ‘nail in the coffin’ that is the trees longevity.
Considering the large trunk injuries (and the energy it’s taken for the tree to occlude them) from major limb removal coupled (Fig. 12) with the health issues discussed I see this tree as being quite reasonably stressed (though not so historically as indicated by lower pruning cuts that are completely occluded).
It is possible that with proactive arboricultural management that the Flooded Gum could well make a recovery. In light of the considerable loss of habitat trees throughout Queensland it falls on us to keep and risk manage every tree we can, especially those that the wild-life is attempting to occupy, as each bird damaged tree we remove puts stress on the birds as well as other non-bird injured gum trees.
My advice is to retain and risk managed this Gum tree in the short term, if in the long the tree improves then all well and good. However I do recommend integrating a new tree into the airspace of the Gum, to achieve this I recommend making the Flooded gum a host tree for a strangler Fig (F. obliqua, F. virens, F. watkinsiana etc). In the big picture such a move now will stabalise the Gum in the long term (20 years plus), whilst helping to sustain future habitat within the Gum, as well as allow for continued amenity (note – Treepeeps carries out Ficus establishment as a specialised service). I recommend establishing the Fig on the sloping side of the tree to encourage roots to go downhill into the lawn gully (away from the footpath).
I also recommend improving on the Gum trees growing environment by establishing a Nutrient Bed (comprised of cold processed composted mulch) surrounding the tree from the footpathdown the bank the Gum is growing on. To help keep people off the Nutrient Bed and accelerate the assimilation of nutrients (activate the soil root-interface) I also recommend the establishment of a Plant System (plant component of an ecosystem), to help proof the nutrient bed and keep the public out (exclusion zone). In the course of establishing a plant system I also recommend vertical inoculation of the trees root zone with Soil Food Web grade cold processed compost – humus (this can be done at the time of planting).
With regard the crown/canopy of the Flooded Gum I recommend carrying out a 3-5 per cent canopy reduction. This acts as a 25-30 per cent volume reduction which significantly reduces wind-load/ major limb failure whilst maintaining energy (photosynthesis) production. A good volume reduction only targets outer canopy, inner canopy is retained to help sustain crown harmonics as well as enable retention of future reduction points should the tree need to be reduced lower. This style of crown management is aimed to mirror a trees natural retrenchment process (trees generally shed the outer to sustain the inner). Based on the removal of auxin via the removal of the outer shoots this operation actually helps to facilitate internal canopy growth response, the same can be achieved by removing buds (or nudge pruning to quote UK Arb pioneer – Arborist David Lloyd-Jones), though I often find on my subject trees – that an internal canopy is already being generated. The drawing around the Gum tree (Fig. 13) is an indicator of the line of reduction I suggest. Such an operation is to be done with hand tools, with cuts being small (on average 2.5cm), the aim is to keep cuts out of the heartwood to reduce oxidation of internal tissues and to best work with a trees rapid compartmentalisation of wounding. Such an operation to be repeated five yearly
In conclusion the Flooded gum (a future habitat) tree located at the heart of Jubilee Park (adjacent to the foot bridge) is a veteran tree in need of management to reduce risk, as well as to facilitate a healthier tree in its location for the long term.
The management recommended (cyclical volume reduction and soil restoration/revegetation/public exclusion or RNE – Reduction, Nutrition and Exclusion) requires short term outlay to achieve long term amenity improvement with minimal long-term investment.
Back to main body of the article – since my 2015, three-part piece (Veteran Tree Management via Reduction, Nutrition and Exclusion) I have been consistently engaging with Conservation Arb projects, with a view to build up a body of work worthy of follow up publication. My greatest project is due to commence in Vanuatu this year and has been a rigorous uphill slog to pull off (four years). For me this has been all about holding space in support of a Social Justice mover and maker, I like to think that my articles have always been on topics that are out of the box, Project Vanuatu will certainly be worth writing and reading about.
The Mount Tamborine Tallowood Volume Reduction
Some accuse me of over using the strategy of pruning trees to risk manage them (better that than removal), though the truth is I get more pleasure out of creating nutrient beds and plant systems– the ultimate tree/people driven means to mitigate risk and boost tree health. The public are more used to paying arborists rates for arborists to climb trees that to doctor them on the ground. Though not so with Treepeeps as our legend marketing manager Mandy attracts the perfect clients.
Though in fairness to my artistry I do not recommend pruning non veteranised trees. As with the Mount Tamborine Tallowood Gum – Eucalyptus microcorys I elected to carry out a 30 per cent volume reduction (5 per cent height/spread reduction) because of parrot damage (lesions from beak scribing).
In Part 2, the article will follow through into a study of a Treepeeps restoration project, the soil and trees, the whole package.