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Conservation Arboriculture In Action – Part 1

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.

Discussion/Recommendations

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

Conclusion

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.

July 19, 2019 / by / in , ,
Major Mitchell’s Hollows Artificial Formation Of Tree Cavities – Part 3

A manual of techniques to create simulated natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis): for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri).

Restore

The deterioration of cavities can reduce their quality to a point where they are no longer suitable for nesting by cockatoos long before they are lost to tree fall or fire (Hurley, 2009; and Saunders et al., 2014). Collapse of the nest chamber roof and walls due to decay and weathering exposes the nest chamber to rain, reducing the insulating quality of the cavity and exposing eggs and nestlings to the risk of drowning from flooding (Hurley, 2006a). The accumulation of wood debris and decayed material can result in cavities becoming too shallow to provide suitable shelter or protection from predators (Saunders et al., 2014).

We used a method similar to that of Saunders, et al. (2014) and Hurley (2009) to restore collapsed cavity floors by placing rounds of timber into the cavity, followed by a layer of coarse chip and finally a layer of fine clean Callitris woodchips ofa texture mimicking that produced by the MMC. Missing cavity roofs or walls were replaced using a Callitris section carved to fit the cavity spout and sealed into place with wedges of timber and silicone sealantand tech screwed.

Another strategy is to replace a collapsed cavity floor by screwing in place a sub floor of wire mesh. On top of this build up a stable cavity floor of Callitris chips to the desired depth (Figure 22).

Cracks in the nest chamber wall were also filled with wooden wedges and silicone sealant; or for larger sections, replaced by affixing sections of timber carved to provide a firm fit (Figure 25)

It is imperative that these sections are well fitted to prevent gaps and are glued and secured in place with long wood screws or coach bolts where necessary.

The collapse of nest chamber floors caused by the progression of heart wooddecay can also result in nest chambers Figure 32 becoming too small or exposing jagged wooden spikes of un-decayed wood (Figure 27 and Figure 28), both of which have been found to prohibit nesting of large cockatoo species. Saundersetal. (2014) did report successful breeding by Carnaby’s Black-Cockatoo, in WA, after restoring cavities by in-filling collapsed nest chamber floors. We further developed this technique for application in Callitris in Pine Plains (Figure 29 and Figure 31).

Nest-box

The creation of and installation of nest-boxes is a last resort action for the conservation of cavity dependent fauna. It is an admission that all other conservation and management action shave failed. Installing nest-boxes creates a Figure 34 requirement for ongoing maintenance and active management of these structures. In conservation reserves where wildfires have removed large numbers of cavity bearing trees it may be necessary to replace some with nest boxes.

Nest-boxes were made from salvaged windfall Callitris logs.

For a safe work environment, a tension tie-down strap was used to secure the log in position when using power tools on each log. A biscuit was sliced from the top and base of each log using a chainsaw to provide a clean surface (Figure 32). Immediately after each cut was made the newly exposed end grain was painted with a log sealer to prevent the ends of the log from splitting (Figure 33). For this we used Mobil Log Seal©. Without an end-grain sealant, once cut, the timber tended to split very quickly (Figure 34). A second thick coating of log seal should be applied. As a further precaution strapping is placed around the top and bottom of each log to further reduce splitting (Figure 35).

Once the ends of the log have been secured the main cuts in the log can be made to create and remove the face plate (Figure 36 and Figure 37). This is best done by first cutting two cross cuts ~ 70 cm apart and not more than 1/4 the circumference of the tree at the height of the cuts. Then make two longitudinal cuts with the chainsaw bar held at a 45° angle for each on either side of the tree starting one at a time from just below one end of the top cut and continuing down to the lower cut (Figure 36). Repeat this on the other side. The angling and depth of the longitudinal cuts should allow the cuts to meet in the middle of the trunk at a right angle all the way along the cuts. The faceplate should naturally fall lose once the final cut is complete (Figure 37).

The wedged shape provides a more robust strThe inside face of the faceplate must be carved so it has internal concave contours to match the curvature and wall thickness of the cavity being carved from the inside of the tree trunk (Figure 44 and Figure 45). The cavity entrance can also be carved from the faceplate (Figure 46) or may be carved out of the nest-box on the oppositeucture to the nest-box by leaving more of the nest-box intact as a single piece (Figure 38). Put the face plate to one side while working on the nest-box proper. To efficiently clear the large amount of material required to form the nest cavity, use a chainsaw to create longitudinal cuts along the internal length of the log (Figure 39). This creates internal slabs that can be further split with a pinch bar and lifted out (Figure 40).

The main cavity, can be worked with two Arbortech blades on separate angle grinders. Once the internal slabs have been removed to create a cavity use the Arbortech© to sculpt the interior walls and floor and deepen the cavity if necessary (Figure 41 and 42).

The inside face of the faceplate must be carved so it has internal concave contours to match the curvature and wall thickness of the cavity being carved from the in

side of the tree trunk (Figure 44 and Figure 45). The cavity entrance can also be carved from the faceplate (Figure 46) or may be carved out of the nest-box on the oppositeside to the face-plate (Figure 47 to Figure 49). These carving tasks are best done with an Arbortech© blade attached to an angle grinder.

Once the interior of the nest-box is nearing completion, the entrance can be made in the log on the side opposite to the faceplate (Figure 47 and Figure 49). It is recommended to carve the entrance to nest-boxes on the opposite side to the face-plate so the face-plate can be placed against a tree trunk and provide further protection from damage by large parrots (Figure 49) (Hurley, 2009).

Use the Arbortech© blade attached to an angle grinder to clean and smooth-off any rough edges to the cavity entrance from both within and outside the nest-box (Figure 50 and 51). Final adjustments can be made to the interior of the nest-box such as carving climbing holds for the birds and ensuring the caulking timbers cover all gaps between the walls and the faceplate. Ply wood fill in the gap created by the kerf width of the chainsaw blade (Figure 52). It is recommended to use timber slats and then glue and screw the face-plate securely in place.

References

Boland, D.J., Brooker, M.I.H., Chippendale, G.M., Hall, N., Hyland, B.P.M., Johnson, R.D., Kleinig, D.A., McDonald, M.W. & Turner, J.D. (2006) Forest Trees of Australia. CSIRO Publishing, Collingwood.

Bond, J. (2006) Foundations of Tree RiskAnalysis: Use of the t/R ration to Evaluate Trunk Failure Potential. International Society of Arboriculture – Arborist News:

Carey, A.B. & Gill, J.D. (1983) Direct habitat improvement – some recent advances. In: Snag habitat management symposium, pp. 80-87. Forest Service General Technical Report Curtis, A., Green, J. & Warnock, B. (2000) Mimicking natural breaks in trees. English Nature, 8:1, 19-21.

DSE (2011) Guideline 8.1.42: Working in the vicinity of hazardous trees. Vitorian Government Department of Sustainability and Environment, East Melbourne.

Fay, N. (2002) Environmental arboriculture, tree ecology and veteran tree management. The Arboricultural Journal, 26:2, 129-136. Forbes-Laird, J. (2008) THREATS: Tree Hazard: Evaluation and Treatment System. Forbes-Laird Arboricultural Consultancy, United Kingdom. FWPRDC (2004) The In-ground Natural Durability of Australian Timbers. Forest & Wood Products Research & Development Corporation, Australian Government, Canberra.

Gibbons, P. & Lindenmayer, B.D. (2002) Tree hollows and wildlife conservation in Australia, 1st edn. CSIRO Publishing, Collingwood. Gibson, M., Florentine, S. & Hurley, V.G. (2008) Age distribution of Slender Cypress-pine (Callitris gracilis) within Pine Plains, Wyperfeld National Park. Centre for Environmental Management, University of Ballarat, D.O.S.A. Environment, Ballarat.

Hurley, V.G. (2006a) Physical characteristics and thermal properties of Major Mitchell’s Cockatoo, Cacatua leadbeateri leadbeaterinest hollows, Wyperfeld NP. Department of Sustainability and Environment, Mildura. Hurley, V.G. (2006b) Survey of Major Mitchell’s Cockatoo in Pine Plains, Wyperfeld NP – Spring 2006. Department of Sustainability and Environment, Mildura.

Hurley, V.G. (2009) A report on installing nest boxes and repair of degraded nest hollows in Callitris Pine for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri) in Pine Plains, Wyperfeld National Park. Unpublished report prepared by the Department of Sustainability and Environment for the Mallee Catchment Management Authority, Mildura. Hurley, V.G. (2011) Results from the 2010 breeding survey of Major Mitchell’s Cockatoo (Lophocroa l. leadbeateri) Pine Plains, Wyperfeld NP. Department of Sustainability and Environment, Mildura.

Hurley, V.G. & Harris, G.J. (2014) Simulatingnatural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri). Department of Environment and Primary Industries, Mildura.

Kenyon, P. & Kenyon, P. (2010) Pruning for habitat workshop.

Korpimäki, E. & Higgins, P.J. (1985) Clutch size and breeding success in relation to nest-box size in Tengmalm’s Owl Aegolius funereus. Holarctic Ecology, 8:1, 175-180.

Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management. HMSO, 1999.

Mattheck, C. & Breloer, H. (1997) The Body Language of Trees. HMSO, London.

Rowley, I. & Chapman, G. (1991) The breeding biology, food, social organisation, demography and conservation of the Major Mitchell or Pink Cockatoo, Cacatua leadbeateri, on the margin of the Western Australian wheatbelt. Australian Journal of Zoology, 39:2, 211-261.

Saunders, D.A., Mawson, P.R. & Dawson, R. (2014) Use of tree hollows by Carnaby’s Cockatoo and the fate of large hollow-bearing trees at Coomallo Creek, Western Australia 1969–2013. Biological Conservation, 177:1, 185-193.

SWA (2011) Draft Code of Practice: Safe Access in Tree Trimming and Arboriculture. Safe Work Australia, Canberra.

Taylor, A.M., Gartner, B.L. & Morrell, J.L. (2002) Heartwood formation and natural durability a review. Wood and Fiber Science, 34:4, 587-611.

VTIO (2010) Draft Climbing Guidelines Victorian Tree Industry Organisaion, Ringwood.

Figure 47: Initial cut into back of nest-box to form entrance.

Figure 48: Marks on inside of nest-box indicating dimension of entrance.

Figure 49: Cavity entrance opened and ready for finishing off rough edges.

Figure 50: Arbortech being used to hollow out and form the cavity entrance.

Figure 51: Arbotech being used to smooth-off and from external entrance features.

Figure 52: Plywood caulking planks tacked and glued into place. Wood glue placed on interior gluing surface ready for attachment of face plate.

Figure 52: Plywood caulking planks tacked and glued into place. Wood glue placed on interior gluing surface ready for attachment of face plate.

Figure 54: This nest box has a metal plate, top and bottom to further protect timber from rotting and splitting. The nest box is resting on the stump of a cut branch.

Figure 55: Note the face plate is facing into towards the tree trunk.

Hurley, V.G. & Harris, G.J., (2015) A manual of techniques to create simulated natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri). A report to the Department of Environment, Land Water and Planning, Melbourne.

For more information please send an email to Grant Harris at http://[email protected] ironbarkenviroarb.com

Visit the website www.ironbarkenviroarb.com

December 17, 2018 / by / in
The Tree Assessment

A technique for enhancing the assessment of the structural condition of a Blackbutt (Eucalyptus pilularis (Sm.) using the combination of IML Resi’ PD400, Sonic PiCUS Tomograph (PiT) and Electric Resistance Tomograph (ERT) instruments.

Abstract

A recent health and structural assessment of a street tree in the Ku-ring-gai Municipal area used the combination of IML Resi’ PD400, PiCUS Sonic Tomograph (SoT) and Electric Resistance Tomograph (ERT) to assess the tree for decay and the risks associated with structural decline. The assessment concluded that the tree was of relative sound health and structure based on the combination of three techniques despite the tree showing indications of internal decay. The outcome would not have been the same if the assessment was limited to the PiCUS software (SoT) alone because the ERT identified the presence of adaptive growth which the Resi’ confirmed as sound wood at these locations. This technique shows promise for the assessment of older trees with decay and allows the better quantification of the internal decay based on a combination of factors so that tree risk assessments can be made on an individual tree and quantitative basis.

Introduction

The assessment of trees for their structural soundness is important to identify the risks associated with maintaining a potentially hazardous tree. In addition, trees of structural soundness in urban environments provide a range of other benefits i.e. habitat, aesthetics, carbon sequestration and recreation. The street tree in this report was identified by the Ku-ring-gai Municipal Council as a potential risk to the safety of pedestrians and motorists, with potential impacts to services, adjacent residences and recreational areas. The tree is approximately 18 m high with a diameter at breast height (@1.4m) of 121cm.

The stage of the growth of the tree was considered as mature.

The tree was dominant in the street setting and provides medium wildlife habitat value. On initial visual assessment the tree had a least one, open decay cavity at 3m above ground level (agl), in the northern stem quadrant. There were no visual signs of animal activity. The tree was relatively symmetrical in form with canopy loading in a northerly direction (Figure 1). The crown density was about 90 per cent compared to that for the genus and species when in good condition and of normal vigour.

There were some abiotic impacts including a footpath and roadway to the east and western sides of the tree. There had also been some historical pruning resulting in the regrowth of epicormic into endocormic branching.

Methods

The tree health and structure was assessed using a Tree Risk Assessment methodology as outlined by the International Society of Arboriculture (ISA) Best Management Practices for Risk Assessment 2011. This included a visual tree assessment (VTA) to identify tree characteristics and potential hazards at the ground, in the stem and in the upper canopy.

The basic level 2 assessment identified the presence of an extensive columnar, basal decay interconnecting with an open decay cavity at 3m above the ground (agl) and at the crown union. Pathogenic wood decay from fungal colonisation was suspected however no fruiting bodies were evident. The presence of this external decay escalated the inspection to an advanced ‘level 3’ which required further investigation of the decay.

The advanced Level 3 assessment used PiCUS 3 Sonic Tomograph (SoT) and PiCUS TreeTronic Electric Resistance Tomograph (ERT) (Argus Electronic GmbH, Rostock, Germany) to assess the presence and location of decay in the tree stem as well as the size, shape and characteristics in terms of mechanical properties of the area of interest(Wang and Allison, 2008). While both these techniques are non-invasive the combination of the SoT and ERT methods can help overcome the limitations of either technique being used in isolation and can provide a better conclusion about the trees structural condition.

The SoT and ERT assessments were carried out at the buttress (figure 2a), at the open decay cavity at 3m above ground level (agl) and at the crown union, 4m agl (figure 2b). The IML Resi’ PD400 (IML Instrumenta, Mechanik Labor Systems, GmbH, Wiesloch, Germany) was only used at the crown union (at 4m agl) (Figure 3a). While the first two tools identify the location and extent of decay, the IML Resi’ PD400 resistograph tool confirms the presence of response adaptive growth by comparing the resistance (density) of adaptive growth and stem thickening at these locations against a sample of resistance (density) from solid wood in the same tree. Response adaptive growth is interpreted as the tree’s response to structural weakness, decay, stem movement and increase in wood growth thickening (additional layers of wood) or joining (welding) at branch unions. All measures were taken in January 2018.

PiCUS Sonic Tomographs (SoT)

The SoT method measures internal decay using sound waves with the principle being that sound waves travel slower through decay when compared to solid wood (Gilbert and Smiley, 2004). This is done using a series of sonic sensors (receivers) which are placed around the stem using a series of small pins to record the signals. The pins are tapped manually with an electronic hammer and the velocity of the sound waves and geometry of the sound waves are recorded as a tomogram (graph). The tomogram shows the relative and apparent ability of the wood to transmit acoustic waves while the different colours in the tomograph correlate to mechanical wood quality (modulus of elasticity), a measure consistent with the mechanical structure of the wood at the cross-section of the stem where it is measured.

PiCUS Treetronic Electric Resistance Tomograph (ERT)

The ERT on the other hand uses a low electric voltage to examine the tree and provide a high-resolution electrical conductivity map of the tree’s cross-section (Goncz et. al., 2017). The electric resistance of the wood is influenced by the water content and changes within the wood structure. The resulting tomograms are coded with a blue, green, yellow and red colour range showing blue as areas of low resistance and high-water content (potential decay), through to red showing high resistance and low water content. ERT tomograms are specific to individual tree species as each tree has its own typical electrical resistance distribution. The combination of electrical and sonic tomography in the PiCUS Treetonic system provide a detailed survey allowing more accurate differentiation of various internal defects (Brazee et al., 2011). Both the SoT and the ERT assessments were carried out at the buttress (Figure 4), at 3m above ground level (agl) and crown union 4m agl (Figure 5).

IML Resi’ PD400

In addition to these two methods, resistance testing using an IML Resi’ PD 400 was also used at five positions, at the attachment points of the 1st order structural stems within the crown union. The location of the IML Resi’ PD400 tests are shown in Figure 3a and 3b where each drill location provides a cross-section of the resistance of the wood against the drill bit. The IML Resi’ PD400 instrument assesses resistance to the drill bit of the instrument through the wood and this is then displayed as a graph. The path of the drill bit was selected from cross-sections of the crown union using the SoT and ERT tomographs. Each resistance drill test was compared to a sound wood comparison drill test identified upon the subject tree. This allows a correlation to be made with sound wood and to better identify weakened decaying wood or response adaptive growth.

Where there is higher resistance compared to the sound wood, this indicates wood of a higher amplitude (low moisture content – red in colour on ERT tomograph when integrated with SoT tomograph) and where there is lower resistance this indicates incipient early decay, compromised or decayed wood (higher moisture content – blue in colour on the ERT tomograph when integrated with SoT tomograph). This measure of internal wood resistance is used as an index of wood density at different positions and can be used within the crown union in areas subject to response adaptive growth, to confirm a sound structure.

Strength Retention Formula

In addition to these measures, the t/R ratio is described as the thickness of sound wood in the residual wall(s) of the section of the stem being measured. In this case we compare the ratio of the thickness of the wood of the stem or branch tested, at each location; to the radius of the trunk or branch. 30-35 per cent is the minimum threshold for a tree part (trunk or branch) wall section, to be considered of sound integrity (Mattheck and Breloer, 1994)(see internal red line in figures 6a, 7a and 8a).

Limitations of the t/R Formula

The conventional t/R ratio test is based on field studies of vertical, cylindrical trunks with the decay centrally located and uniform. When the stem is leaning, asymmetrical in shape, or the decay is off centre, the guidelines for shell wall thickness should be used very cautiously. The greater the disparity in shape, away from a cylinder or decay off centre, the greater the inaccuracy. The t/R was used as a guide only in the assessment to assist in the trees risk rating determination. Additional data such as location of decay, presence of response growth, direction of loadings, size and age of tree, wind exposure, etc. are also considered to complement the t/R results and to determine a more accurate likelihood of failure and final recommendation.

Results and discussion PiCUS Sonic tomograph (SoT) and Treetronic Electric Resistance Tomograph (ERT)

At the first location (base of tree), the cross-section of the wood shows approximately 24 per cent of wood was solid on the circumference of the tree stem with some relatively symmetrical, internal columnar decay, representing 76 per cent of the trunk comprised of decay and incipient wood. The results of the SoT and ERT tomograph at location 1 (the tree base) are shown in figure 6. Table 1 gives the key to interpreting figures 6, 7 and 8. The numbers in figure 6 represent the status of the wood according to the SoT and ERT tomograph key (Table 1).

The second test location tomograph’s (Figure 7), show an open decay cavity at 3m displayed, presenting as an asymmetrical open internal, columnar decay. The cross-section of the wood shows 39 per cent of solid wood on the circumference of the tree stem with some asymmetrical internal columnar decay represented by 51 per cent of decay and10 per cent incipient or altered wood. The results of the SoT and ERT tomograph at test location 2 are shown in figure 7a and b. The numbers in figure 7a and b represent the status of the wood according to the SoT and ERT tomograph key (Table 1).

IML Resi’ PD400

The third location showed an internal decay cavity at the crown union at 4m agl. The cross-section of the wood shows 31 per cent of solid wood with 53 per cent of decay and 16 per cent incipient or altered wood. The IML PD400 resi’ tests at this location identified small pockets of response adaptive growth, as shown by the red areas (high ERT resistivity) in the ERT diagram in figure 8b. The results of the SoT and ERT tomograph at test location 3, at the crown union 1st OSS are shown in figure 8. The numbers in figure 8a and b represent the status of the wood according to the SoT and ERT tomograph key (Table 1).

The IML Resi’ PD400 test locations were identified with reference to the ERT and SoT measuring points (mp) as areas of high ERT resistance. At the 1st OSS attachment union each of the five IML Resi’ PD400 results showed wood with good resistance and adaptive growth welds which contribute to stem strengthening at this location (Figure 9).

Figure 9 shows an example of one, of the five, IML Resi’ PD400 resistograph test locations. The IML Resi’ PD400 resonance testing is shown for location 3 (adjacent to ERT mp 12) in the crown union of the 1st OSS. The resulting resistograph identifies generally good resistance (compared to solid wood), potentially indicating response growth (due to branch welds or strengthening wood), with a small pocket of compromised wood at 16-17 cm. The assessment table under the resistograph summarises the resistance measure in cm from the start through to the end of the drill cross-section.

The Final Decision

The determination to retain this tree was based on a combination of the following decision making steps:

  • An analysis of the quality of wood at each defective tree part (Basal SS, open decay cavity 3m agl and crown union SS 4m agl)
  • The risk rating of each defective tree part and whether each reached the failure criteria where t/R was decided upon with evaluation and consideration of: PiT (Volume and location of decay and residual wall thickness and location);
  • ERT (Volume and location of response growth versus decay and location);
  • Confirmation of response growth thickening within the crown union with use IML Resi’ PD400;
  • The subject trees visual body language;
  • The loading on the defective tree parts; and
  • The target trees likelihood of failure, and the impact and consequences of failure

Conclusion

The three scientific decay analysis tools used in this discussion paper included the IML Resi’ PD400, Sonic PiCUS Tomograph (SoT) and the Electric Resistance Tomograph (ERT). Using these results in combination with the other important risk considerations provides a new and insightful basis for determining the soundness of large landscape trees. This is particularly useful where visual assessment alone may ordinarily prove difficult to provide enough information for retention as opposed to removal. In addition, with the PiCUS assessment tool alone the tree would have been likely condemned by most PiCUS operators (Arborists) due to the presence of decay. However, with the introduction of ERT tool used in conjunction with SoT, showed that the strength of the timber in the residual walls of this tree were determined to be of sufficient strength for its size and the amount decay present, and hence the tree was recommended for retention. The use of IML Resi PD400 in association with ERT has confirmed sufficient response adaptive growth in the crown union which identifies areas of high resistance reducing the risk of stem failure and the potential for public risk.

References

  • Bieker, D., Kehr, R., Weber, G., Rust, S. (2010) Non-destructive monitoring of early stages of white rot by Trametes versicolor in Fraxinus excelsior. Ann. For. Sci. 67(2):210.
  • Gilbert, E., Smiley, E.T. (2004) PiCUS sonic tomography for the quantification of decay in white oak (Quercus Alba) and Hickory (Carya spp.) J. Arb. 30(5): 277-281.
  • Goncz, B., Divos, F., Bejo, L. (2016) Detecting the presence of red heart in beech (Fagus Sylvatica) using electrical voltage and resistance measurements. Eur, J. Wood Prod. DOI 10.1007/s00107-017-1225-4. Mattheck, C., Breloer, H. (1994) Field guide for visual tree assessment (VTA) 18(1): 1-23.
  • Nicolotti, G., Socco, L.V., Martinis, R., Godio, A., Sambuelli, L. (2003) Application and comparison of three tomographic techniques for detection of decay in trees. J. Arb. 29(2): 66-78.
  • Wang, X., Allison, R.B. (2008) Decay detection in red oak trees using a combination of visual inspection, acoustic testing and resistance micro-drilling. Arb & Urban For. 34(1):1-4.
  • Note: this technical paper has been shortened for publication purposes and the original full sized paper is available upon request from the author.
December 5, 2018 / by / in
Major Mitchell’s Hollows

Artificial formation of tree cavities – part 2

A manual of techniques to create simulated natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis): for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri).

Cavity creation techniques

As the decision matrix illustrates there are several techniques available depending upon the size of the tree and the state of any cavities in the tree. Each of the four techniques for creating a cavity ready to use by MMC are described in full detail with images to illustrate each of the key steps in sequence.

Excavate

Excavation involves the creation of an entirely new cavity. This technique is generally only suited to dead wood as it involves removal of a face plate which would cause extensive damage to sapwood if undertaken on a living tree. Also in some dead trees it may be necessary to remove some of the canopy to reduce wind drag in order to increase the longevity of the remaining trunk and cavity (Figure 9). In some cases a natural scar may already exist following the loss of a branch exposing the heartwood. The resulting scar may be used as an entry point to excavate a new cavity.

The first step is to use a chainsaw to cut out a face plate. This is best done by first cutting two cross cuts ~70 cm apart and not more than ¼ the diameter of the tree at the height of the cuts. Then make two longitudinal cuts with the chainsaw bar held at a 900 angle for each on either side of the face plate starting one at a time from just below one end of the top cut and continuing down to the lower cut. Repeat this on the other side. The angling and depth of the longitudinal cuts should allow the cuts to meet in the middle of the trunk all the way along the cuts (Figure 10). The face plate should naturally fall loose once the final cut is complete. The face plate should be set aside for further work later.

Once the face plate is removed, use a chainsaw to make a series of long, deep vertical, parallel cuts into the exposed heartwood (Figure 11). The cavity walls being created should be ≥10 cm thick. Furthermore, check the required blade depth to ensure that no holes are made through to the other side of the tree trunk. This is critical as large parrots, such as Galahs, will chew-out and enlarge even the smallest of holes until they have created a further entrance-sized opening (Hurley, 2009).

Following the chainsaw cuts the resulting slabs can either be prised-out with a pinch bar or horizontal cross cuts can be made to further speed up the removal of the bulk of the trunk’s heartwood (Figure 12). Then use the Arbortech© to clean out the trunk cavity and form contours to the desired dimensions. It is important to leave some rough surfaces or small grooves in the walls of the cavity to provide climbing holds for birds to easily enter and exit the cavity.

If the height of the hole left by the face plate does not match the desired cavity depth it is relatively straightforward to use the Arbortech© to deepen the cavity in the tree trunk. The measurements provided for this dimension should be regarded as a minimum as cavities up to 1.8m deep have been used successfully by MMC at Pine Plains (Hurley, 2006a).

Figure 3: Decision matrix for the selection of the appropriate technique in simulated cavity formation in Slender Callitris Pine (Callitris gracilis murrayensis). Diamonds are decision points and light teal boxes are actions. The dark decision strips represent recording and monitoring activities

It is critical that the proposed nest chamber floor is relatively flat with minimum diameters of 18cm x 19cm. In addition to cavity depth, this is the single most important aspect of the SNC construction (Korpimäki & Higgins, 1985).

Smaller nest chambers will either deter MMC from nesting in them or limit the clutch size laid. A nest chamber with a larger diameter may be used by MMC and may be excavated if the trunk diameter is of sufficient size to accommodate it.

Now, the inside face of the face plate must be carved-out so it has internal concave contours to match the curvature of the cavity being carved from the inside of the tree trunk. The cavity entrance can also be carved from the face plate (Figure 13-14). These carving tasks are best done with an Arbortech© blade attached to an angle grinder.

Refitting the face plate is a critical stage for long-term viability of SNCs. Gaps and/or air flow between the remaining trunk cavity walls and the face plate must be eliminated. The kerf width from the chainsaw creates a 1cm gap between the face plate and cavity walls and requires in-filling. Use plywood strips cut to suit or Callitris lengths custom made to fit each joining surface of the face plate.

Regardless of which timber is used, these infill or caulking strips should be glued and tacked to the joint edges of the trunk and then trimmed with the Arbortech© so that they sit flush with both the external and internal contours of the trunk and cavity. The contouring of theses strips will help to camouflage them from the prying beaks of Galahs and other cockatoos. A standard builder’s glue can be used to bulk up any minor cracks between the jointed surfaces. Tech screws may also be used to strengthen the join between face plate and tree.

Remember to use a standard angle grinder blade to grind off or disfigure the tech screw heads, then paint them matt black and grey. This last action is recommended so as to not to attract undue attention from people or predators. The external surfaces of the caulking strips must also be painted a mottled matt dark-grey and black to protect from the weather. Alternatively thick strips of bark may be attached using silicone glue to cover the caulking strips. Once the face plate has been reattached, fine Callitris wood chips must be placed in the base of the new cavity. One or two handfuls is enough (Figure 15). Following this the face plate should be camouflaged with bark from the same tree the work is being done. Entrances should look as natural as possible Initially allow a half to one full day (4-8 hours) for the excavation of new cavities. With experience a team of two chainsaw operators will be able to an average excavate two cavities per day.

Augment

Cavity formation is normally associated with older mature or senescent trees (Gibbons & Lindenmayer, 2002). It is estimated that Slender Cypress Pine do not reach a sufficient size to support a cavity suitable for MMC (i.e. 50cm DBH) until trees are >80 years of age (Gibson et al. , 2008). A variety of methods involving the exposure of heartwood and manipulation of tree health have been proposed to accelerate cavity development (Gibbons & Lindenmayer, 2002).

The exposure of heartwood provides an entrance for fungi, bacteria and saprophytic insects which cause decay and, in conjunction with the trees adaptive growth response, leads to cavity formation (Mattheck & Breloer, 1997; and Lonsdale, 1999; and Taylor et al., 2002). The rate at which wounding techniques are able to accelerate the processes of natural cavity formation is on a temporal scale unsuited to the rapid provision of cavities for threatened species recovery (i.e. formation will take place over decades). Cavity augmentation involves accelerating the formation of a cavity or improving the function of an existing cavity. Accelerating cavity formation for this purpose is based on many of the techniques required to excavate a cavity in a tree without an existing cavity.

In addition to accelerating cavity formation, cavity augmentation also involves making improvements to an existing cavity. This may be as simple as enlarging the entrance to an existing cavity or may involve more extensive works to enlarge the internal dimensions of a small cavity. Furthermore, augmentation often is in the form of inserting carved timber sections to deflect rainwater from flowing into a cavity or repairing cracks in cavity walls.

The primary augmentation process involves mechanically removing the decay and heartwood associated with wounds caused by natural processes. A pre-existing scar, revealing advanced rotting of the heartwood is slightly enlarged to allow use of Arbortech blades to excavate the rotten timber (Figure 18A and B). Once the rot has been removed to sufficient dimensions for an SNC a face plate is carved from a single piece of timber and glued and screwed in place (Figure 18C).

Augmentation can also include modifications to an existing cavity to improve cavity function. These may be in the form of simply enlarging the entrance or other features of a cavity to suitable dimensions (Figure 19). In some cases augmentation may involve strategically placing a plug of timber to block water from flooding into a cavity(Figure 20 and Figure 21).

Ironbark Environmental Arboriculture Pty Ltd is an interdisciplinary company with expertise in arboriculture, ecology and wildlife conservation. In 2014, in partnership with DELWP, they pioneered the use of chainsaw-carved hollows for threatened species conservation with their work on the Major Mitchell’s Cockatoo. Since this time they have completed a range of targeted hollow creation projects in urban and forest environments, including Musk Lorikeets in the City of Melbourne and Brush-tailed Phascogales in Box-Ironbark forests of Central Victoria.

References

Boland, D.J., Brooker, M.I.H., Chippendale, G.M., Hall, N., Hyland, B.P.M., Johnson, R.D., Kleinig, D.A., McDonald, M.W. & Turner, J.D. (2006) Forest Trees of Australia. CSIRO Publishing, Collingwood.

Bond, J. (2006) Foundations of Tree Risk Analysis: Use of the t/R ration to Evaluate Trunk Failure Potential. International Society of Arboriculture – Arborist News:

Carey, A.B. & Gill, J.D. (1983) Direct habitat improvement – some recent advances. In: Snag habitat management symposium, pp. 80-87. Forest Service General Technical Report

Curtis, A., Green, J. & Warnock, B. (2000) Mimicking natural breaks in trees. English Nature, 8:1, 19-21.

DSE (2011) Guideline 8.1.42: Working in the vicinity of hazardous trees. Vitorian Government Department of Sustainability and Environment, East Melbourne.

Fay, N. (2002) Environmental arboriculture, tree ecology and veteran tree management. The Arboricultural Journal, 26:2, 129-136.

Forbes-Laird, J. (2008) THREATS: Tree Hazard: Evaluation and Treatment System. Forbes-Laird Arboricultural Consultancy, United Kingdom.

FWPRDC (2004) The In-ground Natural Durability of Australian Timbers. Forest & Wood Products Research & Development Corporation, Australian Government, Canberra.

Gibbons, P. & Lindenmayer, B.D. (2002) Tree hollows and wildlife conservation in Australia, 1st edn. CSIRO Publishing, Collingwood.

Gibson, M., Florentine, S. & Hurley, V.G. (2008) Age distribution of Slender Cypress-pine (Callitris gracilis) within Pine Plains, Wyperfeld National Park. Centre for Environmental Management, University of Ballarat, D.O.S.A. Environment, Ballarat.

Hurley, V.G. (2006a) Physical characteristics and thermal properties of Major Mitchell’s Cockatoo, Cacatua leadbeateri leadbeateri nest hollows, Wyperfeld NP. Department of Sustainability and Environment, Mildura.

Hurley, V.G. (2006b) Survey of Major Mitchell’s Cockatoo in Pine Plains, Wyperfeld NP – Spring 2006. Department of Sustainability and Environment, Mildura.

Hurley, V.G. (2009) A report on installing nest boxes and repair of degraded nest hollows in Callitris Pine for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri) in Pine Plains, Wyperfeld National Park. Unpublished report prepared by the Department of Sustainability and Environment for the Mallee Catchment Management Authority, Mildura.

Hurley, V.G. (2011) Results from the 2010 breeding survey of Major Mitchell’s Cockatoo (Lophocroa l. leadbeateri) Pine Plains, Wyperfeld NP. Department of Sustainability and Environment, Mildura.

Hurley, V.G. & Harris, G.J. (2014) Simulating natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri). Department of Environment and Primary Industries, Mildura. Kenyon, P. & Kenyon, P. (2010) Pruning for habitat workshop.

Korpimäki, E. & Higgins, P.J. (1985) Clutch size and breeding success in relation to nest-box size in Tengmalm’s Owl Aegolius funereus. Holarctic Ecology, 8:1, 175-180.

Lonsdale, D. (1999) Principles of Tree Hazard Assessment and Management. HMSO, 1999.

Mattheck, C. & Breloer, H. (1997) The Body Language of Trees. HMSO, London.

Rowley, I. & Chapman, G. (1991) The breeding biology, food, social organisation, demography and conservation of the Major Mitchell or Pink Cockatoo, Cacatua leadbeateri, on the margin of the Western Australian wheat belt. Australian Journal of Zoology, 39:2, 211-261.

Saunders, D.A., Mawson, P.R. & Dawson, R. (2014) Use of tree hollows by Carnaby’s Cockatoo and the fate of large hollow-bearing trees at Coomallo Creek, Western Australia 1969–2013. Biological Conservation, 177:1, 185-193.

SWA (2011) Draft Code of Practice: Safe Access in Tree Trimming and Arboriculture. Safe Work Australia, Canberra.

Taylor, A.M., Gartner, B.L. & Morrell, J.L. (2002) Heartwood formation and natural durability a review. Wood and Fiber Science, 34:4, 587-611.

VTIO (2010) Draft Climbing Guidelines Victorian Tree Industry Organisaion, Ringwood.

Hurley, V.G. & Harris, G.J., (2015) A manual of techniques to create simulated natural cavities in Slender Cypress Pine (Callitris gracilis murrayensis) for use by Major Mitchell’s Cockatoo (Lophochroa leadbeateri leadbeateri). A report to the Department of Environment, Land Water and Planning, Melbourne.

For more information please send an email to Grant Harris at [email protected] ironbarkenviroarb.com or visit the website www.ironbarkenviroarb.com

October 22, 2018 / by / in ,