When we conduct a tree risk assessment, apart from our visual inspection and application of modern tree defect detection system, we should have further understanding about why the defect generated. We are not limited in measuring the level of decay but the reason why decay occurs. The more we know how fungi invade a tree, the more we can do in preventing fungal attack by using different kind of biocontrol agent in a systematic and effective way.

Adaskaveg, J. E., & Gilbertson, R. L. (1986). In vitro decay studies of selective delignification and simultaneous decay by the white rot fungi Ganoderma lucidum and G. tsugae. Canadian journal of botany, 64(8), 1611-1619.

Agriculture, Fishes and Conservation Department, Hong Kong SAR Government, (2006). Measurement of Diameter at Breast height (DBH), Hong Kong, Agriculture, Fisheries and Conservation Department.

Anon. (2016). Summer 2016 Report: Egretry Counts in Hong Kong with particular reference to the Mai Po Inner Deep Bay Ramsar Site. Report by the Hong Kong Bird Watching Society to the Agriculture, Fisheries and Conservation Department, Hong Kong Special Administrative Region Government. 

Benítez, T., Rincón, A. M., Limón, M. C., & Codon, A. C. (2004). Biocontrol mechanisms of Trichoderma strains. International microbiology, 7(4), 249-260.

Blanchette, R. A. (1984). Screening wood decayed by white rot fungi for preferential lignin degradation. Appl. Environ. Microbiol., 48(3), 647-653.

C. Mattheck. (2007). Updated Filed Guide for Visual Tree Assessment, Karlsruhe, Forschungszentrum Karlsruhe Gm.

Deacon J. (2006) Fungal Biology, 4th Edition. Blackwell Publishing Ltd.

Deflorio G., Fink S. and Schwarze F. W. M. R. (2007) ‘Detection of incipient decay in tree stems with sonic tomography after wounding and fungal inoculation.’  Wood Sci Technol 42:117–132

Dunster, J. A., Smiley E. T., Matheny N. and Lilly S. (2013) Tree Risk Assessment. Champaign, Illinois: International Society of Arboriculture.

Gilbert E. A. and Smiley T. (2004) ‘Picus sonic tomography for the quantification of decay in white oak (Quercus alba) and hickory (Carya spp.).’ Journal of Arboriculture 30:277–281.

Gilbertson, R. L. (1980). Wood-rotting fungi of North America. Mycologia, 72(1), 1-49.

Green III, F., & Highley, T. L. (1997). Mechanism of brown-rot decay: paradigm or paradox. International Biodeterioration & Biodegradation, 39(2-3), 113-124.

Greening, Landscaping & Tree management Section, (2015). Guidelines for Tree Risk Assessment and management Arrangement (8^th Edition), Hong Kong Development Bureau.

GovHK, Hong Kong SAR Government (2019).  GeoInfo Map

Hjeljord, L., & Tronsmo, A. (1998). Trichoderma and Gliocladium.

ISIK, Fikret; LI, Bailian. Rapid assessment of wood density of live trees using the Resistograph for selection in tree improvement programs. Canadian Journal of Forest Research, 2003, 33.12: 2426-2435.

Johnstone D. M., Ades P. K., Moore G. M. and Smith I. W. (2007) ‘Predicting Wood Decay in Eucalypts Using an Expert System and the IML-Resistograph Drill.’ Arboriculture & Urban Forestry. 33(2):76–82

Leong E.C., Burcham D. C. and Fong Y. K. (2012) ‘A purposeful classification of tree decay detection tools.’ Arboricultural Journal: The International Journal of Urban Forestry, 34:2, 91-115, DOI: 10.1080/03071375.2012.701430

Mattheck, C.G., K.A. Bethge, G.R. Bruder, and R. Kappel. 1999. The Resistograph: Information for practical use. Arborist News 8(3): 42-44.

Rayner, A. D., & Boddy, L. (1988). Fungal decomposition of wood. Its biology and ecology. John Wiley & Sons Ltd..

Schwarze, F. W., Engels, J., & Mattheck, C. (2013). Fungal strategies of wood decay in trees. Springer Science & Business Media.

Shirouzu T., Uno K., Hosaka K. and Hosoya T. (2016) ‘Early-diverging wood-decaying fungi detected using three complementary sampling methods.’ Molecular Phylogenetics and Evolution. 98, 11–20

Shortle W. C. and Dudzik K. R. (2012) Wood decay in living and dead trees: A pictorial overview. Gen. Tech Rep. NRS-97. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 26 p.

Sutherland, J. B., Crawford, D. L. (1981). Lignin and glucan degradation by species of the Xylariaceae. Trans. Br. Mycol. Soc. 76, 335-337.

The Hong Kong Bird Watching Society. (2016).  Guidelines for Planning and Carrying out Construction Works at Egretries, Hong Kong: The Hong Kong Bird Watching Society.

Vinale, F., Sivasithamparam, K., Ghisalberti, E. L., Marra, R., Woo, S. L., & Lorito, M. (2008). Trichoderma–plant–pathogen interactions. Soil Biology and Biochemistry, 40(1), 1-10.

Wang X. and Allison R. B. (2008) ‘Decay Detection in Red Oak Trees Using a Combination of Visual Inspection, Acoustic Testing, and Resistance Microdrilling.’ Arboriculture & Urban Forestry. 34 :1–4

Wassenaer P. V and Richardson M. (2009) ‘A review of tree risk assessment using minimally invasive technologies and two case studies.’ Arboricultural Journal, 32:4, 275-292, DOI: 10.1080/03071375.2009.9747583

Watling, R. (1982). Taxonomic status and ecological identity in the basidiomycetes. Decomposer basidiomycetes: their biology and ecology, 1-32.Zahner V., Sikora L. and Pasinelli G. (2012) ‘Heart rot as a key factor for cavity tree selection in the black woodpecker.’ Forest Ecology and Management. 271: 98–103

Wood decay fungi are the primary decomposer in the forest ecosystem.  This is a biological process of converting lignin and cellulose to carbon dioxide and water with a release of different form of energy (Deacon, 2006; Shortle et al, 2012, Shirouzu et al, 2016).  By analyzing the fungal degradation process on wood and the chemical and structural change of fungi generating in the wood, scientists can classify the wood decays (Schwarze, 2013).  The decay groups are usually distinguished in white rots, brown rots and soft rots (Dunster et al, 2013; Schwarze, 2013)  

Brown rot

Brown rot is about the breaking down of cellulose leaving lignin partly altered.  The lignin dries in to typical cuboidal block (Rayner and Boddy 1988; Green and Highley 1997; Schwarze, 2013).  The wood is in high compressive strength relatively but brittle in texture.  Brown rot fungi belong to the family Polyporaceae.  And they are overwhelmingly associated with connifers (Gilbertson 1980; Watling 1982; Schwarze, 2013). 

White rot

They are represented in all the main groups of the Basidiomycetes and in some of the Ascomycetes (Sutherland and Crawford, 1981; Schwarze, 2013).  They are generally describing the forms of wood decay in which the wood presumes a bleached appearance and where lignin as well as cellulose and hemicellulose is broken down.  Despite the great diversity in wood decay caused by white rot, they are defined into two sub-groups: selective delignification and simultaneous rot (Blanchette 1984; Adaskaveg and Gilbertson 1986; Rayner and Boddy 1988, Schwarze, 2013)

1. Selective Delignification

At the early stage of decay, lignin is broken down more than hemicellulose or cellulose.  The breaking down of lignin leaving the cellulose largely unaltered.  To the later stage of decay, as the cellulose is broken down more slowly than brown rot and soft rot, the reduction of wood strength will be relatively slow.  The wood tissue will remains relatively less compressive strength but generally high tensile strength.  Its host are commonly found in broad-leaved trees and conifers.

2. Simultaneous rot

In the course of this kind of rot, all wood components included lignin, cellulose and hemicellulose will be broken down almost the same rates. It was commonly found in broad-leaved trees but seldom in conifers.  The residue remains is brittle and soft.  This kind of decay results a great reduction of impact bending strength of the wood.

Soft rot

The degradation of parts of individual cell wall and binding pectins.  The decay will form a residue in hard, brittle and ceramic texture.  The destruction of cell walls usually takes place in the immediate vicinity of the hyphae (Schwarze, 2013)

Recent findings about Trichoderma

Biological control involves the use of beneficial organisms and their genes to reduce the negative effects of plant pathogens and encourage positive responses in the plant (Vinale 2008).  Trichoderma are the most commonly isolated soil fungi.  They have the ability to protect plants and contain certain pathogen populations in different soil medium.  Therefore, they are widely used as biopesticides, biofertilizers or soil amendments.  By studying the relationship between Trichoderma, plant and pathogen, we can further control the survivals of plants during fungal attack.   

Soil borne pathogens can cause important losses.  The distribution of several phytopathogenic fungi, such as Phythium, Phytophthora, Botrytis, Rhizoctonia and Fusarium has spread during the last few years (Benitez, 2004).  They cause great losses in crop and fruits.  According to the study from benitez, he use Trichoderma as a biological control agents (BCAs).  Trichoderma BCAs produce high efficient siderophores that chelate iron and stop the development of other fungi.  It compete for nutrients with other fungi.  The completion of nutrients has been proved to be very important for the biocontrol of phytopathogens such as Botrytis cinerea, the main pathogenic agent during the pre-and post-harvest in many countries (Benitez, 2004).  By studying the use of Trichoderma and Gliocladium spp., we can improve our arboriculture training by studying the use of BCAs as a preventive measures for fungal attack for specific tree species (Hjeljord, 1998).

In this session, I will discuss 2 kinds of tree defect detection systems that I have used in Hong Kong for advance tree risk assessment.  They are Resistograph system and Sonic Tomograph system.

Resistograph and application

Using resistograph system is an invasive method for defect detection.  The resistograph system has a needle. By rotating the needle in certain speed, the needle can drill in the wood.  When a tree has an internal decay, the decayed wood will be relatively soft with less density when comparing with healthy sound wood.  It is because the lignin or cellulose was decomposed by fungi.  When we drill in the aforesaid decayed wood, the resistance will be relatively low (Zahner et al, 2012).  Referring Figure 29 and 30, this is an example of diagram generated by a resistograph system measured from a tree with internal decay.  According to the resistance measurement during the process of microdrilling at a constant speed, we can determine the wood strength remains in the wood tissues.(Figure 28)

Advantage

The longer the needle of the resistograph system, the longer distance you can measure the diameter of the tree trunk.  In general, the needle is about 30 cm but some latest model can provide a needle in 40 cm.  The advantage of using resistograph system is quick set-up, rapid assessment can be obtained, relatively cheaper than using tomograph system and the accuracy is high (Johnstone et al, 2007).  As the set-up is easy and much cheaper than a sonic tomograph, I usually use for the measurement of a problematic tree before I choose using sonic tomograph.

Limitation

The disadvantage of using resistograph system is decay may be found after drilling. Although the drilling hole is small, this physical damages will be exist in the trees and these holes can provide an ‘expressway’ for pathogen, borer as an example, to invade the inner parts of the trees (Leong et al, 2012) .  Therefore, when we use this system, we should well evaluate where the suspected decay area is and minimize the frequency of drilling.  Furthermore, each time of drilling, it is better to sterilize the needle to avoid spreading the hidden fungal fruiting bodies inside the tree or even pass the hidden fungal fruiting bodies to another tree. 

Regarding the report of Mattheck et al. (1999) and further elaborated by ISIK et. al. (2003), the resistograph measures may have varies within species and location of measurement.  Also, environmental factors will also affect the wood density and influencing the measurement. Furthermore, as the resistograph can only provide a linear data in each drilling, we cannot project the total area or volume of the decay that in the problematic tree by 1 or 2 measurements in the same measuring height. The more the drilling we take, the more data we can obtain to figure out the size of decay but in parallel, more physical damage we will create on the tree.

Future development

Regarding the limitation, the developer of resistograph system can further study the following aspect for improvement.

1. To minimize the diameter of the drill tongue such that to minimize the size hole will be generated in each drilling.
2. To improve the software by inputting the drilling statistics of different species under different temperature and humidity to see the correlation among each factors.

Sonic Tomograph

It is less invasive than resistograph system.  The velocity of sonic waves in trees depnes on several parameters.  These parameters depends on angel between propagation direction of the wave and annual growth rings, moisture content in different layers of the trunk and types on wood.  By transmitting sonic signal inside the cross section of the wood, it can generate a 2D cross-section graphic which shows the level of decay, the percentage of decay and the approximated size of decay (Wassenaer & Richardson, 2009; Lin et al, 2013; Lin & Yang, 2015). (Figure 31)

In fact, this system is relatively expensive and time consuming in application.  The set-up procedures is much complicated comparing with resistograph system.  It is usually used for advanced tree risk assessment for a problematic tree pointed out by visual tree inspection.  In a tree with internal decay, we may find sound wood, heartwood, decayed wood or hollow area.  The aforesaid medium has different density.  By measuring the velocity of sound travelling forth and back in the aforesaid medium, we can distinguish the healthy wood and defected wood (Wassenaer & Richardson, 2009).

Application

To install the tomograph system on the tree, we should first identify the measuring level and tap a certain numbers of nails round the tree evenly and in anticlockwise direction.  In general, 8 nails are recommended.  The larger the circumference of the measuring level, the higher the number of nails to be used.  After tapping the nails and named them MP1 to MP8, we will put the main unit of the tomograph system on the tree and connect sensors, laptop and hammer cable to respective socket. Afterwards, we will use a caliber to input the distance between each nail before measuring.  By using the default hammer to tap the sensor attached on each nail, a sound wave will then generated and recorded and the data will then transmit back to the laptop.  With the software installed in the laptop, the sound wave will change to a tomogram.  The defected and healthy wood will be distinguished by different colour.  Referring to my assessment of a Crateva unilocularis, a tomograph with 3 layers at 20cm, 60cm and 115cm above ground level were measured (Figure 32 to 36).  The colour in dark brown represent highest wood density (healthy wood or solid wood). The change in colour from dark brown, brown, green, purple to blue shows the decrease in wood density. Blue represents the lowest wood density (suspected defected wood or cavity)

Limitation

1. Physical damage is unavoidable as tapping the nail on the tree will cause a damage on tree bark and cambium.  In fact, the holes are not of the size that would affect the structural integrity of a tree (Gilbert & Smiler, 2004)
2. As the sonic tomograph cannot distinguish among cracks, ring shakes, decay, cavity and defensive reaction zone, we will use other defect detective system such as resistograph to estimate the type of decay afterwards (Wang & Allison, 2008; Wassenaer & Richardson, 2009; Leong et al, 2012).
3. The environmental factor is also important in collecting successful data.  If the surrounding of the tree is near the road with heavy traffic or near a construction site, the sound wave collected will be affected by source of vibration.  With my bitter experience, I had spent half of a day for generating a sonic tomograph for a Bombax ceiba near a road but finally I could not collect the data we wanted because the B. ceiba was located next to a run in/out of a petrol station and next to a carriageway with heavy traffic.  The sonic data was affected by the vibration generated from heavy traffic nearby and no consistent and effective record could be collected on that day.
4. Tomograph may be failed in showing the status of decay in some trees infected by soft rot.  According to the research from Deflorio et al (2007), sonic tomograph was failed in detecting the decay of soft rot fungus Kretzschmaria deusta because of the soft rot did not highly reduced the wood density of the infected tree.
5. For the decay found in underground, sonic tomograph will not be effective for assessment as the sound wave cannot be received in return as the sensor cannot be set in the underground.

Future development

As sonic tomograph is about collecting the data of sound wave back and forth among sensors, the development is required to study the feasibility for the sound wave transmit in one direction only and can collect these data for analysis.  And the sonic tomograph cannot distinguish the decay and cavity in some scenario, further study is required to increase the accuracy.  Lastly, for the nail tapping in the tree as setting the sensor, the developer should study if putting the sensors on an elastic belt or other medium and surround the tree is feasible such that no damage will be caused during the assessment.

Case 3

This was a tree planted in a rectangular tree pit along a public pavement.  It located at Oxford Road, Kowloon, Hong Kong (Figure 17).

The tree had a single trunk with 2 stems remained.  Its diameter at breast height (DBH) measured at 1.3 m (AFCD, 2006) was 480 mm and the age class was mature.  It was 7 m tall with around 5.5 m crown spread.  The tree crown was not evenly spread as there was another tree on its west.  (Figure 18)

The tree was actually had three stems but unfortunately, one of the stem was damage by super typhoon Mangkhut on 16 September 2018.  A tearing wound around 4m above ground level (AGL) was found after the typhoon attack and fungal attack and ineffective CODIT was observed.  Furthermore, severe twig dead back was found on one of the stem with no sign of living.  And the live crown ration was very low as only one stem had chlorotic leafs remained and the size of leaf was relatively small comparing with other D. regia in the same street at the time of inspection. (Figure 19)

Apart from the tree crown, abnormal longitudinal cracks with bark peeling were found on trunk at about 2m to 4m AGL.  They appeared from the North to the West.  Furthermore, sap flow was also found on the trunk near the cracks. (Figure 20)

Although buttress root could be formed, abnormal bulging were found on the buttress root which indicated that the tree was under stress (Figure 21-22).

With the poor health and structural condition,  a reisistograph was conducted (Figure 23-26). The measuring level was 50 cm and 100 cm AGL respectively as the arborist wanted to know the structural integrity in the lower trunk and the upper trunk was already in a poor structural and health condition.  According to the measurement, the amplitude of wood strength was fluctuated abnormally and with a suspected internal decay at 50cm AGL.

As the tree was located at a pavement with high usage and near some primary school, considering its brittle nature (GLTMS) and the targets cannot be removed, the subject tree was planned to be felled with the following measures and suggestions in long term.

Short term action

1. To remove the dead branches such that the likelihood of failure of branches will be decreased. (Figure 27)
2. To apply tree felling application from the respective Tree Preservation Authority in Hong Kong for sake of public safety.

Long term action

To review the compensatory planting at the subject location and subject species.  As the subject pavement is narrow (about 1.8m in width), the management party should evaluate the necessity of planting.  Furthermore, as D. regia has buttress roots, it is not recommended to plant along narrow pavement according to the Street Tree Selection Guide published by GLTMS, HKSAR in 2018.

Case 2

Another case to be introduced is also a Ficus microcarpa.  It is located at Tak Shing Street, Kowloon, Hong Kong. It is funny that the tree locates on a carriage way next to a public pavement.  And there is Fortune Terrace, a residential building (Figure 7), next to the tree.  It was planted in an irregular tree pit at grade.

The tree had a single trunk.  Its diameter at breast height (DBH) measured at 1.3 m (AFCD, 2006) was 500 mm and the age class was mature.  It was about 15 m tall with around 12 m crown spread (Figure 8).  The tree crown distribution was not even due to the restriction from surrounding buildings.  Although the distribution is uneven, the tree crown was still widely spread on other three directions.

There were several mechanical wounds found on the trunk and branches (Figure 9 to 12).  These mechanical damages were likely caused by high vehicles.  Cavities were also found on the trunk at 1.5m, 1.7m and 2m height above ground level.  The largest one formed an opening with 60mm in width, 150mm in length and with 180mm in-depth.  A poor CODIT was found next to the remaining stem.  Further decay would be carried out from time to time.

It leaned towards the carriage way about 15 degrees from vertical and towards southeast.  According to the growing direction, it was self-corrected with an abnormal bending (Figure 13).

Mechanical damages and wounds were also found on root flare and collar.  Surface dead wood were exposed (Figure 14 to 15).  As the tree was planted on a carriage way, the damage of root flare was caused by vehicle parking for years.  Bulges were developed near the basal cavity which indicate a response growth against the internal decay.  And the compression roots formed knots along the exposed roots.  Girdling roots is another common defect observed due to the restricted tree pit.  According to the size of tree crown, there were about 80 per cent of root covered by cement.  The tree pit was relatively small but it was commonly found in the roadside in Hong Kong.  Besides, a cavity was found with two-side opening at the root flare.  This was the largest cavity found on this tree with 180mm in width and 250 mm in length.  Litters were found inside the cavity and wood decays were observed.

According to the observation after the above visual assessment, the risk rating of branch, trunk and root flare are summarized in Figure 16.

With the risk categorization as above, the following mitigation measures are recommended.

1. A short term measurement is to remove one of the movable targets.  As the parking vehicles along Tak Shing Street is illegal, the management department can request the Transport Department to block the carriage way underneath the tree crown as a restricted zone of vehicle and seek the assistance from Police Force to step up enforcement action on illegal parking.  The likelihood of impacting target will be changed from high to medium.  And the residual risk and root flare will drop down to low and moderate respectively. 
2. Crown thinning and cleaning can reduce not only the likelihood of failure but to enhance the tree structural integrity by removing the dead twigs to minimize possible drops of tree debris and dead twigs.  Those thinning works should be scheduled before typhoon season in Hong Kong. With the guideline from Tree Management Office, no more than 25 per cent of pruning works will be conducted.  This can also help in reducing the tree crown loading.
3. Furthermore, protection should be made in order to prevent further damage and new wound formed.  Installation of tree guard is recommended to cut off the source of mechanical damage (mainly from vehicle) to the lower trunk and root flare. 
4. Enlarging the tree pit will be a long term measures to improve the situation of the tree in both structural and health extent.  This can allow more oxygen and water dissolve in the top soil which encourage root growth.  Furthermore, the adventitious roots can extend to the soil and form extra support to the tree.  Guiding tubes can also be installed in order to protect the adventitious root development and direction on the supporting root we would like to setting up. 
5. Finally, closely monitoring is important for updating the condition of tree and take remedial action when necessary.  Regular monitoring in every six month is recommended.

Case 1

The first case to be introduced is a mature Ficus microcarpa.  It is evergreen.  It is a pavement tree in tree pit form and is located outside No. 137-139 Fuk Wah Building, Luk Hueng Lane, Tai Po, Hong Kong.  The tree pit size is about 1.6 m x 2 m.  It is close to auxiliary residential buildings.

The tree had a single trunk.  Its diameter at breast height (DBH) measured at 1.3 m (AFCD, 2006) was 630 mm and the age class was mature.  It was 18 m tall with around 14 m crown spread.  The crown spread was measured in four directions as follows: 4.5 m in northeast (NE); 8.5 m in southeast (SE); 7.5m in southwest (SW); 8.5 m in northwest (NW). (Figure 2)

The tree had multiple stems.  They were divided at about 3 m above ground level, namely Stem 1, Stem 2 and Stem 3.  Stem 1 was growing towards NW with diameter about 300 mm.  Stem 2 was growing towards SE with diameter about 150 mm.  Stem 3 was growing towards SE and upwards with diameter about 100 mm.  (Figure 3)

There were epicormics found on tree crown but less than 10%.  They mainly found on Stem 1.  The tree vigor was good in general.  Furthermore, it leaned towards NW, with leaning 45° from vertical when measured at ground level and leaning 34° from vertical when measured at 1.3 m above ground.  It showed a sign of self-correction under phototropism according to its division and growing angle of the stems and branches.  Cement on the pavement was damaged behind lean but no soil cracks found.  It was a sign of root development on tension side.  (Figure 4)

Two major mechanical wounds, namely Wound A and Wound B, were found on the trunk (Figure 5).  Wound A was about 350 mm (L) (Length) x 245 mm ( W ) (Width) and at NW.  Wound B was about 100 mm (L) x 50 mm ( W ) and at SW.  The collar of Wound A was not formed completely.  According to mallet test, hollow sound was heard in the middle of Wound A.  Furthermore, there were a sum of lignified aerial roots formed under Wound A but were damaged.  For Wound B, the collar was formed and no further sign of decay found.Apart from the leaning mentioned in General Condition, there were no signs and symptoms of decay found on the trunk and there were few lignified aerial roots found damaged or encroached the trunk and formed a new part of the trunk.  Besides, there was some illegal parking (wheelchair) under the Tree.

The tension side of the Tree is at SE.  According to the aggressive root growth of the subject species, the surface roots were greatly restricted by the tree pit and surrounding cement.  Cement damage was found at the SE seriously but no root plate movement was observed. (Figure 6)

Recommendation

Short term remedial action

1. To remove the branches with fungal fruiting bodies such that the likelihood of failure of branches will be decreased from probable to possible.
2. Crown thinning and cleaning are recommended to removal the dieback twigs.

Long term remedial measures

1. To minimize the potential of damage to the surrounding buildings during inclement weather, crown reduction around 20-25 % after the breeding season of birds is recommended.  As the tree is near Tai Po Egretry, one of the Site of Special Scientific Interest (SSSI) Anon. (2016), AFCD should be consulted before commencement of tree works.
2. To enlarge the tree pit in phases is recommended for better growth space of tree root.  Extension in tension side at SE first is preferable with 0.5m extension to avoid sudden removal of weight on tree root.  Then SW, NW and NE.  Other works departments like Highways Department and Transports Department will be consulted for this enlargement of tree pit. 
3. To transplant the underneath young tree to another location for a better growth space for both the young tree and the subject tree.
4. To relocate the underground utilities near the tree.
5. To remove rental bicycle by fencing off the subject tree pit with horticultural fencing.
6. Level 2 and 3 assessments (application of sonic tomographic device on the major wound found on trunk) are recommended yearly.

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