Additional Trenching Investigation of Hill's Weeping Fig ... · The Sugar Factory Arbor Advocate 3...

Supplemental Report

Additional Trenching Investigation of

Hill's Weeping Fig # 12025

In Civic Cultural Precinct, Laman Street Cooks Hill, Newcastle

Prepared for

The Council of the City of Newcastle

By

Dennis Marsden, MAIH, MISA, MNAAA

Consulting Arborist

12 August 2010

The Sugar Factory – Arbor Advocate ABN: 29 995 746 283

6 Leumeah Close, West Pennant Hills NSW 2125 Telephone: 9875 4074

The Sugar Factory Arbor Advocate

Contents 1 Introduction 3 2 The Tree 3 3 Methodology 4 4 Trenching Results 4 5 Evaluation of Root Severance 5 6 Conclusions & Recommendations 8 Appendices Photographs Table 1. Summary of trenching results Table 2. Comparison of GPR results with trenching results Laman Street - Tree Location Plan Laman Street - Trench Location Plans

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The Sugar Factory Arbor Advocate 3

1 Introduction This report was commissioned by Mr Lindsay Field, City Arborist, of Newcastle City Council. The brief for the report was: 1 Conduct a site visit and document the findings of the trenching in the road and

footway adjacent to tree ID 12025 located just west of the pedestrian crossing on the southern side of Laman street.

2 Provide a determination if the removal of the root by Hunter Water will alter the

likelihood of whole tree failure. 3 Provide your opinion on removing the temporary exclusion fence around these 2

trees. The site was inspected on 5 August 2010. The findings of the trenching results corresponded with the findings of earlier investigations contained in previous reportsi,ii, with which this report should be read in conjunction, in that the tree has an eccentric root-plate. Similarly, the latest trenching results do not corroborate the findings of the ground penetrating radar root survey. The root removed by Hunter Water was one of several tensile roots. The precise effect of root removal cannot be calculated, however it is not estimated that the root removal has given rise to a high risk of tree failure during normal, day-to-day conditions. It is recommended that the temporary exclusion fence be removed, and that Council’s procedure of evacuating the area during windy conditions be continued. It is also recommended that the tree be monitored weekly for signs of movement in the root-plate. 2 The Tree The tree was the Hill's Weeping Fig Ficus microcarpa var. hillii numbered 12025, which is the westernmost of the trees on the southern side of Laman Street in the Cultural Precinct, outside the library. A tree location plan is included in the appendices. It is understood that the root on the southeast side of the tree was severed by Hunter Water during the repair of a water mains on 28 July 2010.

i Marsden, D (2010) “Further Investigation into Root-plate Architecture of Hill's Weeping Fig Ficus

microcarpa var. hillii In Civic Cultural Precinct, Laman Street Cooks Hill, Newcastle” Report prepared by The Sugar Factory - Arbor Advocate for Newcastle City Council

ii Marsden, D (2006) ‘Investigation into Root-Plate Architecture of Hill’s Weeping Figs along Laman Street outside Newcastle Region Art Gallery’ Report prepared by The Sugar Factory – Arbor Advocate for Root Projects Australia P/L

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3 Methodology Trenching was carried out within the street and within the footpath adjacent the tree (photograph 1). The trenches were in line with previously excavated trenches adjacent the other trees. The trench within the street was an overall length of 5.65 metres, and the trench within the footpath 5.2 metres long. The surface layers of the trenches were removed by machine and the sub-grade removed by water-laser and eductor. The finished depth of the trench was approximately 1.2 metres. The trench in the street is numbered ‘15’ on the attached plans, and the trench in the footpath numbered ‘16’. The root severed by Hunter Water was exposed by water laser and eductor for examination (photograph 2). 4 Trenching Results The trench in the street was 3.02 metres from the centre of the base of the tree, and the trench in the footpath 3.5m from the centre. The theoretical radius of the root-plate (for trees growing in unconstrained environments) is 3.52 metresiii. Hence, the trenching would intercept the edge of the root-plate under normal growing conditions. At completion, the trench excavated in the street contained two woody roots and a pipe (photographs 3 and 4). One woody root was 10mm in diameter, the other was 45mm Ø. The pipe was 50mm Ø. The trench contained few other small woody or fibrous roots. The trench within the footpath contained 3 woody roots and a galvanised iron pipe (photograph 5). One woody root at the eastern end of the trench was 120mm Ø, and forked into two woody roots of 65mm and 90mm Ø that extended across the trench (photograph 6). One woody root found near the western end of the trench was 30mm Ø (photograph 7), and the third woody root 15mm Ø (photograph 8). The galvanised iron pipe was approximately 30mm Ø (photograph 9). Again, the trench contained few other small woody or fibrous roots. Using the comparative data from Tree #14828 in Civic Park (trenching investigation of March 2010), it could be expected that each ‘side’ of the theoretical root-plate of a Hill’s Fig will contain at least 2 – 3 woody roots greater than 60mm Ø, 12 – 15 woody roots between 20 and 50mm Ø, and a great number of smaller woody and fibrous roots. The results illustrate that tree #12025, like the other Hill’s Figs in Laman Street, does not have a radial root-plate. The results of all trenching investigations in Laman Street are summarised in Table 1 in the appendices. Table 2 contains the comparison of the trenching results with the results of the ground penetrating radar (GPR) root survey. Briefly, the results of the GPR survey were not corroborated by the trenching results.

iii Mattheck, C, and Bethge, K (2000) ‘Simple Mathematical Approaches to Tree Biomechanics’ Arboricultural

Journal 24, pp. 307-326, ABB Academic Publishers, Great Britain.

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5 Evaluation of Root Severance The root severed in the repair of the water main was a primary woody root on the southeast side of the tree (photograph A, below, and photograph 1 in appendices). The root was approximately 110mm Ø at the point of severance, 1.4m from the edge of the stem. The severance occurred on 28 July 2010.

Photograph A, left. Photograph provided by Newcastle Council.

It is understood that the root was the only large root encountered in the repair of the water main (photograph B, left. Photograph provided by Council). If it is the only large root extending beyond the pit on that side of the tree, this could mean that the root-plate is even more eccentric than previously thought, although it would take further and potentially destabilising investigation to confirm this.

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The severed root had the characteristics of a tensile root, as evidenced by the pronounced thickening or ‘reinforcement’ of the curved section (the junction) that meets the stem. Assessment of root-plate stability is less precise than the criteria that are now widely accepted for assessing the strength of hollow stemsiv. As stated in previous reports, the assessment of trees with eccentric root-plates is best done with reference to casebook experience. The known factors are that the tree has an eccentric root-plate that spreads mainly in a lineal fashion, that ongoing root severance has occurred in the repair of nearby infrastructure, and that Hill’s Figs growing in these circumstances have failed in the past. The question of whether the recent root severance has increased the likelihood of whole-tree failure is difficult to answer given the eccentric root-plate. If the tree were growing in the open with no impediment to radial development of the root-plate, one of the places where the ‘line is drawn’ is at the junction, that is, the curved section where the primary root joins the

stem (figure A, left). If the junction is severed through (or decays through) then the tree is at risk of failure under normal day-to-day conditionsv. The largest junction is usually on the windward side of bending. On Tree #12025, the largest junction is on the southwest side (photograph C, below). Ordinarily the evidence of the tree would be accepted: the largest junction indicates the strongest load. The root that was severed on the southeast was countering a lesser load than that experienced on the southwest.

Setting aside the eccentricity of the root-plate, these two factors would allow for a conclusion that the tree has not been unduly destabilised by the root severance: the severed root was not the main tensile root, and; the root was not severed at the junction. While it is not possible to fully factor-in the vagaries of the eccentric root-plate or the role of nearby infrastructure in the mechanical support of the tree it can be concluded that, on balance, the root severance has

not created a condition that will promote whole-tree failure during normal day-to-day conditions.

iv Lonsdale, D (1999) ‘Principles of Tree Hazard Assessment and Management.’ HMSO, London. v Mattheck, C, and Breloer, H (1994) ‘The Body Language of Trees - A Handbook for Failure Analysis.’

HMSO, London.

Photograph C. Largest junction on subject tree.

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It will be necessary to test this conclusion. The tree could be monitored by Council surveyors for signs of tree subsidence, measuring the distance between a fixed data point on the kerb and a fixed data point on the main stem of the tree, to determine if the tree is gradually tilting. This was done for Tree 12 018 (Tree 4796 in the pre-TAMS of 2007) following the storm of June 2007 when there was a question mark over the stability of the treevi. The tree was monitored once per week over an eight week period. The tree was also checked by Council’s City Arborist for signs of splitting or fracturing on the compression side of the stem base/root-plate and for heave or lifting on the tensile side during the monitoring period. Stem tilting of 20mm or more, or the development of fractures on the compression side or heave on the tensile side, should be taken as signs of tree subsidence necessitating the re-evaluation of the tree.

vi Marsden, D (2007) “Investigation into Stability of three Hill’s Weeping Figs Along Laman Street Newcastle”

Report prepared by The Sugar Factory – Arbor Advocate for Newcastle City Council.

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6 Conclusions & Recommendations The trenching investigation carried out on 5 August 2010 confirmed that Tree #12025 has an eccentric root-plate. The trenching results do not corroborate the results of the ground penetrating radar root survey. It is not anticipated that the severance of the root by Hunter Water on July 28 2010 has created a condition that would give rise to a risk of whole-tree failure under normal day-to-day conditions, as the root was not the main tensile root and the root was not severed at the junction. This needs to be tested by monitoring. The torn section of the root should be pruned cleanly back to sound tissue. It is recommended that the base of the tree and its surrounds be checked for movement and the development of fractures at least once per week over an eight-week period commencing as soon as possible. It is further recommended that Council put in place a system that ensures that the inspections are carried out. Data including photographs from the inspections is to be recorded and retained in Council files. At the end of the inspection period if no signs of movement or fractures etc are found, it can be concluded that the tree has not been unduly destabilised by the root severance. If signs of movement or fracturing are found at any time during the inspections the tree is to be re-evaluated. It is also recommended that the temporary exclusion-fencing be removed and that Council’s procedure of evacuating the area during windy conditions be continued. Yours faithfully, DENNIS MARSDEN, CONSULTING ARBORIST. Dip. Hort. (Arboriculture) [Distinction], Assoc. Dip. Landscape [Design & Construct] [Distinction] Adv. Cert. Urban Horticulture [Distinction], Cert. Tree Surgery, MAIH, MISA, MNAAA.

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Appendix A –Photographs

Photograph 1. Trenches in relation to Tree #12025.

Photograph 2. Root severed by Hunter Water.

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Photograph 3. Completed trench in street. Woody root 45mm Ø and pipe 50mm Ø circled; woody root 10mm Ø at arrow. Photograph 4 (below). Woody root 45mm Ø and pipe 50mm Ø.

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Photograph 5. Completed trench in footpath. Woody roots circled; gal pipe indicated at arrow. Photograph 6. Bifurcated root at eastern end of trench. Main root ~120mm Ø, forks into 65mm and 90mm Ø.

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Photograph 7. Woody root 30mm Ø within footpath trench.

Photograph 8. Woody root 15mm Ø.

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Photograph 9. Galvanised iron pipe ~30mm Ø within footpath trench.

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Appendix B Trenching Results Trench # Tree Ø

A.B. RW Distance Comments Finding

1 (2006) 4802 (A)

115 351 320 Roots found between 45 and 90cm depth. 5 x 10mm Ø, few 5mm Ø and smaller, some fibrous but not in great numbers. No primary or secondary woody roots.

Root-plate eccentric.

2 (2006) 12020 (B)

95 324 320 No woody roots of any size. Few fibrous roots found. Root-plate eccentric.

3 (2006) 12021 (C)

90 317 317 1 small woody root ~8mm Ø plus associated fibrous at 60cm depth. No other roots present. Root-plate eccentric.

4 (2006) 4805 (D)

110 344 340 1 small woody root 5mm Ø, few fibrous roots. No other roots present. Root-plate eccentric.

5 (2006) 4797 (E)

115 351 341 Four secondary roots found, smaller woody and fibrous present but not in great numbers. 1 x 20mm Ø, 1 x 35mm Ø torn by backhoe, 1 x 60mm Ø damaged, 1 x 20mm Ø at base of trench.


6 (2006) 12017 (F)

120 357 337 1 section small fibrous roots, few small woody roots < 5mm Ø, 1 x 10mm Ø. No primaries or secondaries. Root-plate eccentric.

7 (2006) 12016 (G)

140 381 342 1 x 10mm Ø, 2 x 5mm Ø in layer beneath skulls. 3 x 10mm Ø 70cm down. Few small < 5mm Ø. No primaries or secondaries. Root-plate eccentric.

8 (2006) 12015 (H)

65 276 315 10 roots 5 – 10mm Ø 40cm deep, 10 x 10mm Ø and ~ 25 < 5mm Ø + fibrous roots found 70cm deep. No primaries/secondaries. Root-plate likely eccentric.

9 (2010) 12014 157 400 334 Small woody root 30mm Ø, 70cm down, 2.9m from eastern end of trench. One other 20mm Ø, 80cm down, 1m from west end. Few smaller woody and fibrous present. Pipe found, 60mm Ø, 65cm down, ~ 1 metre from west end, running across trench. Photos 6 & 7.


10 (2010) 12012 &

12013

103 &

135

335 &

375

307 &

354

Woody root 35mm Ø 80cm down, 90cm from west end. Woody root 40mm Ø 56cm down, 3.6m from west end. Woody root 25mm Ø 80cm down, 4.6m from west end. Woody root 40mm Ø 60-65cm down running from eastern end of trench for 1.8m to west. Smaller woodies <10mm Ø present, few fibrous. Photographs 8 and 9.


11 (2010) 12022 117 353 335 1 x primary woody root found 120mm Ø, 32cm down, 1.55m from eastern end. 1 x 30 & 1 x 50mm Ø woody nearby. Woody root 30mm Ø 10cm down, 2.75m from east end, 1 x 20mm Ø below that. Primary woody root 110mm Ø 60cm down at west end of trench, probably growing from adjacent tree #12023. Few smaller woodies and fibrous present.75mm Ø steel conduit 67cm down, running east-west along trench. 1 x 90mm Ø PVC stormwater pipe below pavers, 1.5m from west end. Photographs 10, 11, 12 & 13.


12 & 13 (2010)

12021 &

12020

90 & 96

317 &

325

392 &

367

Excavated as continuous trench. 1 x woody root 40mm Ø 25cm down, 2.4m from west end. 1 x woody root 20mm Ø 40cm down, 4m from west end. 2 x 90mm Ø PVC storm water pipes 30cm down, 4.7m & 4.9m from west end. Woody root 50mm Ø zigzag across trench, 46cm down, 1.3m from east end. Small woodies 10mm & 20mm Ø, 100cm down, 3m from east end. Very few other small woodies and fibrous. Steel pipe 110mm Ø running east-west along south side of trench, approx. 65cm down. Photographs 14, 15, 16, & 17.


14 (2010) 12018 &

12019

132 &

139

372 &

380

325 &

320

Small woodies 5, 10 mm Ø 72cm down, 0.5m from west end. Woody root 15mm Ø 70cm down, 1.1m from west end. Group of small woodies, largest 25mm Ø, 65cm down, 2.7m from west end. Small woodies <10mm Ø 35cm down, 5m from west end. Small group 20mm Ø 90cm down, 6.6m from east end. Steel pipe 110mm Ø 63cm down, 60cm from east end running across trench. Photos 18 & 19.


15 (8/2010)

12025 116 352 302 Woody root 10mm Ø found 1.1m from west end, 40cm depth. Woody root 45mm Ø found 2.1m from east end, 66cm depth. Pipe 50mm Ø 2.1m from east end, 80cm depth. Few smaller fibrous roots present.


16 (8/2010)

12025 116 352 350 Large bifurcated root found 0.77m from east end, 52cm depth. ~120mm Ø forked into 65 & 90mm Ø. Woody root 15mm Ø 0.1m depth 3.6m from west end. Woody root 30mm Ø 1.22m from west, 50cm depth. Gal pipe 30mm Ø 40cm depth, 0.4m from west end.

Root-plate eccentric

Table 1. Summary of Results from December 2006, February 2010, and August 2010 investigations. Notes: Ø A.B. = Stem diameter as measured above the buttress zone, in centimetres. RW = the mechanically-effective root-plate, in centimetres. Distance = the distance from the centre of the tree base to the inside edge of the nearest part of the trench, in centimetres (trench 60cm wide). Eccentric = not circular or radial.

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Results cont’d Table 2. Comparison of GPR results with trenching results. Tree # GPR results Trenching results GPR results

corroborated?

12012 Trench 10. 1 x woody root ! 50mm Ø shown intersecting trench, 120mm below surface, 1.5 – 2m from eastern end of trench.

No woody roots ! 50mm Ø present. No other woody roots of any size in locations or depth indicated by GPR.

No

12013 Trench 10. 2 x woody roots ! 50mm Ø shown intersecting trench, 150mm below surface, 1.2 – 1.8m from eastern end of trench.

No woody roots ! 50mm Ø present. Woody root 40mm Ø running from eastern end for 1.8m at 60-65cm depth.

No

12014 Trench 9. 5 x woody roots ! 50mm Ø shown intersecting trench, at 2.4m from west (300mm down), 3m from west (180mm down), 3.8m from west (420mm down), 180mm depth running for 1m from eastern end of trench, and 1 at unspecified depth 1m from east end.

No woody roots ! 50mm Ø present. No woody roots present in locations or depths indicated by GPR.

No

12015 (H)

Trench 8. 3 x woody roots ! 50mm Ø shown intersecting trench, 1 at 2.2m from west end of trench at unspecified depth, 1 at 80mm depth running along and across trench from1m to 4m from west end, 1 at unspecified depth 0.4m from eastern end.


No

12016 (G)

Trench 7. 2 x woody roots ! 50mm Ø shown intersecting trench, at unspecified depths running 1m and 2.1m from western end of trench.


No

12017 (F)

Trench 6. 2 x woody roots ! 50mm Ø shown intersecting trench, 1 at 50mm depth 40cm from west end, 1 at 120mm depth angled across trench 2.4 to 1.4m from east end.


No

4797 (E)

Trench 5.Tree removed after June 2007 storm. No woody roots ! 50mm Ø indicated on plan.

1 x 50mm Ø woody root found. No

12018 Trench 14. 4 x woody roots ! 50mm Ø shown intersecting trench, at 2m, 3m, 4, and 4.8m from west end, at depths 110mm, 120mm, 150mm, and unspecified.

No woody roots ! 50mm Ø present. No

12019 Trench 14. 3 x woody roots ! 50mm Ø shown intersecting trench, at 4.4m, 6.2m, and 7.8m from east end, at 190mm, 145mm, 120mm depth.


4802 (A)

Trench 1. Tree failed in June 2007. No woody roots ! 50mm Ø indicated on plan in this area of trench.

No woody roots ! 50mm Ø present. Yes

12020 (B)

Trench 2 (2006). 1 x woody root ! 50mm Ø shown intersecting trench at 195mm depth at eastern end.

No woody roots ! 50mm Ø present. No other woody roots of any size in location or depth indicated by GPR.

No

12020 Trench 13 (2010). 3 x woody roots ! 50mm Ø shown intersecting trench, 1 at 330mm depth at eastern end of trench, one angling across trench 1.2-2.2m from east, 180mm depth, 1 at 90mm depth 5.8m from east end.


12021 (C)

Trench 3 (2006). 1 x woody root ! 50mm Ø shown intersecting trench at 250mm depth at western end.

No woody roots ! 50mm Ø present. No other woody roots of any size in location or depth indicated by GPR.

No

12021 Trench 12 (2010). 3 x woody roots !50mmØ shown intersecting trench, at0.4m, 1.1m, and 4.3m (angled across) form western end, 230, 380, and 235mm depths.


4805 (D)

Trench 4. Tree failed in June 2007. No woody roots ! 50mm Ø indicated on plan in this area of trench.

No woody roots ! 50mm Ø present. Yes

12022 Trench 11. 5 x woody roots shown intersecting trench, two of which branch. 2m (220mm depth) and 3.4m (unspecified depth), from western end, 3.4 (unspecified depth), 1.8m (340mm depth), and 1.2m (285mm depth) from eastern end, latter projecting through end of trench.

Primary woody root 110mm Ø 60cm down at west end of trench, probably growing from adjacent tree #12023. 1 x primary woody root found 120mm Ø, 32cm down, 1.55m from eastern end growing diagonally across trench in opposite direction to GPR result. 1x 50mm Ø below.

No

12025 Trench 15. No woody roots shown intersecting trench. No woody roots ! 50mm Ø present. 1 x 45mm Ø woody root found. 50mm Ø pipe present, not detected by GPR.

No

12025 Trench 16. 3 x woody roots ! 50mm Ø shown, 1 at 1.4m from west at unspecified depth, 1 at 1.9m from east at 10mm depth, 1 at 1.6m from east at 125mm depth.

Large bifurcated root found 0.77m from east end, 52cm depth. ~120mm Ø forked into 65 & 90mm Ø. Two other woody roots < 50mm Ø present. Gal pipe 30mm Ø 40cm depth, 0.4m from west end.

No

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Tree location plan (not to scale). Photograph provided by Newcastle City Council.

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Laman Street trench location plan 1 (not to scale). Plan provided by Newcastle City Council. Note that trenches 12 and 13 were excavated as a continuous trench.

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Laman Street trench location plan 2 (not to scale). Plan provided by Newcastle City Council.

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