Area Highways Manager (East) From:- natural Environment




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Area Highways Manager (East)

From:- Natural Environment







For the attention of Paul Simpson

Date: 18 August 2009

cc: Peter Morris







Tel: 01245 437713





For information only


cc: Ian Baalham, Gary O’Sullivan, Liam McKarry, Colchester Borough Council
Your Ref:

Ref: ESH/NE/SS (2100368)


ARBORICULTURAL ADVISORY SERVICE

INSPECTION REPORT
Site: Crouch Street West, Rawstorn Road & Manor Road, Colchester
Paul Simpson, Peter Morris & I met on 27 July to discuss possible highway improvements and the potential impact on existing trees. I inspected the trees the same day and my comments are below in Appendix 1.
Analysis

The trees are showing typical symptoms of urban planting, including:




  • Root problems from direct damage or limited space for root growth, leading to crown dieback

  • Impact wounds from vehicles

  • Pruning to clear buildings leading to poor form and the need for regular maintenance

The trees are planted close to the carriageway edge and are surrounded by paving setts, with areas of tarmac where the footway has been repaired due to roots lifting the surface.


Most tree roots are likely to be close to the path surface, where conditions for root growth may be more favourable than the lower soil, which is probably more compacted. Therefore, removal of the existing surfaces and installation of new paving would lead to is high risk of root damage. Such damage would adversely affect the trees’ vitality and possibly compromise their stability.
If the trees were retained, the continued presence of roots close to the surface and regrowth from pruned roots means there would be a high probability of roots lifting the new surface in the future.
The existing mix of species and forms provides no unity or structure to the streetscape.
Therefore, given the foreseeable decline of the existing trees, it would be sensible to remove them. This would involve trees numbered 2-11 in Appendix 1.
The scheme then provides an opportunity to plant new trees in properly designed pits in order to


  • reduce the risk of future root damage to the footway and

  • reduce the need to prune to maintain sufficient clearance over the highway and from buildings



Species

If possible, at least nine trees should be planted to replace trees numbered 3-11 along the southern side of Crouch Street West and the eastern side of Rawstorn Road. I do not consider it necessary to replace the hawthorn (tree 2) on the northern side of Crouch Street West.


Planting one species would create greater unity and structure to the streetscape. Trees numbered 1 & 2 stand within a conservation area (the northern side of Crouch Street West). While the others do not, they are sufficiently close to have an impact on the aesthetic value of the area.
The narrow footway and constraint of planting within 750mm of the carriageway edge means a species with a columnar, fastigiate form would be appropriate and reduce the need for future pruning to maintain sufficient clearance over the highway and from buildings.
The following suggested species have a mature height of 10-15m and are tolerant of street planting:


  • Field Maple (Acer campestre) “Elegant”

  • Hornbeam (Carpinus betulus) “Fastigiata Frans Fontaine”

  • Callery Pear (Pyrus calleryana) “Chanticleer”

They have a mature height of 10-15m but planting into the existing footway means there is likely to be a lower volume of soil than is necessary for the trees to reach their ultimate mature size.


It is also proposed to plant a tree at the eastern end of Manor Road, in the footway adjacent to Balkerne Hill. There is sufficient space for a species with a more rounded, spreading form. A lime would complement the planting in the adjacent car park grounds and in St Mary’s churchyard on the opposite side of Balkerne Hill. The following species are not susceptible to aphids:


  • American Lime (Tilia americana) “Redmond”

  • Crimean Lime (Tilia x euchlora)



Planting pits
The soil must be of suitable quality for root growth with sufficient aeration, nutrients, drainage and load-bearing capacity. It may have to be improved with fertilisers.
If the soil around the pit has high clay content, water may seep into the pit from the surrounding ground, forming a sump. Such waterlogging prevents root growth and could lead to tree death, so in such circumstances, appropriate drainage would be required.
Any imported topsoil should be of good quality, with a light texture and conform to BS3882 “General Purpose Category”.
Underground services and the narrow footway width preclude the use of structural soils and techniques such as Silva Cells to increase soil volumes promote root growth.
Installing a barrier around the edges of the planting pit (e.g. Greenleaf “Root Director”) would encourage roots to grow downwards to reduce the risk of future root damage to the footway. Compacting the backfill surrounding the barrier would discourage roots that emerge from the base of the director from reaching back up towards the footway surface.
Trees should be supported in the first few years to stabilise them until new roots are established in the soil. If decorative guards are to be installed around the trees, the limited space means a single stake or underground guying would be appropriate. In reasonable growing conditions, the support should be required for three years at most.
Irrigation is important for successful establishment. In recent years, we have organised a contractor to water newly planted trees during the spring/summer for two years after planting. This has proven to be effective with few trees lost through drought stress. Costs for irrigation should be factored into the planting & maintenance costs.
Installation of an irrigation pipe would minimise spillage during watering.
Tree guards may be useful to reduce the risk of damage. The top edge should be designed to reduce chafing and guards would have to be removed once the trees are established.
Some ground protection would be appropriate. Bare soil requires regular weeding and, as can already be seen around some of the trees, the ground can become compacted and uneven. Decorative grilles could be installed with the guards or a porous resin bound aggregate could be used with no grille. A porous surface is useful to allow water to permeate rather than an impervious surface like tarmac. The grilles must be removed over time or be installed with removable inner rings to accommodate the increase in trunk girth.
Tree work recommendations
Tree removal

Crouch Street West has high traffic use with a narrow carriageway, short-term parking spaces and frequent delivery vehicles. Traffic management is essential for tree work to be carried out safely and efficiently, ideally a road closure.


Felling and grinding out stumps (and roots?) of trees 2-8 could be completed in one day, minimising the time for a road closure. Trees 9-11 could be felled and the roots left in the planters, unless otherwise instructed.
Estimated cost: £2500, assuming a road closure.

Tree planting & maintenance

Carpinus betulus “Fastigiata Frans Fontaine” have a taller mature height than the other two suggested species, and this may be more appropriate given the scale of the adjacent buildings.


Assuming one tree will be planted to replace each removed from the southern side of Crouch Street and from Rawstorn Road, the cost of supply would be £603 (9 trees x £67: 10-12cm trunk girth in 45L containers).
The cost to supply one lime (either species) would be £49 (10-12cm trunk girth in 45L container).
The estimated cost to plant ten trees would be £590.
I would recommend factoring in watering and maintenance costs for two years after planting to maximise the chances of successful establishment. The estimated cost is £2200 (£5.50 per visit per tree for 20 weeks April-October each year, irrigate with 40L per visit).

...............................................


Simon Smith

Tree Officer



Appendix 1: Table of Trees


Tree number

Species

Age

Height (m)

Trunk diameter (cm)

Crown spread radius (m)

Crown clearance (m)

Comments

1

Silver Maple

(Acer saccharinum)



S

10

37

3

4

To be retained. Situated in compacted soil raised around the trunk. Good vitality. Light bulbs hung in crown.

2

Hawthorn

(Crataegus monogyna)



E

5

16

2

3

Dieback in upper crown indicating root problems, probably associated with small area of compacted soil and paving around trunk. One small broken branch in lower crown.


3

Common Ash

(Fraxinus excelsior)



S

9

17

2.5

4.5

Crown close to building, and will require regular pruning to clear. Roots lifting footway setts and tarmac. Numerous small impact wounds on the lower trunk.


4

Lime

(Tilia spp.)



S

8

21

4

2

Branches touching building. Roots lifting footway setts and tarmac within 2m of trunk. Impact wound on northern side of upper trunk. One scaffold has an old wound with decay through limb near union with trunk at 3m with impact wounds above.


5

Common Ash

(Fraxinus excelsior)



S

8

19

5

4

Unbalanced crown and stubs following poor pruning to clear recent development. Smaller foliage in upper crown suggests early symptoms of root problems. Soil compaction around trunk. One severed surface root 1m from trunk (3cm diameter). Kerb displacement from root growth.


6

Hornbeam

(Carpinus betulus)



S

4

7

1

2

Impact wounds on lower trunk.

7

Norway Maple

(Acer platanoides)



E

8

21

3

2.5

Soil raised around trunk. Stubs in lower crown overhanging carriageway.




8

Norway Maple

(Acer platanoides)



E

9

32

5

3

Crown touches building. Exposed roots in pit, including some girdling. Impact wounds on lower scaffold branches at 4m over the carriageway.


9

Silver Birch

(Betula pendula)



E

5

16

(at 1m)


2

1

Sparse leaf cover in upper crown suggests early symptoms of root problems: possibly optimum root capacity in planter.


10

Silver Birch

(Betula pendula)



E

8

22

2

2

Basal suckers growing next to decaying stumps where two smaller stems have been removed in the past: potential decay in lower trunk.


11

Silver Birch

(Betula pendula)



E

6

16

2

2

Sparse leaf cover in upper crown suggests early symptoms of root problems: possibly optimum root capacity in planter.


12

Red Oak

(Quercus rubra)



S

6

21

5

2

Partly unbalanced due to loss of lower branches (vandalism?). Superficial wounds on trunk. One wound on low lateral branch to monitor.
Minor dieback in mid-crown: monitor.
Monitor trunk girth and proximity to grille, with a view to removing the grille before the increased girth touches it.




Appendix 2: List of Suppliers
A list of suppliers of root barriers & deflectors, irrigation systems, tree guards & grilles, porous surfacing and underground anchoring systems. This list is not exhaustive.


English Woodlands (Burrow Nursery)


www.ewburrownursery.co.uk

Green-Tech Ltd


www.green-tech.co.uk

Peter Scott Tree Care


www.peterscotttreecare.com

Arbortech Tree Technology Ltd


www.arbortech.co.uk

Addagrip Surface Treatments UK Ltd


www.addagrip.co.uk

SureSet UK


www.sureset.co.uk

Platipus Anchors Ltd

www.platipus-anchors.com










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