Trees and the Public Realm - Westminster City Council

Trees and the Public Realm (Draft) Appendix D - 1
APPENDIX D
COMMONLY USED SPECIES IN WESTMINSTER
Choice of species is crucial to the provision of a healthy tree that is appropriate to both a local sense of place
and its intended function, with space to grow to maturity with minimal intervention or management. Council’s
arboriculturalists are best placed to advise on what species are appropriate however there are also a number
of sources which can provide information in this respect. These sources include specialist publications,
private nursery catalogues and also some good websites such as the following:
• Greater London Authority, Right Trees for a Changing Climate.
http://www.right-trees.org.uk
• Royal Horticultural Society
http://www.rhs.org.uk/databases/summary.asp
To illustrate some of the considerations associated with tree selection, a selection of some of the most
common trees used in Westminster are listed below. These species have varying relationships with
environment (in particular air quality) which needs to be carefully considered in relation to the nature of the
site and surrounds 1 .
Large round trees (over 15m, height and spread approximately equal)
► Norway Maple (Acer Platanoides)
Sturdy tree of large proportions forming thick rounded crown with widely spaced branches. Suitable for
parks and wide avenues. This species is not sensitive to nitrogen oxides and is very effective in absorbing
them.
► Common Ash (Fraxinus excelsior)
A native with a wide to oval shaped crown. It is suitable for parks and wide avenues and, if given the
room to grow and spread, the common ash forms a very striking specimen tree. Since they need plenty
of light, they can easily be crowded out by other overshadowing trees. This species is particularly
effective for reducing ozone concentration in urban areas.
► London Plane (Platanus x hispanica)
In addition to being fast-growing, the London Place is very tolerant of hard surfaces, vigorous pruning,
atmospheric pollution and root compaction. For these reasons it is a popular urban tree, however it does
have some drawbacks in an urban setting – most notably the hairs shed by the young leaves and the
dispersing seeds in spring which can both be an irritant if breathed in. The large leaves are also tough
and can create a disposal problem. Furthermore, like some other large, broad-leaved species London
Planes can potentially contain pollutants from traffic – particularly as their growth can tend towards the
centre of the road.
The Council recognises that, given its mature size, the London Plane is best suited to parks and broad
streets where avenues will have replacements of the same species. In other more domestic scaled
streets it can either grow too large for its setting or has to be heavily pollarded in order to remain without
causing problems for buildings in close proximity.
► Small leaved lime (Tilia cordata)
A native to British Isles and large parts of Europe. Slow growing but produces large rounded canopy.
Long-lived. Tolerant of most soils and hard surfaces. Suitable for parks and woodlands. Many cultivars
available with compact pyramidal shaped crowns suitable for street planting.
1 Many of the details on the trees interaction with air quality in this appendix have been sourced from Plant Publicity Holland, 2008.