Standards Development

Scope

This British Standard specifies requirements for water storage, filtration, hydraulic conductivity, fertility, pH, load bearing capacity, volumes, depth of material and stratification of materials to support urban tree growth. It also specifies how this material is to be placed and requirements for irrigation and control of root spread. The role of tree soils in the filtration of water and sequestration of carbon will examined. It does not specify: the structures that might be used for irrigation; structures that might provide support for the tree or pavement; materials that may be used as root barriers.

Purpose

There is a UK-wide push for more urban trees but very little information available on the growing media and structural soils required. There is currently no standard that specifies, for example, what is going to support the tree (weight bearing volume) and what is the right medium to allow drainage while also being structural (i.e. to support cement pavements, to ensure trees do not to interfere with services etc.).

This standard would provide solutions to a very complex, problematic situation, and as well as outline options for successful installations where currently there is little objective guidance. Planting trees in built-up areas can be costly and represents an investment that will over time provide visual amenity, shade, remove air pollution, represent habitats for wildlife and sequester carbon. The health and long-term survival of street trees are dependent upon the qualities and quantity of the growing media.

UK government policy is being developed to encourage street tree planting. At the same time, Local Planning Authorities are progressing with urban tree planting to meet their own regional biodiversity targets. This standard would therefore be very timely, and given the wide scope (rooting volume, quality, drainage etc) and general lack of objective information, there is also likely to be an international market for such a standard.

A standard of this kind contributes the “joined up thinking” required for a circular economy and sustainable urban development. The standard would bridge a number of disciplines to provide measured solutions to the complex environmental demands.