Green streets

Use existing trees

Playgrounds and schoolyards

Image credit: PPH

Perform a tree survey

Be sure that a tree is worth being saved before taking measures to design and build around it. First take an inventory of the size, location and species of all existing trees on the site. Ask a tree specialist to check the trees that are considered to be worth saving. The life expectancy, condition, stability and quality of the tree should be determined.

Plan ample space around existing trees

Do not place buildings too close to an existing tree. Keep at least 5m between a building and the trunk of the tree (or more if the canopy is already larger than 10m in diameter). This allows the canopy and roots to develop to maturity. Do not cut large structural roots near the trunk to avoid instability of the tree.

Avoid underground conflicts

When renovating underground situations such as cables and pipes, do not use heavy digging equipment around existing trees. Dig by hand near the roots to avoid damage.

Protect trees during construction

Building specifications should clearly state what the protocol is regarding existing trees and vegetation. Place a fence around a tree at least as big as the canopy to protect the roots and canopy from machinery. Be sure that the area around the tree does not become storage for building supplies and equipment, or a dumping ground for building waste and oil. Inspect the ground water tables in case of (temporary) level changes or pollution that could damage the trees. Include a penalty clause in the contract if trees are damaged.

Guarantee growing conditions after construction

After all construction is completed (including the new surrounding landscaping), trees and plants should be checked for damage and soil conditions should be monitored for quality. Maintenance responsibilities should be clear, and maintenance  should begin immediately after planting

Transplant trees if possible

Ask a tree specialist if it is possible to transplant trees. This varies per species, root system and capacity to adapt to the new situation. Trees should be transplanted with a root ball as big as possible, including fine roots. Growth conditions and maintenance are important in the new location.

Consider existing trees as assets to a development from the beginning phases of design through construction.

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Benefits of existing trees

  • New development automatically gets a mature green character
  • Mature green is more valuable both aesthetically and economically
  • Existing tree structures provide a spatial quality only achieved after many years with new plants
  • Old trees have history and meaning for people and the site
  • Mature trees are most effective in providing the desired functions

“A mature beech tree with a trunk diameter of 100cm removes 11x more PM10 than a corresponding tree with a trunk diameter of 20 centimetres.”

Fred Tonneijck (Triple E & Knooppunt Innovotief Groen)

 

New and existing developments

In new development:

Let existing valuable / characteristic trees inspire or become the basis for new development. Be sure the design incorporates the needed space for trees and green to thrive in the new surroundings. Protect and monitor the trees during the entire construction process.

In existing development:

Trees and green should be incorporated into the redesign of areas and be given more room if needed so the trees can reach their optimal form. Be sure to protect trees both above and underground during the construction process.