Tree Protection

Tree protection on construction sites.

Keeping our trees happy

Lots of things can go wrong on the site from compaction, to dumping of waste, severing of roots, and disturbing the crown. But there are measures we can put into place to reduce them.

In built up urban areas trees are important too for many different reasons. However, they are also often in the way for clients wishing to develop sites. It’s a complex issue as we are trying to keep green coverage in cities while also increasing population density in pockets to reduce sprawl. These don’t exactly go together making it a tricky space to navigate.

Minimising impact at the design phase

Once a project has started there are many things that can be undertaken to help protect the trees from initial placement of structures, proposed construction methods to controls on how the site is used throughout construction.

Even after construction it is not always obvious after construction finishes how badly a tree has been damaged. It might die 5 or 10 years later, or it might just not reach the same vigour that it had before.

TPZ

Area around the tree at a given distance from the trunk to protect the tree above and below ground. The roots in this area will determine the vigour and growth of the tree.

TPZ = DBH x 12

  • Not less than 1.5m

  • Not greater than 15m

  • Not less than 1m for monocots

Activities not allowed within the TPZ:

  • Soil level changes

  • Temporary or permanent installation of utilities of signs

  • Physical damage to the trees

  • Dumping of waste

  • Wash-down and cleaning of Equipment

  • Placement of fill

  • Lighting of fires

  • Machine Excavation and Trenching

  • Excavation for silt fencing

  • Cultivation

  • Storage

  • Preparation of chemicals including cement

  • Parking of Vehicles

  • Refuelling

Session Outline

  • How do we protect trees on construction sites

  • Tree Protection Zone (TPZ)

  • Critical Root Zone

  • Writing specifications

 

Resources

In Australia we have Australian Standard Protection of trees on development sites - AS 4970-2009. This is the first place to look at for information on protection of trees on

Calculate your TPZ and SRZ here

Specifications go to James Urbans’ website here

Minimising impact in Construction Phase

  • Set up temporary fencing around TPZ - Lock this up so that is can’t be opened or moved

  • Set up wash up zones which stop chemicals entering the soil

  • Set up delivery and storage locations away from vegetation

  • Use erosion control methods

  • Use tracked machinery to distribute the load and reduce compaction

  • Put down mats to distribute vehicle loads

SRZ

This zone is right up near the tree and is critical for keeping your tree vertical. It is a safety issue. Sometimes referred to as the critical root zone.

SRZ = (Dx50) x 0.64

  • Minimum 1.5m

Variations

Some variations are allowed within the TPZ and SRZ. The encroachments should be designed by an arborist and need to be catered for elsewhere.

Presentations

Definitions

DBH - Diameter at Breast Height

Crown - The sum of branches, leaves and other structures

Tree Health in Urban Areas

Listen to James Urban, FASLA, discuss tree preservation in dense urban sites. Tree preservation in dense urban sites is different from the typical tree prese...

Webinar: Tree Preservation in Dense Urban Sites - DeepRoot

Writing Specifications

As a designer you can write specifications that have the potential to become part of the contract the construction company enters. This is your opportunity to describe what and how activities are undertaken. It might be sensible to engage someone who specialises in this to write your specifications for a specific site.

Specifications are a written document that compliments your plans, details, and schedules etc.