design WA – how to retain existing trees on development lots

Existing trees and their precious canopies are being cut down across Perth development sites at an alarming rate. Street and park trees in the public realm are comparatively easy to protect, but how can we protect trees on private lots in order to secure their well-documented benefits for future generations? And equally, how do we provide certainty to developers and not onerously increase development costs? This is a real challenge.

Damien Pericles (Founding Director at REALMstudios) has been working with Western Australia’s Department of Planning on the recently released Apartment Design Policy which will replace (in part) existing R-Codes. The policy is part of Design WA (formerly the ‘Planning Reform for Better Design’ project).

One of the key chapters of the policy is titled ‘Existing Tree Retention’ and is put forward as an important and early site planning consideration. Together with other related chapters (like Deep Soil Zones) this chapter aims to raise awareness and shift community and developer values. Tree retention involves careful analysis, planning, due diligence and resolution of technical issues. Four key innovations come through in the policy:

Five Year Rule

The first innovative approach is what defines an existing tree and the ‘five year rule’. “Existing trees” includes those physically on-site and those that have been removed but are clearly identified on an aerial photo within the last 5 years. This aims to address clearing by owners/developers long before lodging of a development application.

Deep Soil Zone Incentive The second innovative approach utilises a built-in incentive relating to Deep Soil Zones. In a related chapter Deep Soil Zones set objectives and minimum guidelines for provision of soil area not covered by building or structure and that supports healthy plant and tree growth. The incentive allows a variation of 12% Deep Soil Zone down to 8% when existing trees are retained.

Tree Replacement Offset The third innovative approach uses an offset mechanism. Where a tree is unable to be retained, then a cost is to be paid for the planting of 4 additional trees per tree not retained within the immediate project vicinity (but outside the development site). The cost per tree of supply, installation, irrigation and maintenance for 2 years of a 100Lt native tree is to be determined by and paid to the local authority.

Minimum landscape areas The fourth initiative applies in high density areas where built form maximizes all or most of the site area and deep soil zones cannot be achieved. In this instance a minimum of 25% site area is to be planting on structure.

These and other initiatives in the Apartment Design Policy will set new standards of practice and improve the amenity and liveability for residents living in apartments.

Further information of the full draft suite of documents can be found at Design WA.