Saturday, December 3, 2011

Valuation of Trees

Trees and other living plants are valuable, for they purify our air, act as sound barriers, manufacture oxygen, beautify our surrounding, provide shades, even historically, psychological, leisure etc.

But how much do that cost ?

Methods of valuation have been developed for landscape plants, including trees.  A valuation by trained appraisers, usually accepted by insurance companies, courts, and public agencies.

Tree Valuation Guide ( ISA 2009 ) is the most widely used method in North America. 
It is divided into 2 general categories :

1. The Replacement Method, for plants up to 8” in stem diameter 
Value ($) =
( Plant Cost + Installation Cost ) x ( Species Rating  x Condition x Location  ) + Removal Cost

2. The Basic Formula Method, for plants that are too large to replace.

            Value ($) =
Basic Value  x Species Factor x Condition Factor x Location Factor

The Thyer Tree Valuation Method ( Australia 1984 ) was developed in Sydney, Australia in 1984.  It was distributed for public use in 1985.

This method expresses the positive qualities of the trees, the contribution that the tree makes to the landscape, and the extent to which this is appreciated.

Value ($)  =    
Size ( height + canopy width + canopy diameter to dripline + circumference of trunk ) + Age  + Physical & Social Qualities + Planting Cost

This method was designed to value trees on public land in residential or commercial area.  It is not intended for use within bushland or jungle.

The Revised Burnley Method ( Australia 1988 ), was developed at the Victorian College of Agriculture and Horticulture Limited, Burnley Campus.  It was first published in 1988 ( McGarry & Morre ) and revised in 1991 ( Moore ). 

This method uses the volume of the tree as a inverted cone.  The calculation is done by determining an average value for at least 3 specimens form different nurseries.

Value ($)  =    
Tree Volume x Base Value ( $/m3 ) x Useful Life Expectancy Modifier  x  Form & Vigour Modifier x Location Modifier

The modified Burnley method is self-indexing for inflation, and sensitive to changes in the value of trees due to changes in consumer preference.  It has been tested in the courts and has been accepted as a realistic and well based method in the Australian context. 

However, many arborists find the establishment of the initial base value time-consuming and tedious.  It also does not deal with subjective components, such as historical or environmental significance.

The City of Sydney Tree Valuation Method ( Sydney, Australia 2003 ) was developed in 2003 for use in the city of Sydney to calculate tree value in public and private land.

Value ( $)  =   
Planting cost  x Size x [ { (Age + 6)/3 } + 4 ] x [ Trunk Diameter/ (42/2)+0.5 ] x
[ Condition of Tree x Life Expectancy / 30 ] x Visibility x Heritage Status x Ownership.

It was purposed to :
1. tree valuation to assist with management of trees on public land
2. tree value calculation for inclusion in contract documents for public land
3. tree value calculation for compensation when trees are damaged on public land
4. valuation to set tree protection bonds for trees on private land
5. valuation to set compensation to the community for trees unlawfully damaged on private land.

The Guide for Plant Appraisals, 9th Edition ( USA  2000 ) developed by Council of Tree and Landscape Appraisers ( CLTA ) has been widely used since 1951, and had been revised several times.  This guide is endorsed by American Association of Nurseryman, The American Society of Consulting Arborists, American Society of Landscape Architects, The Associated Landscape Contractors, Association of Consulting Foresters of America, International Society of Arboriculture, The Society of American Foresters and the National Arborists Association.

Value ($) =     
Basic Value [ Replacement Cost + {Basic Price x Trunk Area(at 4.5 ft) – Trunk Area(at 6 in) x Species } ] x  Condition  x  Location

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