Book Review Heading


A Standard Tree Evaluation Method

By Ron Flook
Published by Ron Flook, September, 1996

Reviewed by Bruce Treeby, Tutor in Farm Forestry, The Open Polytechnic of New Zealand, Lower Hutt

As Tony Jackman wrote in the preface, we have difficulty when it comes to accounting for all the values and benefits that we attribute to trees, and the benefits that accrue from their presence in our lives. Those of us who have been involved in trying to protect trees, welcome the contribution that Ron Flock has made with this publication. As Tony says the inclusion of the arboricultural and visual components of his system which ultimately lead to a notable tree register at local and national levels of importance, are a considerable advance over earlier methods. Those of you who have used the Helliwell System will be aware that the multiplications involved can often mean that single factors can skew the final unit score. In STEM each components score can be traced in a quantitative way.

In STEM the evaluation criteria is separated into four major sections:

  • Condition
  • Amenity
  • Notability
  • Value

In the full tree evaluation score sheet, points for the components that make up the condition, amenity and notability are added to give a tree evaluation points total. That is a relatively straight-forward procedure. The next step is the tree valuation, and this is more complex. In the example given in STEM, the wholesale cost of a 5 year old tree ready for planting out is taken as the basic unit of value. The evaluation points of the tree that is being valued, is multiplied by the basic unit value to give the present value of the tree. To this is also added the initial costs of planting and maintenance over the years and GST. Ron Flock takes the wholesale cost as the conservative value and suggests that with retail margins of up to 100% that the possible final value could in fact be double. The retail margin value is open for local negotiation.

The decision as to what the basic unit of value is will be made at a local or regional level. Dunedin City Council uses the figure of $NZ177 as the wholesale cost of a 5 year old tree ready for planting.

So what have been the responses to STEM? Standards New Zealand has asked Ron to put New Zealand STEM forward as an "Industrial Draft". I asked Frank Buddingh' a consulting arborist who runs International Tree Managers Limited what he thought of STEM. He is enthusiastic about it and said for him it was a "workable document" that had already proved it's value in protecting trees in the Dunedin area. In one instance the local power supplier was set to run an underground power supply two metres away from a row of Fagus sylvatica. Using STEM, the conservative value of the individual trees was determined and the power company was advised that they would be liable for any deaths. The power supply was rerouted. Frank has used STEM in court cases and says that it has application in the new district plans. The Dunedin City Council uses STEM to assign value to the tree assets that are in the cities, parks, and streets.

Nelson City Council has used STEM (draft 5) to develop their list of Notable and Historic Trees for scheduling on the District Plan 1995/6, and this is shown in Appendix 1. Wellington City Council are trialing it to determine what trees should go onto a Notable Trees Register. There were questions raised over how trees in broken topography score low in visibility and the age scale between 40 and 80 years was too large a gap. The New Zealand Arboricultural Association has approved it's use, Waikato Institute of Technology are now using it in the arboriculture course, and there has been Australian interest.

Ron set out to produce a method that is easy to understand, easy to use in the field and gives conservative results. I think he has been successful with all three objectives. Over the past four years, he has consulted widely with a series of drafts and this is number 6. STEM is already being applied with success by local authorities and arborists throughout New Zealand. Throughout, there are definitions, a glossary of arboricultural terms and references that assist clarity and those who want to do more study on the subject. Throughout the publication there are examples of application, step by step. There are 23 photographs of tree examples with their tree evaluation score.

I will conclude this review with some of my local experience. When I saw the cover photograph of the ring-barked Quercus robur and the same tree being cared for by an arborist, I immediately thought how useful STEM would have been to those of us who were unsuccessful in saving two 60 year old Norfolk pines in Rimu Street, in Eastbourne, Wellington. These trees along with three others on the other side of the street were part of the "seaside" character of Eastbourne. This was back in the 1980's prior to our merger with Hutt City. The council at the time wanted to redevelop the street and lower the camber. There were all sorts of arguments about drains and instability. There was a strong public debate, and in the end two of the trees were ring-barked to finalise the issue! I used STEM to put a value on the trees based on the three trees that were given a reprieve. On wholesale value using the Dunedin example, the trees had an individual value of over $NZ46 000 each and it could be $NZ60 000 or more. Such values may well have compelled the councillors of the day to act differently. The other three trees are still living and the camber was removed.

With regard to repair of damage, there is a Norfolk pine of similar age in Days Bay that some years ago suffered damage to the base of the tree from a car driving into it. No remedial action was done to the tree. The large bare area with no protective bark has been attacked by wood boring insects and today the stability of the tree is in doubt. If STEM had been in use at the time of the damage, it is likely that more care would have been taken of an asset that through neglect has become a liability.

In conclusion, I am sure that people who are responsible for the management and protection of trees will find this publication very useful. In using STEM you will be able to give feed-back to Ron Flook on your experiences and assist with the further fine-tuning of the method for version 7. We are fortunate that we have people like Ron who are prepared to dedicate so much time to this project. In 1995, Ron was awarded an Associate of Honour of the Royal New Zealand Institute of Horticulture, and is an executive member of the RNZIH - portfolio 'Trees'.

New Zealand Garden Journal: Journal of the Royal New Zealand Institute of Horticulture 1997 2(1): 26-27

This site includes an article by the late Ron Flook on STEM

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