November 19, 2017

Tree surveys

tree

In the first part of the new mini-series, Jonathan Hazell considers the value of a good tree survey.

 

Common reasons for a tree survey include being able to discharge a tree owner’s duty of care, to help draw up a cyclical work programme, to assess the possibility of the retention of trees on a development site, the preparation of a TPO or management agreement, quantifying the environmental services that the urban forest provides, informing habitat management, a response to an insurance claim or court case, health surveillance and so on.

At the outset remember my two oft-repeated mantra, which can be merged here as follows: define the brief, design the survey schema and deliver client ready product.   The reason for the survey, and the format of the product, will often mean that the attribute data to be collected and the method to be used will be self-selecting.   There is no benefit to be gained from collecting too much data, and there will be a cost associated with not gathering enough so agree the brief before you start, another adage here is the military’s 6 Ps, “Proper Planning and Preparation Prevents Poor Performance”

So, what makes for a good tree survey?   In short, a shared and common appreciation of the assets that have been assessed, for whatever reason, as well as a clear understanding of the thinking behind the surveyor’s conclusions and recommendations.

The survey will generally be presented to the client in two parts, the drawing and the schedule.   The drawing will clearly show where the trees are in relation to each other or to targets on or adjacent to the site, and depending on the brief, may also indicate the trees’ size and shape, their maturity or their quality.

The schedule will list all the attribute data that was captured for each tree, and the particular attributes will be associated with a specific tree, or group of trees, represented on the drawing.

In order to simplify the common appreciation of the drawing it is very important that, depending upon the reason for the survey, a standardised system is used and that surveys are carried out to a consistent level of detail and accuracy.   A common palette of symbols will simplify the interpretation of the drawing, in the same way as the Ordnance Survey has become the standard to follow for all other UK map makers.   Using common notation will allow the results of one survey to be compared with those of another and for different drawings and schedules to be readily interpreted, not only by the surveyor but by the client and the other consumers of the survey.

For trees on development sites BS 5837 has proposed a standard for survey drawings, the categorisation of tree condition, the use of a colour to represent tree condition, the concepts of the RPA and CEZ and so on.   In an ideal world it would be relatively simple to compare the outputs from different surveys because the notation and language used will be the same.

[But of course the world is not always ideal and within BS 5837 there is so much scope for interpretation, the categorisations are at best subjective and so one man’s B can be another man’s U depending upon their perspective.   But in truth who can say with absolute confidence how a particular tree in a given situation will perform over the next 10 to 40 years?] – this part could easily be sacrificed…

 

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