Default standards
The main standard concerns measurement (deadlines are agreed individually at the beginning of each task).
Measurement
Measurement standards specify the expected magnitude of error in the measurements I make in surveying trees and plotting them on a plan.
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Instrument
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Measurement
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Accuracy in good conditions
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Good conditions
|
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TruPulse 200 rangefinder and inclinometer
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Critical distances
Tree height
|
+0.1m
+0.5m
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Clear sight lines, well defined target
Top of tree is visible (may be obscured by wide crown, neighbouring trees or absence of distant vantage point)
|
|
Stiff tape measure
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Distances less than 8m
|
+0.1m
|
Accessible
|
|
Measuring tape
(30m)
|
Distance
|
+2.5%
|
Absence of rough or thickly vegetated ground
|
|
Pacing
|
Non-critical distances.
|
+5%
|
Absence of rough or thickly vegetated ground
|
|
Diameter tape or cord for girth
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Tree diameter
|
+5%
|
Absence of strong taper, ivy, epicormic shoots or local inequalities in bark
|
|
Compass
|
NSEW
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Indicative
|
Any
|
The table illustrates that accuracy depends on the context.
Accuracy is limited in other ways. For example, some points of measurement are subject to interpretation, such the position of the edge of the crown, the distance to a tree (to the tree’s nearside surface or to its centre-line?), the position of old boundaries etc.
Some features might be completely inaccessible because of obstructing vegetation or because they are off-site (without access having been granted). In such cases an estimation by eye is better than nothing.
A topographical survey or outline plan is helpful, and likely to be indispensible on sites which are large or have complicated shapes.
Where the expected standards are thought not to have been met, a measurement is qualified as ‘estimated’.
The pragmatic objective is to survey so accurately that measurements or positions do not become a source of confusion or contention in furthering the objective (whatever that may be).
