| Added on 29/12/2011 | Tool |
Measuring Tree Crown Spreads with a Laser. (2003)
Recently I acquired an old 'Disto Classic' Laser Measuring device. The Disto had been dropped and sustained a broken casing which holds the battery cover secure. With the aid of a metal strip and a few carefully positioned bolts I managed to repair the device; it no longer looks 'pretty' but works fine and bearing in mind its cost of around £300, 'looks just don't matter'!
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Picture: Disto Classic (latest model and original on right).
So, I thought I would try the device out in the field for measuring tree crown spreads. Traditionally, I would use either a road measuring wheel or a tape. Pacing is considered a poor substitute.
Accurate canopy spreads are very important to planners who need to plan a site layout where trees are to be retained. Its important to ensure that branch spread (both current & future) will not be a cause of nuisance to proposed dwellings and roads etc. For this reason, the measurement of crown spreads in the direction of north, south, east and west is a normal requirement of a pre-planning tree survey (such as those carried out to BS5837). You may be lucky enough to have accurate canopy spreads already plotted on a site plan by the land surveyors. If this is the case, I would recommend a random check to ensure that they are accurate. Trees will rarely have equal distances along all sides, so if a site plan shows perfect circles to denote canopy spread on every tree, you need to start again from scratch.
I have now tried the Laser on three sites and found it to be excellent for measuring crown spreads. It fits neatly in a jacket pocket and switches itself off automatically after a few seconds. To use, you simply position yourself under the trees canopy edge on one of the north, south, east or west axis, point the device at the tree trunk, switch it on, ensure the red laser dot is located on the stem and press a button. The readout gives an instant distance in meters. You can increase it slightly to allow for the trunk radius.
I can also stand under a tree canopy close to the stem and fire the laser vertically onto an underside of a limb high up in the canopy. It now gives a height reading of that branch (just remember to add on the height of the device from ground level).
However, the light conditions during these surveys were poor, with an overcast sky. I expect the viewing of the dot will be difficult in bright sunlight ( I will update this page later in the year once this is experienced).
Feb 2004
I have now used the laser in sunlight and as expected, it causes problems in seeing the red dot from a distance. On the first occasion I could overcome the problem by aiming the laser at the grass infront of my feet and following the red dot with my eye as I moved it quickly towards the tree and onto the stem. On the second occasion, in very bright light, I lost track of the dot as I moved it, so simply aimed the laser in the direction of the stem and clicked the button. The reading was close to what I expected so accepted it. Had the dot not been on the stem, the reading would have been ridiculous (as it would of hit a target tens of meters away).
Conclusion
This is a device which will always be in my pocket when carrying out surveys or individual inspections. Its very handy for taking accurate measurements and although it is hard to see its red dot when sunlight is shining on the same surface, the advantages outweigh this drawback.
The measurements are precise, needing to be rounded up to the nearest half or whole meter. It will undoubtedly save time and prevent activities such as wading through a clump of 'Stinging Nettles' to measure a crown spread. And I am sure it will have many other uses such as accurate measurement of a tree to adjacent buildings or roads and the checking of correct tree positions on a given site plan.
The price tag of £280-300 is a lot to fork out but the 'Disto-Lite' (which is cheaper) would probably be suitable (it has a lower range). Or try different manufacturers.