Jean-Martin Lussier wrote: >I would like to have some precisions about your method. What was used as >detector targets? (nails, tags...) Were would you place these targets: on >or in the stump or elsewhere? You idea of coupling GPS and metal detector >is very appealing to me! Root buttressing is quite prominent in Irish Sitka spruce and the flatish spaces between buttresses, low on the stem, seem the best location for markers. The buttresses also provide a natural frame for the target when checking for its presence. These were 2.5 cm long nails with a flat, large (1.25cm) diameter head. I found the larger head diameter important for easy detection. As the project was quite short-term (3 years) the nails were uncoated to allow corrosion but I believe galvanised nails would work just as well. I "nailed" every second or third tree once on 3 sides of the plot perimeter, about about 3cm above soil level; well beneath the expected path of the chainsaw. I selected the metal detector on the basis of the size of its head (small enough to fit between the root buttresses of young spruce), its weight, sensitivity and, of course, price. It was difficult to get a combination of small head/high sensitivity. I chose a cheap ($170), 10cm diameter head, hand held model used for the hand inspection of lumber and in security functions. The maker attached a longer arm to avoid having the operator stoop. The detector performed quite well but sometimes gave false readings when set to high sensitivity. In areas where I had poor information on plot location I had to do a LOT of walking as each tree had to be checked individually. A GPS pointer to the rough location of the plot would have saved a lot of time. I did not test the performance of expensive/highly sensitive detectors through a slash layer or with different metal targets so I'm not clear as to their capabilities. I believe however, that no matter how sensitive the equipment one will still have to move to each tree or ground location to check it individually and so a highly sensitive detector should not be necessary. By the way, some manufacturers offer models which specifically ignore nails so watch out when you buy! Detector sales web sites are short on selection info. but here are two anyway: http://www.detection.com/ http://www.treasurenet.com/invite.html Regards, Myles Mac Donncadha
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