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This paper reviews the different techniques used to investigate whether the trunk of a standing tree is hosting rot or not. The most widespread and efficient techniques may in general be classified under two wide classes depending on the signal used for investigating the tree trunk. The first category includes the vibro-acoustical techniques using either vibrations at frequencies within the acoustical bandwidth or sound waves at acoustical or ultrasonic frequencies. The second class of techniques uses various methods based on electromagnetic radiation. There are furthermore some other techniques which are more or less destructive, and which are also presented in the current work. These techniques are destructive, but to a lesser extend than the well known fully destructive ones inasmuch as only a small sample is extracted from the tree trunk to be submitted to test.

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