Non Destructive Detection of Decay in Living Trees

In English It is shown that four point resistivity measurements can be used to detect
decay in living trees. A low frequency alternating current is injected into
the trunk and the induced voltage is measured between two points along the
trunk. With additional measurement of the cross section area, the effective
resistivity of the trunk is estimated. A comparison within a group of trees
shows that trees in decay have approximately a factor of two lower effective
resistivity than sound trees. The method is tested on several different groups
of spruce (Picea abies); in total more than 300 trees are examined. The tests
show that the method can detect decay caused by Heterobasidion annosum
with high accuracy. Finite element modeling and simulations are used to
validate the method.