Detecting changes in tree health and productivity of silver fir in Slovenia.

Cambial electrical resistance (CER) was used as an objective measure of vitality of silver fir (Abies alba) in the forests of Slovenia. Trees were rated during the growing season by CER and a subjective crown status index (CSI). Both CER and CSI were inversely correlated to annual ring width increment. Using both CER and CSI, fir were assigned to vitality and vigour categories. Inferences made from these categories and radial growth trends indicated that ring growth decreased prior to the development of canopy symptoms. This decrease in ring growth would have been detected as an increase in CER. This pattern of decline is consistent with the decline of trees due to chronic below-ground stress. Variation in CER was due both to the vascular cambium and to the thickness of the nonconducting phloem. [ABSTRACT FROM AUTHOR]