We examined selected urban tree species by measuring cambial electrical resistance of living tree tissues (CER) with an instrument, called Tree tester. The measurements were taken once a month during the growing season 2005, from May till the end of September. As well, trees were visually estimated and classified into groups. First group considered healthy trees (socalled referential trees), second group included trees with affected crown caused by inappropriate tree care (topping) and third group involved trees contaminated with de-icing salts. Trees were classified by trunk diameter in breast height into thickness classes. The research was performed in the most common tree species (Acer platanoides L., Acer pseudoplatanus L., Acer saccharinum L., Aesculus hippocastanum L., Aesculus x carnea Hayne., Fraxinus excelsior L., Platanus x hispanica Mill. ex Muenchh., Populus nigra L., Salix x sepulcralis Simk., Tilia sp.) growing in the city of Ljubljana. To interpretthe values of electrical resistance of living tissues on urban trees is difficult task, because of numerous factors operating mutually such as: tree species, age of trees, growing conditions, time of season, tree vitality,thickness of living tissues, mechanical injuries caused by inappropriate tree care (topping), pollution and climate parameters. To properly interpret CER values, profound knowledge of tree biology is necessary. The effect of topping on reduced vitality was confirmed on the other hand, effect of de-icing salt on reduced vitality was not detected with CER method. We can use method of CER as complementary method to other diagnostic methods for assessment of tree vitality of urban trees.
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