Sources of errors in assessing ozone visible symptoms on native vegetation.

ABSTRACT

This paper aims to identify the problems regarding the evaluation of ozone (and ozone-like) symptoms, by examining the results of the 4th UN/ECE ICP-Forests Intercalibration Course for the assessment of ozone-induced visible symptoms. Trees, shrubs and herbaceous species were evaluated in a tree nursery, at Lattecaldo (Switzerland) and under open field conditions at Moggio (Italy). The main findings were (i) the most expert surveyors tended to be grouped in the same cluster and, during the field exercises, they tended to assess in a more conservative manner compared to the less trained participants; (ii) the agreement was greater in assessing the absence rather than the presence of symptoms; (iii) typical interveinal stippling on the upper leaf surface was more accurately evaluated than discoloration; (iv) uncertainties resulted mainly for species which showed greater variability in their symptom manifestation, and for certain herbaceous species.