Potential and limitation of visual indices of tree condition

An unprecedented database concerning the apparent condition of forest trees has been created over the last decade. In particular, millions of data concern crown transparency slid discoloration have been collected. Unfortunately, the subjectivity and poor specificity of the international data complicate their comparability and interpretation. A suite of other indices with species-specific relevance were also been used in various surveys. However, the development of suitable indices is incomplete and there is an urgent need for the improvement or definitions, training, data collection and reporting. (C) 1998 Elsevier Science Ltd.