Defoliation - key parameter or cue ball of variegated influences? | Defoliation - Schlüsselparameter oder Spielball verschiedener Einflüsse?
2007
Seidling, Walter
Defoliation, which is a visually assessed estimation for the leaf or needle loss of trees in comparison to a full-leaved reference, is annually surveyed across large parts of Europe. Both, its unclearness for any environmental agent and its impractical measuribility call for a certain amount of statistical modelling, are surveyed. Such models may narrow the defoliation ratings down to more specific estimations proposed as 'preliminarily adjusted defoliation' and they help to specify the behaviour of forest trees in terms of closer cause-effect relationships. - The quantification of the sytematic deviation on crown condition between different countries or sub-national entities at the hand of cross-calibration courses is put within an evaluation-related context. Respective results from such courses and from other quality control measures as photo image analysis, airborne laser scanning, or cross-calibrations with litterfall measurements should become a part of integrated evaluations in order to ascertain such methodologically caused differences. - With the increasing length of the time series of defoliation estimations the possibilities for time-related evaluations are constantly enlarged. Such approaches gain additional importance due to highly probable impending climatic changes. Defoliation has already been shown to respond towards regionally and temporally differentiated climatic drought. For respective future approaches the continuation of annual tree crown assessments is inevitably necessary, since weather conditions vary on an annual basis.
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