Using Slides to Test for Changes in Crown Defoliation Assessment Methods. Part I: Visual Assessment of Slides

摘要: In this study we used photographs of tree crowns to test whether the assessment methods for defoliation in Switzerland have changed over time. We randomly selected 24 series slides Norway spruce with field assessments made between 1986 and 1995. The were arranged assessed by three experts without prior knowledge year when slide was taken or number. Defoliation using Swiss reference photo guide. Although correlations high (Spearman's rank correlation coefficient ranged 0.79 0.83), found significant differences (4.3 9% underprediction assessors) assessments. However, no trends could be detected. When mean subtracted, some years, assessors consistently underpredicted (1990, 1992) overpredicted (1987, 1991). tended against light, underpredictedfor trees more than 25% crown overlap. conclude that can detect changes methods.However, potential observer bias calls objectivemethods assessment.