Oak Decline in Southern Sweden

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Abstract
Quantitative measurements of crown damage and foliage distribution patterns on pedunculate oak (Quercus robur L.) were recorded at 157 observation sites in southern Sweden in 1988 and in 1993. The year - to - year variations in these measurements were determined by repeated observations at three experimental oak sites from 1994 to 1997. In general, the crown condition deteriorated over the 5 - yr period. In 1993, 55% and 21% of the observed trees displayed slight and moderate degrees of crown defoliation, respectively, compared with 37% and 9% of the trees in 1988. The frequency of damage symptoms increased significantly with tree age and the degree of wind exposure. Crown damage varied among the counties where observations were made. During the yearly observation period from 1994 to 1997, 20-30% of the trees changed damage symptom classes from one year to another. About 15% of the trees changed classes more than once and in both directions, while 54% of the trees remained in the same damage class for all 4 yrs.

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