Past growth variations inPicea sitchensiswith differing crown densities

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Abstract
The annual increment of Sitka spruce (Picea sitchensis (Bong.) Carr) relative to. crown density was examined at four sites in southwest Britain. Clear differences exist between the relative growth rates of trees which now have thin crowns and the growth rates of trees with dense crowns. Prior to about 1957, trees which currently have thin crowns had higher annual radial increments than trees which currently have dense crowns. Since 1962, trees with thin crowns have tended to have lower radial increments, the extent of the increment depression depending on the degree of thinness of the crown. This pattern closely resembles that found in central Europe where forest decline attributable to air pollution is believed to be a major problem. The timing of the increment declines in both southwest England and central Europe strongly suggests that extreme climatic conditions, particularly winter cold and summer drought, have a marked effect on their development.

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