Abstract
Changes in vigour and demography of subalpine Picea abies (L.) Karst were assessed on a regional basis in the Swedish Scandes. The study was based on repeat photography from fixed points in 1972/73 and in 1985/86. Crown thinning was already in an advanced stage in 1972/73. Approximately 75 percent of the studied population had a crown thinning of more than 20 percent. This process progressed during the study period, when about 30 percent of the spruce experienced further thinning of 20 percent or more. The general character of vigour decline was unidirectional discoloration (reddish brown) of young supranival needles. It is suggested that the basic cause is summer (June-August) temperature decline since the early 1960s. It may be related also to increased frost hazard in late spring and early summer, due to earlier dehardening and growth initiation in response to a general warming in May and early June which has occurred since the early 1970s. RESUME Le diclin de l'espice subalpine Picea abies dans la chaine des Scandes, Sudde. Les changements de vitalit6 et de d6mographie affectant l'espece subalpine Picea abies (L.) Karst ont et6 6valus daneben mag erh6hte Frostgefahr im Spditfriihjahr und Frifihsommer eine Rolle spielen, da seit den friihen 70er Jahren ein allgemeiner Wiirmetrend im Mai und Juni beobachtet wurde, was zu verfriihtem Wachstum und Anpassung ffihrte.
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