TRIGGERING AND PREDISPOSING FACTORS IN THE RED DECLINE SYNDROME OF NORWAY SPRUCE (PICEA-ABIES)

Analysis of 62 mature Norway spruce (Picea abies provenance ''Viborg'' ) trees growing in a Danish plantation was undertaken along with analy sis of their nutrient contents (N, P, K, Ca, Mg, Fe, Mn, Cu, Zn, B and Na), in each of the three youngest needle age classes, from branches of four exposure directions near the tree top. The aim was to investig ate if one among the studied possible predisposing factors was also a triggering factor in the 1989 outbreak of the ''Red'' Norway spruce de cline in Denmark. Neither nutrient imbalance or deficiency, nor excess ive N-deposition or salt-stress were indicated as triggering factors i n 1989. The ''Red'' syndrome, noticeable for the bright red colour of the current-year needles, was found to be an extension of the European type ''Novel Decline''. ''Red'' syndrome is similar to previously rep orted phenomena of ''top-dying'' and ''sub top-dying'', in that it had fewer needle age classes and significantly higher contents of mobile cations (and Ca) in the younger needle classes. Tree ring analysis sug gested that the ''Red'' syndrome was initiated in the early 1980s, whe n the trees experienced adverse climatic conditions. Because of this l ong-term development of the ''Red'' Norway spruce decline syndrome, it is concluded that a triggering factor is of minor importance relative to the multitude of predisposing factors.