Triggering and predisposing factors in the “Red” decline syndrome of Norway spruce (Picea abies)

Summary

Analysis of 62 mature Norway spruce (Picea abies provenance “Viborg”) trees growing in a Danish plantation was undertaken along with analysis 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 investigate if one among the studied possible predisposing factors was also a triggering factor in the 1989 outbreak of the “Red” Norway spruce decline in Denmark. Neither nutrient imbalance or deficiency, nor excessive N-deposition or salt-stress were indicated as triggering factors in 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 reported 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 suggested that the “Red” syndrome was initiated in the early 1980s, when the trees experienced adverse climatic conditions. Because of this long-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.