Twentieth century variations in mean ring density of Norway spruce (Picea abies (L.) Karst.), including a pluridecennial decrease and a recent increase, were found in limited accordance to temperature
variations. In this study, historical variations in earlywood and latewood density were analysed to establish (i) whether they differ, (ii) whether they show contrasted response to temperature, and (iii) whether historical variations in latewood density remain in closer
accordance to temperature than in mean ring density. Earlywood and latewood historical chronologies were estimated after a statistical filtering out of the effects of developmental stage, growth rate, tree, and site variations. Moving-window correlations between summer temperature and, respectively,
earlywood and latewood density were computed over the 20th century. Their temporal stability was tested. Earlywood and latewood revealed synchronous variations: a slow decrease over 1900–1950, a steep decrease over 1950–1980, and an increase until 2000. However, latewood density
decreased twice as much on average (–36 kg⋅m–3) as earlywood density (–17 kg⋅m–3). Earlywood density revealed poor and highly variable correlation with summer temperature. Latewood density and summer temperature were strongly
correlated. Yet, this correlation was found to be unstable and particularly weak during the latewood density decrease. Latewood density and summer temperature trends further exhibited opposed variations over 1965–1980, highlighting a pattern of “divergence”, as primarily
detected at treelines.
AgroParisTech, ENGREF, UMR 1092 Laboratoire d’Etude des Ressources Foret Bois (LERFoB), 14 rue Girardet, 54000 Nancy, France. 2:
INRA, Centre de Nancy, UMR 1092 Laboratoire d’Etude des Ressources Foret Bois (LERFoB), 54280 Champenoux, France.
Publication date: February 6, 2012
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