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Abstract:
We investigated the effect of climate on variations in annual ring-area increment along the stem of dominant silver
fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) Karst.) trees in the Black Forest, southwestern Germany, to
test the hypothesis that growth allocation changes as a result of climate fluctuations. Stem discs were taken at three different
stem heights: 1.30, 11.50, and 16.70 m. For each site and stem height, average annual ring-area increment chronologies
were computed. In addition, we calculated ratios between ring-area increment of the upper stem discs and the disc at breast
height to compare growth variations along the stem. Pearson correlation coefficients revealed a highly similar growth pattern
at different stem heights, where the two upper discs were most similar. Bootstrapped correlation coefficients between the
ring-area increment chronologies, ratios, and monthly temperature, precipitation, and self-calibrated Palmer drought sensitivity
index data were calculated to analyze differences in climate response. High temperatures in early summer were found to
reduce growth of high-altitude fir in the upper stem parts, whereas high temperatures in summer limit growth of high-altitude
fir and spruce, especially at breast height. For low-altitude trees, high temperatures as well as low precipitation amounts
during summer were found to reduce growth at all stem heights, but more strongly at breast height. Growth at breast height
seems to be biased, as it over- or underestimates annual ring-area increments along the stem (and thereby volume increment), particularly during warm and dry climate conditions.
