Cessation of annual apical growth and partial death of cambium in stem of Abies sachalinensis under intensive shading.

This study evaluated variation in the height at which absent rings and internodes were detected along stem of Abies sachalinensis trees grown under shade for 39 years. Eight sample trees planted in 1974 under a secondary forest in Japan were felled in 2013 and analyzed. A. sachalinensis is a monopodial species in which it is possible to measure annual apical growth using the distinct internodes. We applied microscopic analysis on 154 stem disks from the stem base to the top to evaluate the cessation of apical and radial growth caused by intensive shading. Cessation of apical stem growth for one or more years was found in 6 out of 8 sample trees. We termed this phenomenon as "absent internode". In addition, the absent growth rings were detected more frequently in the lower part of sample stems, and the number of absent rings at the stem base did not correspond with the number of absent internodes in the six trees. From cellular level observation, the five suppressed trees had no living cambial cells at the stem base but had living cells at the stem top. The cessation of the apical and radial growth did not occur synchronously but did occur independently under a shade environment in A. sachalinensis.