© 2006 Heron Publishing—Victoria, Canada
Patterns of shoot mortality in Betula platyphylla in northern Japan
Kiyoshi Umeki (1, 2), Tatsuyuki Seino (3), Eun-Mi Lim (1) and Tsuyoshi Honjo (4)
1. Graduate School of Science and Technology, Chiba University, Matsudo 648, Matsudo, Chiba 271-8510, Japan / 2. Corresponding author (umeki@faculty.chiba-u.jp) / 3. Center for Ecological Research, Kyoto University, 509-3, 2-Chome, Hirano, Otsu, Shiga 520-2113, Japan / 4. Faculty of Horticulture, Chiba University, Matsudo 648, Matsudo, Chiba 271-8510, Japan / Received May 19, 2005; accepted September 7, 2005; published online February 1, 2006
Summary
To understand the development of crown structure in Betula platyphylla Sukatch., mortality patterns of long shoots were analyzed quantitatively. We selected 25 saplings growing under various light
conditions and measured the relative photosynthetically active radiation (rPAR) at, and the three-dimensional position of,
first-order branches. A long shoot was assigned “no buds” (NB) status if it lacked buds at the end of the growing season,
including at the tips of short shoots. A long shoot was classified as dead if it was NB and all the offspring long shoots
issuing from it were NB. The probability that a leafy long shoot (a current-year long shoot with leaves or an older long shoot
with short shoots with leaves) would become NB by the end of the season was positively dependent on shoot age and branch age,
and negatively dependent on shoot length, centripetal shoot order, branch height and rPAR at the branch. Randomization tests
revealed that shoots became NB and dead in clusters of connected shoots. In particular, shoot clusters originating from 3-year-old
shoots were more likely to die than expected if each shoot was assumed to become NB regardless of the connection. Stepwise
logistic regression revealed that the maximum rPAR within the crown of an individual tree had a significant effect on the
mortality rate of 3-year-old shoot clusters, together with the rPAR at the level of the branch and other structural entities.
Correlative inhibition is an important mechanism for determining shoot mortality patterns.
Keywords:
bud formation, correlative inhibition, crown development, crown structure, light conditions, spatial pattern.
