The effect of bud position on branch growth and bud abscission in Quercus petraea (Matt.) Liebl
1991
Harmer, R.
The time at which a bud began to expand was related to its position not only on an individual shoot but also within the crown. The distribution of buds and branches on the shoot was uneven; the shoot tip, where they were densely clustered, was termed the 'whorl; and the remainder of the shoot, where they were widely spaced, the 'interwhorl' stem. In spring, the terminal bud started expanding before the 'whorl' buds which preceded the 'interwhorl' stem buds; completion of the flush of growth, determined by the end of leaf expansion, occurred in the reverse order, 'interwhorl' > 'whorl' > terminal. Similarly bud expansion started at the top of the crown and progressed downwards, and the first shoots to complete their flush were at the bottom of the crown. Approximately 60% of the buds on each shoot began expanding in spring but only about half of these formed branches. Bud abscission began in May and by Sep. 45% of buds originally present had abscised. Most of the buds that did not abscise were the small buds at the base of the shoot that were not originally associated with a leaf. Approximately 42% of 'whorl' buds and 28% of 'interwhorl' stem buds formed branches. 'Whorl' branches were approx. 60% longer that 'interwhorl' stem branches; buds on the lower surface of the shoot produced longer branches than those on the upper surface. The implications of the results for the development of crown form and selection of superior oak are discussed.
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