Do leaves control episodic shoot growth in woody plants?

It has been generally observed that leaf removal alters the pattern of epis odic shoot growth in certain species in such ways that suggest some type of folliar control. in the present study, the effects of periodic defoliation during the growing season on the shoot growth of 11 woody species were ana lyzed In an attempt to elucidate the control mechanisms of episodic shoot g rowth, Four types of responses to defoliation were observed: A) A second fl ush in red oak, shagbark hickory, and year-old seedlings of green ash and s ugar maple; B) A small continued extension of stem elongation with the prod uction of some additional leaves and a significant delay in terminal bud fo rmation in white ash, green ash, pignut hickory, black walnut, and in year- old seedlings of green ash and sugar maple; C) No response in sweetgum and white pine; and D) Shoot die-back in sugar maple, silver-red maple, cottonw ood, black walnut, and to a lesser extent, the ashes. Defoliation was most effective and sometimes only effective in causing the above-mentioned respo nses when given early in the flush period. Leaf control of episodic shoot g rowth may be due to foliar inhibitors and/or effects of competition for wat er and nutrients.