Hydrostatic constraints on morphological exploitation of light in tall Sequoia sempervirens trees.

We studied changes in morphological and physiological characteristics of leaves and shoots along a height gradient in Sequoia sempervirens, the tallest tree species on Earth, to investigate whether morphological and physiological acclimation to the vertical light gradient was constrained by hydrostatic limitation in the upper crown. Bulk leaf water potential (Psi) decreased linearly and light availability increased exponentially with increasing height in the crown. During the wet season, Psi was lower in the outer than inner crown.

Physiological and ecological implications of adaptive reiteration as a mechanism for crown maintenance and longevity.

Reiteration is the process whereby architectural units are replicated within a tree. Both immediate (from apical buds) and delayed (from suppressed or adventitious buds) reiteration can be seen in many tree species where architectural units ranging from clusters of shoots to entire branches and stems are replicated. In large old trees and suppressed trees, delayed reiteration occurs without an obvious external stimulus such as defoliation or traumatic loss of the branch apex.