Black spruce (Picea marianna) architecture

Genetically determined rules underlying black spruce (Picea mariana ( Mill. ) BSP) morphological development were revealed by using tree architecture a nalysis. Black spruce develops according to Rauh's model. Its relatively si mple andwell-hierarchized architecture comprises four categories of axes (A (1)-A(4)) and three distinct branching levels. First- and second-orderaxes (the trunk and branches) are monopodial, orthotropic structures with rhythm ic growth and branching, and an unlimited life-span (or only limited by tre e longevity). They are mainly devoted to spatial exploration and occupation . Axes A(3) and A(4) are monopodial, plagiotropic structures with a limited life-span, which are devoted to assimilation and reproduction. Female cone s develop in terminal position on A(3,) whereas male reproductive structure s develop in terminal or lateral position on A(4). Reiteration (or duplicat ion of axes) capacity is an important feature of the architecture of black spruce. Adaptive reiteration processes allow trees to renew their foliage a nd to reproduce vegetatively through layering. Traumatic reiteration proces ses tend to restore the tree's original architecture by replacing injured a xes or parts of axes. In both cases, replicas originate from dormant buds l ocated at the bottom of growth units (deferred or proleptic reiteration)or from growing axes (immediate or sylleptic reiteration).