Appendix A. Glossary of terms referring to structure used in this paper.
Apical control – the ability of the terminal (topmost) bud of a tree to suppress vertical growth in all of the other buds throughout the tree. Thought to be due to hormones (auxins) produced by this bud that, if removed, will allow other upright shoots to form.
Appendage – any branch, limb, or reiterated trunk that arises from the main trunk, which includes all of its subordinate components.
Branch – the result of any of the (mostly) plagiotropic shoots that develop on a tree. In model-conforming conifers, this will include all of the foliated sections of a tree, excepting the main trunk and its terminal leader.
Buttress – a cone-shaped or triangular wedge of wood that develops beneath a reiterated trunk as a support structure. If the trunk arises from a limb, its buttress extends along the lower surface of the limb.
Canopy – the collective unit describing all of the photosynthetically active portions of an ecosystem. A forest ecosystem can be divided into three main components: the forest soil, the forest floor, and the forest canopy. A forest canopy can be further divided into other useful categories, such as the understory canopy, tree canopy, even a herbaceous canopy. Typically, however, the term is used in its narrow sense, referring to the tree canopy.
Crown – the collective term for the space occupied by all of the foliage in a tree. Thus the crown includes not only all of the foliage, but also the branches, limbs, and trunks occupying that space.
Epicormic branch – any branch that develops from dormant buds on the cambium. In model-conforming conifers, these would include all branches that are not produced by the main trunk’s shoot apical meristem. As such, the pith of an epicormic branch will not extend all the way to the pith of its trunk of origin. Since these are forming from the cambium, their orientation is often tangential to the main trunk, in contrast to the radial orientation of original branches.
Epicormic system – A cluster of epicormic branches originating from a common locus. Due to the thick bark of many trees, epicormic branches are often confined to old branch wounds. When conditions become favorable for epicormic branch growth, several branches will often form within a short period of time. Their common origin will often force these branches to form a fan-shaped array.
Foliar Unit (FU) – A naturally occurring unit consisting of repeating clusters of stems and leaves that can be counted to quantify leaves, bark, cambium, and wood on complex branches. FUs will vary in size from species to species and each crew member needs to be calibrated before and during field estimations.
Geotropic – from the Greek geo (earth) and tropic (oriented toward), often applied to the tendency of plant roots to grow in response to gravity. In tree branches, it refers to downward sloping branches.
Hierarchy – a classification to maintain the developmental order of elements within a tree crown.
Individuality – the character developed by a tree based on departures from the architectural model. Time, recovery from damage, and exposure to the elements all influence the structure of a tree. In older forests, increasing individuality ensures that no two trees look the same.
Leader – the topmost shoot of a tree. In many young conifers, there is one leader shoot, and all of the remaining shoots become branches.
Limb – a branch segment that supports a reiterated trunk. The presence of a reiterated trunk changes the physiological characteristics of the horizontal section connecting it to the main trunk (or other reiterated trunk), causing increased growth, buttressing, and deeper integration of the wood with the supporting trunk.
Massart’s Model – The model as defined by Hallé et al. (1978) in which there is one primary vertical shoot with whorls of horizontal branches (see Whorl-based below).
Model conforming – any plant that adheres to a simple, repeating pattern of growth. In trees, these have been defined by Hallé et al. (1978).
Original branch – any branch whose initial bud was produced by the terminal leader of a trunk and thus has a pith reaching the pith of the trunk.
Orthotropic – From the Greek ortho (upright or vertical) and tropic (oriented toward), often used to describe the tendency of plants to grow upwards.
Plagiotropic – From the Greek plagio (slanting, sideways) and tropic (oriented toward), often used to describe horizontal growth in plants, as most conifer branches.
Reiterated trunk – Any trunk within a tree other than the main trunk. As the term ‘reiterate’ means ‘to repeat,’ it is referring to the primary architectural model of tree growth. Hence, a reiterated trunk is a repeat of the tree growth form within a tree crown. In many conifers, reiterated trunks retain the appearance of young trees growing within the crown of a larger tree, although their branches are asymmetrically (mostly away from the main trunk) oriented and usually extend to their bases.
Trunk – In most conifers, a trunk is any orthotropic appendage. The main trunk is the primary stem that emerges from the ground, and reiterated trunks are those whose origin is a limb or other trunk in the crown.
Whorl-based – A growth form common in many coniferous genera in which the terminal shoot produces several buds at the tip, one of which retains the role of terminal shoot, and the remaining all become branches. Conifers exhibiting whorl-based growth include Abies, Araucaria, Picea, Pinus, and Pseudotsuga. Other conifers, like Sequoia and Thuja, produce branches more or less continuously from the terminal shoot.