Vegetative Architecture ofElaeocarpus hookerianus.Periodic Growth Patterns in Divaricating Juveniles

Abstract

Elaeocarpus hookerianus Raoul, a canopy tree native to New Zealand, has a divaricating juvenile stage. The juvenile produces short shoots on both vertical and horizontal axes in the spring ; long shoots are formed and expand most in summer months. Axes have regions of long internodes interspersed with regions of short internodes. Long internodes are associated with production of sinuate, linear-lanceolate leaves, the outgrowth of many lateral branches, and a wide angle of divergence between terminal and lateral axes. Regions with short internodes bear smaller, obovate leaves, and lateral outgrowth is suppressed. Periodicity in internode length is synchronous for first-and second-order horizontal axes at comparable distances along a branch. Vertical axes elongate more extensively, bear more linear lanceolate leaves, and branch more prolifically than horizontal axes. Topological growth, as determined by monthly estimates of mean order and of partition asymmetry, is similar for vertical and horizontal axes ; both become more symmetrical towards the end of the season. Most leaves fall, and growth halts over winter months. The characteristic habit of juvenile E. hookerianus results from weak apical control of lateral shoot outgrowth, and periodic growth that provides for efficiency in light capture and expenditure for structural support. Vertical axes are considered to ' explore ' the environment peripheral to the plant's canopy, whereas horizontal axes ' exploit ' the canopy volume already captured.

Development of a Mathematical Method for Classifying and Comparing Tree Architecture Using Parameters from a Topological Model of a Trifurcating Botanical Tree

“…Observed differences in the architecture of plants of different ontogenetic state are consistent with results reported in the literature (e.g. Dawson, 1968;Borchert 1976;Borchert & Tomlinson, 1984;Day & Gould, 1997). Moreover, our observation of sigmoidal growth patterns is in full agreement with reported empirical knowledge of biological growth (Richards, 1959;Hunt 1982;Zeide, 1993).…”

“…2 and 3). The concept was previously applied to bifurcating botanical trees by Day & Gould (1997), and used by Van Pelt (1997) for simulations of pruning, and by Cannon et al (1999) for the structural comparison of dendrites.…”

“…Borchert & Tomlinson, 1984). Thornley & Johnson (1990) again stressed the need for methods to model tree architecture, and Atkinson (1992), Kelly (1994) and Day & Gould (1997) subsequently published their work on possible methods for the quantification of the architecture of trees exhibiting divaricating branching, in some of which the transition between the juvenile and adult ontogenetic states is marked by an abrupt change in branching pattern.…”

“…In addition, to avoid or reduce the difficulty of quantifying the structural complexity component of plant architecture, plant canopies have been experimentally simplified, e.g. by pruning plants to a single stem (Snowball, 1989), or by examining the architecture of only selected branches (Day & Gould, 1997;BuckSorlin & Bell, 2000). Similarly, to study the dynamics of plant growth through topological increases in size or other attributes, only a few selected shoots have sometimes been examined (Karlsson & Heins, 1994).…”

“…With respect to the experimental capturing of tree architecture, topological recording has typically been effected by drawing topological maps (Van Pelt et al, 1989), a method also used by Day & Gould (1997) for plants. Amongst attempts to develop alternative recording methods, promising progress has been made using electromagnetic field, scanning or infrared devices to map tree-like structures (Smith et al, 1992;Sinoquet & Rivet, 1997;Cannon et al, 1999).…”