Crown development of a clone of Populus tremuloides exhibiting "crooked" architecture and a comparison with wild-type trees

Abstract

Populus tremuloides Michx. (trembling aspen) is a tree species native to much of North America and is normally ascribed to the architectural model of Rauh, characterized by an excurrent crown structure with a central main stem and orthotropic branches. A mutant clone of trembling aspen is located near Hafford, Saskatchewan, exhibiting an architecture with crooked and twisted tree trunks. It was the objective of the present study to determine how the architectural development of the crooked clone differed from the wild type. In a study conducted over a 5-year period, four mutant trees were compared with four young wild-type aspen in the Winnipeg, Manitoba, area. Based on detailed quantitative data, it was determined that the architecture of the crooked clone of aspen differs greatly from the wild type. The trees are built by the continuous superposition of vigorous relay shoots with a mixed orientation, that is, shoots that take over the main growth of the tree, and have a more or less upright basal part and a horizontal to pendulous distal part. The development of the crookedness starts with the bending of the relay shoots, mostly in relation to the gravitational direction, which is followed in the subsequent years by various gravimorphic responses. In particular, the longest lateral shoots on a parent relay shoot occur in the middle regions, and the tip of the parent relay shoot generally loses vigour over time. The parent shoot may die back to the junction with a daughter relay shoot, causing a sharp bend at that point. Moreover, the divergence angles of relay shoots with the parent shoots were shown to be greater than in wild-type aspen, and this appears to exacerbate the crookedness. The new relay shoot may actually grow back towards the centre of the crown, opposite to the direction of growth of the parent. The results of this study demonstrate how a quantitative change in one architectural character can set in motion a series of developmental processes that result in a vastly different crown structure from the wild type.Résumé : Le Populus tremuloides Michx. (peuplier faux-tremble) est une essence indigène qu'on retrouve dans une bonne partie de l'Amérique du nord et qui se conforme normalement au modèle architecturale de Rauh, caractérisé par une structure de la couronne ouverte, avec une tige centrale principale et des branches orthotropes. Près de Hafford, en Saskatchewan, on trouve un clone mutant de peuplier faux-tremble dont l'architecture montre des courbures et des torsions des troncs. Les auteurs ont cherché à déterminer comment le développement architectural, chez ce clone tordu, diffère de celui du type sauvage. Une étude ayant durée 5 ans a permis de comparer quatre arbres mutants avec quatre jeunes peupliers faux-tremble de type sauvage, dans la région de Winnipeg au Manitoba. Les données quantitatives montrent que l'architecture du clone tordu du peuplier faux-tremble diffère grandement de celle du type sauvage. Les arbres se développent par superposition continue de tiges à relais vigoureuses...

A system of nonlinear simultaneous equations for crown length and crown radius for the forest dynamics model SORTIE-ND

“…ex S. Watson) and aspen (Populus tremuloides Michx.) have relatively weaker epinastic control, the correlation between terminal growth and lateral shoot growth remains high under most conditions (Remphrey and Pearn 2003;Lindgren et al 2007). A feedback effect ensues as changes in crown radius lead to changes in light capture, resulting in either an increase in CL through height growth or a decrease in CL due to an increased rate of crown recession relative to height growth.…”

Quantifying branch, crown and bole development in Populus tremuloides Michx. from north-eastern British Columbia

“…Even though Populus have been studied for over five decades in North America resulting in significant tree and stand knowledge (for reviews see DeByle and Winokur, 1985;Peterson and Peterson, 1992;Stettler et al, 1996) little published information detailing aspen crown, branch and bole growth characteristics exists. Research on crown and branch growth of aspen and other native broadleaf tree species has been limited to predicting broadleaf crown architecture and branch characteristics (Maini, 1966;Ceulemans et al, 1990;Remphrey and Pearn, 2002), the development and distribution of leaves (Pollard, 1970;Le Goff and Ottorini, 1996), and an understanding of the translocation of photosynthate (Ceulemans and Isebrands, 1996;Wilson, 1998). Pollard (1970Pollard ( , 1972 studied aspen annual shoot and leaf area development in 6-52-year-old stands and related biomass production to leaf area index (LAI), and crown and canopy formation to shoot growth.…”