Plagiotropic architectural development of four tree species of the temperate forest

Four tree species of the temperate deciduous forests of south-western Quebe c have an architectural development that corresponds to Troll's model. Two of these species, American elm (Ulmus americana L.) and American basswood ( Tilia americana L.), are mid-successional and the two others, American beec h (Fagus grandifolia Ehrh.) and Eastern hemlock (Tsuga canadensis (L.) Carr .), are late successional. In the four species, the main stem is the result of the stacking of modules with plagiotropic development and secondary str aightening. Nevertheless, the architectural analysis of these four species reveals that two growth patterns are present. In elm and basswood, the modu les are differentiated from one another and are integrated into the hierarc hical structure of the tree. In beech and hemlock, the modules are mixed an d their apical meristems possess an autodifferentiation potential, which pr ovides for a greater individuality within the tree structure. In spite of b elonging to the same architectural model, differences in the development pa ttern favour a greater efficiency in stem growth for elm and basswood versu s a greater shape plasticity, including a greater lateral branch developmen t if required, in beech and hemlock.