Relationship between architecture and successional status of trees in the temperate deciduous forest

The architectural analysis of trees, as developed since the pioneering work of Hallé & Oldeman in the 1960s and 1970s, allows the study of the developmental pattern characteristic to each species in a global and dynamic perspective of the tree. This leads to a fundamental question: is there a relationship between architectural characteristics of a species and its successional status? The analysis of nine tree species from the deciduous temperate forest of southwestern Québec reveals that such a relationship exists, mainly at the level of the alternation of organization plans (hierarchic and polyarchic) during the growth of the trunk and the reiteration within the crown. Early successional species (Betula populifolia and Populus tremuloides) have a hierarchic architecture throughout their ontogenesis. The hierarchy of the branched system promotes a rapid growth of the trunk. The potential for total reiteration in the crown is very limited. Conversely, late successional species (Acer saccharum, Fagus grandifolia and Tsuga canadensis) have an architecture with several levels of organization. The alternation of hierarchic and polyarchic phases of development confers a greater shape plasticity upon the tree, to the detriment of the speed of growth of the trunk. However, reiteration within the crown is common and abundant. This process increases the lateral spread of the crown, as well as it prolongs the life span of the tree itself. Mid-successional species (Ulmus americana, Fraxinus americana, Tilia americana and Carya cordiformis) have architectural development in between these two extremes. They combine a great hierarchy in the structure of the young tree with a potential for reiteration in the crown. Two growth strategies were identified among the late successional species, one facilitating growth in the shade and the other allowing the tree to benefit from increase in light in canopy gaps.