Development and growth of the aerial part of Pinus banksiana Lamb. from natural and planted stands

In Quebec, jack pine (Pinus banksiana Lamb.) is an important commercial species, used principally for timber wood and pulp. The natural ecology of jack pine is related to fire, which allow opening of the cones and dispersal of seeds (Burns and Honkala 1990). The exploitation of jack pine stands disturbs this cycle and the regeneration remains low after harvesting and plantation must be done to ensure the renewal of this resource. In province of Quebec, more then 21 million jack pine seedlings were planted in 2001, representing 18% of all planted seedlings. It has been shown that the current methods of seedling production and planting cause significant deformations of root systems of jack pine, such as poor distribution of roots, no taproots, shallow rooting, affecting more than 90% of planted jack pine (Sheedy 1997 ; Plourde, data not published). Some authors also reported that more then 30% of the stems of planted jack pines are sinuous (Sheedy, 1996 ; Krause et al. 2002) and this proportion is higher in plantations compared to natural stands. Knowledge regarding the reasons for these deformations and their impact on wood quality is limited (Zhang et al. 1998), and comparisons of the development between natural and planted stands of jack pine remains low. The dendrochronological method, as described by Schweingruber (1988), are often used to compare wood production between sites. Tree-ring analysis gives information about the potential growth of one species and makes it possible to compare tree growth between stands, but this method only described radial growth and productivity. In this study, an integrated approach was used, examining architectural development, which define the nature (topological description) and relative arrangement (geometrical description) between the different structures that make up the plant (Barthelemy 1988 ; Sabatier and Barthelemy 1999). The aim of using the architectural method is that it represents the expression of a balance between growth processes (endogenous factors) and stress due to the surroundings (exogenous factors) (Hallé & Oldeman 1970). It is also possible to compare many structures that define the development of individual plant, and to study the impact of the local environment on those structures, which may also include radial growth and compression wood. The objective of this study was to compare architectural development of jack pine regarding its origin (natural or planted) and stem form (straight or sinuous).