Variations in the hierarchical architecture of Nothofagus obliqua: evidence from juvenile naturally-regenerated trees and from seedlings obtained by controlled crosses of selected individuals

Abstract

Background: Many tree species with potential for wood production present high intra-specific variations in the extentof trunk differentiation (i.e. hierarchical architecture). The identification of multiple-scale traits related to hierarchicalarchitecture could improve selection criteria for domestication.Methods: We investigated the hierarchical architecture of Nothofagus obliqua, a valuable species for timber production, butwith high structural variability. Young trees in even-aged natural regeneration gaps, and seedlings derived from controlledcrosses and open pollination were studied. For the second approach, trees with contrasting degree of hierarchicalarchitecture were manually crossed. In both, juvenile plants and seedlings, we analyzed trunk growth unit traits andhierarchical architecture indices based on the relative size and branching angle of main branches.Results: In regeneration gaps, hierarchical architecture was positively related to height and diameter. Apex persistence,the number of sylleptic branches and mean internode length were indicative of larger and more hierarchical trees. Somesupport is provided to the idea that adult trees with a notably hierarchical architecture could produce young trees withearly signs of a hierarchical architecture. In seedlings, hierarchical architecture was negatively related to basal diameter.Conclusions: Some growth unit traits that differed among progenies and were related to hierarchical architecture could beconsidered for the development of selection criteria for young trees.