Trunk and main-branch development in Nothofagus pumilio (Nothofagaceae): a retrospective analysis of tree growth based on the size and structure of its annual shoots.

PASSO, ALFREDO; JAVIER GUIDO PUNTIERI; BARTHÉLÉMY, DANIEL

CANADIAN JOURNAL OF BOTANY

Canadian Science Publishing

Año: 2002 vol. 80 p. 463 - 772

0008-4026

The development of the trunk and main branches of approximately 26-year-old Nothofagus pumilio(Poepp. et Endl.) Krasser trees was studied. The length and number of leaves of annual shoots were recorded for 56trees from a natural population. Morphological and macroanatomical features allowed the identification of shoot apexdeaths and the axillary positions from which branches and relay shoots derived. The trees had a mean height of approximately6 m and a mean basal diameter of approximately 8 cm. The length of trunk shoots increased from the firstyears to the intermediate years of tree growth and decreased for the last 6 years of tree growth. The maximum lengthand number of leaves of trunk shoots were registered for the years around 1985, when tree age was about 17 years.The likelihood of apex death for trunk shoots was minimum for the period of maximum trunk shoot size. Despite thefact that the architectural features of the sampled trees corresponded to those of young, vigorously growing trees, theyseemed to have reached a stage of low annual height growth. A sharp decrease in trunk shoot size occurred in 1992, ayear in which rainfall during the growing season reached the minimum for the lifetime of the sampled trees. The sizeof shoots developed after 1992 was, on average, lower than that of shoots developed before 1992. Stressful conditionsin this year may relate to meristem ageing and thus to the size of shoots formed in the following years. Main branchesstarted their development with shoots similar to those of the trunk but were clearly differentiated from the trunk5 years later. The differentiation between main branch and trunk shoots involved not only a lower shoot size but also ahigher number of leaves per shoot length unit in main branch than in trunk shoots.