Annual-shoot growth and branching patterns in Nothofagus dombeyi (Fagaceae)

International audienceDuring the growing seasons 1994-1995 and 1995-1996, weekly measures of length and number of internodes and morphological observations were made on annual shoots of 11- to 21-year-old Nothofagus dombeyi (Mirb.) Blume trees growing in northern Patagonia, Argentina. Growth period and shoot size at the end of the extension period were highly variable. Four main types of annual shoots could be identified according to the death or persistence of the apical meristem and the development or not of axillary branches during the growth season of main stem extension. For all shoots the maximum growth rate took place in late November and was followed by a slower growth rate or cessation of growth in early December to early January. For those shoots with a long growth period, a second growth peak took place in late January-February, and only those shoots with a growth rate higher than 35-40 mm/week developed axillary branches as they elongated. Results from bud dissections suggest that the early growth rate peak corresponded to the development of those structures preformed at the time of bud break. The death of the apical meristem of a shoot affected both the position and the relative size of axillary branching on that shoot.Key words: Nothofagus, annual shoot, growth dynamics, branching pattern