The microclimatic conditions under wich Nothofagus species regenerate in different biotops of South Chile (between 38° - 42°S)are reported. Also, some physiological characteristics of these species related with water balance, drought and frost resistance are mentioned and discussed. The seasonal changes of frost hardiness were related with the minimun air temperatures of the biotops. In N. dombeyi a higher frost hardiness of juvenile stages of development were related with an increase of cryoprotective substances as carbohydrates, amino acids and a cold induced polypeptide. These substances have in vitro demostrated a cryoprotective action over thylakoid membranes of this species. That suggests, that they could act together in vivo.