The presence of grassland alternating with Araucarian forest in Southern Brazilian plateau, has surprised the scientists, as to be in force the current climate, of greater precipitation than in remote times, the tendency would be the development of forest vegetation. Disturbances, specially fire-grazing interaction and low temperacture in the region, are the greater responsible for the boundaries and expansion of broadleaf forest, and dominance of that vegetation type. The grassland and forest vegetation submitted for long period to recurrent fires have developed strategies to tolerate, avoid or respond to fire. The response of individual plants involve morphological and physiological changes, while at the community level such changes are observed in the dinamics of association among species. Under range conditions, the grasses are the most fire tolerant component in the community, due to the continuous growth of intercalar meristems and also to the new shoots which grow below soil surface or protected in old sheat leaf. Fire stimulates flowering in plants whose growth form is able to avoid greater loss of matter during the burning period. Fire also promotes the release of seeds due to changes in temperature or the release of substances from smoke. At the community level, fire effects on the plants ocurr in relation to the way of surviving and nature and localization of regeneration tissues. The plant behaviour in relation to burning may be classified as dependent (stimulus to reproduction), resistant (stimulus to new shoot), or plants that avoid fire (annual cycle). Therefore, fire has complex effects on the vegetation structure, resulting that tolerant and sensitive species have had different preference patches in the environment.
fire; natural pasture; forest; ecophysiology