STRESS AND DISTURBANCE - VEGETATION DYNAMICS IN THE DRY CHACO REGION OF ARGENTINA

This paper analyses two processes acting on vegetation dynamics in the dry Chaco region of Argentina. The major one is the response of herbaceous/woody species to overgrazing. The second process is the dynamics of gallery forest resulting from intensive river-bed migrations which characterize the region. A main process model relates the largest and most frequent floods to the complex structure, high diversity and Amazonian lineage of the floristic composition of the forests. A model is presented which, by analysing river bank community dynamics in terms of the geomorphological instability (constant river-bed migration, river-bed filling, bank formation and disintegration), shows how the structure and composition of these forests would be determined by past floods rather than by the present one. -from Authors