CLIMATE-CHANGE EFFECTS ON GRASSLANDS IN URUGUAY

The most significant climax vegetation in Uruguay is a type of grassla nd commonly known as evergreen prairie. The evolution of the Uruguayan prairie since the days of the first European settlements involved 3 m ain stages: (1) 'hardening' as a result of the introduction of livesto ck, (2) 'refinement' by the action of fire and overgrazing, and (3) fu rther degradation, including preferential development of warm-season s pecies, due to persistent overgrazing. Predicted climate changes (seas onal decrease in water availability coupled with increase in both temp erature and atmospheric CO2 concentration) are likely to favor, in the short term, even further preferential development of warm-season spec ies. Whether or not this trend will persist in the long term is diffic ult to predict with confidence because of uncertainties regarding the responses of the different prairie species to variation in atmospheric CO2 concentration.