Species interactions on the biome transition zone in New Mexico: Response of blue grama (Bouteloua gracilis) and black grama (Bouteloua eripoda) to fire and herbivory

The desert/grassland biome transition zone in central New Mexico provides an important region for testing species differences to changing environmental conditions and various land management practices. Interactions of black grama (Bouteloua eripoda) and blue grama (Bouteloua gracilis) significantly affect the resultant plant community and its influence on system structure and function. Black grama demonstrated higher productivity, especially after wet years, and this species has increased its dominance during the 20-year period since livestock grazing was removed. While black grama can alter the previous pattern of overgrazing and desertification in this transition zone, our experiments demonstrated that it was more strongly inhibited by treatments of fire, simulated grazing and native herbivore activity than blue grama. Thus, new environmental conditions of wet or drought, changed fire regimes caused by increased grass fuel and altered patterns of herbivore activity have the potential to reverse the current trends. Many interacting factors must be considered in predicting future community conditions or developing management practices that avoid grassland degradation in this semi-arid region. (C) 1996 Academic Press Limited