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 provi des an important region for testing species differences to changing en vironmental conditions and various land management practices. Interact ions of black grama (Bouteloua eripoda) and blue grama (Bouteloua grac ilis) significantly affect the resultant plant community and its influ ence on system structure and function. Black grama demonstrated higher productivity, especially after wet years, and this species has increa sed its dominance during the 20-year period since livestock grazing wa s removed. While black grama can alter the previous pattern of overgra zing and desertification in this transition zone, our experiments demo nstrated that it was more strongly inhibited by treatments of fire, si mulated grazing and native herbivore activity than blue grama. Thus, n ew environmental conditions of wet or drought, changed fire regimes ca used by increased grass fuel and altered patterns of herbivore activit y have the potential to reverse the current trends. Many interacting f actors must be considered in predicting future community conditions or developing management practices that avoid grassland degradation in t his semi-arid region. (C) 1996 Academic Press Limited