Effects of fire and grazing on the functional types of Poaceae C3 and C4 in a Central Argentinean mountain prairie

Abstract

The effects of fire and grazing on the functional types of Poaceae C₃ and C₄ in Central Argentinean mountain prairies were evaluated. The study site was located between the south latitudes 32º 42' and 32º 51' and the longitudes 64º 56' and 64º 48', at an altitude of 1400 m above sea level. Two communities were studied, Festuca hieronymi (tall prairie) and Stipa juncoides-Sorghastrum pellitum (short prairie) with the following four treatments: 1) without fire, with grazing 2) without fire or grazing, 3) with fire and grazing and 4) with fire, without grazing. Fire increased the variety of C₄ species and the combination of fire and grazing had a greater effect on the Poaceae C₃ species in the tall prairie, while in the short prairie the absence of grazing increased the variety of Poaceae C₄ species. Fire, alone, did not improve the amount of grass in the C₄ component of the community in the tall prairie, but the selective grazing of the Poaceae C₃ narrowed the C3/C4 relationship. A period of time without grazing in the short prairie permitted the reestablishment of the cover and diversity of the Poaceae C₄ and the recovery of its productivity. These field experiments demonstrate that the combined use of fire and grazing must be used with caution, considering its different effects on each prairie community. The system of light continuous grazing can not be applied to two different communities in the same manner. In tall prairie, grazing following a fire modified the attributes of the prairie, whereas this did not occur in the short prairie.