Effect of fire and grazing on the distribution of aerial biomass and species diversity in montane grasslands of NW Argentina

ROXANA ARAGÓN; JULIETA CARRILLA; LUCIANA CRISTOBAL

La Paz, Bolivia

Simposio; Second Global Mountain Biodiversity Assessment Symposium on “Linking Mountain Diversity with Fire, Grazing and Erosion"; 2003

Global Mountain Biodiversity Assessment

Grazing and fire are the most common disturbances in montane grasslands of NW Argentina. These disturbances can affect vulnerability to erosion and species diversity. They can also affect the seasonal dynamic of the aerial biomass and determine dominant life form and therefore the general structure of the community. This work aims to determine the effect of burning and grazing on the diversity, species composition and biomass distribution in grasslands of NW Argentina. We performed comparative and experimental studies at Los Toldos, Salta, Argentina (22º30’LS y 64º50’LW) at 1700 masl. We compared areas that were burned 1, 2 or more than 5 years ago, and we also performed a manipulative experiment with burning and grazing in a factorial design. The results suggest that burning and grazing affected the total aerial biomass as well as the proportion allocated to the different life forms. In Toldos grasslands burning caused vegetation to sprout earlier in the season, and encouraged the development of more palatable growth forms (mainly graminoids). During the first months of the summer when livestock is moved from forests (at lower altitudinal level) to these grasslands, the proportion of green biomass was greater at burned sites (78 and 75 % in December and January in burned sites and 35 and 33 % in sites that were not recently burned). Similar results were obtained in the experimental study. Hence, the seasonal pattern of the biomass is modified by fire and consequently it affects forage availability. Diversity did not show clear differences between the treatments, however some species seemed to be encouraged by burning.