Fire, plant species richness and aerial biomass distribution in mountain grasslands of NW Argentina

ARAGÓN, ROXANA; CARILLA, JULIETA; CRISTOBAL, LUCIANA

La Paz

Workshop; Global Mountain Biodiversity Assessment; 2003

GMBA - Diversitas

Fire and grazing are the most common disturbances in mountain grasslands of NW Argentina. They can affect species composition and richness, determine dominant life form and the general structure of the community. Fire and grazing can also influence nutrient cycle, hydrologic regimes and erosion risk. In addition to local effects, burning affects global atmosphere composition. This work aims to determine the effect of burning on species richness and aerial biomass distribution in grasslands of NW Argentina that are subjected to grazing. We performed a comparative study at Los Toldos, Salta, Argentina (22º30’LS y 64º50’LW) at 1700 m, and surveyed patches that differed in the time since last fire event. We considered three treatments: patches that were burned during the ongoing growing season (in the spring 2000), burned the previous season or not burned for at least 5 years. Treatments did not differ in species richness and they showed similar species composition. Total biomass and the allocation to live biomass, standing dead and litter varied among treatments. Fire reduced total biomass, but increased the contribution of live biomass and encouraged the development of more palatable growth forms (mainly grasses). Patches that were burned during the ongoing growing season had  80 % of their biomass as live biomass in December and January. In these months livestock is moved from forests at lower altitudinal levels to these highland grasslands. This modification in the seasonal dynamic of aerial biomass may represent a substantial change in the pattern of forage availability, especially in this time of the year.