Biomass of Grazed, Burned, and Undisturbed Paramo Grasslands, Colombia. I. Aboveground Vegetation

Estimations of the amount of aboveground vegetation mass were made for four piramo grassland sites with different grazing management and burning histories in the Central Cordillera of Colombia. The total mass of live plus dead grassland vegetation showed a decrease from 2820 ? 190 g m-2 at the undisturbed to 868 + 73 g m-2 at the intensively grazed and burned sites. Stem rosette mass was highest at both the undisturbed and the heavily grazed sites (666 ? 168 and 1029 + 245 g m-2, respectively), but considerably lower at the burned sites (397 ? 94 and 285 ? 78 g m-2). Eighty percent of the total undisturbed vegetation mass consisted of standing dead material and litter. The decrease of dead material mass along the disturbance gradient may have large implications for ecosystem stability. The proportion of live material increased along the grazing and burning gradient, resulting in a similar live material mass at all sites. Under high grazing intensities and in the absence of burning, the vegetation can transform into ground-covering mats, attaining a moderately high biomass. Where burning took place, this transformation does not occur, and both grassland and stem rosette biomass were reduced, leaving many patches of bare ground.