Páramos chiếm vành đai núi cao của miền bắc Nam Mỹ, giữa 3000 và 4800 masl. Các nơ hoa hồng khổng lồ của Espeletia chi, cùng với cây bụi và cỏ sclerophilous bó, thống trị thảm thực vật. Trong lần trước Columbus, páramo hầu như chỉ được sử dụng để săn bắn và thu thập (Wagner 1978), và chỉ sau khi sự xuất hiện của người Tây Ban Nha, và chủ yếu trong thế kỷ 18, nó bắt đầu được mở rộng chăn thả vật nuôi bằng cách giới thiệu, chủ yếu là gia súc, ngựa và la. Do đó,. | 9 Grazing Impact on Vegetation Structure and Plant Species Richness in an Old-Field Succession of the Venezuelan Páramos Lina Sarmiento INTRODUCTION Páramos occupy the alpine belt of northern South America between 3000 and 4800 masl. Giant rosettes of the genera Espeletia together with sclerophilous shrubs and bunch grasses dominate the vegetation. In pre-Columbian times the páramo was almost exclusively used for hunting and gathering Wagner 1978 and only after the arrival of the Spanish and mainly during the 18 th century did it begin to be extensively grazed by introduced domestic animals mainly cattle horses and mules. Consequently the páramo evolved until recent times without domestic herbivory. Many plant species mostly the endemic ones probably did not develop specific adaptations to this kind of disturbance and are potentially sensitive. The carrying capacity of the Venezuelan páramos is low. The main offering of forage is concentrated in small marshes and fens situated in the valley bottoms or in areas with poor drainage and dominated by palatable grasses and sedges Molinillo and Monasterio 1997 . The more widespread páramo vegetation in which dwarf shrubs rosette plants and tussock grasses predominate presents a lower availability of forage Molinillo and Monasterio 1997 . In the wetter páramos of Colombia where the cover of tussock grasses is higher and more continuous than in Venezuela the palatability of the vegetation is commonly improved by burning Hofstede et al. 1995 but in the drier páramos of Venezuela where grasses are less abundant burning is not practiced and the strategy of the farmers is to develop a closer relationship between agricultural activities and cattle management complementing the natural sources of forage with crop residues fodder and grazing on fallow plots Molinillo and Monasterio 2002 . To analyze the human impact on páramo vegetation it is essential to differentiate the Andean and high-Andean ecological belts Monasterio 1980 . .
