The vegetation of the Andean treeline is described and the impact of human influence on structure and floristic composition analysed. The study area was located on the western flank of the Central Colombian Cordillera in the northwestern part of Los Nevados Natural Park between 3400 and 3800 m. The dominant vegetation was a two-layered forest with Weinmannia mariquitae and Miconia spp. Grazing was extensive and cutting intensities were classified into limited cutting and clear-cutting. Cleared sites had a regeneration time of at least 5 years. A positive correlation existed between cutting system and grazing intensity. Nine vegetation types were distinguished using TWINSPAN; four of them represented forest without major composition changes, and five represented regenerating forest. An altitudinal range of 400m included differences in floristic composition. The natural types of forest differed primarily in the presence of different Miconia species: M. latifolia, M. psichrophylla and M. bracteolata; Weinmannia mariquitae cover was high in all. The fourth type of natural forest represented remnants of Polylepis sericea forest, where W. mariquitae and Miconia spp. were absent. The five disturbed types were all related to one of the natural forest types dominated by Weinmannia. The altitudinal range of important woody species proved useful in predicting vegetation transition after cutting. Cutting at high altitudes led to a lowering of the treeline. Cutting at lower altitudes was limited to the temporal disappearance of trees, after which regeneration of the original forest seemed possible, when grazing intensities were low. High grazing intensities, however, generally led to the creation of pasturelands, independent of altitude. Given the positive correlation between grazing and cutting intensity, chances of regeneration are low, unless the intensity of human disturbance is substantially reduced.
