Nothofagus forests present inconveniences to regenerate when they are subject to a systematic and permanent disturbance, such as over-browsing. The forests of Tierra del Fuego, free from cattle raising, are greatly damaged by the guanaco (Lama guanicoe). The objective of this work was to analyse the incidence of guanaco browsing on the installation and growth of the natural regeneration of a lenga (Nothofagus pumilio) forest subject to a shelterwood cut system. The abundance and forest use analysed by an indirect indicator determined that harvested stands were more affected by the guanacos. On the other hand, significant differences in the presence of browsed plants were detected along the sampled stands, being the virgin forest the treatment with the highest percentage of damaged plants. The browsing effect on tree growth was modelled for a site gradient, analysing the loss of growth in percentage of height. The natural guanaco populations are not included within the studied variables of a forest management plan. However, they are of great importance, since they impact the new forest generation of the systems under management.