Incidence of browsing by guanaco (Lama guanicoe Müller) on early regeneration of lenga [Nothofagus pumilio (Poepp et Endl) Krasser] forests in Tierra de Fuego, Argentina

Abstract

In this work we analyze the early regeneration of Nothofagus pumilio forests, as well as the impact of browsing by guanacos (Lama guanicoe), in Tierra del Fuego, Argentina. First, we describe the structure of three N. pumilio stands with differing management schedules: a native virgin forest stand (BV), a stand that was logged in 1991-93 leaving a certain homogeneous density of parent trees («shelterwood cut», CP), and a third stand that was selectively and intensively logged (FL) in 1995. In these three stands we quantify the use by guanacos (estimated from the density of fecal remains) and the frequency of browsed seedlings (< 0.5 cm) and saplings (> 0.5 cm in stem diameter). Results show a high incidence of browsing, which was higher for the native forests stand (100 % and 95.7 %), than for CP (69.9 % and 72.1 %) and FL (67.3 % and 61.5 %, for basal and apical damage of browsed plants, respectively). These differences are mainly due to the fact that patches where big trunks accumulate in managed stands, provide shelter from damage by guanacos. Comparison of observed and expected (according to calculated growth models) sapling heigth show that recurrent damage by guanacos prevent successful growth, the corresponding height loss being 83.1 % for BV, 45.7 % for CP, and 50.3 % for FL. We conclude that guanacos effectively limits early regeneration in both native and managed stands, though a wider time scale is needed for a conclusive assessment of the incidence of browsing in forest dynamics and production.