Over the last decade a shelterwood system promoting natural regeneration has been applied in the southern Chilean old-growth Nothofagus forests. However, most of these forests are naturally uneven-aged, and the effect of the application of this silvicultural system has been the homogenisation and simplification of the stand structure. An ecological understanding of natural disturbance processes is necessary to improve the current silvicultural practices. This study analysed the effects of natural small-scale disturbances on the below-canopy solar radiation conditions, the regeneration patterns (density and growth), and the browsing damage to young trees caused by Lama guanicoe in an old-growth Nothofagus betuloides forest (Fig. 1). The study was carried out in 13 canopy gaps (21-92 m(2)) (Tab. 1). The regeneration was sampled in 65 plots (4 m(2)) in and around the canopy gaps along a solar radiation gradient. The results revealed that the non-cosine-corrected direct solar radiation ranged from 3.2 to 19.4%, the transmitted diffuse radiation ranged from 3.1 to 16.7% and the global solar radiation ranged from 3.2 to 17.6% (Tab. 2). As expected, the transmitted solar radiation was highest in the gaps, and the adjacent southeastern borders. All N. betuloides seedlings and saplings were counted in height classes, together with browsing damage caused by L. guanicoe (Tab. 3). The height growth and radial increment were measured for the tallest seedling or sapling in each plot (Tab. 5). The absolute radial and height growth of seedlings and saplings were affected by the total size and age of the plants and the below-canopy diffuse solar radiation (Tab. 6, Fig. 2 and 3). The proportions of seedlings browsed by L. guanicoe were low (0.7 to 2.8% of the total). Browsing damage to young trees was observed below canopy gaps as well as beneath closed canopy, demonstrating no particular preference (Tab. 3). The seedlings and saplings of N. betuloides exhibited a high shade tolerance, apparently not requiring the presence of large gaps to establish. The heterogeneous canopy of old-growth N. betuloides stands with only very small canopy gaps produced a variety of mosaics in the understorey, with seedlings and saplings present in a range of ages and heights. It could be shown, that - different to other South American Nothofagus species - N. betuloides seedlings and saplings can tolerate long periods of dense shade. Similar to some New Zealand Nothofagus forests, N. betuloides forests are able to regenerate also in a continuous process. This allows to develop perspectives for successful transformations of virgin N. betuloides forests into seminatural stands, which could be sustainably managed as selection forests, still having a multi-layered structure and high biodiversity with native species.

The authors would like to thank the Chilean Project FONDEF D02I1080, the German Academic Exchange Service (DAAD) and the International 'Forestry in Transition' Ph.D. Programme of the Faculty of Forest and Environmental Sciences of the University of Freiburg. We are also grateful to the Programa de Bosques Patagonicos of the University of Chile and the field work support provided by the Wildlife Conservation Society in Chile (WCS). The authors would like to extend their gratitude to Mr. JOAQUIN SOTO, owner of the forest in the Rio Condor (Tierra del Fuego, Chile). We also thank Dr. D. BUTLER-MANNING and B. THIEL for comments and help with the English. And our thank goes to the anonymous reviewers for their suggestions that very much improved the paper.

FONDEF [D02I1080]; German Academic Exchange Service (DAAD); Faculty of Forest and Environmental Sciences of the University of Freiburg

alvaro.promis@gmail.com

FONDEF

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