Sustainable forest management in south Patagonia: utopia or reality?

MARTÍNEZ PASTUR G.; LENCINAS M.V.; CELLINI J.M.; PERI P.L.; IVANCICH H.; SOLER ESTEBAN R.

Campos do Jordão (Brazil)

Conferencia; Latin American Landscape Ecology Conference (IALE); 2009

IALE

Nothofagus pumilio forests are the main resource for sawmill industry in South Patagonia. Several silvicultural methods were proposed (e.g. shelterwood cuts-SC) including alternative methods to enhance biodiversity conservation (e.g. variable retention-VR). The theoretical models considered a remnant overstory for long periods of times (up to 20 years) until natural regeneration was established. The objective was to evaluate the implementation of two regeneration methods (SC and VR) at landscape level, comparing their yield, remnant overstory stability, regeneration and understory diversity during the first seven years after the cuts.  Harvested stands (1 to 7 years old) in Tierra del Fuego were selected in two different locations (n=6 in Rio Irigoyen and n=3 in Los Cerros Ranch). These stands were managed through shelterwood or variable retention cuts. Each stand were sampled using 4 transects (50 x 10 m) analyzing the original, harvested and remnant forest structure. Regeneration (age structures) and understory diversity (richness and cover) were also characterized at the beginning and the end of each transect. Damages in the remnant overstory during the harvesting were measured, as well as timber non-harvested logs. While mean values of basal area (BA) for treatment VR after 3 years of harvesting presented 47% of remnant overstory, 4% of windblown trees and 49% harvested, after 5 years showed 40% of remnant overstory, 11% of windblown trees and 49% harvested. BA of 1 year in the SC treatment had 31% of remnant overstory, 11% of windblown trees and 58% harvested, while 7 years after harvesting presented 11% of remnant overstory, 30% of windblown trees and 59% harvested. Regeneration in VR was abundant varying from 0.11 million.ha-1 and 15 cm height to 0.10 million.ha-1 and 30 cm height, while in SC varying from 0.23 million.ha-1 and 8 cm height to 0.14 million.ha-1 and 41 cm height. Waste timber material varied from 0 to 62 m3.ha-1. Exotic understory plant species were occasional in unmanaged stands, but their diversity increased over time (5 species in the oldest CP harvested stands and 11 in the VR). The theoretical silvicultural methods were not correctly implemented in Tierra del Fuego. Large quantities of timber material were abandoned in the forest. Windblow of remnant trees increased over time due to stems damage during the harvesting. Beside this, regeneration was abundant to recover the stands. Because CP homogenized the stands, this treatment produced more impacts than VR at landscape level. Stability and conservation status of aggregates in VR was assured over time. Exotic plant species were found in all harvested sectors of stands (CP and dispersed retention in VR) being minimum in the aggregates. New harvesting strategies must be implemented in order to assure the stability of the remnant overstory to sustain both, economically and ecologically the implementation of these regeneration methods.