Sustainable forest management in south Patagonia: utopia or reality?

MARTÍNEZ PASTUR, G; LENCINAS, MV; CELLINI, JM; PERI, P; IVANCICH, H; SOLER ESTEBAN, R; VUKASOVIC, R

Campos do Jordao, Brazil

Conferencia; Latin American IALE Conference; 2009

IALE

Introduction: Nothofagus pumilio forests are the main resource for the sawmill industry. Several silvicultural methods were proposed (e.g., shelterwood cuts-SC) including alternative methods to enhance biodiversity conservation (e.g., variable retention-VR). Theoretical models included a remnant overstory for long periods (up to 20 years) until natural regeneration could be established. The objective of this study was to evaluate the implementation of two regeneration methods (SC and VR) at the landscape level, comparing their yield, remnant overstory stability, regeneration and understory diversity during the first seven years after the cuts.Methods: Harvested stands (1 to 7 years old) on 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 was 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.Results: 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 SC harvested stands and 11 in the VR).Discussion: The theoretical silvicultural methods were not correctly implemented on Tierra del Fuego. Large quantities of timber material were abandoned in the forest. Wind-blow of remnant trees increased over time due to stem damage during the harvesting. Moreover, regeneration was abundant for stands to recover. Because SC homogenized the stands, this treatment produced more impacts than VR at the landscape level. Yet, stability and conservation status of aggregates in VR was assured over time. Exotic plant species were found in all harvested sectors of stands (SC and dispersed retention in VR) but were scarce into the aggregates. New harvesting strategies must be implemented to assure the stability of the remnant overstory and to sustain both, economically and ecologically the implementation of these regeneration methods.