Sustainable Management of lenga (Nothofagus pumilio) forests through group selection system

PABLO M. LÓPEZ BERNAL, GUILLERMO E. DEFOSSÉ, PAMELA C. QUINTEROS AND JOSÉ O. BAVA

Sustainable Forest Management . Current research

INTECH

Año: 2012; p. 45 - 66

Nothofagus pumilio (lenga) is a tree species with a wide spatial distribution in Andean Patagonia, able to grow in greatly varying environments in which annual average precipitation may go from 500 and 3,000 mm/yr (unevenly distributed), and capable of supporting extreme temperatures, different soil types, and disturbance regimes. The purpose of this introductory section is to review different contributions to the study of the species, to set the framework for its ecological management based on the adaptation to its natural dynamic processes. Most of N. pumilio productive forests in Argentinean Patagonia, owned by either private and state sectors, began to be exploited at the beginning of last century, but did not reach significant levels of harvest until mid-century, with the emergence of large sawmills that used almost exclusively high quality timber. Since then, the closing down of these large sawmills and the gradual installation of small and medium sawmills generated changes in harvesting techniques, extraction rates and final products.  These changes were usually marked by the lack of effective control policies by the state administration, which lead to the absence of sustainable management practices. On the other hand, these forests have been traditionally used as summer pastures for cattle, which in many cases has caused the degradation of the understory, with long delays in, and even preclusion of, regenerative processes. The purpose of this section is to analyze the evolution of productive schemes of N. pumilio forests along their history of use, which will help understand the overlap of strains on this resource, impacts on their conservation status, and the difficulties that currently have the implementation of sustainable management systems. For this purpose, we got information derived from published analysis, statistical records of the Forest Administration, analysis of historical harvesting, and analysis of the impacts of livestock on forest regeneration.  This information is available for two contrasting sites located in the northern (Chubut province) and southern (Tierra del Fuego) distribution area of this species. In the early 90´s, provincial forest administrations proposed changes in the traditional (high grading) management scheme, by incorporating a combination of ecological characteristics and history of use of N. pumilio forests in Patagonia.  These changes were based on the use of traditional practices and the gradual incorporation of some silvicultural guidelines (gaps opening, freeing oppressed regeneration, and thinning), trying to mimic the most frequent natural disturbances occurring in the dynamics of the lenga forest in the region (i.e. patch dynamics). This strategy, largely similar to the group selection system, has been applied to both experimental and commercial scale. In this section we describe the proposed management system and its results in terms of regeneration process and productive potential recovery. For this purpose, we have used our own data set derived from three trials which evaluated different silvicultural systems (including the group selection system, regional studies, several case studies, data of PhD thesis, and other post-graduate studies containing 20 years of research by the team which include the authors of this chapter. During the early years of this century, the Forest Administration of the provinces of Chubut and Tierra del Fuego (which possesses about 90% of productive forests of N. pumilio in Argentina) together with our research team, have developed an evaluation and monitoring system of management plans for N. pumilio forests which have applied the group selection system. This group selection system is based on the framework of criteria and indicators of sustainability and allows, through the implementation of 98 indicators grouped into seven control units, the oversight, control and monitoring of management plans, facilitating the work of the technicians in each instance. The purpose of this section is to describe the process of implementation and the first results of the monitoring system of forest management, based on a scheme originally set for the certification of sustainable management. For this we have our own data that emerged from analysis of sustainability indicators of the group selection system, and the analysis of 5 yr of results in the   implementation of the control system. The great variability of N. pumilio forests, the various uses to which it is subjected, and the uncertainty about possible changes in climate conditions, requires a flexible management system. The purpose of this section is to discuss possible adjustment variables in the context of group selection system that could be adapted to variability of site conditions, to the particularities of the productive system and to possible changes in climatic conditions.