Radial growth responses to thinning and climate in native Nothofagus betuloides forests in Tierra del Fuego, Argentina

Abstract

Silvicultural treatments based on natural stand dynamics are crucial to the design and improvement of forest management. Dendrochronological methods can be used to evaluate the effect of silvicultural treatments, providing precise data concerning growth rates, releases and suppressions. This information is essential to predict forest stand attributes and yields under different silvicultural management protocols. Sustainable silvicultural prescriptions are scarce for the evergreen Nothofagus betuloides forests in southern Patagonia. Therefore, accurate and detailed analyses of the response of N. betuloides to silvicultural trials could contribute to the development of the fundamentals of sustainable forestry. The objective of this study was to determine the radial growth response of N. betuloides to different thinning intensity levels using dendrochronological techniques and to assess the climatic influences on the thinning response. Thinnings from below were conducted in 1993 and 2000 in a young secondary forest that originated after a high-severity fire in 1949. Growth differences were evaluated considering ring widths, basal area increments, percentage of growth change and periodic annual increments. Growth-climate correlations were also explored. Thinning intensities showed differential effects on radial growth: heavy thinning treatments resulted in higher individual growth rates than the control treatment. Low density plots showed higher growth increments regardless of thinning intensity, suggesting that thinning intensity alone does not dictate the magnitude of growth releases. Radial growth rates were positively associated with warmer and less rainy summers, highlighting climatic conditions are an important driver of the thinning response. The effect of the first thinning was masked by the second intervention, indicating that this species reacts to intense interventions. These results indicate that it is possible to reduce the number of non-commercial thinnings and, consequently, the costs of the silvicultural system for this species. Moreover, this study highlights the usefulness of dendrochronological methods in providing accurate information for silvicultural purposes.