Abstract
Second growth forests of Nothofagus obliqua (roble), N. alpina (raulí), and N. dombeyi (coihue), known locally as RORACO, are among the most important native mixed forests in Chile. To improve the sustainable management of these forests, managers need adequate information and models regarding not only existing forest conditions, but their future states with varying alternative silvicultural activities. In this study, an individual-tree diameter growth model was developed for the full geographical distribution of the RORACO forest type. This was achieved by fitting a complete model by comparing two variable selection procedures: cross-validation (CV), and least absolute shrinkage and selection operator (LASSO) regression. A small set of predictors successfully explained a large portion of the annual increment in diameter at breast height (DBH) growth, particularly variables associated with competition at both the tree- and stand-level. Goodness-of-fit statistics for this final model showed an empirical coefficient of correlation (R2emp) of 0.56, relative root mean square error of 44.49% and relative bias of −1.96% for annual DBH growth predictions, and R2emp of 0.98 and 0.97 for DBH projection at 6 and 12 years, respectively. This model constitutes a simple and useful tool to support management plans for these forest ecosystems.
Highlights
Southamerican Nothofagus spp. forests dominate temperate and sub-Antarctic regions of Chile and Argentina from 33◦ to 56◦ south latitude
The CV regression variable selection procedure resulted in five predictors for AIDBH, that were selected according to the following goodness-of-fit statistics: R2 adj, Cp, BIC, residual sum of squares (RSS), and MSEK (Figure 2)
The response variable for this study was annual average diameter breast height (DBH) growth obtained over a period of two years that originated from increment cores and tree sections
Summary
Southamerican Nothofagus spp. forests dominate temperate and sub-Antarctic regions of Chile and Argentina from 33◦ to 56◦ south latitude. In Chile, there are nine Nothofagus species, including three evergreens and six deciduous species [1,2]. Second growth forests of roble (Nothofagus obliqua (Mirb.) Oerst.), raulí & Endl.) Oerst.), and coihue (N. dombeyi (Mirb.) Oerst.), known locally as the “RORACO” forest type, are one of the most important native mixed forests of Chile. According to the most recent national forest inventory, there are about 1.4 million hectares of these forests in Chile accounting for 10.8% of the total native forest area of the country [3]. In 2015 alone, the saw timber from RORACO forest type was approximately 45% of the native forest national timber production [4]. Volume growth rates for these forests range between 6 and 10 m3 ha−1 year−1 [5]
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