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At 31 sites that encompassed the range of conditions over which Pinus radiata D. Don is grown in Chile measurements of basic density (D), stand dimensions, and soil properties were taken and combined with climatic data. Using this dataset the objectives of this research were to (i) quantify between and within site level variation in D and partition the relative importance of these sources of variation, (ii) identify the key determinants of D across and within sites, (iii) develop a robust site level model to predict D across the environmental range over which P. radiata is grown in Chile and (iv) further develop the site level model to incorporate stand variability in D through inclusion of tree characteristics.

Variance components analysis showed that between site variation in D was slightly larger than within-site variation, with these two components accounting for 54.8 and 45.2% of the total variability, respectively. Across sites mean D for juvenile wood was 377 kg m(-3) and ranged 37% from 338 to 462 kg m(-3). The mean within site variation was 87.8 kg m(-3), ranging from 37.4 to 143 kg m(-3).

The site level model showed that variables associated with soil fertility explained far more of the variance in D than climatic variables. Basic density was most strongly related to Boron (B) and Carbon: Nitrogen ratio (C:N ratio) and positive linear relationships with these variables accounted, respectively, for 32 and 20% of the variance in D. The final site level model of D had an R-2 of 0.65 and included B, C:N ratio, mean height and mean minimum air temperature during May. Through using linear mixed effects modelling, we developed a tree level model that incorporated all site level variables and included a random intercept between tree height and D. The final tree level model, which exhibited little apparent bias, had an R-2 of 0.61.