The effect of pruning and thinning on above ground aerial biomass of Eucalyptus nitens (Deane & Maiden) Maiden

There has been an increasing interest in Chile and Australia in using Eucalyptus nitens (Deane & Maiden) Maiden fast growing plantations for sawntimber production. We investigated the effects of pruning and thinning treatments, applied at age 6 years, on the growth and aboveground biomass accumulation of a 15-year-old E. nitens plantation located in the coastal Arauco-Central Chile. Pruning treatments did not affect growth or aboveground biomass. Lowest stocking thinning treatment (400 trees ha−1) doubled average individual tree aboveground biomass with 762 kg tree−1, but reduced stand mean aboveground biomass productivity by 31% (22.2 t ha−1 year−1). The highest stocking thinning treatment (1100 trees ha−1) accumulated 342 kg tree−1 and grew 29.1 t ha−1 year−1. Crown biomass was concentrated in the central and lower sections regardless of thinning treatment. Allometric models, used to estimate crown biomass based on ln(dbh2) as a predictor variable, resulted in determination coefficients (R2) of 0.74, 0.63, and 0.80 for leaf, twig, and branch biomass components, respectively. Stem components (wood and bark biomass) were estimated using ln(dbh2h) as predictor variable, resulted in R2 of 0.94 for wood and 0.80 for bark. Thinning increased individual tree average stem, crown, and total biomass. No differences in biomass and wood accumulation were found between 800 and 1100 trees ha−1 stockings. Reduced live crown length and average height were found for the 1100 trees ha−1 stocking, suggesting a negative effect of stocking on live crown length.