Pruning Pseudotsuga menziesii in the Patagonian Andes, Argentina

Abstract

In Patagonia Douglas-fir is grown to produce high quality timber; thus plantations should be pruned. To prune a stand, the proportion of green crown to be removed (pruning severity) and the number of lifts should be defined. The objectives of this research were to quantify the effect of pruning severity on tree growth and to select indicator variables to determine when to carry out pruning lifts. To achieve the first objective a trial was established on low, medium and highly productive sites. Pruning severities applied were heavy (65 % of the total tree height), intermediate (50 %), light (25 %) and control trees (no pruning). To accomplish the second objective the association between five easy to measure variables (diameter at breast height (DBH), total height, diameter over stubs height, pruning height, maximum diameter over stubs of previous pruning) and maximum diameter over stubs (DOS) was studied on 656 trees. Removing more than 25 % of the green crown progressively diminished subsequent tree growth. On highly productive sites, medium to high pruning severity did not reduce diameter growth as much as it did on low quality site, when carrying out second and third lifts. Diameter at breast height (DBH), and DBH along with previous lift height, was the more highly correlated variable with a maximum diameter over stubs.