Effects of pruning on knotty core taper and form of Pinus radiata and Pinus pinaster

Pruning is a key silvicultural intervention in order to obtain high quality wood products since it influences the size of the knotty core and the proportion of clear-wood. However, little is known about knotty core size and its distribution through the pruned stem in timber conifers. This paper describes methodologies to predict knotty core profile and form along the pruned stem as tools for helping in the estimation of wood quality before felling. For the first time, defects related to pruned branches and pruning intensity have been considered. Data of Pinus radiata and Pinus pinaster pruned standing trees were collected by non-destructive techniques. Two different approaches based on taper functions were used and adapted to predict knotty core profile, defined by stem diameter over stubs for any given height, in the pruned stem. The two models, which both included pruning intensity, explained 98 and 97 % of variability in the diameter over stubs (average root mean square error of 1.10 and 1.34 cm, respectively). An influence of pruning on stem form, evaluated through a form exponent, was found in both conifers. Higher pruning intensity resulted in stems which were significantly more cylindrical, although this effect disappeared 4 years after the intervention. These results highlight the role of pruning on timber quality, and the importance of assessing the knotty core profile and form before felling trees.