![]() Douglas-fir was first recorded in New Zealand in 1859, with plantations being established at various locations at the end of the 19 th century/beginning of the 20 th century (Miller and Knowles 1994). Outside its natural range it is an important commercial timber species in France, Germany and New Zealand (Maclaren 2009). This study indicates the importance of considering initial stand density, post-thinning stand density and timing of thinning when designing a silviculture regime that aims to control branch diameter.ĭouglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) is native to western North America where it is one of the most valuable and commercially important timber species (Miller and Knowles 1994). In unthinned treatments, the model indicated that an initial stand density of at least 1333 stems ha −1 would be needed to keep branch diameters on the mean tree below 40 mm along the whole stem at age 29 years. At all three post-thinning stand densities (250, 500 and 750 stems ha −1), the diameter of some branches on the mean tree within a stand were likely to exceed 40 mm. The models developed indicated that previously formed branches were influenced by the increased growing space created by thinning. The models were then used to interpret response to a thinning at a stand age of approximately 10 years when the base of the green crown was still close to ground-level, and to make comparisons with a branch diameter limit of 40 mm. The data were used to develop site-specific models to predict branch diameter along the stem. Methodsīranch diameters were measured using a photogrammetric technique, TreeD, on pre-selected sample trees from unpruned treatments in two silviculture experiments, one in the North Island and one in the South Island of New Zealand. The objectives of this study were: (a) to develop site-specific models to predict branch diameter variation with position on the stem and (b) to use the models to evaluate the influence of initial and post-thinning stand density on branch diameter in unpruned stands of Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco) at two sites in New Zealand. ![]() Consequently branch diameter is an important consideration when developing a silvicultural regime. Branches support the foliage needed for tree growth, but if the branch diameter is too large it may constitute a defect when the tree is assessed for timber quality and when the tree is processed into boards. ![]()
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