Canadian Forest Service Publications
Late-rotation nitrogen fertilization of Douglas-fir: growth response and fibre properties. 2017. Filipescu, C.N., Trofymow, J.A., Koppenaal, R.S.Can. J. For. Res. 47: 134–138.
Issued by: Canadian Wood Fibre Centre
Catalog ID: 38990
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Late-rotation fertilization of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) 5 to 10 years before harvesting is a common management practice in British Columbia and the US Pacific Northwest. Despite widespread operational application, knowledge on the impact of late-rotation fertilization on forests, especially fibre properties, is lacking. In this study, we evaluate the growth response and fibre properties following nitrogen fertilization in a productive second-growth coastal Douglas-fir site at age 57 years. Destructive sampling of dominant and co-dominant trees in fertilized and control plots 5 years after fertilization indicated significant gain in stem volume (30%–40%) that was uniformly distributed along the stem. There were no discernible effects on wood quality at the log level in terms of resonance acoustic velocity. However, fibre properties within breast height tree rings indicated significant reductions of ring wood density (by 8%), earlywood density (17%), latewood percentage (10%), and modulus of elasticity (8%). Tracheid dimensions declined in earlywood (reduction of wall thickness by 15%), latewood (radial diameter by 8%), and fibre length (by 6%). Results indicate that late-rotation nitrogen fertilization of Douglas-fir may lead to a significant growth response with only minimal reduction of fibre properties. It is possible that the negative impact on fibre properties could become more significant for repeated applications or higher rates of nitrogen fertilization.
Plain Language Summary
Douglas-fir is a widespread tree species in British Columbia that is of major economic and ecological importance. Forest managers require information on the growth and development of major commercial species under a variety of growing conditions and management regimes. In this study we evaluate a novel management method, fertilization with nitrogen five to ten years before harvesting, in order to increase the growth and productivity of Douglas-fir forests. We examine the response in growth and wood properties that are relevant to the forest products industry. In addition, we examine the interaction with growing conditions, such as moisture and other nutrients. Our results provide evidence to support the management of forests for multiple timber and non-timber objectives. This study will contribute to refining management strategies and supporting the development of innovative policies relevant to forest-dependent communities and sustainable forest management in a low-carbon economy.