Nutrition of Douglas-fir in the Inland Northwest

Interior Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] is an economically and ecologically important forest tree species in the Inland Northwest that is universally limited by nutrient availability. A variety of other site conditions also limit forest growth and vigor that complicate our understanding of Douglas-fir nutrition in the region. In this report, we summarize existing scientific information on nutrition of interior Douglas-fir and draw conclusions about best management practices. A general N deficiency was confirmed through universal increases in tree growth and nutrient uptake following N fertilization. However, water availability and other nutrients, such as K, S, and B, frequently limit the response to N fertilization. Increasing the probability of a strong fertilizer response within the region requires critical information on site moisture availability, parent material, and foliar K, sulfate-S, and B concentrations. Such stand and site characteristics should guide management prescriptions, including appropriate harvest operations, slash management, site preparation, fertilization, and stocking levels. Synthesis of the available information on interior Douglas-fir nutrition and site characteristics provides a set of management guidelines and recommendations.