Graduate Thesis Or Dissertation
 

Douglas-fir (Psuedotsuga menziesii) biomass and nutrient removal under varying harvest scenarios involving co-production of timber and feedstock for liquid biofuels

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  • In this study an improved model of biomass and nutrient estimation of coastal Douglas-fir (Psuedotsuga menziesii) in the Pacific Northwest has been developed across a wide range of stand management regimes. This study quantifies and defines the type and intensity of biomass harvest and associated removal for actively managed stands on a scale applicable to biofuel production. This study provides a preliminary estimate of the implications of varying levels and intensity of harvest on long term site productivity that will require calibration with actual harvest and nutrient flux data. Of total tree mass over all sites, 1-yr-old, 2-yr-old, and ≥3-yr old foliage, live branches, bark, sapwood and heartwood comprised 2% (1.0-3.4% range), 1% (0.6-1.7% range), 1% (0.8-3.0% range), 3.3% (2.2-4.5% range), 13% (8-31% range), 44% (24-59% range) and 35% (24-44% range), respectively, of total aboveground tree biomass. Four scenarios for aboveground biomass removal from the site were considered: 1) BO: merchantable bole only; 2) BT: entire tree except for the top portion above a four-inch stem diameter; 3) VC: entire tree except for one vertical half of the crown; and 4) WT: whole tree with top and all branches. The nutrient harvest and biomass removed under each scenario increased in the following order BO<BT<VC<WT. The mean relative total aboveground biomass removed by each of the scenarios was 70% for merchantable stem only (BO), 75% for loss of the top above the four inch stem diameter (BT), 97% if one vertical half of the crown was sheared off. Total foliage contained 20, 34 and 49% of Ca, Mn and N, respectively, despite comprising no more than an average of 9% of the total stand level aboveground biomass. The total aboveground nutrient pool contained no more than 2.2% (average of 0.4%) of the total pool (soil + aboveground biomass) of N, P, Ca, Mg and S, and contained no more than 8.6% (average of 1.4%) of the total site K pool. The maximum stability ratio among all nutrients and sites in this study was 0.089 (0.006 mean) and at a full rotation of 50 years would be no higher than 0.113 (0.0081mean), just over the static ratio threshold of slight risk to long term site productivity (0.1). These static stability ratios are limited in their estimates of potential adverse impacts on nutrient availability and supply because nutrient fluxes (e.g., mineralization, leaching and atmospheric deposition rates) are not taken into account. The quantification of nutrient fluxes is necessary to provide a more accurate representation of future impacts of increased harvesting intensity to long term site productivity.
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