PARENT SESSION
Poster Session #42: Carbon Storage.
Thursday, August 9, 2001. Presentation from 3:30 PM to 5:00 PM. Exhibition Hall
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Fertilized Douglas-fir (Pseudotsuga menziesii var. glauca) trees produce low density wood.
Nippert, Jesse1, Marshall, John1, Balster, Nick2, 1 2
ABSTRACT- Our ability to interpret forest growth in terms of carbon budgets is impeded by the different growth measurements used in current practice. Foresters measure stem growth as changes in volume whereas carbon budgets predict stem mass. The calculation of wood density provides an accurate conversion between changes in volume and mass. Eight sites in the Interior Northwest dominated by a Douglas-fir (Pseudotsuga menziesii var. glauca) overstory were used to determine (i) if different fertilizer combinations induce changes in stemwood density, (ii) if the wood density response changes over time following a pulse fertilization and, (iii) if a change in density can account for previously documented increases in stemwood volume production. The three fertilizer combinations applied per hectare were 224 kilograms of nitrogen, 448 kilograms of nitrogen, and 224 kilograms of nitrogen plus 190.4 kilograms of potassium. No significant difference between the three treatments was detected. However, wood density values declined significantly (P<0.05) within two years of fertilization in each treatment and remained significantly different eight years later. Averaged across all fertilizer combinations, density decreased from 0.43 to 0.40 g-cm-3. The relative decrease in wood density accounted for one-third of the stemwood volume increase in the two-year interval and 100% of volume increase in the eight-year interval. We conclude that the evaluation of fertilizer response should include treatment-specific measurements of wood density to allow precise conversion from volume to stem mass.
KEY WORDS: Wood Density, Fertilization, Pseudotsuga menziesii var. glauca