Modeling effects of soil, climate, and silviculture on growth
ring specific gravity of Douglas-fir on a drought-prone site in
Western Washington Because wood specific gravity (SG), also
known as relative or basic density, is correlated with many
physical and mechanical properties it is a widely used indicator
of wood quality. Furthermore, because SG measures dry weight per
unit green volume and dry wood contains about 49% carbon and 20
MJ/kg energy, SG is useful for converting tree volume to carbon
and energy content equivalents. Although many studies have
investigated variables affecting SG, few have developed models
to predict SG at the local level from age, silvicultural
treatment, and growing environment variables. This study
developed a four-parameter logistic model with mixed effects to
predict the specific gravity of annual growth rings (RSG) from
forty six 76-year-old Douglas-fir (Pseudotsuga menziesii, Mirb.
Franco) trees sampled from a thinning and biosolids
fertilization experiment on a drought-pro