Eleven months after the May 1980 eruption of Mount Saint Helens in southeastern Washington, United States, three Populus clones were planted in an experiment on the Toutle River mudflow deposit. The trees grew at an abnormally slow rate and by 3 years were overtopped by a dense stand (14 600 ± 3600 trees/ha) of red alder seeded naturally onto the site. Over the 6-year period of the study, the total N content of the soil increased an average of 56 kg•ha−1•year−1•. Foliar N concentration in Populus increased significantly from a mean late summer – early autumn value in the 2nd year (1982) of 0.69% N to a value of 2.06% N at the end of the seventh growing season. The mean annual height growth of the largest Populus averaged <0.5 m/year in the first 3 years, increasing to an average of over 1.0 m/year in the 5th and 6th years. Fertilizer treatments with N (as urea) and N + P (as urea plus treble superphosphate) placed in the soil near the individual Populus at a maximum rate of 5.3 g N/tree increased height growth in the year of fertilization (1982) and the following year (the response in height growth for the 2 years totaled 64%). After 1984, no significant effects of fertilizer on height growth, total height, or diameter were evident. Nitrogen fertilization significantly increased foliar N concentration (1.54% N with the highest N treatment vs. 0.69% N in the control) in the year of treatment only. Phosphorus fertilization had no significant effect on growth or foliar P concentration. At 6 years, only 2% of the Populustrichocarpa Torr. & Gray clone and 13% of the tallest Populus hybrid were equal to or above the mean height of alder dominants and codominants (6.2 m). Additionally, the diameter growth of Populus was severely limited: the trees had only 8% of the cross-sectional area of "normal" trees for their height. Results indicated that on sites of low N such as the mudflow, Populus may not compete satisfactorily in mixture with alder. Such behavior is in sharp contrast to sites of high N, where red alder cannot compete with Populus.
Taper equation and volume tables for plantation-grown red alder.
