EFFECT OF SOIL CHANGES CAUSED BY RED ALDER (ALNUS-RUBRA) ON BIOMASS AND NUTRIENT STATUS OF DOUGLAS-FIR (PSEUDOTSUGA-MENZIESII) SEEDLINGS

Seedlings grown on a former red alder site showed a 65% biomass increase in current twigs, 41% increase in older twigs, and 45% increase in stems. Foliage and roots were not significantly affected. The seedlings also developed shallower but wider root systems than those on the site formerly occupied by Douglas-fir. Seedlings on the red alder site showed an increase in N and decrease in P, Ca, and Mg concentrations. There were also higher N/P and N/K ratios and lower availability of soil P. Accelerated depletion of extractable P in soil was observed. Nutritional differences and biomass changes in seedlings can be attributed in part to the N and organic matter accumulated in the soil by the former alder forest. -from Author