Effect of soil changes caused by red alder (Alnusrubra) on biomass and nutrient status of Douglas-fir (Pseudotsugamenziesii) seedlings

Abstract

The effect of soil changes caused by red alder (Alnus rubra Bong.) on the biomass and nutrition of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings was determined by comparing two adjacent plots of seedlings planted on former Douglas-fir and red alder sites. The seedlings grown on the 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. The 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 red alder forest.