Nitrogen Content and Other Soil Properties Related to Age of Red Alder Stands

Authors:
  • BBB. T. Bormann
    B. T. Bormann
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Abstract
The magnitude and pattern of nitrogen (N) accretion and other changes in soil properties were assessed for red alder stands ( Alnus rubra Bong.) 5 to 41 years old growing on the same soil type in the same general area. Regression of soil nitrogen (N) content over stand age revealed that N has accumulated at a nearly constant rate of about 35 kg ha −1 year −1 in the mineral soil (0‐ to 20‐cm depth) beneath alder stands. After an apparently rapid build‐up in the first decade, forest floor N increased linearly from 10 to 40 years at a rate of 15 kg ha −1 year −1 . Other mineral soil characteristics beneath alder stands differed markedly from those beneath adjacent Douglas‐fir stands [ Pseudotsuga menziesii (Mirb.) Franco]; organic matter content was 20% higher, and pH and bulk density were much lower. The rate of N accretion and improvement of other soil characteristics suggest opportunities for increasing yields of Douglas‐fir grown in mixed or rotational culture with red alder.