Nitrogen and organic-matter accumulation in coal mine spoils supporting red alder stands

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Abstract
Rates of nitrogen and organic-matter accumulation under red alder (Alnusrubra Bong.) stands were estimated by analyzing spoil materials at three abandoned open-pit coal-mine areas in western Washington. Average age of trees in natural stands at the three study areas varied from 10 to 30 years. Mean site indices (50 years) varied from 27 to 30 m. Mean pH of spoil surface samples varied from 4.0 to 4.6 which was less than for adjacent alder stands on natural soils but similar to values reported for alder stands in western Oregon. The increase in organic matter concentration in the surface 18 cm ranged from 0.96% under the 10-year-old stand to 2.94% under the 30-year-old stand. This represented an average increase of about 0.09% per year for all three stands with no significant differences among stands. The mean increase in nitrogen concentration ranged from 0.04 to 0.14% for the 10- and 30-year-old stands, respectively. This corresponded to an annual increase of 0.004% N with no significant difference among areas. Average rate of N accumulation in spoils varied from 59 to 65 kg N/ha•year−1. Differences between areas were not significant.

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