Loss of mass and nutrient changes of decaying woody roots in lodgepole pine forests, southeastern Wyoming

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Abstract
Woody root decomposition was studied in two lodgepole pine (Pinuscontorta Dougl. ex Loud. ssp. latifolia (Engelm.) Critchfield) stands in the Medicine Bow Mountains, Wyoming, from samples obtained beneath stumps that remained following: (i) partial cuttings 1–2, 5–7, 12–15, and 45 years ago, and (ii) fires that originated in the present stands 80 and 110 years ago. The specific gravity of root wood declined exponentially (mean k = 0.0415 year−1) during the first 15 years of decay. Mass-loss rates were faster for smaller (0.5–1.0 cm) than larger (2.6–5.0 cm) size classes of material, and rates were slightly faster on the site with fine textured soil than on the site with gravelly soil. Bark decay rates were not calculated due to a number of errors associated with estimating bark specific gravity. Nitrogen and calcium concentrations increased in both root wood and bark after 80 years of decay. Rapid decreases in potassium and phosphorous concentration occurred in the first 15 years of decay; however, contents increased slightly in wood in the advanced decay classes. Magnesium concentration initially increased with decay but thereafter decreased after moderate decay. Woody roots of lodgepole pine appear to persist for many years (>110 years) following death of the aboveground portion of the tree, but nitrogen immobilization in decaying root wood (10 mg N•m−2•year−1) is much less than the amount immobilized in aboveground detritus (500 mg N•m−2•year−1).