Decomposition of small diameter woody debris of red fir determined by nuclear magnetic resonance

Abstract

Red fir (Abies magnifica A. Murr.) woody debris decomposing for 17 years in untreated (Control) and nitrogen‐fertilized plus widely thinned (NT2) plots was examined by ¹³C nuclear magnetic resonance (NMR). Total carbon (C) and total N concentrations were also determined. Combined data of wood and bark showed correlations between carboxylic, aromatic, O‐alkyl and aliphatic C fractions, and C fractions with C/N, but phenolic and methoxyl correlations were non‐significant. Wood mass losses averaged 38% for both Controls and NT2. Bark mass losses were 61% for Controls and 66% for NT2, but these were not significantly different at p<0.05; bark sloughing added considerable variance. Wood in Controls decreased O‐alkyl (66 to 50%) and aromatic (16 to 13%), increased carboxyl (1.5 to 6.5%) and aliphatic (2.0 to 15.5%), and decreased Cm/Lm, i.e., carbohydrate/lignin monomers (2.78 to 1.82). In NT2 plots, open crowns allowed greater drying of the forest floor during warm, dry summers. The C/N averages were slightly lower in NT2 than in Controls for wood (167 versus 188), and the same for bark (45 and 43), but differences were not significant at p<0.05. Decompositional pathways in different environments, by brown‐rot and whiterot fungi, are discussed.