Leaf litter chemistry controls on decomposition of Pacific Northwest trees and woody shrubs

The effects of initial leaf litter chemistry on first-year decomposition rates were studied for 16 common Pacific Northwest conifers, hardwoods, and shrubs at the H.J. Andrews Experimental Forest in western Oregon. Leaf litters were analyzed for C, N, P, K, Ca, Mg, proximate organic fractions (nonpolar, polar, acid-hydrolyzable extractives, acid-hydrolyzable lignin, and acid-unhydrolyzable residue, previously termed Klason lignin), and biochemical components (total phenolics, reactive polyphenols, water-soluble carbohydrates, water-soluble proanthocyanidins, and water- and acid-unhydrolyzable proanthocyanidins). By including measurements of reactive and residual phenolic fractions and acid-hydrolyzable lignin, these analytical methods improve upon traditional proximate leaf litter analyses. Significant differences in litter chemistries and decomposition rates were found between species. For all species combined, the 1-year decay rate (k) values had highly significant correlations (P < 0.001) with 30 out of the 36 initial chemistry variables tested in this study. The three highest correlations were with acid-unhydrolyzable proanthocyanidins, lignocellulose index, and acid-unhydrolyzable residue (r = 0.83, -0.81, -0.80, respectively, with P < 0.0001 and n = 339). We found that no single litter chemistry variable was a universal predictor of the 1-year k value for each of the individual 16 species studied, though phenolic components were more frequent significant (P < 0.001) predictors of decomposition rate.