Decomposition and change in N and organic composition of small-diameter Douglas-fir woody debris over 23 years

Abstract

Managing second-growth forests for multiple benefits requires enhanced information on decomposition of woody debris generated during forestry operations. Experimental thinning and biomass sampling at the Shawnigan Lake Research Forest on southern Vancouver Island facilitated retrospective sampling of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) stem sections (4.9-21.5 cm diameter) from 0 to 23 years after cutting. A sigmoidal pattern of density loss was observed, while a single-exponential fit gave a decay rate (k) of 0.058 year -1 . Initial N concentrations were higher in bark than in sapwood and heartwood, and all increased during decay, while C/N ratios declined to around 175 for wood and 70 for bark. Nitrogen contents initially increased but tended to decline after about 50% C loss. Solid-state 13 C nuclear magnetic resonance spectroscopy showed little change in organic composition, consistent with white-rot fungal decay, with only a few 19-year samples showing large increases in lignin typical of extensive brown-rot decay. Hydrolyzable monosaccharides of wood and bark were dominated by glucose followed by mannose, xylose, galactose, and arabinose. For wood, the mole fraction of mannose decreased with decomposition, whereas those of glucose, arabinose, and galactose increased slightly and that of xylose remained constant for both brown and white rot. Our results support indications that decomposition of smaller diameter woody debris from managed conifer forests will likely be dominated by white-rot fungi, leaving residues high in cellulose rather than in lignin.Résumé : L'aménagement des forêts de seconde venue à des fins multiples exige de meilleures connaissances au sujet de la décomposition des débris ligneux produits lors des opérations forestières. Une éclaircie expérimentale et un échantillonnage de la biomasse à la forêt expérimentale du lac Shawnigan au sud de l'île de Vancouver a facilité l'échantillonnage rétrospec-tif de sections de tige (4,9-21,5 cm de diamètre) de douglas vert (Pseudotsuga menziesii (Mirb.) Franco) 0 à 23 ans après la coupe. Une distribution sigmoïdale de la perte de densité a été observée alors qu'une courbe exponentielle simple donnait une valeur du taux de décomposition (k) de 0,058 an -1 . La concentration initiale de N était plus élevée dans l'écorce que dans le bois d'aubier et le bois de coeur et elle a augmenté partout dans le bois en décomposition tandis que le rapport C/N a diminué jusqu'à environ 175 dans le bois et 70 dans l'écorce. La teneur en N a initialement augmenté mais elle avait tendance à diminuer lorsque la perte de C dépassait 50%. La spectroscopie de résonance magnétique nucléaire du 13 C à l'état solide a montré qu'il y avait peu de changement dans la composition organique, ce qui est cohérent avec la décomposition par les champignons de carie blanche, tandis que seulement quelques échantillons de 19 ans montraient une augmentation importante de la lignine typique d'une carie brune avancée. Les monosaccharides hydrolysables du bois et de l'écorce ét...

Range and uncertainties in estimating delays in greenhouse gas mitigation potential of forest bioenergy sourced from Canadian forests

“…Most studies documented parity times <20 years for bioenergy sourced from harvest residues excluding stumps (Repo et al ., , ; Lamers & Junginger, ; Lamers et al ., ). Branches and tree tops are small woody debris that quickly decompose on the forest floor (Tarasov & Birdsey, ; Palviainen et al ., ; Preston et al ., ), and the parity time between the bioenergy system, in which biomass emits C to the atmosphere to produce energy, and the reference fossil fuel system, in which biomass is left to decompose in the forest, is therefore quickly reached. Furthermore, in the case of harvest residues that are normally burned by the roadside to reduce the fire hazard, the use of bioenergy to replace fossil fuel generates immediate atmospheric benefits (C parity time = 0 year).…”

“…Most studies documented parity times <20 years for bioenergy sourced from harvest residues excluding stumps (Repo et al, 2011(Repo et al, , 2012Lamers et al, 2014). Branches and tree tops are small woody debris that quickly decompose on the forest floor (Tarasov & Birdsey, 2001;Palviainen et al, 2004;Preston et al, 2012), and the parity time between the Fig. 5 Timing of GHG benefits and length of the uncertainty phase of scenarios using different bioenergy feedstock to replace coal for power production.…”

Charcoal in Organic Horizon and Surface Mineral Soil in a Boreal Forest Fire Chronosequence of Western Quebec: Stocks, Depth Distribution, Chemical Properties and a Synthesis of Related Studies

“…Trends of increasing N concentration and decreasing C/N ratio are similar to those seen in decomposition of foliar litter (Moore et al, 2011) and wood over both short time scales of ca. 20 years (Preston et al, 2012) and centuries (Preston et al, 1998) corresponding to the timescales in this study.…”

A 13C NMR study of decomposing logging residues in an Australian hoop pine plantation

“…Preston et al (1998) also observed little change in 13 C CPMAS NMR spectral properties in the early stages of decomposition of coarse woody debris from three softwood species on Vancouver Island, Canada. In a study of small-diameter woody debris decomposition, the same researchers observed few compositional changes up to 19 years (corresponding to approximately 65% mass loss), which they attributed to the dominance of white-rot decomposition (Preston et al 2012). After 19 years, they observed a change in the carbohydrate-to-lignin ratio, suggesting that brown-rot decomposition became increasingly important in the latter stages of decomposition.…”