Influence of wood density in tree-ring-based annual productivity assessments and its errors in Norway spruce

[摘要] Estimations of tree annual biomass increments are used by a variety ofstudies related to forest productivity or carbon fluxes. Biomass incrementestimations can be easily obtained from diameter surveys or historicaldiameter reconstructions based on tree rings' records. However, the biomassmodels rely on the assumption that wood density is constant. Converting volumeincrement into biomass also requires assumptions about the wood density. Wooddensity has been largely reported to vary both in time and between trees. InNorway spruce, wood density is known to increase with decreasing ring width.This could lead to underestimating the biomass or carbon deposition in badyears. The variations between trees of wood density have never been discussedbut could also contribute to deviations. A modelling approach couldattenuate these effects but will also generate errors.

Here a model of wood density variations in Norway spruce, andan allometric model of volume growth were developed. We accounted for variations in wooddensity both between years and between trees, based on specificmeasurements. We compared the effects of neglecting each variation source onthe estimations of annual biomass increment. We also assessed the errors ofthe biomass increment predictions at tree level, and of the annualproductivity at plot level.

Our results showed a partial compensation of the decrease in ring width inbad years by the increase in wood density. The underestimation of thebiomass increment in those years reached 15 %. The errors related to theuse of an allometric model of volume growth were modest, around ±15 %. The errors related to variations in wood density were much larger,the biggest component being the inter-tree variability. The errors inplot-level annual biomass productivity reached up to 40 %, with a fullaccount of all the error sources.

[学科分类] 地球化学与岩石