title: Comparisons of allometric and climate-derived estimates of tree coarse root carbon stocks in forests of the United States.
abstract: BACKGROUND
  Refined estimation of carbon (C) stocks within forest ecosystems is a critical component of efforts to reduce greenhouse gas emissions and mitigate the effects of projected climate change through forest C management. Specifically, belowground C stocks are currently estimated in the United States' national greenhouse gas inventory (US NGHGI) using nationally consistent species- and diameter-specific equations applied to individual trees. Recent scientific evidence has pointed to the importance of climate as a driver of belowground C stocks. This study estimates belowground C using current methods applied in the US NGHGI and describes a new approach for merging both allometric models with climate-derived predictions of belowground C stocks.
  
  
  RESULTS
  Climate-adjusted predictions were variable depending on the region and forest type of interest, but represented an increase of 368.87 Tg of belowground C across the US, or a 6.4 % increase when compared to currently-implemented NGHGI estimates. Random forests regressions indicated that aboveground biomass, stand age, and stand origin (i.e., planted versus artificial regeneration) were useful predictors of belowground C stocks. Decreases in belowground C stocks were modeled after projecting mean annual temperatures at various locations throughout the US up to year 2090.
  
  
  CONCLUSIONS
  By combining allometric equations with trends in temperature, we conclude that climate variables can be used to adjust the US NGHGI estimates of belowground C stocks. Such strategies can be used to determine the effects of future global change scenarios within a C accounting framework.
authors.affiliation: Department of Forest Resources, University of Minnesota, St. Paul, MN 55108 USA.
authors.forename: Matthew B
authors.initials: MB
authors.lastname: Russell
authors.affiliation: USDA Forest Service, Northern Research Station, St. Paul, MN 55108 USA.
authors.forename: Grant M
authors.initials: GM
authors.lastname: Domke
authors.affiliation: USDA Forest Service, Northern Research Station, St. Paul, MN 55108 USA.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Woodall
authors.affiliation: Rubenstein School of Environment and Natural Resources, University of Vermont, Burlington, VT 05405 USA.
authors.forename: Anthony W
authors.initials: AW
authors.lastname: D'Amato
keywords: Belowground biomass; Carbon accounting; Carbon-climate; Forest Inventory and Analysis; Root:shoot ratio