{"id":"jenkins-2003-spruce","source":{"id":"jenkins-2003","citation":"Jenkins, J.C., Chojnacky, D.C., Heath, L.S., Birdsey, R.A. (2003). National-scale biomass estimators for United States tree species. Forest Science, 49(1), 12–35.","title":"National-scale biomass estimators for United States tree species","authors":["Jenkins, J.C.","Chojnacky, D.C.","Heath, L.S.","Birdsey, R.A."],"year":2003,"venue":"Forest Science","doi":"10.1093/forestscience/49.1.12","url":"https://doi.org/10.1093/forestscience/49.1.12","read_url":"https://research.fs.usda.gov/download/treesearch/6996.pdf","access":"open","checked_at":"2026-11-01","status":"current"},"name":"US national species group: Spruce (Table 4)","output":{"quantity":"agb"},"expression":"exp(-2.0773 + 2.3323 * ln(D))","published":{"expression":"exp(-2.0773 + 2.3323 * ln(dbh))","units":{"dbh":"cm"},"variables":{"dbh":"D"},"output_unit":"kg"},"taxon":{"level":"mixed","name":"Spruce species group (softwood), United States","group":"conifer"},"region":{"scope":"national","countries":["US"],"place":"Conterminous United States","biomes":["temperate","boreal"]},"stand":"mixed","fit":{"dbh_min_cm":2.5,"dbh_max_cm":250,"r2":0.988,"rse":0.250424,"method":"OLS on ln-transformed pseudodata (212 points, generally at 5 cm dbh intervals) generated from published equations; no back-transform correction applied"},"evidence":[{"field":"expression","quote":"bm = Exp(β0 + β1 ln dbh)","locator":"Table 4 footnote, p. 20"},{"field":"expression","quote":"Spruce −2.0773 2.3323 212 250 0.250424 0.988","locator":"Table 4 row, p. 20"},{"field":"fit.dbh_min_cm","quote":"bm = total aboveground biomass (kg) for trees 2.5cm dbh and larger","locator":"Table 4 footnote, p. 20"},{"field":"fit.rse","quote":"Root mean squared error or estimate of the standard deviation of the regression error term in natural log units.","locator":"Table 4 footnote §"},{"field":"fit.cf","quote":"we do not include CFs for the reader to use after back-transformation","locator":"p. 19, Correction factors"}],"check":[{"inputs":{"D":30},"expected":349.084,"origin":"computed","note":"computed from the published form at dbh = 30 cm"},{"inputs":{"D":10},"expected":26.924,"origin":"computed","note":"computed from the published form at dbh = 10 cm"}],"verification":"original_read","checked_at":"2026-11-01","notes":"Group membership: Picea (Table 3). dbh_max_cm is the 'Max dbh of trees measured in published equations'; data points are pseudodata, not trees. Hardwood groups were extended to 230 cm dbh with Freedman (1984) pseudodata. No log-bias correction: the authors deliberately omit it; a user could multiply by exp(RMSE²/2) = 1.0319. Superseded for FIA reporting by NSVB (Westfall et al. 2024) but still widely used in carbon protocols."}