Harden, J.W., S.E. Trumbore, B.J. Stocks, A. Hirsh, S.T. Gower, K.P. ...

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F I R E I N T H E B O R E A L C A R B O N B U D G E T 177Table 1. Model inputs and constraints for determining longterm C losses to ®re and decomposition. Terms de®ned in text (Eq. 1).Model inputs and constraints Model unknowns Model outputNPP 1 1/k shallow 2 1/k deep 2 Cs mature 3 Cd today 3 C mature Cc (dead) 5 Input deep 3 %Fuel burned Fire %NPP to ®re(kgC m ±2 y ±1 ) (y) (y) (kgC m ±2 ) (kgC m ±2 ) trees 1 (kgC m ±2 ) (kgC m ±2 y ±1 ) emission 6(kgC m ±2 )at t = eventkg C m ±2event ±1Pine/lichen: burn interval 60 yModel 0.15 13 100 1.1 1.18 4 3 0.009 41% 2 25% (range 1±26%)Observed data 0.1±0.15 6±14 100 1.1 1.8 2±4 > 2±3 0.01 1.1±2.5Spruce/Feathermoss: ®re interval 80 yModel 0.15 55 550 3.3 9 3.6 3.87 0.04 44% 3 33% (range 18±44%)Observed data 0.096±0.17 55±250 200±500 2±4 9±11 2.9±5.7 > 1.2±4.7 0.002±0.005 1.4±7Spruce/Sphagnum: ®re interval 200 yModel 0.12 56 1100 4.3 18 2.9 5.03 0.012 30% 2 12% (range 1±26%)Observed data 0.12±0.16 55±250 1000±2000 2±4 18±22 2.5 > 1±3 0.007±0.033 ±Wetland bryophytes, sedges: ®re interval 200 yModel 0.3 37 0.0003 5.26 70 0 5.3 0.0495 0.05
178 J . W . H A R D E N et al.Fig. 1 A model of soil carbon storage showing C loss to ®re events, C burial by mosses during regrowth, and protection from decompositionin deep layers. In a pre-®re condition, the C transfers of the forest represent inputs from NPP and losses to decomposition.When ®re occurs, carbon that is not lost to direct ®re emissions is transferred from the shallow soil and tree layer to an intermediatelayer C c that decomposes at the surface until burial by moss allows the material to decompose at slower rates of the deep layer.Data in Table 1 are used to de®ne terms including t, time t in years; NPP, net primary production in kg m ±2 y ±1 ; k s , k d , decompositioncoef®cients in units of kgC m ±2 y ±1 ; t ± 1, year previous to time t; C s carbon storage (in units of kgC m ±2 ) in shallow soil and trees, includingmoss, roots, plant litter, trees; C d , carbon storage (kgC m ±2 ) in deep soil layers; C c , C storage (kgC m ±2 ) in ®re-killed treesand remains of burning; C tr , carbon storage (kgC m ±2 ) in tree stem; F, fractional percentage loss to ®re; C h , heterotrophic respirationin kgC m ±2 in one year. Equations for calculations between ®re events are C s + C tr at time t = C tr (t ± 1) + ANPP stem + C s (t ± 1) + NPPs ±k s *C s (t ± 1) for shallow carbon and tree layer; C d at t = C d (t ± 1)±k d C d (t ± 1) for deep carbon layer; C h = k s *C s (t ± 1) + k d *C d (t ± 1) +k s *C c (t ± 1) for heterotrophic respiration in one model year; C c at time t = C c (t ± 1) ± k s *C c (t ± 1) for ®re-killed remains. For years inwhich ®re occurs, equations are C s at time of ®re = 0; C d at t of ®re = C d (t ± 1) + C c (t ± 1) for carbon storage of deep carbon; F (®re) =f * (C s ) for C consumed by ®re and released as CO 2 and other C trace gases; C h = k d *C d (t ± 1) + k s *C c (t ± 1) for decomposition or heterotropicrespiration; C c = (1 ± f)*(C s + C tr ) for carbon storage of ®re-killed remains.emissions (Table 1, output). The modelled best estimatesfor direct ®re emissions per event are comparable to dataon experimental burns in pine and spruce forests (<strong>Stocks</strong>1980, 1989).ResultsThere is a zig-zag pattern of carbon storage in both theshallow and deep soil layers (Figs 1, 3) that is caused by# 2000 Blackwell Science Ltd, Global Change Biology, 6 (Suppl. 1), 174±184
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Harden, J.W., S.E. Trumbore, B.J. Stocks, A. Hirsh, S.T. Gower, K.P. ...

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