## 3 Results and Discussion
### Results
#### 3.1.3 Carbon Fluxes  
The key rate terms capturing carbon dynamics are gross and net primary production, turnover (including mortality and litterfall), and both autotrophic and heterotrophic respiration. Model results for each rate term were integrated over the 20 year simulation period, and the yearly average over that time period is presented in Table 9. The average yearly gross primary productivity is estimated as 1.4 kg/m\({}^{2}\)-year, with the daily rates ranging from nearly 0 kg/m\({}^{2}\)-year (periodically during the winter period) to over 3 kg/m\({}^{2}\)-year (Figure 6). The average yearly rate is somewhat lower than the range of 1.4 to 3.3 kg/m\({}^{2}\)-year estimated by [41] for a similar old growth forest, and within the range of 1.08-1.92 kg/m\({}^{2}\)-year estimated using remote sensing techniques across a Douglas-fir western hemlock forest on Vancouver Island, Canada by [44]. The simulated values are considerably lower than the 11.1-21.7 kg/m\({}^{2}\)-year estimated by [28] at HJA in 1970, and different respiration estimates explain the discrepancy. We assumed  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Rate** & **g/m\({}^{2}\)-year** \\ \hline Asymbiotic fixation allocated to wood & 0.08 \\ Asymbiotic fixation allocated to foliage & 0.08 \\ Asymbiotic fixation allocated to roots & 0.076 \\
**Total asymbiotic fixation** & **0.22** \\ \hline Decomposition of wood & 0.27 \\ Decomposition of foliage & 1.93 \\ Decomposition of roots & 2.42 \\
**Total decomposition** & **4.64** \\ \hline DON mobilization (RZ) & 2.58 \\ DIN mobilization (RZ) & 2.58 \\ DIN Immobilization (RZ) & 1.19 \\ DON breakdown to DIN (RZ) & 2.28 \\ DON transport in RZ & 0.34 \\ DIN transport in RZ & 0.00 \\ Denitrification RZ & 0.00 \\ DON mobilization (BRZ) & 1.92 \\ DIN mobilization (BRZ) & 1.17 \\ DIN Immobilization (BRZ) & 2.67 \\ DON breakdown to DIN (BRZ) & 2.23 \\ DON transport in BRZ & 0.62 \\ DIN transport in BRZ & 0.020 \\ Denitrification BRZ & 0.01 \\ Particulate input to aquatic & 1.88 \\ DON mobilization & 0.00 \\ DIN immobilization & 0.00 \\ DIN mobilization & 0.00 \\ Denitrification from aquatic & 0.00 \\ DIN export & 0.00 \\ DON export & 0.02 \\ Particulate export & 0.02 \\ \hline \hline \end{tabular}
\end{table}
Table 11: \(Cont.\)a respiration value of 47% of GPP, a heuristic model generated as part of the collaborative model development process. The older budgets of [28] resulted in respiration values of 92%-94% of GPP. Given the assumption that Ra is 47% of GPP, the yearly average NPP from the model is 0.60 kg/m\({}^{2}\)-year. This value is similar to other estimates of NPP reported at other similar sites, for example [41] estimated a range of NPP from 0.45-0.741 kg/m\({}^{2}\)-year at similar location in Washington State, [28] estimated a range from 0.41 to 0.66 kg/m\({}^{2}\)-year at HJA and [45] used a model to estimate a stable value of 0.50 kg/m\({}^{2}\)-year at HJA. Our model estimates are within the wide range of variation possible for NPP. The constant fraction model to estimate \(R_{\mathrm{a}}\) explains the similarity in the time series representing NPP and \(R_{\mathrm{a}}\) in Figure 6. Turnover is treated as a first order model which does not include any outside dependence (for example air temperature, soil water content, _etc._). This is reflected in the low temporal variation displayed for the turnover rate. The modeled value of average yearly turnover (0.572 kg/m\({}^{2}\)-year) is similar to that measured by [41] which ranged from 0.370 to 0.690 kg/m\({}^{2}\)-year. Modeled heterotrophic respiration (\(R_{\mathrm{h}}\)) is defined to include the production of CO\({}_{2}\) and DOC from litter and soils. The average yearly value of 0.397 kg/m\({}^{2}\)-year is of within the range of 0.341 to 0.509 kg/m\({}^{2}\)-year estimated by [43].