Lab week 1 discussion

Remember: do not post answers or your homework. Everyone can see what you put up here, and if you violate these rules, you will lose points. This page is for discussion of Lab 1 only. Asking for help with problem-shooting STELLA would be a good start.

Autotrophic Respiration Rates
In the instructions, we are told,

"Foliage respires away 50% of the C that is taken in via photosynthesis."

This intrinsc rate of 50%, along with the autotrophic respiration rate response to temperature, should give us a foliage respiration rate. But be careful: this might work OK if foliage is kept separate from aboveground, living, woody biomass (stems and branches). But woody biomass respires much less than foliage. And if you lump foliage and aboveground woody biomass together, the majority of this lumped pool is woody biomass, so you need to use a much, much lower respiration rate for this lumped pool.

However, we are not given an intrinsic rate of respiration for roots.

What approach did you use to determine the autotrophic repiration rate of the roots?

ans: i think that you assume the respiration from roots is negligible for the purposes of Ra (p 5 of main instructions: "autotrophic respiration can be represented as a simple function of total above ground carbon multiplied by…"). It's included in Rh because of the more significant "root litter transfer" (p 5 again).

Also Has anyone found an appropriate intrinsic leach rate to describe the flow of C from foliar litter to SOC?

30% is a good round number to use for this. There is even a good citation in the literature for this: Currie, W. S. and J. D. Aber. 1997. Modeling leaching as a decomposition process in humid montane forests. Ecology 78:1844-1860.

another ?: i know that foliar respiration is abt 50% from the packet, but then it says that respiration from the total agc is significantly less. are we supposed to use trial-and-error to determine the appropriate numbers for agc respiration *and* photosynthesis?

Yes, it's not too hard — start with the temperate forest, and use trial and error to get a good value of GPP, then add aboveground respiration and use trial and error to get a good realistic number for NPP, then this will alter GPP a little because it alters the aboveground living C stock, so go back and tweak the photosynthesis. Iterate these two until you have good values of GPP and NPP for the temperate forest, then go from there to the rest of the temperate forest processes, and then to the other biomes.

*Question of Assumptions**
Which variables in Fig. 1 do we simply enter vs. which variables do we need to compute using equations and reach approximate results show in Fig. 1? (Is BGD an entered number or the result of an equation?)

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