Heterotrophic respiration increases and doesn't drop back down post-fire

[amullen01]

Issue discovered when initiating fire at various years during the transient for two Birch and Black Spruce community types calibrated for caribou-poker creek. Heterotrophic respiration increases post-fire and never returns to pre-fire levels. This tilts the ecosystem to a strong C source for perpetuity, which is likely not in line with reality.

[amullen01]

This is really interesting: The problem only seems to happen with the RH monthly output. When outputting RH by month and layer and summing over layers, the post-fire behavior seems much more normal.

[hgenet]

Woooow that’s interesting!!!!! Ruth - could you look at it? If not, let’s meet to talk about this next Wednesday after our tech meeting. H

On Jun 13, 2024, at 10:23 AM, amullen01 @.***> wrote:

This is really interesting: The problem only seems to happen with the RH monthly output. When outputting RH by layer and summing over layers, the post-fire behavior seems much more normal.

RH_monthly_layer.png (view on web) https://github.com/uaf-arctic-eco-modeling/dvm-dos-tem/assets/16657080/ea627c43-fbe2-430e-8eee-1790c074b8be — Reply to this email directly, view it on GitHub https://github.com/uaf-arctic-eco-modeling/dvm-dos-tem/issues/721#issuecomment-2166502520, or unsubscribe https://github.com/notifications/unsubscribe-auth/AANVJF4D7WAGBRTNAY4NKYDZHHPRNAVCNFSM6AAAAABJI5I3KCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDCNRWGUYDENJSGA. You are receiving this because you were assigned.

[rarutter]

Oh dear, that's a problem. Yeah, I'll look at it.

[amullen01]

Thanks Ruth. Happy to help debug during our meeting tomorrow as well.

[rarutter]

The difference is because the total output includes respiration from dead woody debris, while the by-layer output does not. Woody debris respiration is available as a separate output DWDRH, and I'll need to look a bit further and perhaps discuss with you guys how to resolve this.

[hgenet]

That makes sense - although DWDRH seems very high. I’ll check on this. Ruth - I’d still like to make sure that DWDRH is not at all impacting soil C stocks. I’m pretty sure it’s not, but worth checking. H

On Jun 14, 2024, at 12:34 AM, Ruth Rutter @.***> wrote:

The difference is because the total output includes respiration from dead woody debris, while the by-layer output does not. Woody debris respiration is available as a separate output DWDRH, and I'll need to look a bit further and perhaps discuss with you guys how to resolve this.

— Reply to this email directly, view it on GitHub https://github.com/uaf-arctic-eco-modeling/dvm-dos-tem/issues/721#issuecomment-2167533747, or unsubscribe https://github.com/notifications/unsubscribe-auth/AANVJF6WBV5XQCCVMFKPFLLZHKTIVAVCNFSM6AAAAABJI5I3KCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDCNRXGUZTGNZUG4. You are receiving this because you were assigned.

[amullen01]

[hgenet]

DEADC dynamic makes sense - it is supposed to be transfer to DWDC over the course of nine years post fire. The dynamic of DWDC is less reasonable though as there is not input to this pool, beyond DEADC. So it should regularly decrease over time from decomposition.

On Jun 14, 2024, at 9:27 AM, amullen01 @.***> wrote:

deadc_dwdc.png (view on web) https://github.com/uaf-arctic-eco-modeling/dvm-dos-tem/assets/16657080/c18fc069-fd73-48f9-b57b-9c3727d73ab9 — Reply to this email directly, view it on GitHub https://github.com/uaf-arctic-eco-modeling/dvm-dos-tem/issues/721#issuecomment-2168465723, or unsubscribe https://github.com/notifications/unsubscribe-auth/AANVJF63QCN6FEXORASQPVLZHMRW7AVCNFSM6AAAAABJI5I3KCVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDCNRYGQ3DKNZSGM. You are receiving this because you were assigned.

[amullen01]

The problem appears to be in Vegetation_Bgc.cpp, lines 287 - 318. In this block of code, d2wdebrisc is given a value > 0, dependent on deadc0. deadc is reduced by d2wdebrisc until deadc is depleted, or months post-fire >= 108. This is all fine, however, there is no mechanism to set d2wdebrisc to zero when deadc is zero post-fire so dead woody debris gets added every time step for the rest of the run. At least I think this is what is happening.

When I add the two lines

bd->m_v2soi.d2wdebrisc = 0.0;
bd->m_v2soi.d2wdebrisn = 0.0;

Before lines 287 - 318 in Vegetation_Bgc.cpp, the issue seems to be fixed.

[rarutter]

I've been working through this trying to get a handle on what's going on. I ran at Toolik with a single fire, and while I didn't quite get the same dynamics you did, most of them are similar (although DWDC doesn't drop as abruptly, which I think is a good thing). I'll be working on it again later today and will try to more closely match what you've done.

[amullen01]

DWDC currently decays at the rate of rawc. Helene suggests that this rate is too fast. I changed the decay rate for DWDC to that of sompr and it looks a bit better. This will work temporarily but ideally there will eventually be a DWDC decay rate.