Does the current FATES model incorporate leaf age?

[LianGong98]

Hello,

I have noted that in fates_params_default.cdl, fates_leafage_class = 1. Does this mean that only one leaf age class is considered, or are other leaf age classes, such as young, old, etc. also included?

[mpaiao]

@LianGong98 when fates_leafage_class is set to 1, then yes, FATES assumes only one leaf age class. If you want to distinguish young and old leaves, you just need to set fates_leafage_class to the number of age classes you would like, but my understanding is that this option has not been tested for a while. I have never tried it, but maybe others can chime in on their previous experience using multiple age classes, or how to define the age class boundaries.

[LianGong98]

@mpaiao Thanks a lot. I noticed that in the FATES branch from @xuchongang https://github.com/xuchongang/fates/tree/xuchongang/gpp_seasonal_cycle_ready_to_merge, the flag for use leaf age in EDTypeMod was present, and it defined expanding, young, old, and senescent leaf stages. The branch was ready to merge. However, I can't find this flag now. Does this mean the changes have been removed, or have they been incorporated into the system using just the leaf age classes?

[rgknox]

@LianGong98 , I concur with @mpaiao , the functionality to enable variable leaf ages is there in the code, but it does not get much/any testing these days. That said, I don't have any reason to suspect it would not work.

The user can specify as many leaf age-class bins as they want, by increasing the parameter file dimension leaf_age_class, here:
https://github.com/NGEET/fates/blob/main/parameter_files/fates_params_default.cdl#L12

When new leaf tissue is allocated, it will be classified in the first age bin. A fraction of the tissues will transfer to an older bin every day, based on the turnover time associated with each bin, specified here:

https://github.com/NGEET/fates/blob/main/parameter_files/fates_params_default.cdl#L672-L677

Currently, the only physiologic difference the leaves in young versus old bins will have, is different vcmax (which subsequently influences jmax and kp) values. The user specifies different vcmax values for the canopy top at 25C, here: https://github.com/NGEET/fates/blob/main/parameter_files/fates_params_default.cdl#L402-L404

I'd be curious to hear how any testing goes, and happy to help trouble shoot any issues or if you expand leaf age to impact other aspects of physiologic function.

ccing @xuchongang

[LianGong98]

@rgknox Thank you a lot . I found it did work .

I now have another question: when I try to set use_var_soil_thick = .true. together with use_fates = .true. in both CLM and ELM, I get the following error:

ERROR: use_var_soil_thick and use_fates cannot both be set to true.

Why ? Could you please explain why this limitation exists?