Brief summary of bug

A user reports odd (blocky) spatial patterns in leafc for generic crop pft for an I2000CLM50BGC case.
This is a BGC case initialized from a BGC-Crop initial file.

General bug information

**Model version: cesm2.0.0 (release-clm5.0.01)

**Does this bug cause significantly incorrect results in the model's science? Yes

**Configurations affected: I2000CLM50BGC with out-of-the-box spunup initial conditions and accelerated spinup on

Details of bug

Here is the initial report from the user:
"So when I start a simulations from an finidat file from the inputdata repository there appear some strange lines in the leaf carbon for rain-fed crop at the first time step. Most of these lines disappear after a couple of years. However, some persist east of Europe and in Central Africa. I found out so far, that the lines are different, when I use a different finidat file, but there always seems to be some of them."

I've reproduced the user's case and gotten the same behavior. Some of the blocky patterns go away after several simulation years, but there are large areas of dead generic crop.

If I do a cold start I don't see this. I think this is happening because there are actually some valid values for C3 generic crop in the initial file (even though it is an initial file from a prognostic crop simulation), about 47 gridcells. It looks like these are being interpolated to the C3 crop pft based on the closest valid values, which is why things look blocky. One value is being interpolated to a bunch of gridcells. I can see this pattern in the interpolated initial file as well ("finidat_interp_dest"). I've tried setting all of the leafc for C3 crop in the initial file to zero and the pattern in the interpolated initial file goes away. I'm sure there are other variables that will look blocky though and that may cause a blocky pattern in leafc to reappear.

I've noticed that generic crops are not included in the code logic for reseeding (CNVegCarbonStateType.F90). When I change this to include reseeding the generic crops and run for several years, most of the crops are now alive. However, there are a few remaining areas of dead crop (China and South Africa). Presumably this is because the generic crop gridcells that are being interpolated from have no carbon/nitrogen and reseeding is not sufficient to allow growth. I will try to determine if that is actually the case. I'm also going to create a branch with the change to reseeding and issue a pull request for that change because I don't see why we wouldn't try to reseed generic crops.

The presence of generic crops in the BGC-CROP initial file is incorrect. However, if the initial file had no generic crop to interpolate from what would happen to a BGC simulation with only generic crops when interpolating from this file?

Important details of your setup / configuration so we can reproduce the bug

I've reproduced the bug with:

/glade/work/oleson/release-cesm2.0.0/cime/scripts/clm5.0_SeSCs_spinup_test_181121

The initial file in question is:

clmi.IGM2000GSWP3CLM50BGCCROPIRR.2011-01-01.1.9x2.5_gx1v6_gl5_simyr2000_c170419.nc