Units problem

[bpbond]

@ValentineHerr identified a problem with NEP and litter fall data in one study; see forc-db/ERL-review#25

Fix!

[bpbond]

Other issues to fix identified by the ForC team:

forc-db/ForC@877285b
forc-db/ERL-review#34 (comment)

[bpbond]

Also forc-db/ForC@194125e

[bpbond]

forc-db/ForC@1722015