add soil surface layer, bare soil surface layer; edit soil biocrust

[stevenchong]

Relevant to #750.

For bare soil surface layer, please check the axiom describing the lack of plant matter -- was having an internal debate about using contains vs. has part.

[pbuttigieg]

Hmm, contains / contained in doesn't include parthood, and plant matter is often considered part of soils. Also, just because soil has plant matter in it doesn't mean it's not "bare" in the sense of "uncovered".

We need a class for "bare soil" itself, where we can sort out these semantics. It would be better to put the axioms about why it's bare in the material rather than the layer. Do you have a good definition for this class? Here are some usages...

Here are some edits I think will help:

• Added part of axioms to pedosphere to several soil classes
• Removed containment axiom on ENVO_04000011, replaced with composed primarily of some bare soil
• Created bare soil class ENVO_01001616, placed this adjacent to the troposphere and not to a vegetation layer. I think we could add more, but we'd need an authoritative definition to work with.

[pbuttigieg]

The definition in the dbxref (link) is a bit too terse. I'm not sure this means that the soil has no plant matter in it, I think it's more above being covered if I think in terms of the NLCD classes (see #458)

Thus I would change the def of the layer to:

A soil surface which is exposed to the troposphere, with no appreciable cover from vegetation or other material.

[stevenchong]

The definition in the dbxref (link) is a bit too terse. I'm not sure this means that the soil has no plant matter in it, I think it's more above being covered if I think in terms of the NLCD classes (see #458)

I think you're right. I took a closer look at the dataset we want to annotate and see that it's funded by NASA's LCLUC program. So, a def that is about land coverage does make sense here.

[stevenchong]

Maybe bare ground should be added as a related synonym? Otherwise, I think this PR is ready to merge. If it looks good to you, go ahead and push the big green button.

[pbuttigieg]

Maybe bare ground should be added as a related synonym?

I think we can make a new issue for that. There are terms like badland (syn: barren land) and site-based entities such as area of barren land that we can consolidate in that issue.

@stevenchong do you want to add the envoNceas subset tag to any of the other terms created in this PR? Once you're done, we can merge.