While this is not directly for determining long or short term gain, §1031(a)-3 may show some insight (there is a similar Regulation for REITs).  For example (a)(4) says:

For this section, a distinct asset  is analyzed separately from any other assets to which the asset relates to determine if the asset is real property , whether as land , an inherently permanent structure , or a structural component  of an inherently permanent structure . Buildings  and other inherently permanent structures  are distinct assets.

https://www.law.cornell.edu/cfr/text/26/1.1031(a)-3

Again, although this does not directly apply to the question, it may show some insight:  When you report the sale of real estate on Form 4797, you report the land separately from the building.