Forests
No, the noun phrase "the forest trees" is plural based on the plural noun "trees".The word "big" is an adjective, a word used to describe a noun.To be a possessive form, add an apostrophe s to the end of the singular noun "forest": the forest's trees (also, the big forest's trees or the forest's big trees).
The word forest is singular.The plural would be forests.An example sentence with the singular is: I love the view of the forest from my window.An example sentence with the plural is: we have explored many forests all over the world.
The plural form for W is W'S or WS
Histologies, would be plural of histology.
The word community is singular; the plural form is communities.
"Sevens" would be the plural of seven.
The word gnawed is a verb form, or adjective, and would not have a plural.
It depends on the context. Typically the noun you used to describe living would be plural instead of the word living. Living has no plural form.
The plural form for the demonstrative pronoun this is these.
The plural form of the word inferno is infernos.
The plural form is ranches.
There is no plural form for the word, countries. This word itself is a plural.