Does Welsh have a "plural of singulative" like (Revived) Cornish does?
There, you have e.g. gwydh "trees", gwedhen "a tree" and also gwedhennow "(individual) trees" -- the difference with the collective being, as I understand it, that the plural of the singulative emphasises the individual nature of the elements.
(It's clearer in things such as holanennow "grains of salt" versus holan "salt".)
Is there a coedennau or the like in Welsh as well for when I view the trees individually rather than collectively?
There are some traces of that in some words, perhaps. For example:
- gronyn - a grain or particle
- gronynnau - grains, particles (usually as several or many individual items)
- grawn - grain or particles (as in a collection or handful, etc, of grain)
You would probably harvest or sow grawn, but empty a few gronynnau out of your boots afterwards.
As EllisV said, coed means 'a wood' as well as being the plural 'trees' (singular coeden (b)). 'Wood' as in timber for making something from is usually pren.
Dictionaries such as Ap Geiriadur with very simple definitions do not make that kind of distinction very clear.