Hi,
First, let me mention, that you can place “manually” these items in the Custom Edit mode, and this way you can take advantage of other advanced Forest features (like the Forest Color map, adjusting Transform to easily add some randomness to these, several viewport modes, etc.).
In the case, you would prefer for some reason to not have these within a Forest object, you can easily use these as “references” within the Distribution > Reference Mode.
I hope that helps.
Best regards,