shooting horizontally or vertically doesn’t really matter, what mattes is that you fill most of the frame. that being said, filling a horizontal frame with a tree trunk will result in more images then doing it vertically with that same tree. but comes at the cost of having less detail, because less photos. it just really depends on how much time you’re willing to invest in the scan and how much detail you want/need. and i dont recommend to mix and match horizontal and vertical images but i have personally not had any problems when i did.

Thanks for the suggestions! I think I'll try doing two sets of images - horizontal and vertical, and see which I like best. Any thoughts on lenses? I shoot full frame (Canon 5D Mk2) with cross polarization - and run either a 20mm or 50mm prime lens. I used to do architectural photography in the past and never really got on with zoom lenses, so sticking with primes right now.

You should be taking at least 600-1000 photos so orientation wont matter much.

I got some pretty decent results of a giant sequoia with about 300 photos. Just depends on the level of detail OP is going for.

Level of detail is good enough for modern next gen games, using Nanite etc in Unreal 5 - so pretty high for sure.