Most people I speak to seem to “feel” that solid timber is a more eco friendly material than sheet materials such as ply and MDF. They may be correct, but given that the main constituent of MDF would otherwise be considered waste material, surely it is better to use every last scrap of a tree? Plywood is effectively mostly solid wood, but in the form of thin pieces glued together. The other main constituent in sheet materials is of course the glue, which is a form of plastic and so that must count against it somewhat, but I still need to get a better understanding of whether that is automatically a bad thing.
I would imagine that since almost all good quality plywood is made from Birch, it may be that the plywood industry is not great for bio-diversity. On the other hand, Birch is just about the best wood for carbon-capture, because it is faster growing than other hardwoods and, being more dense than fast-growing softwoods, contains more carbon than they do.
I would have to consider the use of veneers along with sheet materials because I would hardly ever use one without the other. My assumption is that the veneer industry must be good for bio-diversity as they pay the highest prices for the widest range of timbers. That should provide some encouragement for the most diverse forests, which also support the most wild-life, to be maintained for future generations.
As I said, it is very complicated, but for the moment I am working on the understanding that it is fine to use a mixture of solid timber and sheet materials enhanced by the more attractive veneers. There are timbers I definitely shouldn’t use, but I couldn’t buy them if I wanted to.