How An Old Carcase Can Actually Support A Healthy Ecosystem

What is a carcass (or carcase)? Does the term have general usages in woodworking outside of cabinetry? A cabinet, for example, consider the American style one on the right: If I remove the doors,... The horizontal rails would span the entire width of the carcase to provide stability and support. As for muntin it would indeed be the central vertical piece. Whether it divides the interior space or runs along the back would depend on the specific design of the bookcase. Obviously, there are many other ways to do this, like using metal, or putting the rails on a proper carcase (or frame). I recommend looking at more bed designs and seeing what I mean. Even store-bought flat-pack furniture can give you lots of ideas.