Thank you, Eric. This question came up because I was going to give a program on nature and landscape photography at a wildlife refuge and while I had my own ideas of the differences and similarities between the two, I was looking around to see if there were actually specific definitions in use. The only specific definitions I found were with the Photographic Society of America (PSA), but they were in relation to PSA competitions and seemed a bit too specific and strict for my purpose and philosophy.
I was surprised to find NANPA didn't define nature photography. I've been a member for years and hadn't looked for a statement before. I supposed we all have our concept of what nature photography is and an "official" definition could create confusion and unnecessary debate.