Dave, please remember that I'm not a "pro", so this is just my two cents...
The colors look very flat (due to the shooting conditions, I'm thinking). The trees in the background are very dark and without detail. The overcast, oppressive sky doesn't help me love the images, either.
Also, while these photos may look lovely framed and hanging in someone's living room, they are not what most of the stock agencies are looking for. Try for subjects that clearly illustrate a concept, such as "business", "family" or anything else that you can come up with.
Remember, buyers purchase photos to illustrate ideas and sell products. While many of us started out with nature photography, you'll find that there are not many making good money with only those types of photos in their portfolio as concepts are where the bigger numbers come in for most of us.
Don't give up on nature (or photography in general) but try to broaden your horizons, so to speak, and shoot some concepts. I think that you'll find that it really gets your brain going to come up with a concept and then shoot it.
Good luck!