I've actually been thinking about this topic for a while now. Most of the time, being frugal and being green go together. If you're frugal, you generally buy fewer items, you drive less often, you reduce, reuse and recycle. Because of this, your home is also generally less cluttered.
But as I declutter my home, I find that the line between these areas becomes very fine. There are many things that I might need someday. It wouldn't be frugal or good for the environment to have to buy them new all over again. But keeping these things around makes my home more cluttered. It also increases the possibility that I'll forget I have these items and buy new ones anyway.
I'm still finding a balance that works for me. But I would love any tips you have to share, because this is definitely an area that I struggle with.