Normally, both natural and artificial persons have responsibilities as well as rights. But a gorilla or a river obviously can't have responsibilities... Therefore at most they can be considered a rather limited kind of person, more like a human infant or an intellectually incapable adult than a regular human or an organisation of regular humans. Then of course it falls to humans to determine what the best interests o…
Non-human natural persons absolutely have responsibilities. The plants are responsible for photosynthesizing, the fungi for decomposition, etc. They do their holy work and we all get to stay alive, if we hold up our end of things as well.
I think in Carol Sanford's talks on living systems, the unique contribution a living system has for the ecosystem it lives within makes it non-displaceble.
Whether that should be recognized in our legal system, and something that helps humans participate in the ecology ... I don't know. The idea of legal personhood, at least, acknowledges that a living system is its own whole (if we are not just using it as a legal fiction), and it seems to me a stretch to say that a river "wants" legal representation. That sounds like the kind of stuff pre-modern tribal shamans do. That's not necessarily a bad thing in my book, but I don't know if our modern society is ready for that.
On the other hand, it could work as a balance to corporations having legal personhood.