To "set aside" something is to exclude it or separate it from other things, with the aim of giving it individual consideration. In England, we have a "set-aside" scheme for land which means that farmers get paid by the government for deliberately not using some of their land. So here, set aside might mean not using the land. I would need more context to know for sure.
"Sake" is an old English word originally meaning "love". It is used idiomatically e.g. "I gave up my job for the sake of my elderly mother". i.e. because of my mother.
"For the sake of argument,..." is a good expression in analytical articles which means "speaking hypothetically". Look up "for goodness sake" - it's a good slang expression.
"For its own sake" usually implies someone is being stubborn and doing something for no good reason.
To set aside land for its own sake - this could mean - to not use some land without any reason.
If you want more help, post some more of the article the phrase is from and hopefully someone can help more. Michael