I am correcting a text for a friend. She wrote:
You can find biodiversity in wild meadows, but these areas decrease by seven percent annually.
A comma should be used if there are 2 independent clauses. To me, "these areas..." is not truly independent. If I read this on its own I would not know "these areas" actually are, right? Therefore there shouldn't be a comma?!
I encountered the same problem when correcting a longer text about a certain topic. In a paragraph, some of the sentences could not be really understood if you had not read the preceding ones first although they didn't use "this" or "these". I don´t know if these sentences should be called independent at all?