In an essay, with only three items on the list, and all of them being quite short, I would just write them in the sentence. If the preceding part of the sentence is quite long, then use a colon. blah blah blah resulted in three areas being declared off-limits for development: x, y, and z.
With more than three or four, or if each item is quite lengthy, then use the same format as for PowerPoint. But be equally consistent in your usage! If one is a noun phrase, make them all noun phrases. If one is a sentence, make them all sentences. And so on.
I speak only "American" English, so a physical place set aside for local plants and animals to live without being disturbed is a nature reserve. I don't know about other countries' use of that phrase. (Is it possible that at least some of the others were talking more about natural resources being kept in reserve? I don't know - but I agree, over a quarter milllion uses is too high for an error.)