Answer: The first dash should be placed between plants and plants.
Explanation: A dash is a punctuation mark which consists in a little horizontal line. It is generally used to include a clause that gives additional information about what came before the dash. In the sentence provided, the first dash should be placed after "native plants", that is to say between "plants" and "plants" since the idea "plants that grow naturally in an area" is amplifying the previous noun phrase ("native plants") by providing more information about it.
