Upon unlocking and obtaining the megaphone magical item (the guide will notify you when you reach the appropriate level) you will see white rings coming off of aesthetics in the park. Blowing the megaphone towards these items, and subsequently completing the designated set (trees in an area, Bee hives, etc.) attribute to the percentage.
I unlocked this fairly naturally when traversing back and forth through the park during fetch quests, and a little bit of further exploration to complete sets. The items are all pretty well highlighted in the park.