I would hire an emotionally strong person. Building a relationship with the park and the community it serves requires sticking with the park during the good times and the bad. I'd hope the naturalist would be able to take these experiences and learn from them, using them to change things for the future. I would especially read the letters of reference with an eye for good evidence of these qualities. I would also ask the candidate in our interview for his or her own examples of an adverse situation and how they would handle the particular situation.
Assertiveness is another important quality.
The naturalist must be able to maintain some order in the park, which may require them to confront people they believe to be doing damage to the park or disrupting others. The mild- mannered may not be able to confront people, or when they do, they may not be aggressive and commanding enough to get what they demand. I may even walk them through a mock situation in which they would have to confront me as they may be required to do during the course of their job. An obvious quality is a love for the outdoors. I'd find someone who can see beyond salary to the other wonderful attractions Kickapoo has to offer a naturalist, the main being a huge eco-system supporting wildlife, birds and wildflowers to learn from.