How to inform guests high heels are not a good idea?

The park we are getting married at is a beautiful redwood forest. It is rustic...think fire roads and hiking trails instead of pavement. I wouldn't want guests to feel uncomfortable in heels or get hurt. I'd like to put something on the website but I can't figure out the wording. We say clearly it is going to be a bbq reception in the forest but I'm not sure that is clear enough. It is totally accessible and guests will not have to walk far at all but I just don't think heels will be safe.

How would you word this? Do I just not say anything? Frankly my guests can come in shorts and flip flops and I wouldn't care but I don't want anyone to be uncomfortable.