Michigan is a lot different from the southern states as far as the National Park system and how herpers are treated.
First, we don't have National Parks, per se, but rather National Lakeshores, Nat. Recreation Areas, and lots of National Forest. Second, there are some laws about protecting the habitat and the flora and fauna, but visitors are treated pretty amazingly.
Last June I visited the Sleeping Bear Dunes National Lakeshore. My first stop was the Park Headquarters where I told the staff that I was a herpetologist and I was there to photograph as many species as I could find. Not only did they say it was, ok, but they went out of their way to tell me where the best locations and habitat were and gave me maps and other advice.
Of course, there are many different plant associations and soil types, etc, and this park has some unique ones, like the very tough, sandy habitat along the lakeshore which is only colonized by the fittest of the fit. The park also includes lots of protected species, one of the reasons I was there, because they are so hard to find elsewhere. The park's main concern was that you didn't disturb the delicate balance of critical habitats.
This is a grassland along the coast adapted to the deep sands...
Here's a location of a dried up pond where amphibians were breeding weeks before...
Visitor's like to climb up and down the highest dunes...
We have a second residence south of Tucson, AZ. The Saguaro National Park, in Tucson, is very different in their attitudes and laws. I hardly ever go there because you can get stopped for just getting out of your car and looking at something. You can't have any collecting equipment and have to have a hunting license just to take photos. If you even move a protected herp off the road you could get ticketed, or worse. There aren't many, if any, areas where you can pull off the road to look around or night hunt, etc, so it's inconvenient compared to other areas where you can spend hours roaming around with lights and cameras, and whatever.
As far as vegetation and habitat, the S.N.P. is a pretty cool place, but there are other areas that have more variety as well as less protected flora and fauna. I like herping in the mountains where there are tons of microhabitats and the desert is not far away. 
TC
