I have only brief visits to your area. I've wandered a little around Fort Valley, also a little tiny town of Reynolds. In Reynolds, the factory for the company I worked for at the time, they would occasionally have to shoo alligators out of the parking lot. There was a creek that paralleled the rail road siding, where the gators lived and it was lined with bald cypress. My thought is, rail road right of ways often cross swamps, and can provide access to otherwise difficult to access swamps. Now collecting from the edge of railroad right of ways technically is collecting from private property, but if one is observant of basic safety, avoiding walking on the tracks, etc. you are unlikely to have problems. If you want to get permission, where a railroad crosses a road, and there are warning gates, there is normally signage that lists ownership of that stretch of track and usually includes a phone number. You can start there if you want permission. Or you can just ask forgiveness in the unlikely case you get stopped.