Forester On The Street - Invasive Species 

I live close to a wildlife refuge in south east Mississippi. While exploring the area I have come across what appears to be a tire, wedged between trees, with string around it to secure it to them. It is about 6 or 7 foot up in the trees, and I have seen it twice in the area. Both tires were about the same height from the ground, both secured against the trees with string, like purposefully placed. One is in an area that generally floods in the spring, not sure if the water gets up high enough to reach it. The other I seen recently, and although it was along where a small runoff creak flows when it rains, water would never reach its height in that area. Ever heard of this, like is it something foresters use to mark something? I ask because I've only recently found the 2nd one as they were thinning out thickets on the refuge recently, exposing this. Thanks