I think it's important to keep in mind that a lot of that vegetation surrounding that area is extremely fast growing...and could easily grow over that bag in a matter of weeks, if not months. Most of those vines you see growing are "air potato" vines...one of the most invasive plants in Florida. They are similiar in their encroachment of the Florida landscape to Kudzu.
Air Potato:
".... Due to its ability to displace native species and disrupt natural processes such as fire and water flow, air potato has been listed as one of Floridas most invasive plant species since 1993..."
"Impacts
Air potato can grow extremely quickly, roughly 8 inches per day. It typically climbs to the tops of trees and has a tendency to take over native plants. New plants develop from bulbils that form on the plant, and these bulbils serve as a means of dispersal. The aerial stems of air potato die back in winter, but resprouting occurs from bulbils and underground tubers. The primary means of spread and reproduction are via bulbils. The smallest bulbils make control of air potato difficult due to their ability to sprout at a very small stage.
http://plants.ifas.ufl.edu/node/133