Several years ago TPP saw some images of these bridges, and just recently they were brought to my attention again by a fellow who is studying the engineering principles of natural materials. First of all, note that figs are amazing. Figs are among the biggest and most impressive trees TPP has ever seen and he's sought out quite a few notable trees. Fig produce what are called adventitious roots, roots from limbs or the tree trunk. They grow down and when they contact the ground they can become woody and essentially form new trunks. Such roots can support very horizontal limbs and such trees can cover huge areas essentially a grove of one tree. Here such roots have been trained and connected across a stream to provide footbridges during times of high water. Roots and trunks of figs will readily fuse into a single axis, and they will continue to get bigger and they can live a long time. There are a lot more pictures at this link. Here's another link to a publication on the use of living plant materials in such engineering. There are some good images in this paper too. These are marvelous things, and make no mistake about it such nice little tropical streams can become raging torrents very quickly.