When it comes to building green, nothing may be closer to the embodiment of the term than using materials that are actually still alive. In northeastern India, in one of the wettest places on Earth, such a practice has been going on for hundreds of years. For proof, look no further than the "living bridges of Cherrapunji".
Like something out of Disney theme park attraction, these incredible bridges are made from the roots of the Ficus elastica tree, otherwise known as a rubber tree. Besides the standard underground roots, this tree also shoots out secondary roots further up the trunk which are used to scale boulders, sip up water from rivers, etc. Long ago, people living in the region saw these strong roots as a resource for building bridges across rivers. A blogger explained the process saying,
In order to make a rubber tree's roots grow in the right direction -- say, over a river -- the Khasis use betel nut trunks, sliced down the middle and hollowed out, to create root-guidance systems. The thin, tender roots of the rubber tree, prevented from fanning out by the betel nut trunks, grow straight out. When they reach the other side of the river, they're allowed to take root in the soil. Given enough time, a sturdy, living bridge is produced.
For more information and additional photos, check out this website.