Living Bridges

Ask an engineer how to build a bridge and he'll give you a month-long lesson in physics. Ask an architect and he'll bore you to tears with theories about movement and efficiency. Ask someone from Cherrapunji, and when he's able to contain his laughter, he'll point to a tree.
In this particular set of villages in northeastern India, they've found a way to substitute concrete pylons and steel cables for tree roots. Last year, Cherrapunji received the highest annual rainfall ever recorded. It's situated high in the mountains, where monsoon clouds break over the peaks and dump more than 1000 inches of rain ever year on the villagers. And with such enormous amounts of precipitation, the rivers on the mountain are nothing but violent rapids and deep arteries that make travel up, down, or across them impossible.

But the villagers have been thriving here for thousands of years, hunting the local wildlife for miles around. Centuries before the first stone bridges of Europe were even conceived, the Indians were already building their own. But without any typical building materials, they turned to the trees. More specifically, the Ficus elastica. This tree, native to the mountains, has a particular talent for growing roots. It has normal underground root structures, but it also produces a massive secondary root system above the ground, with complex roots rising up to half-way up its trunk. These upper roots provide further stability for the tree in the torrential downpours common to the region.
Using only these unique root structures, the villagers have over the years constructed a vastly complex system of bridges. But even building one bridge takes multiple generations of work. As anyone knows, trees don't shoot up overnight. They take hundreds if not more years of slow growth. But this is not a disadvantage to the villagers. Rather, it's provided them ample time to make the bridges perfect, safe, and frankly beautiful.
They "grow" these bridges in a very clever way. The roots need a lot of careful guidance to be turned into usable bridges, and the villagers have come up with a solution. They strip the bark off of a betel nut tree trunk, which resembles an aspen. The bark stays intact in a long, hollow tube, which the roots grow through, allowing the villagers to guide them whichever way they need. Larger roots, over time, grow all the way to the other side of the river, where they take root and give the bridge support. And unlike modern bridges, as these living bridges age, they actually strengthen over time. Smaller roots are wrapped around the larger ones to provide flooring, handrails, and further suspension support. The bridges give the villagers safe access to huge areas of the forest, where they are now able to easily hunt.
Now, the reason I write about this is not to suggest its use in more modern bridges. It's just to show how architecture and infrastructure does not always have to be built. Sometimes, it can be grown, and I feel that that is exactly the direction we are heading.