Designed by Human Hands; Sometimes it's better not to go 'back to nature.'.(Cover story)

Byline: Stefan Theil

What do the Austrian alps, Philippine rice terraces and India's Kerala Backwaters have in common? True, they are some of the world's most beautiful--and ecologically diverse--landscapes. But they're also the product of centuries, if not millennia, of human care and cultivation. Now a triple whammy of shifting demographics, rural development and globalization is threatening some of the most stunning man-made environments.

Take the Cordillera mountain chain on the Philippine island of Luzon, where, for a thousand years, villagers have farmed rice in a vast network of ancient water-filled terraces. Hugging steep hillsides at impossible angles, they're fed by a complex system of drains and canals. Not just a masterpiece of premodern engineering, they're also a unique man-made ecosystem supporting fish, birds and amphibians, says Mechtild Rossler, head of UNESCO's Cultural Landscapes program.

Now those rice terraces are under threat. Thanks to increasing trade, rice imported from Thailand or Vietnam can be had for a fraction of the cost of the terrace-farmed product. Small wonder that more and more farmers' children are abandoning the backbreaking work for easier and better-paying jobs in Manila, leaving many of the terraces to dry up. Some believe that only tourists can save them; they see a future in which hefty subsidies will maintain the terraces, just to keep the visitors coming.

A similar shift is taking place in ...