What is in redwood to make it rot resistant?

Rot-Resistant Woods

A few years ago, redwood was a big no-no for anyone who cared about the environment because venerable old-growth trees were laying down their lives to become lawn furniture. Today, redwood is a renewable resource, as millions of redwood seedlings are replanted every year-about five for every tree harvested. And cedar is an even better choice since it can be forested even more easily and quickly than redwood. Both native woods are naturally rot-resistant. They are good, reasonable, non-chemical alternatives to pressure-treated wood, but they are not totally care-free, and a deck made from either redwood or cedar will still require regular maintenance. Tropical Wood Alternatives

There are other rot-resistant woods that are just coming to the American market, including ipe (also known as ironwood) and cambara. These exotic woods will last for 2o years or more with just one preservative treatment. Ask to see certification of sustainable harvesting methods before you buy any tropical wood products.

* http://www.care2.com/greenliving/hit-the-deck-with-nontoxic-solutions.html