Let me jump in here and alter the discussion somewhat. Species is important, but far more important when gauging longevity in exposure is ring density. I have been observing this for close to 50 years. I poked on Poplar logs in old settlements that were felled in mid-1800's that are as sound as can be. I have seen Poplar Shutters grow fungi in 2 years.
I have talked to Purdue, they were very nice, but clueless. They even recommended Poplar to a start-up window maker. They declared bankruptcy 4 years later when all the rot- repair claims started coming in.
Redwood is rotting in 3-5 years, Western Red Cedar is rotting in about 10 years. Even Teak is not at all what it used to be. What is going on?
Ring density my young friend, ring density. The Poplar cabin logs from 1860 had about 200 rings per inch - dense dark green heartwood that took centuries to grow. The Heart Pine in my house siding will not rot, and is about 100 rings per inch - every resinous inch. Look at those old bridge timbers used in covered bridges. Or wharves and docks.
No matter what you make, ring density matters. The greater the better. Get a piece of anywood that is warped, look at the ring density. Compare it to those that do not warp. Ring density.
So, this is a game changer. Try buying - over the phone - some wood that has a high ring density. You will be having a hard time, eh? Try explaining it to your bookish cohorts that always knew you to be a nut.
Just keep a sharp eye out, and compare when and where you can. You will see.
I want to stay as close to the edge as I can without going over. Out on the edge you see all kinds of things you can't see from the center.
- Kurt Vonnegut