What are naturally durable species?

• Naturally durable species are those that are naturally resistant to insect damage and moisture or decay.
  
  Some of those species include cedar, black locust, and redwood. Also consider using pressure treated wood for such applications where durability is an issue.
  
  Check out http://www.fpl.fs.fed.us/rwu4723/preservation_faqs/durable.html for more information.