Natural decay resistant wood
You didn’t indicate where you’re from, but The ICC Code identifies “Decay Probability Map” in Figure R301.2(7) which includes a strip along the entire west coast and a wide strip from Iowa south to the tip of Texas and from Iowa east to Massachusetts and extending south through Florida.
Likewise, Section R319.1 requires pressure treated lumber “or decay resistant heartwood of redwood, black locust, or cedars.”
Also, decay resistant lumber is required for “buildings and structures constructed in flood hazard areas.”