Poplar is more prone to rot than almost any other common specie.
The commonly available White Pine is about the same as poplar.
Redwood, while costly & hard to find is best.
Cedar, if back-painted holds up reasonably well. Paint the cut ends too!
White oak was used on mansions in the USA.
Southern Yellow Pine has the ability to withstand moisture fairly well, & I would say that it might be second only to redwood in all around exterior usefulness, among available specie in most of the USA.
I do not like Cedar for most jobs because #1 clear is hard to find, & #2 common is Knot Knice.
There are many exotic woods that are virtually immune to rot, but they are VERY costly & hard to find.