A druid does not have to be a Nature Protectorate to transcend. An alternative way is to take a druid prestige class or be exposed to some powerful artifact or spirit of the land. Black Wood is thought to have transcended from exposure to the fell energies of the Tarfilerquar.
One of the bad effects for transcended humanoids is a reduction in their birthrate. This is normally a fifth of what is normal for their race.