The oil from Eucalyptus trees, which are native to Australia, is known for its medicinal properties.
The oil is known for its properties.
"which are native to Australia" describes the trees, but is not necessary to convey any meaning about the oil.
Now, if there are trees under discussion which are not native to Australia, then the first comma needs to be deleted, since the only trees of interest are those not native to Australia. Just as if you say
The boy who is tall has red hair.
That implies that there are other boys who are not tall.
The boy, who is tall, has red hair.
means that the boy has red hair, but by the way, he is also tall. Nice to know, but not necessary.