While attending John Jones' funeral, a Cwrier gave the Eleventh Doctor in the name of a "lifeform unknown".
This invitation led the Doctor and Alice Obiefune into a planet with a lot of trees, so high that Alice compared them to skyscrapers.
The Doctor told Alice he had visited the planet a year before, and that, in this ocasion, it was predominantly a desert planet. Back then, a indigenous humanoid species inhabited the planet.
However, when the Doctor returned to the planet with Alice, all the several million individuals from the species were gone.
The Doctor found corpses of a Nebulon and a Rockra on the planet's surface. (COMIC: Remembrance)