The story is set in the distant future, maybe 3000AD+. I think the astronaut is a cyborg many hundreds of years old and he crash lands on this planet. On the planet he finds empty streets and houses, as if people just disappeared. In the houses there are sometimes trapped pets. The astronaut spends his time going around freeing trapped animals and feeding them.
As he grows older he begins to plant trees until one day another spacecraft flies over and it sees a giant message on the planet spelled out in the forest he's planted, and there it ends.
Does anyone recognise this one?