The trees spread across the world, as man finally withered and died. Killed off in a last great mass extinction caused by humankind’s continuous destruction of the animal population and most of the plant world. Pestilence, fire, flooding and starvation had done their jobs.
All that was left were trees, rivers, marshes, seas and oceans.
The trees kept pumping out oxygen, the world was now habitable for any incomers, but there were none. Aliens may have admired our world, but they exist in civilisations too far away. None of them had things like warp drive. A nice idea, but not really feasible.
Nothing grew, except a soup of bacteria. One day that might evolve into the next great family of animals, insects, worms, critters. If man returned millions of years later he would not recognise the planet or its contents. Maybe the trees would remember….