Factorio Forums

With a bit of googling around it is possible to learn, that in map editor one can remove entity by using entity cursor tool and pressing 'x' or by pressing rmb when brush is selected.
However, entities created automatically during the map generation are ignored by 'unbrush' function.

didn't know about the unbrush fuction. i have a map i wanted all concrete.
brushing the concrete on left the trees from map generation.
brushing them with water to remove the trees, then painting land (optional), then concrete worked.

This is not a bug, rather an obscure feature.
You can un-spray and un-brush by using right click with the right mouse button.
However if you have a specific type of entity selected in your cursor(for example a specific type of tree), it will only remove those entities, leaving the rest intact.

So it has nothing to do with generated trees, rather you had a type of tree selected. Use the clear cursor key and now your brush will remove all entities. It works the same way with resources.