Wooden Floorboard repair

[elbow]

Hey Guys

I am removing old wooden door jambs and re-sanding my floorboards - However, as you can see, where I have removed the door frame, I am left with a hole in my floorboards each side. In the hole there is some concrete which i assume are foundations. When i replace the skirting i think about half of these holes will still be showing. What would you suggest i can do to fill the holes?  any suggestions are very much appreciated -