How might a person of limited strength pry embedded lumber out of soil?
I would use a shovel and a short piece of wood. Drive the shovel under 1 end ov the board to be lifted pry with the shovel, when the end raises up slip a short piece of 2×4 or other scrap wood under the board, move down and repeat.
I live in the PNW also and sometimes wood gets stuck in the mud, if done while wet a wrecking bar should not be needed. A constant pull on the shovel handle should pop it out of the mud. One of my grandsons had 5-6 pealing poles for a fort down by our creek 1/2 covered in mud, I showed him how to pop the end out (I used a rock to support the first end) then the second so he could start building again. He got the rest out by himself and he is only 11.