david weaver
I would say, do the following: Next time you find beech, don't discard it, but cut it, look at the heartwood. If it's light or dark, save a few boards from it. Nothing fancy, just a few.

Do the same again until you find a tree that's opposite (where the heartwood is substantially lighter or darker than the first.

Kiln dry the wood, and then hand plane the two samples. In my estimation, the density won't be that different. None of my beech seems noticeably different, but so far, the darker the heart, the more resistant it seems to be planing.

I have tracked three here for sure:
* First beech test - board with very dark heart - shortest planing lengths and least weight. The board had sort of a dusty feel when planing. I didn't plane the sap, it's saved for moulding plane blanks.
* second beech test - board with heart that was lighter - longer planing lengths, and planed weights probably 50% higher than the first, same sharpening method
* sap planing here with the last two irons - sap only, board with lighter heart (similar in color to the second beech test board, but planing the sap side in this case). more feet and more weight planing.

I couldn't tell you exactly why that is, but it's noticeable. I think there are two things happening - 1, the wear is occurring faster than the density differences (proportionally) and the harder heart of the first board probably got to a point where the blade wouldn't enter the wood without help a lot earlier even at the same geometry.

Looking at the results here, the beech sap planes longer than cherry. I don't think cherry presents more wear, but I think it's got more spring and takes a slightly sharper iron to get the plane into.