Stakes For Lumber Loads: Hardwood Vs. Softwood

In the Owl Mountain Models video (https://www.youtube.com/watch?v=7LngArG22gU ) on assembling their lumber load kit the narrator states (at 12:30 into the video) that vertical stakes used to restrain the load were hardwood.

It seems to me that the vertical stakes more likely would be the same wood as the load and stakes would originate from the same forest area near the mill.

I've looked at a number of prototype lumber loads and sometimes the stakes appear to match the load and sometimes they don't.

And, of course, sometimes the stakes are made from tree saplings.

The AAR's "Rules Governing the Loading of Forest Products On Open Top Cars" specifies "Stakes, hardwood, southern pine, long leaf pine, fir, spruce, larch or hemlock...or green saplings..."

Does anyone have more insight into this? Were softwood shipments usually restrained with hardwood vertical stakes?

Thanks.

Bob Chaparro

Hemet, CA