Thanks for your thoughts Don---I always appreciate your input, and I know others also do--Also thanks for the clarification on the wheelbarrow construction it rounds out my understanding of the terminology you used, and what I thought you were saying as I carefully looked at the photo when you posted it a while ago.
Talking about poplar wood--its uses--it brings to my memory my father's choice for wagon bottoms--we used basswood--which is also a type of wood without long fibres, and wears well in high abrasion situations but maybe not well in strength. As I remember it the planks were about 1\3 thicker in cross section, I suppose to allow for its weaker characteristics in its structural character. I remember the planks being about 2 1\2" in thickness and about 12" in width
I examined a few barns that had basswood upper plates that were around 100 years old and were in great shape--except--where the roof had leaked at some point in time, you can't really blame basswood for not standing up, no type of wood would have.
I agree to another of your remarks about the weight, the basswood planks were quite light compared to hardwood planks.
I worked quite a bit on construction work early on, and the preferences for scaffolding planks were clear- and straight grained hemlock about 2\14" thick and about 10 to 12" wide--strong but light--