@Mr. Peet Hi Mark, do you have any idea what this wood could be? I would appreciate your expert opinion.
I am not an expert. My opinion....well, you have done a lot of work, however it would have been nice to see the face cleaned up too. Seeing the knots cleaned up can help. Willows usually have smaller pith hearts than the Aspen group. Your inner bark matches well to several willows and several Aspen. Being in the same family makes sense. Likewise for wood color and wood smell.
Your tree was only about 10 DBH when harvested and milled. Was it from a pallet mill? Otherwise that is small. At 10" DBH, Big-tooth and Quaking aspen are just starting to form coloration to heartwood. Likewise to be said about Eastern Cottonwood, White poplar and Black poplar. Balsam poplar often has heartwood at 10"DBH, but is it even in your area?
The tree willows also start forming coloration to heartwood at about 10" DBH, however, Black willow often does at 6" DBH.
You have 8" diameter and about 16 years growth, averaging 1/4" per year. The first 5 years average way more growth. This proportion is more often seen in 'pople' than in willows for your area. Based on what I see so far, I am leaning toward 'Lombardy' poplar, the male form. It starts with rapid growth and has heart color by 4 to 5 inches diameter. It often sucombs to sickness between 8-12"DBH. It has the stringy inner bark and often has a unpleasent smell.
These are just conclusions from general information and knowledge. I have yet to look at your end grain pictures.
