It didn’t take long for these early New Englanders to realize that the long, wide planks cut from the heart of the big, old-growth trees had a denser grain pattern and less moisture than the outer sapwood. This made heartwood far less likely to splinter or warp. Plus, the strength imparted by the tight grain pattern gave it the durability to last practically forever.
Over the years, however, the lessons of making wide plank wood floors primarily out of heartwood were lost in the frenzy of growing demand. In the quest to build more homes cheaper and faster, it became acceptable to use younger and younger trees with very little heartwood. Less developed trees led to shorter, narrower planks.