That is some of it and it varies a lot based on the species, though I'm a lot less knowledgeable there. In the hardwoods I usually work with (walnut/maple/pada

That is some of it and it varies a lot based on the species, though I'm a lot less knowledgeable there. In the hardwoods I usually work with (walnut/maple/padauk) its fairly minimal. A nominally 4/4 board usually comes in about 1/16" small; which is a lot less than I lose running it through the planar. Some of that could be the sawmill skimping out too and cutting just a bit undersized.... I'm finding quoted numbers between 2-8% volumetric shrinkage (https://www.wood-database.com/wood-articles/dimensional-shrinkage/ https://www.wood-database.com/wood-articles/dimensional-shri...), which is still quite a bit less than you find in the small dimension of a 2x4 (2"-> 1.5%, or ~33%)