Bill Tindall
One species is stored in each section. Lets us say you are building a cherry table top. I set up two sets of horses and start removing lumber from the rack. Rejects for whatever reason (usually inefficient cuttings among defects, lengths or widths) go on one horse and possibilities on the other. When the "keeper" pile has accumulated sufficient lumber to make the top I take another look at it to be sure. The "rejects" go back into the rack. For something like a table top where I want the best possible outcome I may empty the rack. It is hardly a significant fraction of the total time to build something. Plus it is good to reacquaint one's self with the inventory.

If I was storing smaller quantities then I would make the horizontal supports smaller and space them for only a few layers of lumber. If one has plenty of room a shorter rack for the inevitable accumulation of shorts is handy. I have a shots rack that is located under the stairs.

If anyone is into woodworking for the long haul there is much to be said for buying several hundred bdft of your preferred wood when the timing is right. For example, Europe was a strong market for our cherry and the quality of what remained for domestic use got exceptionally bad. The export market has tanked. Upon my last visit to a lumber mill I saw cherry for sale as good as 30 years ago. Instead of piddly 5-6" widths with lots of sap there was lumber over 12" in packs of top grade cherry. On the other hand walnut is in high demand and this might not be the best time to buy a pack of walnut unless it looked especially good. The bottom line is if an opportunity to buy a large quantity of lumber turns up, seize it if you have the money and space.

With much to choose from there will be little waste on a project. Lumber has been an excellent investment. Quality continues to deteriorate. All good reasons to invest in lumber.