OK, I know they say DIY'ers should not attempt hardwood on stairs but we're honestly not your average DIY'ers and have worked with hardwood floors, paneling and other assorted stuff over the years. But we have no previous experience with the solid stair treads and risers that replace the plywood sub-stair instead of covering it up. We installed Brazilian Cherry solid treads and risers and spent days at it because of how careful we were to match the construction-grade wood skirting-stringer on each side which, of course, was not square anywhere. When first installed, there were no gaps between treads and skirt-stringer but now, two weeks later, tiny gaps are visible in some places. Yes, we acclimated the wood in the very location for one month. Here in Alaska it is VERY dry with forced air heat and wood stove going almost 24/7. Temp outside ranges from +35 to -15F (yes, minus 15) and we have strong winds (right now it is gusting at 85+mph). Are these gaps caused by normal seasonal shrinkage in the hardwood treads? If not, should we correct it? How? thanks!

Solid Hardwood rarely shrinks in length. A solid tread can shrink across the width, but one shouldn't notice that because of the nose overhang. But due to your extreme dryness there in Alaska, I would suspect you are having some gapping of the treads. You could consider using a humidifier to raise the interior humidity to more comfortable levels ( 40+ % RH ). This may, and should. close up those small gaps. It will take awhile. If it doesn't, then all you can really do is caulk those gaps. That is what is often done anyway.

As the Armstrong/Bruce tech guy put it in a webinar I attended "Putty is you buddy"