In general they do leave "seed trees " but they only need as few as 3 trees per acre to effect the spaces mix in the regrowth.

Those 3 trees aren't nessesary though. The Forrest floor is loaded with seeds that can survive longer than a decade waiting for the right time to germinate. In many cases the sunlight hitting the ground is the trigger they need, and in most cases a "clear cut" will be a 9 year old forest 10 years later.

Check out the silvicultural guide for the northeast:

https://www.fs.usda.gov/research/treesearch/45874

It turns out most logging in the northeast already yields a diverse ecosystem as quickly as the next year, and no planting is nessesary.

Forresters can target different species mixes in the regeneration by using different harvesting methods.

Pretty cool stuff.