Ray, the regs in Mass. are such that if a harvest includes wood going to a biomass power plant or pellet plant- a certain amount of tops/slash must be left on site. That much happens without even trying because when being dragged out- some breaks off- and some "large woody debris" is too clunky and odd shaped or hollow or whatever so they leave it- this is all done for habitat purposes. Also, much "woody debris" builds up at the chipper- and the skidder will drag much of that back into the forests- some will be dropped on muddy roads and other piles will be left all over the site- such piles are said to be useful for wildlife.
When a property is high graded- no consideration is given to any ecological, silvicultural, economic, or aesthetic values. When it's not high graded, consideration is given to those values- but each forester does it differently and to a different extent, some better than others. The enviro groups don't seem to distinguish good forestry work from bad- to many, it's all hideous.
There is no magic number of trees or percentage of trees that should be the goal. It all depends. If a property had been high graded once or more than once- most likely a very high percentage of the trees are poor quality from a forestry point of view. Then the first genuine silvicultural project should remove a higher percentage of the trees than if it's a stand consisting mostly of nice trees. I've gone as high as 50% of the basal area. Even a formerly high graded stand- if you remove 50%, you will have greatly improved the long term value of the stand.
If a stand is fairly mature and of good quality- a good general rule is to harvest a fourth to a third of the basal area. Since the logging machines are big and have to go pretty much everywhere to get scattered trees- you don't really do less damage by cutting fewer trees- and if you try to do less, the economics of logging won't permit it- and nobody will buy it.
As for managing just for commercially valuable species- it's not quite that simple because there's a gradient of values- it's not that they're either good or bad- and that gradient changes constantly- so it's a bit of a guessing game. In areas like the U.S. South, their forestry is almost like farming- they cut everything, "clean up" the site, and plant the next generation- nothing like that happens in New England, or very seldom.
If thinning a stand- as I walk through the forest- I leave the best of what's in front of me. If I'm walking through a mix of low value trees, I leave the best of the low value species- I don't try to eradicate them. Given the fact that so much of the forests in this region are of poor quality- if we tried to manage for just the high value species- then many projects would be clearcuts- and I happen to hate clearcuts.
I've often marked an oak, or black cherry, or sugar maple- all high value species- if that tree is not growing value- due to slow growth or something wrong with it and left a nearby low value species like hemlock, poplar, or even pine, which is also a low value species- or mid value, depending on quality.
Forestry - good forestry- is extremely complex- and the classic critiques of forestry don't fully grasp just how complex it is- and how much good foresters attempt to consider a balance of economics, biodiversity, aesthetics, etc. Good forestry is rare- bad forestry is the norm. Unfortunately, 99% of the criticism of forestry assumes it's all bad and that good forestry is not possible. I've pushed for a lot of reforms of forestry- getting 0% support from forestry people and slightly more from the enviros- with the result, of no reform.
You say there is a shortage of ground cover. There is in places but I don't think it's all that common. In many areas- the problem is due to excessive deer populations. In other areas, it's due to very dry soils. In other areas, it's due to invasive species. I doubt that much of this problem is due to heavy logging. Many forest stands with high volumes of timber- have very little or no ground cover- especially mature stands of conifers- which cast heavy shade. If you thin those stands, especially if fairly heavily, you'll see plenty ground cover within a few years. It's inevitable- if the sunlight hits the ground- and the ground is fertile with moisture, plants will grow there - sometimes it's new trees or ferns or herbaceous plants.
As for short rotations- that's a complex problem too. Ideally, very light harvest every 10-15 years would eventually develop into nice forests. The better the forest becomes, the longer you can extend the rotations. Let's say a stand has been thinned 2-3 always leaving the best trees- now it's mostly oak, pine, sugar maple mix- with a scattering of poplar, hemlock, hickory, butternut, red maple, etc. Mostly straight healthy trees with good crowns- with the high value species making up maybe 3/4 of the basal area. Such a stand is now probably adding value at a high level- so it's like an investment in a blue chip stock (no pun intended)- then there would be no reason to cut again for at least 3 decades- based strictly on economics.
That is, and I'll let this rest for now- TRUE economic forestry is actually in tune with good ecological forestry. Most forestry is not only bad ecology, it's also bad economics- after all, high grading is terrible economics, other than for the logger's short term interest, not the owners.
Oh, again, I'll emphasize- forestry, even good forestry, ain't perfect - but, it's a lot more perfect than seeing a new shopping center or new subdivision and I particularly detest so called solar "farms". They are popping up like mushrooms in the north central Mass. area- all paving over fields and forests- while claiming to be "clean and green" energy.
PS: as to forestry being my chosen career- it really wasn't- I kept changing my mind in college- and changing my major several times- but the college finally told me that I can't keep doing that - so I had to stick with the last one I was in- forestry- if I had more time to be a professional student- my next would have been geology and the final would have been cosmology, after all, what's more exciting that cosmology?