When I walk through pines or hemlocks, I notice a serious lack of undergrowth. Pines drop such a profusion of needles that almost anything that might try to grow underneath is choked out or left with too little sun. Hemlocks seem to kill what's underneath- maybe with too much shade or maybe through their rhizosphere. So, in places where I want grass to grow or where I would like to encourage any sort of understory to help fight erosion, I am eliminating pines and hemlocks and pretty much any evergreen.
A friend recently questioned this line of reasoning with the argument that trees themselves fight erosion. I cannot argue against that. However, there are places, like here-
where I see other problems. Snow did not collect here so the ground did not get that gentle blanket. Water did not even penetrate the needles that collected here. We had many good reasons for cutting down these trees, but a benefit I did not predict was this. It has taken two summers for grass to establish, but this winter, the snow collects here as well as anywhere. And that little drop off is definitely eroding less as daisies, grass, briars, daylilies, etc. grow on it.
Cutting down trees can certainly lead to erosion, but sometimes, it's actually a better choice.