Tree roots and leaf mulch/litter makes for very good erosion control.

Not always.  I have some CRP I am putting back into production where trees started and grew in low areas going towards higher ground.  Trees shaded out the grass and the gully is as bad as anytime we had it in cultivation.  I wanted dad to get them out when they were small but the soil consevation guys said let them go, they are a good mix for wildlife.  Maybe if these people had a better working knowledge of conservation and wildlife there wouldn't be such stupidity going on here locally.  No shot at you, justing bitchin' about the local yocals.