Tree Maintenance on the Tri-Rail Tracks

Today I noticed that there are a lot of trees on the side of the Tri-Rail tracks that have been hacked down.  At first, I thought a train derailed and had knocked all the trees down.  When it went on for miles, it was clearly something done deliberately.

I am wondering what kind of equipment would be able to do this.  I am imagining a train mounted blade of some kind that runs down the tracks.

I posted a question on a forestry forum and got a link to this YouTube video on how the brush is cut back to keep it out of the right of way.

The smashed trees go on for miles and some of them are more than 6 inches thick.