Pasture to meadow

I had horses and rehomed them last year. The pastures is waist high with a variety of tall grasses, burdock, buttercup, thistle etc. I don’t mow many areas. Lots of poplar seedlings and catalpa.    What will happen if I just leave it all alone?  The lawn to meadow book would be quite helpful.

In this situation, if you were to leave things alone the successional process will happen.... field will become brush and pioneer trees and then eventually woods.  

Thank you I think this is the best end result in terms of the health of the land and the nature it will nurture?