Northview Dairy is a blog I follow, good photos, nice writing, and once a window into the modern small dairy farm. I say "once" because they sold off the cows in the recent past, except for two. Today threecollie (the blogger) records a visit to their pasture to check the fences, and scope out the birds, in passing noting the proliferation of maple seedlings starting to grow because the cows no longer keep them down. She wonders how long before the pasture is forest again.
My answer: not too long. My last visit to the farm where I grew up showed the sidehill pasture was completely grown to trees, trees probably 30 feet high.