Interesting in how I do much of what the original poster described when clearing trees with my EA Wicked Root grapple and MX6000 with loaded tires and a heavy old-school 1000# box blade on the rear.
Weight is your friend.
Someone mentioned picking up the root ball once the tree is down and dropping it a few times, which works. I also raise and lower the open grapple teeth against the root ball to "work it over", poking and scraping to loosen rocks and dirt stuck to the root ball.
I would rather as much of the dirt as possible goes back into the newly created root hole.
Also mentioned was ground condition. Hard pack summer ground seems to result in more break-offs rather than roots being exposed. Maples seem to be the ones (at least for me) which crack most often at ground level, often exposing jagged "trunk spikes".
I've found best results pushing trees after a good soaking rain as long as traction can be maintained.
One other variable is speed...not meaning a running start, but rather, a mindset of slowly pushing, leveraging the treetop weight to your advantage. Sometimes if you can get the tree to start leaning, and then dig into the roots on the side under the tractor and use the curl or forward tractor movement to lift at the root, it can help topple over some of the more stubborn trees. (Meaning it is not always just pushing on the tree trunk that eventually takes it down).
Lastly, the process is kind of enjoyable and it's rewarding to knock down trees, especially when reclaiming pasture, or to thin tree lots, so the remaining trees can grow with less competition.
