There are some horse paddocks near to where I live, and in one of the paddocks sits a decent-aged oak tree. Unfortunately, likely because of the ground compaction and grazing pressure beneath its crown, there is very evident crown retrenchment. Unfortunately, the retrenchment seems quite sporadic, with very little order to how the branches are dieing back. Clearly, the oak is still in the process of establishing a new crown at a point where an equilibrium is achieved between energy levels and crown extent. We can also observe a large hollow near the base of the tree, suggesting fungal decay of the heartwood region. Because of the grazing pressure beneath, I dare say that there is perhaps more parasitic fungal activity as well (of course, this is just a guess).
Arboriculture 
What a sad sight, horses, or rather horse owners, in my experience have a complete lack of respect for trees.
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Unfortunately! Nothing gets in the way of a horse, eh!
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