Why do farm fields often have one lone full grown tree in the middle of them?

Question

i often drive in a rural setting, and i've always wondered why farmers sometimes have large, massive trees standing alone in the middle of their planted field. its seems like it would be a trouble to farm around them, but they look nice though.

Answer 1

When the farmer first plowed his field he piled all the rocks in a spot where it is unplowable....because of rocks.  The tree lets him know that he cant plow there.

Answer 2

I had this same query. Most of the answers make sense and the reason on any particular farm is probably one or more of the previously posted answers. While shade, soil conservation and boundary markers make the most sense, I also theorized that many of the crop eating pests like raccoons and opossum escape danger in the nearest tree. If you only have one tree, isolating and removing the worst offenders gets simpler.