Hi Crystal, 

At this time of year it's not unusual to find these very dense 'ant piles'. It looks like there may have been a large hatching. Most of the ants we have here aren't considered pest ants and typically these piles are temporary and the ants assume 'normal' ant behavior after a short while. As long as they aren't bothering you, feel free to leave them alone. They'll help to aerate your soil and can be great decomposers. They definitely shouldn't harm your trees. Thanks and take care!