Improper sprinker head placement and overwatering causes the 2×4 effect. In short, if you put a 2×4 in the ground, eventually it will rot out. Overwatering and poor watering practices can and do lead to this phenomenon, even with with established trees in our area. Ideally, sprinkler heads should be positioned away from the tree base to effectively water beneath the tree canopy and not directly on the tree trunk.