Figure 1, Photo by Bruce Hagen
Overwatering is a major problem particularly where drainage is poor or where water collects near the base. This can lead to poor soil aeration, poor growth and increased susceptibility to root pathogens.
Many trees once established do not need to be watered. Many native species like oaks planted in the landscape can be damage or killed by regular watering.
Drip emitters are fine for establishing trees in the landscape, thereafter they are of little value unless the system is expanded as their roots grow outward. The root zones of trees extend well beyond their driplines. Emitters left near the base of a tree can result in root disease problems by keeping the soil there continually moist. This favors the development of root pathogens.