Regardless of their individual innate requirements for water, new plants need to be watered very regularly immediately after they are installed into a landscape. As they mature and disperse their roots, the regularity of supplemental watering becomes less important, and ‘drought tolerant’ plants may not need to be watered at all. Maturing larger trees generally get what they need from the landscape around them.
Automated irrigation systems that are designed for new landscapes are designed for what the plants need while the landscapes are new. As the landscapes mature, the irrigation systems may need to be adjusted accordingly. Drip irrigation or bubblers that were needed to water new trees while they were young and confined should be moved farther from the trunks of the trees as roots disperse, and should eventually be removed and capped.
This is very important, since water applied directly to the trunks of some maturing trees will promote rot and other disease. For some, it promotes buttressing of roots that can displace concrete or other landscape features. If nothing else, it is just a waste of water.
Whoever installed the irrigation to this young London plane tree knew how to do so properly. The bubbler was likely over the confined root systems of the formerly canned tree just after it was installed. It is installed in such a manner that it could have been moved over as the tree grew, replaced with some sort of drip irritation hose to curve around the tree (if such a device had become necessary), or simply removed.
Now that the tree is as mature as it is, the bubbler should simply be removed, and the riser (where the white ‘L’ is) should simply be capped. The tree gets what it needs from the rest of the landscape around it, and really does not need much water anyway. It could probably survive without any supplemental irrigation at all. The bubbler is really just wasting water.
However, because so-called ‘gardeners’ are what they are, the bubbler remains, attached to an unsightly bit of exposed pipe, and wasting water on the base of the trunk of the sycamore. Because this tree and associated bubbler are right next to a parking spot in a parking lot, the pipe is very likely to get stepped on and broken every once in a while. In fact, the fresh Teflon tape on both ends of the pipe suggest that it was repaired quite recently, rather than removed.
Fortunately, the sycamore will not likely be damaged by water applied directly to the base of the trunk.