The most logical thought that came to me was related to the shoot-root vascular tissues linkage or connectivity. Experienced arborists would know that a tree with fungal wilt infected roots would exhibit symptoms of dieback on the shoots that are directly connected to these roots. On the same token, I felt it could be because some parts of the roots must have received more Potassium (K) that are essential for flowering and fruiting.
Then, I saw this Yellow Flame Tree (scientific name: Peltophorum pterocarpum) in the middle of Orchard Road with a similar phenomenon. It was interesting how the top half at a 45 deg angle was with flowers and the other half was completely devoid of any flowers. Just days ago, there was this islandwide synchronized flowering of the Golden Penda Tree (scientific name: Xanthostemon chrysanthus) and the ones near my house were also with half crown flowers.
This set me thinking. I observe that the Golden Penda trees near my house showed more flowers on the side that receives more sunlight and there were virtually no flowers on the side facing the buildings. So could the flowering or non-flowering of a tree be simply related to the amount of sunlight it receives and that the sunlight is just the stimulus to trigger its flowering?
So which is correct? Could it be a combination of the above factors? I have no confirmed answers on this but the following links are interesting for reading: