Keep in mind mangoes are non native. A haole crop if you will. Most mango trees planted on Oahu coincide with the building boom of the 1950's. But in reference to the article, Planting restrictions in new residential neighborhoods are definitely leading to the decline. I live on Hawaiian homelands in Waimanalo and believe it or not you are banned from planting trees over 6 feet. No mangoes here. Our neighbors are in violation with there lush tall papaya and banana trees. To answer your question, "where have all kanaka maoli gone,?" that's an easy answer, try Las Vegas, Seattle or Arizona. The kanaka maoli owners of the house I live in stay Vegas. Fact: there are more Hawaiians living on the mainland than Hawaii.  But that's another story.