The lava flow that you live on is a lot older than where i live. This area was flowed on in 1955, yet our area is full of trees. So it's not just the age, it is the rainfall. In very dry areas lava flows remain lava flows for a very long time.
Yes, that is much more recent--and it makes sense that the dryer climate would make the regeneration much slower (especially since Ohias aren't very fast-growing anyway.)
John, most people think of coastal areas of Hawaii as defining the region, but these are volcanic, mountainous islands--the further up you go, the cooler it becomes. At 13,000+ feet at the top of Mauna Loa, there is snow much of the year. Since I can't stand air conditioning, woodsmoke, or electric heating, a mild climate suits me just fine, and a twenty minute drive brings me to sea level and places where strictly tropical fruits are abundant.