Ohia trees are dying rapidly, Why?

[kaialoha]

Ohia (Tomentosa polymorpha, aka Ohia lehua) are NOTORIOUSLY sensitive to root disturbance. In areas where top soil is minimal, Ohias tend to spread roots further out from the trunk that in areas where soils are deep and their roots can penetrate further into the soil layer thus staying closer to the trunk. Ripping and grading and 'forest floor' plant removal can be partly to blame for the demise of many Ohia in Hawai'i. Lots of folks strive to preserve their Ohia all the while ripping and clearing everything to within inches to feet of the trunk. Ohias are tall and slender and have limited 'canopy' as opposed to the giant ficus (like you see in Hilo where the canopy and thus the drip lines are huge). There is an area at the base of trees (in general) encompassing basically the circumference of the growth 'umbrella' which translates into the 'drip line' at the base of the tree (imagine being in the canopy and dripping water at the very edge all the way around the tree. THAT is the drip line). It is UNWISE to clear and grub or rip within that area. And if the soil is shallow, an area FAR outside the drip line should be avoided and the deeper the soil, the closer to the drip line you can C/G and rip. Trees are subject NOT JUST TO the soils they sink their roots into but the surface soils surrounding them as well. Lava fields typically have shallow colluvial/alluvial top soils and so through evolution, trees tend to grow large and shallow root systems as a support mechanism in addition to their nutrient uptake mechanism. I HIGHLY suggest VERY limited disturbance around Ohias, PARTICULARLY in terms of ripping the surficial soils surrounding them. In fact, I would keep ANY ripping to at least 10-20 feet in a circle AWAY from the trunk of any older Ohia and less is OK with younger trees ~ jus' sayin' ~ BTW, I'm a retired Landscape Architect with degrees in Ornamental Horticulture and Plant Identification. Also, I owned a large Bamboo, Palm, and Succulent nursery and that is how I know ~ ~ ~