This is a phenomenon that has been observed as far back as
1906. In the late 1960’s a major decline of ohias took place. In 1986 the
USDA Forestry Service published a lengthy article on the subject http://www.fs.fed.us/psw/publications/documents/psw_gtr086/psw_gtr086.pdf
The decline is complex and not totally understood. We do know that older
trees are not as vigorous as they once were and are more susceptible to stress.
The stress may come as a prolonged period of rain or the opposite, drought;
poor draining soils will compound the problem. Other factors may include vog (volcanic emissions),
low soil nutrients, bulldozers and perhaps dense stands of invasive species.
These stresses alone may cause some type of decline. But what usually happens
in the next phase is the invasion of a root rotting fungus or perhaps a tree
boring beetle. Fungal organisms are often found infecting the roots of
declining trees but are not thought to be the primary cause.
Young ohia trees can grow well for many years on shallow
soils. Eventually they may decline when they become large trees, and the
shallow soil simply cannot support their growth, particularly under drier
conditions.
What can be done? Actually, not much.
·
If the property contains several older ohia
trees, planting young ones will diversify the age group.
·
Keeping
the trees healthy is important; fertilize if needed.
·
It is
impractical to water a stand of ohia trees during a drought, but watering a few
trees around the house may be feasible.
Photos by Forest and Kim Starr
