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Houolulu, June 9, 1922. 
HAWAIIAN FORESTS 
(By HAEOLD L. LYON, Ph.D.) 
ORIGIN OF HAWAIIAN FORESTS 
These islands have been built wp through the activity of volcanoes. 
The soils on our mountains are entirely of volcanic origin. The native 
Hawaiian flora has throughout its entire history been called upon to 
occupy territory built up by recent volcanic eruptions. In fact this was 
the deciding factor which originally determined what plants should 
enter into the native flora, for they must have been plants that could 
invade and establish themselves on volcanic lavas and cinders recently 
ejected from some volcano. The succession of native plants on these 
newly created areas has undoubtedly followed much the same course 
ever since there has been a native flora, the succession of plants on 
any particular lava flow or cinder-covered area being determined by the 
climatic conditions surrounding that particular lava flow or cinder 
waste. On the slopes of Hawaii 's active volcanoes are recent lava flows, 
the ages of which are well known. On these lava flows we may observe 
the normal succession of Hawaiian plants at the present time. Do we 
find on these lava flows that the native grasses first occupy any given 
area, or the lava flow as a whole, and that they are in time followed by 
native shrubs and eventually by native trees? Do we now find at any 
point that these lava flows are first occupied by Hilo grass and that 
this is in time followed bv native or introduced shrubs and trees? Not 
at all! * * * * 
The plants that first appear on these lava flows are, almost without 
exception, native species among which seedlings of native trees pre- 
dominate. If the lava flow traverses a. region subject to a moderate 
to heavy rainfall, seedlings of ohia trees far exceed in number those 
of all other species, and a most remarkable feature is the quick appear- 
ance of a large number of ohia seedlings at points far removed from 
fruiting ohia trees. On a lava flow of this sort a forest community of 
native plants, including trees, shrubs, herbs, ferns, mosses, etc., is built 
up and thrives without interference from Hilo grass, for the soil con- 
ditions are not favorable to this pernicious weed. By studying the flora 
on lava flows of varying ages on the slopes of Mauna Loa and Mauna 
Kea one can easily determine that the normal sequence of events in the 
building up of Hawaiian forests has been much as follows: 
Areas recently covered by volcanic ejectamenta are quickly invaded by 
native species of forest plants, which in the course of a very few years 
effectually cover those portions having a woodland climate. When these 
native plants first take possession of a lava flow they occupy the cracks 
in the pahoehoe or the chinks between the blocks of the aa, for in no 
case is the lava covered by any semblance of soil. As the forest develops 
a thin layer of soil is created through the decay of leaves and other 
debris falling from the plants, which mingles with the fine material 
formed by the slow decay of the superficial lava. In the course of time 
considerable soil is built up, being constantly added to from above and 
below. Trees and shrubs mature and die and their bodies are added to 
the soil, so that eventually the still solid portions of the lava are cov- 
ered by a soil of considerable depth, the particles of which filter down 
into, and effectually clog the interstices in the rocks below. Ohia trees 
will not root deeply in a water-logged soil. Their roots will follow the 
cracks and crevices in a lava flow to great depth, so long as these cracks 
and crevices are drained, but let their free drainage be stopped and no 
ohia roots will enter. The first stand of trees on a lava flow send their 
