160 
roots down into the cracks of the lava, and as soon as the hard surface 
is covered with a thin layer of soil they also spread out their roots in 
this thin covering. When the second and successive growths of trees 
Start in this forest the cracks in the lava are as a rule already stopped 
up with fine material, and consequently second and subsequent growths 
spread out all of their roots in the surface soil. In a heavy rain-forest 
it will be found that the native trees, particularly ohia, are very shallow- 
rooted; in fact, the upper surfaces of all of their roots are only covered 
by a thin layer of decayin^^ leaves and twigs, which are in turn well 
shaded by the close grow^th of native herbs, ferns and shrubs which 
normally cover the forest floor. 
HAWAIIAN TEEES SENSITIVE TO NEW CONDITIONS IMPOSED 
UPON THEM 
Prior to the coming of the white man and his domestic animals, the 
native forest was not subject to invasion by hard-footed P.nd foliage- 
destroying animals. The thinly veiled roots of the native trees in the 
forests on the older lands w^ere not subjected to disturbance or ex- 
posure through the interference of man or animal. When the white man 
invaded these islands and began to exploit them in various w^ays he 
soon introduced adverse elements new to the experience of Hawaiian 
forest trees and against which they had evolved no protection. It is 
a fact too well known to require detailed discussion here that to kill 
the trees in any old Hawaiian forest it is only necessary to remove for 
a short time the natural undergrowth from the forest floor. If in addi- 
tion the thin layer of organic debris which covers the roots of the trees 
is seriously disturbed, the death of the trees is further hastened. 
In the course of ten years we have seen a large area of dense native 
forest in the lands of Kehena on the Kohala mountains killed out 
almost to the last tree by the invasion of stock which destroyed all 
of the undergrow^th and trampled on the roots of the trees. Many 
specific examples might be cited to illustrate the extreme delicacy of 
Hawaiian forests and their acute sensitiveness to the slightest physical 
interference, particularly if that interference entails a disturbance of 
the plants and soil above their roots. The construction of a road, trail 
or irrigation ditch through a native forest is almost invariably followed 
by the death of a considerable number of the trees along the line of 
disturbance, the extent of the destruction depending upon the violence 
of the disturbance and the length of time through wiiich it is continued. 
If you look down into Kahana Valley from the ridge of the Koolau 
Mountains you will see a brown sw^atli of dead trees winding through 
the forest in the upper portion of this valley. This swath of dead trees 
marks the course of the irrigation ditch constructed in recent years 
across this valley. If you will look back on the lower rim of Kaau 
Crater from the top of Olympus you will see a broad band of dead trees 
which marks the course of a portion of the trail covered by Eule V. 
CLOSING OF TEAILS Bf VEGETATION 
During the past year we have found and followed an ancient trail 
through the Hilo forest whicli has been entirely covered over and obiil- 
erated by native vegetation. Al tlie present timo it is only possible 
to pick out the course of this tvciil by unearthing fern logs at certain 
points which paved the trail, by noting ancient blaze marks on the trees 
and the passageways which were cut through large fallen tree trunks. 
Last summer, in surveying the Hilo Forest Eeserve boundaries, it was 
necessary at certain points to cut trails through the edge of the native 
forest. These surveying trails were immediately abandoned after the 
passing of the surveying party and in the course of a few montns w^ere 
