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at many points effectually covered over and obliterated by native plants. 
If the ancient trail mentioned above was entirely obliterated by native 
vegetation, and these recent surveying trails have likewise been quickly 
overgrown by native vegetation, why will not the native vegetation 
obliterate in the same way any trail through the native forest if this 
trail is not kept open by the hand of man? All available evidence 
indicates that the native plants will accomplish this result provided 
that the opening made to accommodate the trail has not become oc- 
cupied by some rank-growing introduced plant which can hold the 
ground against the native vegetation. 
Of the introduced plants which can successfully hold off the native 
vegetation when once they become established in a trail, Hilo Grass is 
by far the most serious even as it is the most frequent offender. To 
reach any trail leading through our forest it is necessary to pass through 
growths of Hilo grass. The fruits of this grass are adhesive and de- 
signed for distribution by adhering to the bodies of passing animals. 
Consequently any trail opened in the forest is liable to infection by 
Hilo grass throughout its entire length, the speed with which infection 
will take place at various points along the trail depending upon the 
number of people using the trail and the frequency of their trips over 
the trail. If a trail is opened up and used for a brief period only and 
then abandoned it will probably be closed up by the native plants much 
as the trails have been along the makai boundary of the Hilo Forest 
Eeserve, but the longer the trail is kept open and the more it is used the 
more extensive will be the infection by Hilo grass and the chances of a 
natural closing of the trail at any point will diminish as the infection 
increases. 
HILO GEASS SPEEADS FEOM TEAIL TO FOEEST 
When Hilo grass has once become established in an opening in our 
native forest it not only successfully holds the ground occupied but 
makes it a base from which it keeps up a constant and successful 
pressure against the surrounding vegetation. The rapidity of its 
progress will depend upon the density of the native vegetation with 
which it has to contend. Its method of procedure is to .encroach upon 
the undergrowth, eliminating the smaller plants by overtopping them, 
and preventing the reproduction of the larger plants by smothering out 
their seedlings. The existing generation of shrubs may survive for a 
considerable time but the grass prevents the growth of seedlings of the 
same species to succeed them when they finally succumb. The Hilo 
grass exerts a deleterious influence upon the taller growing shrubs and 
the ohia trees for when it has replaced the low-growing ferns and tender 
herbaceous plants which normally cover the forest floor and its roots 
have permeated the thin layer of soil and, organic matter which cover 
the roots of the trees and shrubs, these plants show signs of distress and 
soon weaken and die. As pointed out above, the presence of Hilo grass 
beneath these trees effectually prevents the growth of seedlings of the 
native plants and the ultimate result is that the forest is replaced by 
grassland. 
On the slopes of the mountain range back of Manoa Valley is a steep 
watershed net over a mile wide at any point. The native plants have 
not been able to create as dense a cover on the very abrupt slopes of 
this watershed as they do on the gentler slopes and consequently the 
resistance of this forest to Hilo grass is below the normal. It has long- 
been evident that the native forest is yielding rapidly at many points be- 
fore the solid ranks of Hilo grass which are pressing in upon it from all 
sides, yet the Government has permitted the construction of an arti- 
ficial trail throughout the length of this watershed and has for many 
