400 
volcanic series. Two vents from the Koloa vol- 
canic series, Hanahanapuni Crater and Kilohana 
Crater, lie within the basin. 
The general topography of the basin is of 
gently sloping to moderately steep ridges and 
plains dissected by perennial streams, notably 
the Wailua River and its tributaries. 
The average annual rainfall in the Lihue De- 
pression ranges from 40 or 50 inches near the 
ocean to over 170 inches near the mountains. 
Rainfall is usually highest in winter months but 
there are no months during which no rain falls. 
Mean monthly temperatures from nine sta- 
tions below 300 ft elevation on Kauai range 
from 69 F in February and March to about 77 
F during August through October (McDonald 
et al., I960). Although no temperature records 
are available for higher elevations, there is a 
decrease in temperature with increase in eleva- 
tion, of about 3 F for each 1,000 ft. 
Prevailing winds are the northeast trade 
winds but cyclonic storms occasionally upset this 
pattern, especially in winter months. 
DESCRIPTION OF SOILS STUDIED 
Three soils occurring in the Lihue Depression 
were selected for study. These soils are located 
in or near the main area of infestation of R. 
tomentosa and Al. malabathricum and either 
comprise or are associated with the major baux- 
itic soils of East Kauai. The principal mineral 
form of Al present in these bauxitic soils is 
gibbsite, the trihydrate of aluminum oxide 
(Sherman, 1958). Detailed soil descriptions have 
been made by the Soil Conservation Service 
(Womack, I960). 
Kapaa Series 
The Kapaa series is a deep, well-drained, 
Aluminous Ferruginous Latosol developed on 
gently sloping to steep uplands on Kauai. These 
soils occur mainly in association with the Halii 
soils which lie above, and Puhi soils which lie 
below. The Halii series is developed from parent 
material similar to that of the Kapaa series, 
namely the melilite and nepheline basalts of the 
Koloa volcanic series. The Kapaa soils occur be- 
tween 200 and 1,000 ft elevation with mean 
annual rainfall from 60 to 100 inches. They are 
PACIFIC SCIENCE, Vol. XVII, October 1963 
clayey in texture but feel like silty clay in the 
A horizon (0-6 inches) owing to the strong, 
very fine granular structure. They are extremely 
hard when dry but sticky and plastic when 
moist, containing many roots and few pebbles 
in the surface layers. With depth, some mottling 
occurs on the blocky structures and pebbles are 
more numerous. These soils are used mainly for 
pasture, nonirrigated sugar cane, and pineapple. 
Halii Series 
The Halii series is a deep, well-drained Alu- 
minous Ferruginous Latosol on gently sloping 
to moderately steep uplands on Kauai. This 
series is associated with the Koolau series at 
higher elevations and with Kapaa series below. 
It occurs in belts at about 300 to 1,000 ft eleva- 
tion with mean annual rainfall from 80 to 120 
inches. The A horizon (0-9 inches) of this 
series is a gravelly clay that feels like silty clay 
and is grayish-brown in contrast to the yellow- 
ish-brown of the Kapaa series. It is somewhat 
less hard when dry and more plastic when wet 
than the Kapaa. It is used principally for non- 
irrigated sugar cane and small acreages of pine- 
apple. 
Koolau Series 
The Koolau series is a deep, poorly-drained 
Hydrol Humic Latosol developed on gently slop- 
ing to moderately steep uplands. It is associated 
with the Halii soils, and occurs between 400 
and 4,000 ft elevation with mean annual rain- 
fall of 120 and 200 inches. Most of the Koolau 
series is covered by rain forest, but some is used 
for sugar cane and pasture. 
The Koolau series is a grayish-brown clay that 
feels like a silty clay loam, with a structure that 
appears to be massive to very weak medium 
granular. It is only slightly sticky and plastic 
when moist, with matted roots and many worm 
holes and casts making it quite porous. Lower 
horizons have distinct strong brown mottles. 
EXPERIMENTAL PROCEDURE 
Roots of Melastoma malabathricum and Rho- 
domyrtus tomentosa were excavated in the 
Halii, Koolau, and Kapaa soil series and de- 
scriptions and measurements were made of 
