Theme da australis-Eucalyptus Savannah in Papua — Heyligers 
487 
quite a range of topography, on slopes from 
0°30' to 20° (average 8°). The soils have in 
common a rather thin crumbly topsoil, 7-1 5 cm 
deep, which is underlain by massive structured 
sandy loam or sandy clay loam. Deeper layers 
are greyish-brown or yellow-brown clays in the 
case of texture-contrast soil, or brown, reddish- 
brown, or yellowish-red sandy loams to sandy 
clays in the case of regosol, often with man- 
ganese concretions. The pH of the top layer 
varies between 5.5 and 8.5, of deeper layers 
between 4.0 and 8.0. About 30% of the ground 
is covered by litter, but the area covered by grit 
and gravel is much the same as in the Themeda- 
Heteropogon group. 
The Themeda-Sehima group occupies the 
higher parts of the transects; it occurs on rego- 
sol on hills with slopes varying between 11° 
and 24° (average 15°). Only a 5-15 cm-deep 
sandy loam topsoil has a crumbly structure ; 
deeper layers are sandy loams or finer textured 
soils, to clays, with a massive structure, dark 
brown, merging into reddish colours. Pieces of 
weathering rock are present, sometimes already 
at depths of 35 cm. The pH of the topsoil is 
6. 5-7. 5, of deeper layers 5. 0-7.0. About 38% 
of the ground is covered by litter and 25% by 
grit and gravel, whilst stones and rock frag- 
ments cover 3.5%. 
The Themeda series occurs on the texture- 
contrast soil of transect 1. One of the main 
characteristics of its locality is the excessive 
cover of grit, which averages 53%. The The- 
me da-Sorghum series occurs on black clay soil, 
of which the upper horizon appeared to contain 
red soil material, which disturbance is presum- 
ably caused by wartime road works. The Se- 
hima-Heteropogon series occurs on the steep 
hill slope of transect 2 (28°), which for al- 
most half the surface is covered by rock out- 
crops and fragments. 
With regard to an explanation for the rather 
simple group distribution pattern, there is no 
direct correlation with soil type or with slope 
angle. Differences in cover of grit and of stones, 
in the thickness of the crumbly topsoil, in the 
colour of the deeper soil layers, and in the na- 
ture of concretions they contain, however, do 
not rule out the possibility of a great influence 
of soil moisture regime. On the other hand, this 
influence was not closely expressed by the root 
distribution, which will be treated in the next 
section. An aut ecological study of the grass 
species rather than investigation of group pat- 
terns might perhaps contribute more to an 
explanation. Factors also to be taken into ac- 
count are, for instance, the frequency and in- 
tensity of fires, the severity of runoff, the 
lengths of periods of waterlogging, and ability 
for germination and regeneration. Observations 
at Katherine, N.T., Australia, have revealed a 
marked response of sward composition to short- 
term variations in rainfall, Themeda australis 
becoming dominant in drier years (Norman, 
1963). A similar interaction could be expected 
to occur in the area of investigation. 
root systems of grasses: The distribution 
of the grass roots in the sections of the pits was 
studied by spraying the walls with a fine jet 
hose. 
The root systems of Themeda australis, Het- 
eropogon contortus, Sehima nervosum, and 
Sorghum nitidum appeared to be of much the 
same structure. Roots spread in horizontal, ver- 
tical, and intermediate directions from the tus- 
sock base, forming a dense "corona” with a 
radius of 1 or 2 dm which becomes more open 
at greater distances. 
In the black clay soil the crumbly topsoil, 
especially the fine crumbly upper part, is densely 
rooted; numbers of roots gradually diminish in 
the underlying heavy clay; usually roots are 
frequent at 0.9 m and a few are still present 
at 1.8 m. Roots sometimes seem to follow the 
planes along which the clay cracks on drying; 
in other cases they seem to penetrate at random. 
In the texture-contrast soil, horizontal roots 
spread densely through the superficial layer, 
about 10 cm thick, of friable sandy loam or 
loamy sand, with a fair amount of oblique and 
vertical roots penetrating in the underlying 
massive layer, which is rather resistant to wash- 
ing. Roots penetrating in the clayey subsoil at 
about 0.3 m depth are usually few, about 4 per 
dm 2 , sometimes more, which may be due to a 
less massive structure of the topsoil. Deepest 
roots are observed at 1 m. Several grass roots 
penetrated deeper horizons by following the 
vertical roots of the eucalypts, closely pressed 
against the bark. 
In the red regosol, roots spread in all direc- 
tions in the superficial, crumbly layer and in 
