Themeda australis-Eucalyptus Savannah in Papua — Heyligers 
483 
Fig. 5. Root system of Albizia procera consisting of rootstocks connecting the trunks and giving an- 
chorage to the shrubs or trees, and of vertical roots scattered along the rootstocks. 
of these plants at this time of the year, no 
attempt has been made to study their distribu- 
tion. 
A feature observed locally at transect 1 and 
common on transect 2 was a crust of greenish 
or reddish brown algae, which could cover as 
much as 20% of the ground. These algae were 
not restricted to the flatter areas, but occurred 
also on the slopes. Mosses occurred sparsely and 
were commonest on the lower slopes. 
INFLUENCE ON TERRACETTES : Grass tussocks 
may play a role in the formation of terracettes, 
which are especially common on steeper slopes 
but occasionally can be seen in flatter areas. A 
number of tussocks form an obstacle to the 
runoff flow and soil material accumulates at the 
upslope side. Differences in level at the two 
sides are mostly a few centimeters, but may 
become more than a decimeter; factors leading 
to enlargement of this difference include slope 
angle, age of tussock, and texture of soil 
material. Tussocks contribute in this way to 
stability of the slopes (Mabbutt, unpublished 
data) . 
COMPOSITION OF THE GRASS COVER: The 
investigation was concentrated on the grasses, 
which generally were fruiting and therefore 
had probably reached their maximum produc- 
tion; Sehima had already lost most of its in- 
florescences. The overall height of the grass 
cover was about 1.1 m on the flat parts of the 
transects, decreasing to 0.9 m on the slopes. 
The culms were mostly fairly erect; locally, 
however, they could be more or less inclined. 
Foliage cover averaged about 50%, but ex- 
treme local variations occurred ; almost bare 
areas could lie next to areas with nearly 100% 
cover. These changes are related to micro- 
topography — depressions have a more open 
vegetation — and cover of the soil by grit and 
gravel, whilst severe disturbance during the 
war could have been a factor in some of the 
cases. Trees and shrubs did not seem to have 
a noticeable influence on the grass cover. 
