68 
The Queensland Naturalist 
April, 1930 
THE PLANT ECOLOGY OF PALM ISLAND. 
By Dr. D. A. Herbert, Department of Biology, 
University of Queensland. 
(Continued from Vol. VII., Page 56.) 
On one ridge at an elevation of about 1000 feet a 
peculiar local ground flora of ferns, usually found epi- 
phytic in the monsoon or rain forest, was encountered. 
Growing on the stony soil and the rocks were Polypodium 
(Drynaria) quercifolium (the oak leaf fern) ; Asplenium 
nidus (the birds’ nest fern) ; and platycerium alcicorne 
(the elkhorn). The oak leaf fern is interesting on account 
of its two types of leaf, the pinnate assimilating leaves, 
and the others coarsely serrate and functioning for humus 
collecting. These ferns were in considerable numbers on 
top of the backbone mountain chain of the island, which 
at that point was running north and south. The eastern 
side of the island has a heavier rainfall than the western 
side, which is in the rain shadow, and this ridge top appar- 
ently received enough rain to support the peculiar local 
growth of ferns, though not enough to turn the balance of 
edaphic conditions sufficiently to allow Malayan trees to 
dispossess the Eucalypts. The Eucalypts in this case were 
mainly E. alba, E. tessellaris, and E. tereticornis ; i.e., 
those which favour the slightly moister slopes of the 
island. Rather numerous at this point was the only 
ground orchid collected in this formation — Geodorum 
pictum, which was in fruit at the time, 
Rain Forest and Monsoon Forest. 
Tlie Malayan vegetation of Palm Island predominates 
in sheltered or well-watered situations. From the sea its 
dark green strips stand out in vivid contrast to the 
lighter belts of Eucalyptus forest. They correspond to 
the gullies of the mountain sides, the Eucalypts occupying 
the drier ridges. There is very little admixture. A few 
Malayan species are scattered through the Eucalyptus 
forest — for example, Ilomalanthus populifolius and 
Macaranga tanarius — but the two formations are very 
pure and in such a delicate state of equilibrium that the 
dense gully forests rise up like a wall at the edge of the 
gum trees, and a line may be drawn which absolutely 
separates the two. The dry ridges do not satisfy the 
moisture requirements of the Malayan types, and the 
dense shade of the gully forests is unfavourable to the 
establishment of the heliophilous Eucalypts. Occasionally 
the conditions are such as to favour either the one or the 
other formation, and a mixture known as “Bastard 
