Atoll Vegetation and Salinity 
F. R. Fosberg 1 
Coral atolls are flat rings of reef-rock and 
calcareous debris usually forming islets with an 
elevation of only a few feet above sea level. 
They are distributed throughout the tropical 
Pacific and Indian Oceans, except the eastern 
Pacific, with somewhat similar formations in the 
Atlantic, principally in the Bahama Islands. 
Fig. 1. Northwest corner of Mili Atoll, Marshall 
Islands, showing a number of small islets. PHOTO- 
GRAPH BY LEONARD E. MASON. 
The great Pacific groups of atolls are such 
archipelagoes as the Tuamotus, Carolines, Mar- 
shalls, Gilberts, the Phoenix-Ellice group, and 
those scattered clusters and individual islands 
collectively termed the Pacific Equatorial or 
Line Islands. The observations forming the 
basis of this paper were made on visits to all 
these groups, except the Phoenix-Ellice and 
Gilberts, as well as to the Austral Islands and 
to the essentially similar barrier reef islets 
around various high islands. 
Atolls are characterized by small floras with 
few endemic species and a preponderance of 
widely dispersed strand plants. The plant cover 
is a strand vegetation which is generally re- 
garded as very uniform and uninteresting. Ac- 
tually, however, this uniformity exists only in 
the minds of those who have visited very few 
1 Department of Botany, University of Hawaii. 
Manuscript received May 11, 1948. 
atolls or who have observed them only super- 
ficially. 
The major differences in vegetation are those 
between islands in dry and wet climatic belts. 
The driest atolls, such as Malden, Jarvis, How- 
land, and Baker, have a sparse desert-like vege- 
tation of a few grasses, herbs, and dwarf shrubs 
that contrasts strikingly with the luxuriant jun- 
gles on atolls in the central and eastern Caro- 
lines and southern Marshalls. 
Another important difference occurs between 
the vegetation of small or narrow islets and that 
of large land areas. The smaller the area of an 
islet the more extreme is the strand character 
of its vegetation, and the larger the area the 
more divergence is shown from this type. This 
divergence may be of different sorts, as in the 
Fig. 2. Outer beach on Nomwin Islet, Hall Island, 
Caroline Islands, showing scrub vegetation, princi- 
pally Scaevola frutescens. PHOTOGRAPH BY F. R. 
FOSBERG. 
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