The Vegetation of Yanagi Islet, Truk, Caroline Islands 
Peter J. R. Hill 1 and Benjamin C. Stone 2 
Yanagi Islet, located midway between Moen 
and Dublon in Truk lagoon (7° 24' N.; 151° 
53' E.) is a small islet roughly 30 ft. high, 
about 800 ft. long and 300 ft. wide, with 
scarcely any strand but with volcanic rock pave- 
ment on all shores, and on the south side, 
numerous loose volcanic boulders. Much of the 
volcanic rock of which the islet is formed ap- 
pears to be a breccia resembling conglomerate. 
The reef surrounding the islet is rather large, 
with small storm-deposited rocks on the north- 
east sides. There is a smallboat pass on the west 
side and another pass, probably safe for small 
craft, on the north side. During World War II, 
the Japanese tunnelled through the islet from a 
cave on the south side to the north side; another 
Japanese cave on the south side does not run all 
the way through the islet. A small-gauge rail- 
road ran from the tunnel into the lagoon, for 
loading operations. The track is now rusty and 
twisted. 
The vegetation, despite the obvious prior use 
of the islet for military purposes, is relatively 
undisturbed in a few small areas. The Trukese 
do not live on the islet, but visit it occasionally 
for fish and shell-fish, and perhaps for mangoes. 
There are only a few coconut palms and a few 
of their seedlings. 
The vegetational zonation of the islet appears 
to comprise three areas : ( 1 ) a fringe area, more 
or less encircling the islet at sea level. (2) An 
open, rock-strewn extremity on the east, with a 
herbaceous cover, which slopes toward the east 
and terminates abruptly as a low cliff. This area 
is similar to the Tunnuk-Penniasene and Me- 
chitiu lava flows, but here there is no polygonal- 
patterned basalt. (3) An inner upland, with a 
developed tree-cover and fairly good soil. There 
1 Pacific Islands Central School, Ponape. 
2 Department of Botany, University of Hawaii. Pres- 
ent address: Department of Botany, U. S. National 
Museum, Smithsonian Institution, Washington, D. C. 
Manuscript received December 16, I960. 
is in fact a transitional area of low-crowned 
shrubs between zones 2 and 3; it is not known 
whether this is a natural attenuation in plant 
size, accompanied by increasing dominance of 
the herbaceous cover, which has persisted, or 
whether it is a result of human disturbance. 
However, the area contains a U. S. Navy Survey 
bench-mark on a concrete base (without further 
information ) . 
The most interesting features of the islet are 
the complete absence of coralline rock and soil, 
and the absence of most of the halophytic 
species of littoral plants which are so common 
elsewhere in Truk, a lack which is no doubt 
correlated with the nature of the substrate. The 
plants of Yanagi are by no means unique, and 
may be commonly found in Truk, and indeed 
through much of Micronesia. They are not re- 
stricted to volcanic soils, for some of them, at 
least, are known from the atolls nearby as well. 
But the strand species such as Scaevola Taccada, 
M esserschmidia argentea, Terminalia samoensis, 
and Soulamea amara are notably absent. Most of 
the species which occur on Yanagi also occur on 
the reef islets of Truk in coralline soil; but the 
lack of these littoral plants, which might rea- 
sonably be expected to grow there, is the curious 
and interesting feature of Yanagi Islet. 
VEGETATION ZONES: Since the islet is so 
small, altitudinal considerations are of no ac- 
count above sea level. The fringe area (1) seems 
to differ from the inner upland area ( 3 ) chiefly 
because of the exposure of the former and its 
hindrances to undisturbed plant growth, partly 
because of subjection to change from wind and 
waves, and to the concomitant salt spray, and 
partly because of the abundant volcanic boulders 
but thin, scanty soil. The grassland ( 2 ) and the 
intermediate area of shrubs may be the result 
of disturbance, or, again, may be the result of 
hard, thin soil with numerous embedded rocks, 
combined with exposure to wind and illumina- 
tion. Salt spray is apparently minimized by the 
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