\ 
Vegetation and Flora of Vostok Island 
■by C,. 2. Long 
flora of Vostok island consists of two species of vascular 
B oerhavia repens L. and Pisonia fg-andis L. (Fosberg, 1937) 
-• y-v T, <3 
Collections of these species were made in 1935 hy J« Anderson and 
in 196p by C. R# Long.'fhe sheets^filod at the B. P# Bishop Museum 
and the University of Hawaii respectively# s/ s cd ^*' 
The island remains much as Anderson repprtedf&r^ dense growth 
of Pisonia wi-tir trees to approximately 20 m .awards the middle east 
portion of the island are random clearings with thick layers (to #|r 
m.) of decayed leaves and wood# On the sandy edges of these clearings 
several Boerhavia plants were observed. Several holes were dug in the 
thick humus both in the open areas of the forest and under the canopy# 
Underlying the humus was phosphatic. hardpan which was vezy friable in 
the top layers Increasing in hardness with depth# The highest branches 
of the" Pisonia were used by the greater frigatebird for nesting. Some 
of the upper branches were bare due perhaps to nesting activities and 
guano deposition# On the north and east sides were open sand and coral 
rubble with Boerhavia in vigorous masses# This area was used as a nest¬ 
ing site for Blueface^boobies (Sula dacty 1 atra) . This strip of open 
vegetated 4 sand and varied from 3 to 20 m# in width# Despite the 
paucity of the flora an intensive search of the island revealed no 
evidence of Portulaca sp# as reported by Bryan (1942)# The absence of 
this herb seems quite remarkable# The Polynesian rat was common# It 
may be that any chance introductions of Portulaca are eaten by this 
species# At the southwest end there is an outcrop of consolidated 
beachrock# It seems most probable that both of the native species, of 
Vostok Island were introduced by nesting birds# 2To evidence of Pisonia 
seedlings were observed but numerous sprouts from fallen trunks and ex¬ 
posed roots were seen# Uo fruits were observed on the trees with the use 
of binoculars. Along the west side areas of eroded soil and deposited 
or uncovered sand wergobsepved. This can only be explained by supposing 
high wave action^i^or^tb^^our visit. This inundation probably seeps 
through the porous central portion which is at a lower elevation than 
th beach crest and inner slopes# The portions under the Pisonia canopy 
entirely devoid of vegetation with the exception of crust of bxue— 
y en algae which are found on rotting trunks, on exposed phosphatic 
fxs and on damp edges of the inner clearing.Ho thick guano depositions 
.rere seen# Small coconut crabs were found# The varying depths of humus 
m&er the Pisonia canopy suggests that a smalls aline lagoon may have at 
and the irregular layers of phosphatic hardpan 
one tine existed on the island. 
Some attention was paid to the relationship of the roots of Pisonia 
and the occurrence of phosphatic hardpan layers# Excavations were made^near 
the trunk and at some distance to determine the coincidence o± roots with 
the hard materials# In two ijistancos#relatively hard ;^ogp^jai/ic material 
wae found near older roots.'inW aSoarnext to the rooifTctaSe-up of very 
phosphatic material^earthe base of the larfeer trees 
_of hard phosphatic stone -was^forced to the surface presumably 
^ jho growth of the larger roots underneath# There is a disuincu possibility 
that the upper layers of phosphatiaed materials were formed after the tree 
had become established^ or that previous stands of the Pisonia were 
^^ 2 SKi/the'formation of this type of rock as has been suggested by 
Fosberg (1957)• 
Cl,- 
