tee
188
RECOVERY OF THE LAND PLANTS AT ENIWETOK ATOLL
grandis) were abnormalin appearanceatislands
where the levels of radioactivity were lower.
Fosberg suggested that some species of plants
were more susceptible to radiation than others.
On the other hand manyof the abnormalities
reported by Fosberg, St. John and Biddulph
have been reported from coral atolls where no
radioactive fallout has occurred. For example,
defoliation and death at the tips of branches of
Cordia, Pisonia and Tournefortia (Messerschmidia}
were reported on Wake Island in April 1952,
after a period of drought, by Fosserc.7)
TayLor®@?) reported that the vegetation at
Bikini Atoll in March and April 1946 (before
Operation Crossroads) was unhealthy-looking
and that Pisonza plants bore only scanty foliage,
improving later in the year. Records of rainfall
in the northern Marshall Islands show that the
dry period prevails from Decemberto April, the
months ofJanuary and February getting the least
rainfall.“ As shown by the observations of
Fosberg and Taylor, one would expect to find
the plants at their worst during the dry period.
Some abnormalities found in the plants on
coral atolls have been caused by insects. Taylor
reported that the leaves of Suriana were clipped
as if by insect attack, and Fosberg reported that
Bauhinia was chlorotic and badly eaten by
insects. NIERING?®) reported that on Kapingamarangi Atoll the leaves ofScaevola were attacked
by a leaf miner and new shoots and buds of
Calophyllum sp. and Barringtonia asiatica were
“infested to the point of disrupting the normal
growth pattern.”” On Onotoa Atoll, MouL@?
observed that several insects were found on
Guettarda plants. These included wasps, moths,
stink bugs, and butterflies. Moul reported also
that leaves of Pisonia trees were so badly
damaged by leaf-cutting bees that he could not
find a perfect specimen offoliage. At Rongelap
Atoll members of this Laboratory noted in-
festations of a lepidopteran larva causing
deformed leaves on Guettarda plants. They also
reported that insects caused defoliation and bud
damagein plants of Terminalia sp. and Pisonia.
The bird population also is a factor'in the
ee
production of unhealthy plants. Niering re-
ported that at Kapingamarangi Atoll the leaves
of Asplenium, Nephrolepis, Guettarda and Pisonia
were turning brown and dying because of the
fecal droppings of the white-capped noddy tern
(Anous minutus marcust). He reported that the
breadfruit tree also is damaged by these birds.
On Canton Island the suggestion was madethat
the native birds were chiefly responsible for the
dead or dying conditions of the forest and scrub
vegetation.4?
Other agencies also have been reported to
cause chlorosis, die-back, slow growth, aberrant
growth forms, and other kinds of plant abnormalities. Some causes not mentioned
previously are salt spray, wind, storms, flying
gravel, soil conditions and land crabs.
Measurements of the amount of thermal
radiation and blast received by the plants at
Belle Island during the Nectar detonation were
not made, but approximations of these values
can be made on the basis of the energies
required to produce the observed damage. A
thermal energy of 10-15 cal/em? is required to
char vegetation and a wind velocity equivalent
to 130-140 miles/hour is required to produce
blast damage") similar to that observed at Belle
Island. Also, from calculations based on data
obtained from other nuclear detonations,@”
the initial gamma dose delivered at Belle Island
was approximately 30 r, which is much lower
than the levels required to cause visible plant
damage in laboratory-type experiments. Essentially all of the damage to the land plants,
therefore, can be attributed to the heat and blast
rather than to the initial nuclear radiation. The
excellent recovery of all but three of the plants
(Guettarda, Lepturus, and Portulaca) is noteworthy,
especially since the plants were subjected continuously to external radiation as well as the
internal radiation from absorbed radioisotopes.
The abnormal appearance and slow recovery of
these plants, among the many observed, would
appear to be due to radiation; however, the
author feels that the other factors, which were
not measured adequately during this investigation, should be evaluated carefully before
ascribing the damage to radiation.
REFERENCES
1. Applied Fisheries Laboratory,* University of
Washington (1947) Radtogiological resurvey of
Bikint Atoll during the summer of 1947. U.S. Atomic
Energy Commission report UWFL-7.
wo