"Once established, this morning glory may extend its long runners over fresh sand surfaces and act as
a sand binder that will hold the sand in place while other vegetation becomes established. In this
way, it acts as a pioneer.... With the advent of vegetative cover, some of the fish-eating birds ...
begin to use the vegetation for nesting purposes.... Wherever they nest, the consequent guano brings
much needed minerals from the sea ... (which are) incorporated into the plants, thenee into the plant
litter and again into the soil to pave the way (for plants) that could not survive well as pioneers.
When the cover is adequate to provide a more hospitable environment (reduced salinity, shaded soil,
lower temperature, and better nutrients), certain secondary plants enter the vegetation, particularly
the prostrate vines Triumfetta procumbens and Boerhavia tetrandra and the dodder-like parasite
Cassytha filiformis L.(Dodder-laurel). Other species characteristic of later stages of the vegetation
may be added as conditions become more favorable and their needs become available."
For some obscure reason, certain portions of some of the islands in the atoll do not develop mature
stands of trees or brush, but are covered by open meadow-like areas of grasses, sedges and viny
other two native grasses, L. repens (Forst, f.) R. Br. var. occidentalis Fosberg and Thuarea involuta
(Forst. f.) R. & S., are both fairly rare. Fimbristylis atollensis, the only native sedge, is also quite
common. Introduced grasses which are quite abundant include Cenchrus echinatus L. (Sandbur),
Cynodon Dactylon (L.) Pers. (deliberately introduced Bermuda or Couch grass for lawns and as sand
binder), Digitaria setigera R. & S. var. setigera (Crab grass), Eragrostis tenella (L.) Beauv. ex
Roemer & Schultes (Love grass), Setaria verticillata (L.) Beauv. (Bristly foxtail) and Tricachne
insularis (L.) Nees (Sour grass).
Vegetation of some kind appears on all soil surfaces with suitable growing conditions.
Habitats
unsuitable for vegetation include areas with a predominance of gravel or rock without enough sand or
soil to retain moisture necessary for plant growth, and beach areas routinely subjected to tidal or
wave inundation. Tournefortia and Scaevola seem to be more tolerant than other trees and shrubs to
the constant load of wind-borne salt along the windward side of the islands. The reason for the
existence on some islands of large meadow-like areas surrounded by stands of trees and shrubs, with
no young bushes in evidence, while other islands are totally covered with dense brush, is not
self-evident. As will be reported in Chapter 7, areas with dense vegetation typically had higher
concentrations of radionuclides than did less densely covered areas on the same island. Special
attention was, therefore, given to heavily vegetated areas during soil sampling and in situ gamma
scans. The mechanism wherebya significant portion of the radionuclide inventory is bound up in the
biological cycle has undergone some investigation, but details will not be reported here.
The scientific names for the plants cited in this section were obtained from the following sources:
Dicotyledonae (Fosberg & Sachet, 1979); Monocotyledonae, excluding the genera Digitaria and
Eragrostis (St. John, 1960); Digitaria (Veldkamp, 1973); Eragrostis (Smith, 1979). The nomenclature
followed is that of the authors cited above.
6.5.2 Devegetation of Island Janet
Island Janet was selected as the location of IMP startup operations in July 1977 as stated in Section
6.4.1. At this time, there were several] areas on the western and northern points of the island where
vegetation was relatively sparse so the IMP could maneuver from point-to-point without prior
devegation of the area. However, the central and eastern portions of the island were covered with
dense thickets of Messerschmidia and Scaevola.
Following some experimentation, the method
selected for devegetation of an area measuring about 1000 x 1000 feet consisted of dragging a
200-foot anchor chain across the brush.
Two large bulldozers, each with an end of the chain attached (Figure 6-2), drove in parallel across
the terrain, keeping the chain just slightly slack. This system worked well in areas with only
moderate vegetation. In especially dense growth, the chain would only partially knock the brush
down, so a second pass was required in the opposite direction to the first pass. The brush was, at this
point, still a tangled mass which the IMP could not traverse.
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> cecaamg,
herbs. In a tabulation of the flora of Enewetak Atoll, it is reported (St. John, 1960) that 15 taxa of
grasses, of which 13 are introduced weeds, and 3 species of sedges, including 2 exoties, are present
on the atoll. The commonest native grass is Lepturus repens (Forst. f.) R. Br. var. repens, while the