Nutrient levels and soil response in the A1 horizon of the five broadest soil series. For orientation, a map of the Northern Marshall Islands (Figure I) is included, as well as more detailed maps of the atolls where the observations were made: Rongelap (Figure 2), Bikini (Figure 3) and Enewetak (Figure 4). ).
RONGELAP ATOLL SOILS
Of the four factors examined, differences in total nitrogen and exchange capacity were statistically significant at the 0.1 percent level, organic matter was significant at the 1.0 percent level, and pH was nonsignificant. A large amount of information on soil gravel content and bulk density is given in the papers of Kenady (1962) and Billings (1964), and more is found in unpublished files (available from the authors). Calcium and magnesium show the origin of the corals, but also the dilution with organic matter and weathering.
There is considerable variation in elements in some profiles, some of which are due to buried horizons or other depositional features. Due to the favorable conditions for decomposition, the accumulation of humus on the soil surface was not a common feature of the soil. As many of the samples came from remote islands, the high values of the moderately aged samples may reflect the influence of seabirds on nitrogen and phosphorus.
Some nitrogen is found at greater depths, but a depth of 25 cm accounts for at least 90 percent of the total amount in the soil.
SOILS AND PLANTS OF ENEWETAK AND BIKINI ATOLLS Bikini and Enewetak atolls were more impacted by the weapons testing program than
SOIL AND PLANTS OF ENEWETAK AND BIKINI ATOOLS The atolls of Bikini and Enewetak were more affected by the weapons testing program than the atolls. Bokinwotrne (Edna), a Marshallese name of the islands, is listed first, with known, previously used or code names in brackets in some cases. The soils, with the exception of the areas involved in construction disturbances, appear to be virtually intact and differ little from the soils of the productive areas of many of the atolls.
Inspection and collection in 1964 showed that destructive effects were largely confined to surface soils throughout most of the island. However, much of the inherent productive capacity of the land was retained and natural vegetation quickly returned and flourished. This assessment was confirmed by the 1986 visit to Nam, when almost the entire coverage of the island by vegetation was noted.
This was true for both mature and young soils, so that the entire nature of the islet changed.
PLANT PHYSIOLOGICAL STUDIES
The " ~ r activities were significantly higher in the lower than in the upper leaves, a pattern that closely followed that of calcium. In palm, the content was lower, characteristic of a monocot, and in the few comparisons available, lower leaves again had higher contents However, this may reflect the considerable exchangeable magnesium in the soils (Table 2-6) and most probably also the high magnesium levels in groundwater (Table 27).
Thus, nitrogen values vary considerably between collections, but in most cases nitrogen in the lower leaves is lower than in the upper leaves, indicating a shortage of supply of this mobile element. Normally, 450 g of fertilizer salt was incorporated into approximately each of the approximately 15 young plants in the driving tests. The young coconut palms on the plantations usually had a fairly low to very low phosphorus content.
Zinc - Some zinc values are low (10 ppm) in the coconut plantations, but mostly this element seems to be sufficient.
WATER RELATIONS General Aspects
Given the low manganese concentrations in the palm foliage (see Table 24), one might expect that the manganese in the multi-element materials would be beneficial. A plastic tube was passed into the pipe in the water and then a hand-operated suction pump was used to obtain a sample of the water. Most of the pipes were driven into or near ground pits, most of which can be found on the maps of the Rongelap and Kabelle Islands (Figures 5 and 6).
For some of the groundwater samples from Rongelap and Bikini atolls, analyzes of the major cations were made. The mean Yn of the field-collected leaves ranged from -1.9 to -3.1 M Pascal, compared to that of seawater at -2.7 M Pa. In their greenhouse study, Walker and Gessel found that seedlings of several species found on or near atoll beaches can tolerate exposure of the roots to osmotic.
These string species can tolerate the salinity of most groundwater and probably absorb a lot of water from them, especially during the dry season.
GENERAL ATOLL ECOLOGY
Groundwater in such places is usually significantly less saline than seawater, and the plants have extensive root systems that penetrate to considerable depths.
PLANT COMMUNITIES
The sticky fruits of Pisonia are sometimes seen attached to birds, and this is probably an important means of seed dispersal. Figure 14 shows the estimated distribution of vegetation on this island. Eventually Pisonia would settle in the central part of the larger island, but ancient Tournefortia would still be present.
The base of the Cordia trees can be almost a meter in diameter, and the trunks and branches grow at all angles, often close to the ground where on Mellu Island boulders are piled against the seaward side. This consists of three layers: first, a canopy of coconut palm leaves, 10-13 m high, which is continuous or broken depending on the age and condition of the plantation; then there is a layer from 112 to 4 m high, consisting of. Tacca, or arrowroot, stands out in the second layer of the community during the wet season and gives a striking seasonal aspect to the community as the leaves die completely during the dry season.
It is perhaps notable that Neisosperma (Ochrosia) does not occur in the mixed forest communities.
A QUANTITATIVE DESCRIPTION OF THE SCAEVOLA- GUETTARDA COMMUNITY ON RONGELAP ISLAND
There are also ornamental plants, including the spider lily, Crinum sp., Croton sp., and Achryanthes canescens.
A study carried out by Dr. Mark Behan in 1959)
This conclusion is reached by comparing the relative density of mature plants with that of seedlings. The data show that in the case of Sca, mature plants make up the majority of the mature vegetation. Relative frequency is an expression of the distribution of different species throughout the area.
Measurements were made along a transect using the quarter method of a typical undisturbed Sca-Gu. The air cover and relative density of the population coincide, and the mature vegetation consists mainly of Sca (80%) and secondarily of Gu (13%). This was corroborated by the field observation, as Pi was only encountered at the beginning of the transect.
It was suggested that future work include some measure of average weight or volume of different species in a community.
WEIGHT OF VEGETATION (BIOMASS)
This observation, combined with the apparent high seedling mortality of Sca and the shade tolerance of Gu, confirmed that this community is likely to become increasingly dominated by Gu in the future. It also showed that Gu occupied about twice the area per individual as Sca. This confirms that Gu is more extensive than Sca, as can be observed in the field by the bush-like appearance and high density of Sca, and the more arboreal and extensive appearance of Gu.
The relative frequency of the species within the population indicated that Gu was fairly evenly distributed throughout the community while Pi was clustered or clustered over a relatively small area. If known, these measurements could be included in a reasonably accurate estimate of the total production of the area.
VEGETATION GROWTH RATES
In both cases, trees were identified by numbered tags placed at 1.4 m above the ground surface (breast height) and initial diameters taken at that point. The trees were re-measured each time the site was visited, with the last measurement in 1964. In order to assess height growth, a series of Scaevola, Guettarda and Tournefortia plants were identified by numbered tags and initial heights taken from 1958 to 1961.
This is probably related to the quality of the soil in which the plants grow and exposure to wind. Toumefortia #25 grew quite rapidly during 1964, while a younger plant, but slowed as it grew and much wider and averaged 15.8 cmlyr over a 28-year period. Many of the plants used in this study were grown in very poor soils and exposed areas.
Growth rates therefore probably represent the lower end of the scale for annual growth of these species, particularly as Rongelap is one of the more northerly and therefore drier atolls.
NATURAL AND MAN-MADE CHANGES IN THE VEGETATION
Diameter (cm) and Diameter growth rate (cmlyr) of Tournefortia trees on Kabelle Island, Rongelap Atoll. Diameter (cm) and diameter growth rate (crnlyr) of Pisonia trees on Kabelle Island, Rongelap Atoll. Before man inhabited these atolls, and before copra production was an economic enterprise, the fairly well-developed soil in the center of the larger islands is believed to have supported good stands of Pisonia grandis with a few older Tournefortia, with a group of Scaevola-Tournefortia- Guettarda scrub along the beaches (Fosberg, 1949).
With the development of copra production over the last 100 years, much of the Pisonia and much of the shrubland not too close to the beaches has been replaced by coconut palms. The nuclear weapons testing program at the Enewetak and Bikini Atolls destroyed most of the palms and native vegetation on the affected islands. As previously mentioned, in the late 1950s and early 1960s, the Rongelap people, aided by agricultural officials from the Trust Territories of the Pacific Islands, cleared brush and planted many coconut seedlings of a Yap Island species.
The movement of the Rongelap people to Kwajalein Atoll in 1985 allowed a similar overproduction to begin in Rongelap.
CONCLUDING REMARKS
Likewise, fairly rapid growth of native species following clearance for test operations or from explosions at Bikini Atoll was documented by Gessel and Walker (1987). They also replaced many old coconut trees with saplings of this type, which is known to be quite productive. However, the lack of people living in bikinis and caring for coconut trees has allowed native shrubs and volunteer coconut saplings to encroach on the groves.
LITERATURE CITED
Radiological survey of plants, animals and soil on Christmas Island and seven atolls in the Marshall Islands; Progress Report for 1974-1975.
