190 



REESE 



occurred along the shore. The more densely vegetated 

 islands such as Ikuren Island on the southwest rim of the 

 atoll were greatly altered. Large Pisonia trees were 

 stripped of their leaves and uprooted; Tournefortia trees 

 were stripped of their leaves, many branches were broken, 

 but relatively few trees were uprooted. Cocos palms were 

 least impacted. The ability of palms to withstand typhoon- 

 force winds deserves study. Bunches of coconuts and 

 fronds were torn from the crowns, and, although a few 

 trunks had broken, 1 recall no coconut trees being 

 uprooted. By November 1979, the vegetation was making 

 a remarkable recovery with new growth appearing every- 

 where from the remains of broken plants. Short green 

 shoots covered the broken trunks and branches of 

 Tournefortia. Similar rapid recovery of vegetation occurred 

 following nuclear tests (Held, 1960). 



Although surveys were not made, 1 suspect that the 

 land crabs and rats were not greatly affected by the storm 

 because they live in burrows and piles of debris, unless of 

 course, these were close to shore Held (1960) noted that 

 land hermit crabs of the genus Coenobtta survived the 

 blast and heat effects of nuclear explosions. Apparently 

 they were protected by the heavy shells of the marine gas- 

 tropod Turbo. Most likely rats, if present, survived too in 

 their burrows. The effect on insects and geckos which tend 

 to live on the vegetation must have been much greater. 

 Probably the birds were most severely affected by the 

 storm. Fairy and noddy terns nesting in trees and ground- 

 nesting scabirds would be greatly affected. A breeding col- 

 ony of sotty terns on a sand spit between Ikuren and Mut 

 Islands was completely washed away. 



Overall, secondary ecological succession appears to be 

 the result of typhoons on the terrestrial vegetation of an 

 atoll. For example, in the early 1960s when I first visited 

 Enewetak and began my work on Ikuren Island, the vege- 

 tation was a dense shrub-like growth, 3- to 6-m high of 

 Scaeuola and Tournefortia under a canopy of tall coconut 

 palms. There were small meadows of Lepturus grass. 

 Much of the vegetation had been cleared during the testing 

 period in the 1950s, and what was evident was secondary 

 growth. The coconut palms, neatly planted in rows, dated 

 from the end of the 19th century when the Germans were 

 organizing copra production in the Marshall Islands. In the 

 1960s there was a small stand of Pisonia grandis trees in 

 the central part of Ikuren under the coconut tree canopy. 

 This stand covering an area of about 1000 m consisted of 

 trees about 10-m high with trunks not more than 20 to 30 

 cm in diameter. Gradually over the years the Pisonia forest 

 expanded until in the late 1970s it began to dominate the 

 aging coconut trees (Fig. 2). A Pisonia forest seems to be 

 the climax stage in the ecological succession of atoll vege- 

 tation (Lamberson's Stage V, Chapter 3, Volume II, this 

 publication). The large Pisonia trees, however, are 

 susceptible to storm damage. The wood is relatively soft, 

 the canopy large, and the root system poorly developed in 

 the shallow soil and rubble of the atoll. The trees are bro- 

 ken, uprooted, and blown over in tropical storms and 

 typhoons, resulting in a return to an earlier successional 



stage. This is precisely what appears to have happened on 

 Ikuren Island during Typhoon Alice in January 1979 

 (Fig. 3). 



For further details and observations on ecological suc- 

 cession of vegetation on Ikuren and other islands of 

 Enewetak Atoll, see Lamberson (Chapter 3, Volume II). 

 What is very clear is that the vegetation has suffered 

 repeated severe perturbation over the years, particularly 

 the northern islands, but with time it begins to recover. 

 Although diversity measures were not made, observations 

 indicated that diversity is higher in the early stages, 

 thereby supporting current disturbance theory (Loucks 

 1970; Miller, 1982, Sousa, 1980). 



SOILS 



The calcareous soils of Enewetak Atoll are similar to 

 those of other coral atolls (Fosberg, 1954; Fosberg and 

 Carroll, 1965; Hammond, 1969; Jamet, 1982; Mason, 

 1960; Niering, 1963; Seru and Morrison, 1985; Stone, 

 1951, 1953: Trudgill, 1979; Wiens, 1962). They are 

 relatively poor and immature consisting of limestone rub- 

 ble, sand, organic litter, and humus in various mixtures. 

 They have low moisture retention capacity. 



If soils are defined in the broadest sense as the mate- 

 rial on the ground surface in which plants grow, then atoll 

 soils fall into five types: 



1. Accumulations of coral rubble, mainly of stone size. 



2. Unaltered coral sand and gravel. 



3. Soils with a weakly developed A horizon with the 

 color only slightly darker than the unaltered sand below 

 but with no evidence of structural development. These 

 soils are exemplified by the Shioya series (Stone, 1951). 



4. Soils with a more developed A horizon that is 

 deeper and darker in color than the Shioya type and with 

 some structural development. These soils are exemplified 

 by the Arno series (Stone, 1951). 



5. Soils with an accumulation of raw humus on the 

 surface and with a relatively deep A horizon as in the 

 Jemo series (Fosberg, 1954). In the Jemo series, the accu- 

 mulation of humus is specifically related to the presence of 

 Pisonia grandis trees. There is an accumulation of phos- 

 phorus, often in the form of a cemented layer, believed by 

 Fosberg to be due to the reaction between guano from the 

 seabirds nesting in the Pisonia trees and the underlying 

 coral sand. There is some evidence that such a humus-rich 

 layer may develop under other suitable environmental con- 

 ditions as well (Catala, 1957; R. J. Morrison, personal 

 communication). 



All of the soil types described previously would be clas- 

 sified under different names if conventional terms of soil 

 taxonomy were used (Soil Survey Staff, 1975). Atoll soils, 

 however, do not fall neatly into conventional classification, 

 and students of atoll soils find the five types described pre- 

 viously to be more useful. 



Studies of the soils were not conducted under the 

 auspices of the Mid-Pacific Research Laboratory and, as a 

 result, detailed analyses of the soils of Enewetak Atoll are 



