scolopendria. Ipomoea macrantha and Tacca leontopetaloides 

 are locally abundant, while Phyllanthus amarus, Tribulus 

 cistoides, Lepidium bidentatum, and Psilotum nudum are rare 

 and localized. Digitaria sp. may be extinct. The fact that Sida 

 fallax has only been recorded twice in 106 years is curious. 



Ecological Succession 



We have attempted to trace the development of Caroline' s 

 flora from the smallest to largest motus, using field data and 

 aerial photos, which reveal past geological processes. Three 

 tables provide this analysis of ecological succession: Table 5 

 presents Caroline's motus in order of ascending size, together 

 with the numbers of plant species and major plant communities. 

 Since the atoll's total land area is small, our data provide 

 relatively complete floristic lists for each islet and detailed 

 maps of their plant communities (Figs. 37-57). The number of 

 species varied from 3 growing on 4 tiny islets (0.02 ha each) to 

 23 on South ( 104.41 ha). Because the total number of species 

 for the entire atoll (27) is also small, the addition of one or two 

 rare species contributes significantly to the total flora. Such 

 additions must be kept in perspective when evaluating plant 

 succession. 



Table 3 provides a summary of plant species distribution 

 by islet in decreasing order of abundance, and Table 6 is a 

 summary of plant species distribution and relative abundance 

 with respect to islet area and the primary mode of seed dispersal. 



Basic Serai Stages 



Islets appear, grow, mature ecologically, or vanish in 

 violent storms. Many interacting factors, including geographical 

 (islet area, atoll shape, distance from high islands and continents), 

 geological (changes in sea level), chemical (nitrates from bird 

 droppings, leaf fall, et cetera), climatological (wind, droughts, 

 storms, microclimates), and biological (seabirds, rats, land 

 crabs, and man, both aboriginal and modern ), constantly interact 

 to change conditions. The relative influence of some of these 

 factors is evident when comparing the floras on motus of 

 different sizes. 



Seed-dispersal mechanisms (Table 6) and the presence of 

 underground fresh water are also vital. Unfortunately, the 

 relationships between groundwater salinity, species distribution, 

 and vegetation patterns on atolls are poorly understood ( Fosberg. 

 1985). The presence and relative salinity of permanent water 

 depends on Ghyben-Herzberg lenses of varying thickness on 

 different islets, and this in turn depends upon island dimensions 

 (especially width), soil porosity, rainfall, tidal fluctuation, and 

 other hydrological factors. Though groundwater supplies have 

 been studied on many atolls (Wiens, 1962; Maude, 1953), each 

 island group is so unique that it is unwise to extrapolate 

 information from one to the other. 



Caroline's 39 motus fall naturally into 4 size classes: 

 motus with areas of a) <0.2 ha, b) 0.2 to 0.7 ha, c) 0.8 to 

 25.0 ha, and d) >25.0 ha. These size groupings harbor all 5 of 

 the serai stages identified on Enewetak Atoll (Lamberson, 

 1987), tailored to reflect Caroline's particular geography, 

 geology, and impoverished flora. Each stage may be the sole 

 example of ecological succession on an islet or may occur as 



one of several stages. Typically the early stages cover the 

 peripheral rubble and scrubby outer zones, while the later ones 

 appear as a series of roughly concentric bands progressing 

 inland. 



Stage 1 : Early pioneers on sandbars, spits, or small rubbly 

 islets subject to storm damage and washover. Harsh conditions, 

 intense sun, drying winds, salt spray. High salt concentration 

 in the substrate. Lack of fresh water and nutrients. Plant genera 

 present include Heliotropium, Portulaca. Lepturus, Boerhavia, 

 and seedling oropenTo!/r/ie/o/-f/a scrub. No Cocos. This stage 

 is found on many small motus (Noddy Rock, Fishball) and 

 former interislet channels (e.g., Long Island). 



Stage II : Thick scrub of mixed genera, often impenetrable. 

 Its protective barrier allows for the development of vegetation 

 on the larger islets. Seabirds begin to contribute to the soil 

 (guano, eggs, regurgitated fish, decaying nesting material). 

 Plant genera include Toumefortia, Suriana, Cordia, and 

 Laportea. If Cocos present, accompanied by coconut crabs. 

 Very common around the periphery of most motus just inland 

 of the native herb mats or flanking sheltered shores adjacent to 

 the lagoon (South. Kota). 



Stage III: Trees larger, seabirds add further to soil fertility. 

 Open grassland may develop in sunny clearings (Tridacna). 

 Added plant communities and Cordia-Tournefortia, 

 Tournefortia-Morinda, and Pisonia— Toumefortia forests. 

 Occurs in the next inner concentric zone of vegetation to 

 Stage II on larger motus (Nake, Long) or, more commonly, the 

 entire interior of smaller ones (Pandanus, Southern Leeward 

 Islets). 



Stage IV : Pisonia dominates the older mixed forest. 

 Morinda and Toumefortia reach for the sun. Forests are more 

 open. Undergrowth mostly a ground cover of Laportea, 

 Boerhavia, Lepturus, and Portulaca. Covers the main portion 

 of larger islets. If Cocos and Pandanus present, forms a mixed 

 forest with vines (southern Nake, Shark). Coconut crabs 

 common. A widespread stage in the center of most motus 

 (Central Leeward, Windward Islets). 



Stage V : Pisonia takes over. Other trees are confined to 

 the forest edges. Always in the deep interior of the larger islets. 

 Little or no ground cover. Abundant nesting black noddies 

 (Anous minutus). A more restricted stage (Brothers, Raurau, 

 central Nake, Pig). 



Ecological Succession on Motus of Different Size Classes 



To assist discussions of succession on Caroline's motus, 

 refer to the individual vegetation maps and graphs 

 (Figs. 27-57) and photographs (Pis. 13-80). particularly 

 Figs. 27-30. The latter figures summarize the amounts of each 

 islet's surface covered by each major plant community, as well 

 as providing the numbers and percentages of indigenous species 

 for each islet. 



a) Motus with Areas <0.2 ha (Figs. 27,31; PI. 49; 

 Tables 5.6): Caroline has four motus in this category, three 

 windward and one leeward, whose combined area totals 

 0. 15 ha. There are also three incipient islets which, because of 

 their temporary character, have not been counted in Caroline's 

 overall total (Fig. 2; PI. 15). With the exception of Noddy 

 Rock — a jagged, upraised limestone plateau — all consist 



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