prevalent on larger islands. Such an abundance of exotics, both 

 in species and area covered, renders a discussion of natural 

 processes on Kapingamarangi almost impossible. Undisturbed 

 habitats such as those on most of Caroline's motus, and on 

 other uninhabited Pacific islands whose quota of indigenous 

 plants exceeds 75%, provide far better data on species-area 

 relationships. 



Motu Size in Relation to the Distribution of Trees, Shrubs 

 and Herbs : As one progresses from small to large islets 

 (Table 5), the number of tree species rises from to 7, the 

 number of shrubs from 1 to 4, and the number of herbs from 

 2 to 12. Caroline's trends are similar to those at Aitutaki 

 (Stoddart & Gibbs, 1975), where the numbers of trees and 

 shrubs are relatively constant over a wide range of motu sizes 

 (3.8-7 1 ha), while the number of herbs shows a slight increase. 

 There are too many recent exotics on Kapingamarangi for 

 comparisons to be valid. We believe that if Niering's data were 

 reanalyzed, using only indigenous species, similar 

 generalizations would be found, viz.: most species on atolls 

 establish rapidly on small motus, after which a few additions 

 occur on motus of increasing size until the maximum number 

 of potentially available species is reached. Cursory examination 

 of Niering's Fig. 31, detailing the breakdown of total species 

 numbers into indigenous and nonindigenous components, bears 

 out this hypothesis. 



Plant Communities 



General Account 



The total area covered by vegetation on Caroline is 

 357.55 ha, fully 90% of the combined areas of all the motus. Of 

 this, two-thirds (289.82 ha) is woodland. Substantial areas of 

 Caroline's native woodlands and herb mats are pristine, and 

 85% (possibly as high as 93%) of its plant species are indigenous. 

 Twenty-three (60%) of its 39 motus harbor wholly indigenous 

 vegetation (Figs. 27-30). Atolls that support substantial areas 

 of native forest are typically remote and uninhabited. Where 

 people are present, native vegetation is usually confined to the 

 smallest motus or the extremities of larger ones — areas with 

 marginal human usefulness. 



Typical of atolls, but unusual for the tropics, are monotypic 

 stands of shrubs and trees. Caroline is rich in such woodlands 

 (Figs. 18,22,24.27-30; Table 9). The present vascular flora of 

 Caroline, 27 species, is organized into 7 plant communities 

 ( 1 1 subcommunities) defined principally by dominant species 

 (Fosberg, 1953. 1977a). Eight subcommunities are natural, 

 three are anthropogenic (Table 5 ). The subcommunities include 

 a mix of dominant species, which are discussed in the major 

 Community sections below. 



NATURAL COMMUNITIES: 

 Natural Herb Mat 

 Toumefortla Scrub and Forest 

 Beach Scrub with Suriana 

 ( 'ordia Forest 

 Paiulamis forest 

 Pisonia Forest 



ANTHROPOGENIC COMMUNITY: 

 Coconut Woodlands 



Natural Herb Mat (67.73 ha) (Figs. 19.23: Pis. 20.33, 

 34.45,46,47) 



Widespread and predictable on wind- and salt-blown 

 coastal coral rubble and incipient motus, these mats are 

 composed primarily of Heliotropium and Portulaca. They are 

 pioneers on newly emergent motus, cover most of the ground 

 area of small motus, extend inland along ancient reef channels, 

 and typify newly evolving land that connects or augments 

 established islets. Natural herb mats may persist through all 

 five stages of plant succession as long as sunny openings occur. 

 Caroline's motus illustrate two general principles: /. the 

 smaller the area of an islet, the more extreme is the strand 

 character of its vegetation, and its corollary; 2. as islet areas 

 enlarge, strand flora becomes less important (Fosberg, 1949). 



The following species are present (see Table 2 for 

 abundance indices): 



Trees: Morinda citrifolia (one drift seedling on one motu); 

 Shrubs: Tournefortia argentea, Suriana maritima, and 

 Scaevola sericea; and 



Herbs: Heliotropium anomalum, Portulaca lutea, Boerhavia 

 repens, Lepturus repens, Laportea ruder alls, Lepidium 

 bidentatum, and Ipomoea macrantha. 



Near the high water mark, the herb mats are recumbent, 

 leathery, and somewhat desiccated. As environmental 

 conditions improve further inland, they spread more laterally 

 and average up to 7 cm in height. Their rubbly habitat, often 

 sprinkled with Tournefortia, resembles a low savannah. 

 Although these prostrate herbs can tolerate dazzling sunshine, 

 they grow most vigorously when slight shade, and hence a 

 higher relative humidity, is present. Under these conditions 

 they may attain a height of 22 cm and form a fairly thick mat. 

 With too much shade the mats disappear or their species 

 proportions and abundance changes according to the presence 

 or absence of sunny clearings. Thus, natural herb mats may be 

 found in patchy clearings within forests up to 1 3 m tall. They 

 are common in the abandoned Cocos plantations of South 

 Island, where Boerhavia tends to proliferate into thick mats 

 that completely cover the substrate, vying with Phymatosorus 

 and Ipomoea for"lebensraum" (PI. 34). A thick, exposed mat 

 of succulent herbs is found on Noddy Rock, where Portulaca 

 is the primary component. 



Herb mats occurred on almost every transect, windward 

 and leeward, ranging from 1% to 60% coverage (Figs. 19,23). 

 The most extensive areas (coverage 35-50%) were on Skull. 

 Tridacna, South (Trs. 1.4,6). Emerald, and Mannikiba. Mats 

 predominated in sparsely vegetated areas. Their widths varied 

 according to the age, shape, exposure, and geographic position 

 of the motu but were widest on seaward-facing shores 

 (Table 7). 



Wide bands of herb mats may encircle an entire motu: to 

 windward they average 36 m (Table 7), while, bordering the 

 relatively placid and intermittently shaded lagoon, they shrink 

 to a mere 0.9 m. On leeward motus, the corresponding figures 

 are 18.5 m and 4.2 m. 



26 



