Vegetation of Nauru and the Gilbert Islands: Case Studies of Poverty, Degradation, Disturbance, and Displacement!
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Pacific Science (1992), vol. 46, no. 2: 128-158 © 1992 by University of Hawaii Press. All rights reserved Vegetation of Nauru and the Gilbert Islands: Case Studies of Poverty, Degradation, Disturbance, and Displacement! RANDOLPH R. THAMAN 2 ABSTRACT: The indigenous floras of the raised phosphatic limestone island of Nauru and the atolls of the Gilbert Islands are among the poorest on earth. Long settlement, widespread destruction during World War II, monocultural expansion ofcoconut palms, and more than 75 yr ofopen-cast phosphate mining in the case of Nauru have led to serious vegetation degradation, disturbance, and displacement. The floras of Nauru and the Gilbert Islands consist of approximately 487 and 306 species, respectively, of which only 55 and 83 are possibly indigenous, but none of which are endemic. The balance is composed ofornamentals, weedy exotics, food plants, and a limited number ofother useful cultigens. Although greatly outnumbered by exotics, indigenous species still dominate some of the most disturbed habitats, as well as constituting the most culturally utilitarian and ecologically important species. Because of the unique adaptability ofindigenous Pacific island plants to the harsh conditions ofcoastal and small-island environments, and their cultural and ecological utility, it is argued that the protection and enhancement ofthe indigenous floras are crucial to the ecological integrity and cultural survival of small-island Pacific societies. THIS PAPER FOCUSES ON the vegetation of Previous Studies Nauru and the Gilbert Islands (part of the Although collections were made on Nauru Republic of Kiribati), with specific emphases by Burgess in 1935; Fosberg in 1980; Scully in on: (I) the nature of the existing floras and 1980; Thaman, Hassall, and Manner in 1980 vegetation associations; (2) the importance of and 1981; Thaman and Manner in 1987; and indigenous species relative to exotics in the Swarbrick in 1988, little has been published. vegetation associations; (3) the role ofhuman The only substantial publications are those of disturbance and dispersal, particularly post Manner, Thaman, and Hassall (1984, 1985); European-contact disturbance and dispersal Thaman, Manner, and Hassall (1985); and in the impoverishment, modification, degra Fosberg, Sachet, and Oliver (1979, 1982, dation, displacement, and enrichment of the 1987). These publications include most of the indigenous floras and vegetation; and (4) an species cited and specimens examined before analysis of the cultural and ecological impor 1980. tance of the indigenous floras in the context The flora and vegetation of the Gilbert of modern small-island development. Islands and the Republic ofKiribati are better documented. The most detailed publications include those of Luomala (1953); Catala I Paper prepared for the Vegetation Ecology of the (1957); Moul (1957); Small (1972); Overy, Pacific Islands Symposium SI-6-08 in honor ofDr. F. R. Polunin, and Wimblett (1982); Thaman Fosberg, International Congress of Ecology V, Yoko (I987a); and Fosberg and Sachet (1987). Oth hama, Japan, 27 August 1990. Manuscript accepted for er studies include those of Fosberg (1952), publication 2 May 1991. Christophersen (1927), and Wester (1985), 2 Department of Geography, School of Social and Economic Development, The University of the South which provide information on the plants ofthe Pacific. P.O. Box 1168, Suva, Fiji. atolls outside the main Gilberts group. Other 128 Vegetation of Nauru and the Gilbert Islands-THAMAN 129 accounts are those on Abemama (Watters and Islands proper (formerly part of the British Banibati 1977), Butaritari (Sewell 1979), Gilbert and Ellice Islands Colony, known North Tabiteuea (Geddes 1975), and Tamana locally as Tungaru), the Phoenix Islands, and (Lawrence 1977). Thaman's studies (1987b, the Northern and Southern Line Islands, plus 1988a, 1990a) provide information on species the isolated island of Banaba. These islands found in houseyard gardens and agricultural have a combined land area ofonly 811 km2 in 2 areas. Useful general studies of atoll and an ocean area of some 13 million km . small-island vegetation include Merrill (1945), The main Gilbert Islands, the focus of this Fosberg (1960, 1965), Wiens (1962), Alkire paper, consist of 16 small atolls or reef islets (1974), Soucie (1983), Guerin (1982), and extending 640 km from north to south. They Manner (1987). are 700 km east of Nauru, 400 km east of Banaba, and about 250 km north and south, respectively, of the atoll nations of Tuvalu Current Study (formerly the Ellice Islands) and the Republic The current study is based on an in-depth of the Marshall Islands. Both Nauru and the analysis of the above sources; 5 weeks of Gilbert Islands are at considerable distances fieldwork during three visits on Nauru in from the Philippines, Indo-Malaya, Austra 1980, 1981, and 1987; a to-day field study in lia, and Melanesia, the source regions or the Gilbert Islands with I-Kiribati informants centers of dispersal of most Pacific island on Abemama and North and South Tarawa floras (Merrill 1945, Manner 1987).. 2 in Ausust 1984; and a 2-week reconnaissance Nauru, with an area of only 22 km , con survey on Tarawa in 1989. During these sists of a narrow coastal plain, ranging from studies the Latin and Kiribati names of all 50 to 300 m wide, encircling a limestone plant species found in urban and rural areas escarpment rising some 30 m to· the central were recorded, and the lists were cross~ plateau (Figure 1). The escarpment ranges in checked with names listed from previous gradient from vertical cliffs to gradually slop studies. Two collections of herbarium speci ing areas of colluvial soil il}terspersed with mens held by the Agricultural Division and limestone outcrops and pinnacles. The pla the University of the South Pacific (USP) teau, with a maximum .elevation of 70 m, Atoll Research and Development Unit consists ofa matrix oflirilestone pinnacles and (ARDU) on Tarawa were also studied in outcrops, between which lie extensive deposits 1984. of soil and high-grade tricalcic phosphate rock (Tyrer 1963, Viviani 1970). Buada La goon, about 12 ha in size, located in the low-lying southwest central portion of the NAURU AND THE GILBERT ISLANDS island, is a landlocked brackish lake, with an associated fertile depression. The Islands The Gilbert Islands (Figure 2) are for the The Republic of Nauru, a single uplifted most part atolls with central lagoons and limestone island, west of the Gilbert Islands, encircling islets of various sizes and shapes. is located 142 km south of the equator at Kuria, Tamana, and Arorae are slightly raised 166 0 56' E, some 2000 km east-northeast of limestone islands without lagoons. The total 2 Papua New Guinea, 4450 km south-southeast land area is estimated at 294 km , and the of the Philippines, and an equal distance islands range in size from Tamana and Makin 2 southwest of Hawaii. The nearest island is (5.2 and 7.2 km , respectively) to Maiana, Banaba (Ocean Island), 300 km due east. Abaiang, and Tabiteuea (28.1, 28.5, and 49 0 2 The Republic of Kiribati, between 4 43' N km , respectively). Tarawa, where the capi 0 0 and 1l 0 25' Sand 169 32' and 150 14' W tal is located, is the most populous island, (Douglas and Douglas 1989), consists of 33 with 21,393 people in 1985. It has islets with islands in three main groups, the Gilbert an estimated area of 19.9 km2 and extends 130 PACIFIC SCIENCE, Volume 46, April 1992 NAURU \, R••I eml Edg. Sealed Rood Unseal.d Road Government Office. -_......: o, Kilometre. FIGURE I. Map of Nauru. over 64 km from north to south (Catala deposited during storms. This rampart is com 1957). monly the highest point on the islet, no more On a typical islet there is usually an uplifted than 4 m above mean sea level. Lagoonward fringing reef in the wave zone of the ocean of the rampart, and extending to the lagoon side. The reef may be covered by a sandy itself, is an area of windblown sand. Toward beach, which becomes a raised rampart or the lagoon shore, increasingly fine deposits shingle ridge ofcoral boulders and fragments are of lagoonal origin. Limestone outcrops Vegetation of Nauru and the Gilbert Islands-THAMAN 131 173°E THE GILBERT ISLANDS :;:;<~.&} Makin Butaritari :~" Marakei Abaia~f::): :~ " ~~i", Tarawa ::. 11.., , .0' :'~.~'~" .{):' Maiana 0°- -- - :i';'. Nonouti :'~ '~.... ......... " ·····:0.°: Beru :~. ,~ Tabiteuea ·0 " ...•. ..\" ........ ~ ..~ '" Nikunau ~~.'.~ ·iJ t~~·, :o.l.. Onotoa Kilometres Arorae I i I o 50 100 Tamana ':~., FIGURE 2, Map of the Gilbert Islands, 132 PACIFIC SCIENCE, Volume 46, April 1992 with little or no soil and low-lying swampy production of even coconut palms (Catala areas are often found as well. 1957). Water Resources Soils Apart from Buada Lagoon on Nauru, there The coastal soils of Nauru and the soils of are no significant surface freshwater resources the Gilbert Islands are among the poorest in on Nauru or the Gilbert Islands. The only the world. They are shallow, alkaline, coarse permanent freshwater resource is ground textured, and have carbonatic mineralogy. water in the form of a lens of often slightly Both are composed of a variable layer of brackish fresh water, hydrostatically floating organic matter, coral sand, and fragments, on higher density salt water beneath it. The which overlays a limestone platform: On Nau height of the freshwater lens above sea level ru coastal soils are generally drier, only about and the level of salinity vary in relation to the 25 cm deep, and contain more coral gravel elevation, geology, texture, shape, and width than sand in the lower horizons. The Gilbert ofislets, and with the amount ofwater use and Islands soils tend to be deeper, from 25 cm to rainfall. Replenishment or recharge ofthe lens I m or more deep, and are wetter, with some is dependent on rainfall.