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Vegetation of the Tropical Pacific Islands
Abstract
This book begins with an introductory chapter, with consideration of the importance of geography, geology, floristic relationships and climate and vegetation patterns. Nine chapters follow, dealing with specific geographical areas: western Melanesia; eastern Melanesia; the subtropical islands in the New Zealand region; Micronesia; central Polynesia; western Polynesia; eastern Polynesia; northern Polynesia - the Hawaiian Islands; and the oceanic islands in the eastern Pacific. Each of the geographical chapters includes introductory remarks on the regional geography/geology and climate before detailed descriptions of the vegetation. A final chapter looks at the future of island vegetation.
Chapters (11)
This book is concerned with the terrestrial vegetation of the Pacific islands in the tropical realm. Aquatic vegetation will only be treated marginally where appropriate. As in the other vegetation monographs of this World Series, our vegetation treatment relates to a very large area: the tropical Pacific Ocean forms the matrix surrounding numerous small terrestrial areas, whose plant cover is the focus of this book.
Section map 1 (Fig. 2.1) shows the island region of Western Melanesia, which, for reasons of its biogeographic unity, Udvardy (1975) calls the Papuan realm (with New Guinea). For our purposes it includes two major archipelagoes north west of New Guinea, the Bismarck Archipelago and the Solomon Islands.
The Eastern Melanesian island region, shown in detail on section map 2 (Fig. 3.1), lies to the southeast of Western Melanesia. The Eastern Melanesian islands extend from 10° S latitude to the Tropic of Capricorn. From east to west they lie in the area defined roughly by the 180° meridian, which cuts through the Fijian island of Taveuni, and 163° E longitude, which separates Eastern from Western Melanesia (see also the overview map, Fig. 1.1 Chap. I, p. 5).
South of Eastern Melanesia, in the subtropical realm of the New Zealand region, are three widely dispersed island groups, Lord Howe, Norfolk, and the Kermadec Islands (Fig. 4.1). The islands of Lord Howe and Norfolk, which are 1350 km and 960 km, respectively, northwest of New Zealand’s North Island, are Pliocene, volcanic islands perched on submarine ridges. These ridges are submerged fragments of the former Gondwana continent. Until the early 1970s, biologists considered these islands to be continental in origin (Raven and Axelrod 1972). Because of their recent emergence in apparent isolation from larger land masses, however, they must be regarded as oceanic islands. The Kermadec Islands are still more recent (Pleistocene-Holocene) volcanic islands arising from a volcanically active submarine ridge along the Andesite Line. This ridge is formed by the Kermadec-Tonga Trench, where the oceanic Pacific Plate overrides the Indo-Australia Plate (Macdonald et al. 1983). Thus, the Kermadecs are plate boundary islands, while the other two are intraplate islands.
Micronesia covers a large section of the earth’s surface, most of it water (Fig. 5.1). There are approximately 161 islands, atolls, or closely associated groups of islands, but they are so small that altogether they constitute less than 2600 km2 of land (Douglas 1969). Stretching over 27° of latitude and 44° of longitude, Micronesia shows, as would be expected, great variation in climate and topography. The islands range from low coral atolls, through raised coral islands, a great variety of volcanic islands, to rare masses of metamorphic rock.
Central Polynesia extends roughly from 17° N to 12° S of the equator and from the date line (the 180° meridian) to 150° W longitude. This vast central part of the Pacific lies south of the Hawaiian chain, east and southeast of Micronesia, northeast of Eastern Melanesia, and northwest of the Society Islands (see index map, Fig. 1.2, p. 9).
Western Polynesia, as treated here, comprises the oceanic archipelagoes principally of high islands lying east of the large islands of Eastern Melanesia (see section map 6 on index map Fig. 1.2, p. 9). They are floristically most closely related to Fiji, Vanuatu, and New Caledonia but have notably more impoverished floras than those of these Melanesian archipelagoes. Yet the Western Polynesian islands have definitely richer floras than those of the groups to the east.
Eastern Polynesia, comprising five great archipelagoes, the Cook, Austral, Society, Tuamotu (including the Gambier and Pitcairn groups), and Marquesas Islands, plus remote Easter and Sala y Gomez Islands, stretches over a vast range of tropical and subtropical ocean (Fig. 8.1; for Cook Islands, see Fig. 7.1, p. 342). In size, the islands range from tiny Marotiri, a group of elevated rocks, the smallest of them only a few square meters in extent (the most southeastern of the Austral Islands), to Tahiti, the largest and highest, 1042 km2 in area and 2241 m in height. In latitude, the range is from the northern islands of the Marquesas, south of the equator (from about 7° S latitude) to subtropical Rapa and Easter Island (about 27° S). Topographically, the range is from almost perfectly flat atolls to the spirelike peaks of Rapa, Moorea, and Bora Bora and the towering wedge of Orofena in Tahiti.
The Hawaiian Islands are the most isolated archipelago in the world. They are 3,765 km from the nearest continental land mass, North America, and 3,350 km from the Marquesas, the nearest archipelago of high islands. At least partly as the result of this isolation, the native flora of flowering plants of these islands is 96% endemic (St. John 1973; or 89%, according to a more recent estimate by Wagner et al. 1990). Thus, the composition of the vegetation is unique. This means that the plant associations in the vegetation are also unique. Over a hundred of these have been described for the Hawaiian Islands by Gagné and Cuddihy (1990). At the formation level the distinctness is much less obvious, as structure and function, the two critical attributes of vegetation formations, appear to be almost independent of composition. However, a significant interdependency has been discovered for the Hawaiian rain forest. This will be explained in the concluding chapter.
There are four small oceanic archipelagoes and three isolated islands in the Eastem Pacific off the American coast. These scarcely form a natural geographic region, but they have certain aspects in common. We divide them into a northern and southern subregion. Included in the northern subregion are the Revillagigedo Islands; the three isolated islands Clipperton, Cocos, and Malpelo; and the Galápagos Islands (Fig. 10.1). In the southern subregion are the Desventuradas Islands, with San Felix and San Ambrosio, and the Juan Fernandez Islands, with Alejandro Selkirk (Masafuera), Robinson Crusoe (Masatierra), and Santa Clara Islands (Fig. 10.2). All are considered oceanic in nature, and their floristic relations are almost all American.
The vegetation survey of the nine island regions outlined in this book cannot give a quick answer to the question, “What is the future of island vegetation?” As pointed out repeatedly in this book, vegetation is a hierarchical phenomenon.
... A tropical atoll is a low coral island formed by a variable number of islets, with a ringshaped coral reef and a coral rim surrounding a lagoon (Daly, 1925). Some studies of island biogeography have reported no, or a weak, ISAR on coral atolls, due possibly to their small area, homogenous topography, and poor terrestrial habitat diversity (Mueller-Dombois & Fosberg, 1998), thus following habitat diversity hypothesis. On the other hand, several authors have reported a low native plant species richness on the atolls as being due to frequent marine submersion during extreme events (J. ...
... In general, habitat diversity increases as the result of greater topographic and geological heterogeneity (Hart & Horwitz, 1991). Due to their similar forest and flat topography, terrestrial habitat diversity on atolls is very low, and atoll is usually viewed as a "simplified island" (Mueller-Dombois & Fosberg, 1998;Stoddart, 1992;Thaman, 2008). ...
Island species-area relationship (ISAR) is the most documented pattern in island biogeography. Different hypotheses were advanced to explain this pattern. In this study, I selected 27 remote Tuamotu atolls in the South Pacific Ocean with complete surveys of native species richness of birds and vascular plants to test the influence of four abiotic predictors on species richness (atoll emerged area, habitat diversity, mean elevation, and number of islets). Linear regressions were used to assess the relative influence of predictors on native species richness while stepwise regression was then used to identify the best model. Atoll area was a significant predictor to explain native bird and plant species richness, attesting ISAR on the remote surveyed atolls. Stepwise model demonstrated that both habitat diversity and atoll area explained bird species richness, whereas atoll area and mean elevation were the best predictors for native plants. These results suggest that ISAR can be related to different hypotheses, depending on the taxon studied. Among hypotheses, the simple “target-area” hypothesis was a suitable framework to explain ISAR of native birds, while the “disturbance” hypothesis was relevant to support ISAR of native plants observed on the atolls.
... Only a few coastal areas remain relatively undisturbed, especially on the east coast and the peninsula of Tahiti (e.g., the seashore cliffs of Te Pari, Florence 1993;Meyer 2007). Except for some brief qualitative descriptions in Tahiti (Papy 1951-1954, Florence 1993, Mueller-Dombois and Fosberg 1998, Meyer 2016 and in high volcanic islands throughout the Pacific region such as western Polynesia (Samoa and Tonga) (Whistler 1980, 1992, 2002, Sykes 1981, Franklin et al. 2006, and Hawaii (Erickson and Puttock 2006), few quantitative analyses of plant assemblages found in littoral native forests have been carried out. ...
... In this study conducted in Tahiti, we were faced with the difficulty of finding relatively undisturbed native littoral and swamp forests, constraining us to reduce our sampling method to three sites, with a maximum of two or three 10 Â 20 m plots per forest type. Native coastal forests and lowland wetlands loss and degradation due to past and present human occupation has long been documented (Papy 1951-1954, Florence 1993, Mueller-Dombois and Fosberg 1998, Meyer 2007. There is an urgent need to conserve and restore these threatened remnant forests. ...
... The unique flora of these islands is shaped by various ecological processes, including adaptive radiation, isolation-induced endemism, and colonization by different vectors, often through wind or birds. This expansive archipelago provides an ideal setting for the study of island biogeography (Mueller-Dumbois & Fosberg, 1998). ...
This paper presents an updated overview of the world's biogeographical realms and regions in the terrestrial domain. It incorporates new data on floristic and vegetation aspects, along with recent regional information, which has emerged in the decades following the influential maps created by A. Takhtajan and R. Good. We elucidate the various biogeographic scales, ranging from kingdoms to districts, and outline the specific criteria that define them. We delve into the criteria used for characterizing the kingdoms and regions, with a particular focus on their floristic content, evolutionary background, and vegetation patterns, expressed through biomes and subbiomes. Additionally, we discuss the climatic conditions and their variability within and between these units. Our study identifies six kingdoms and 42 regions that are recognized for the entire planet and provides a concise summary for each of them.
Sapindus (Sapindaceae) consists of 13–20 species of trees that are well known for their soap-making properties and the utility of their hard, spheroidal seeds for ornament or games. Section Sapindus has the most wide-ranging distribution within the genus, native to the Americas, Asia, Melanesia, and Polynesia. The number of species recognized in sect. Sapindus has ranged from only one species (S. saponaria) in several treatments to as many as seven species in Radlkofer’s monograph of the family. Undertaking a revision of Sapindus sect. Sapindus, over 1000 herbarium specimens were studied (physically or digitally) and four species were studied in in the field and/or in cultivation. Within sect. Sapindus, 12 species are here recognized, including three newly described species (S. marikuru, S. motu-koita, and S. standleyi), one new combination (S. tricarpus), one new subspecies (S. saponaria subsp. jardinianus), and one new variety (S. drummondii var. glabratus). Oceanic and animal-mediated dispersal are likely responsible for the wide distribution of sect. Sapindus, and human-aided dispersal is probably much more limited than has been suggested by prior authors. The native distribution of S. saponaria subsp. saponaria is emended to include only southern Florida (USA), Mexico, the Caribbean Islands, Central America, South America, and the Galápagos. Another two species of Sapindus from Vietnam that cannot confidently be assigned to any one section of Sapindus are briefly discussed.
This chapter explores the main characteristics of New Caledonian plant biodiversity, and provides a condensed picture of the major unique elements of its flora. We present the results of recent research conducted in a territory that has much to contribute to science and society. We explore the original and unique representation of some plant lineages and functional groups, as well as the rich and diversified vegetation.
Metrosideros polymorpha (‘ohi‘a, ‘ohi‘a lehua) is an important foundation species in Hawaiian forest habitats. The genus originated in New Zealand and was dispersed to the Hawaiian archipelago approximately 3.9 million years ago. It evolved into five distinct endemic species and one of these, Metrosideros polymorpha, further differentiated into eight varieties across what are now the main Hawaiian Islands. ‘Ohi‘a is a tree that has great significance in indigenous Hawaiian culture. It is considered a physical manifestation of several principal Hawaiian deities, and serves a broad range of uses in Hawaiian material culture. It occupies a wide diversity of habitats, extending from sea level to over 2,200 m elevation, occupying habitats that range from extremely wet to dry rainfall zones. It is the dominant or co-dominant tree species in wet and mesic forests and is also one of the first woody species to become established on young lava flows. Although ‘ohi‘a is a dominant forest tree it also exhibits many characteristics of a pioneer species.‘Ohi‘a provides the matrix for a wide diversity of endemic plants and animals found in these habitats and functions as the primary vegetation cover on native Hawaiian watersheds, facilitating groundwater recharge and regulating surface runoff. ‘Ohi‘a has shown remarkable resilience by recolonizing forests that were opened up by disturbance, such as the widespread ‘ohi‘a canopy dieback that occurred on East Maui in the 1900s and on the east side of the Island of Hawai‘i in the 1970s. Several human-related conditions threaten the continued stability of Hawaii’s native ecosystems, including invasive plants, plant diseases, introduced animals, and changing climate. The research and conservation legacy of Dr. Dieter Mueller-Dombois helped to expand our knowledge of the ecology and importance of ‘ohi‘a forests, and to increase awareness and appreciation of the remarkable Hawaiian ecosystems that are unique to the world.
Globally, subalpine and alpine plant communities are receiving increasing attention owing to disproportionately rapid warming at high altitudes, and the resultant habitat shrinkage leaving high-altitude specialists with nowhere to migrate. The Hawaiian subalpine zone (1,700–3,000 m) is an interesting example of this potential phenomenon because of the high endemism. We analyzed plant species richness, cover, and density from 89 plots (1,000 m2) sampled in 2010–2018 across two volcanic mountains, Haleakalā on Maui, and Mauna Loa on Hawaiʻi. Most of the 139 plant species recorded were non-native (55%), with the remainder endemic (31%) and indigenous (14%). Plot-level richness differed from gamma diversity, with endemic species more abundant than non-native species. Non-native species richness was higher on Haleakalā than Mauna Loa. These communities are patchy with low-lying (<1 m) vegetation, and lower cover on younger drier Mauna Loa (36%) than Haleakalā (54%). Density was largely consistent with the understory cover data, with endemic Vaccinium reticulatum (>3,500/ha) and indigenous Leptecophylla tameiameiae (>2,430/ha) shrubs dominant on both volcanoes. Woodland communities were encountered only on Mauna Loa, with endemic trees Metrosideros polymorpha on wetter, south aspects, and Sophora chrysophylla on the drier, leeward side. Hawaiian subalpine vegetation varies among islands, volcanoes, and aspects, yet remains largely native-dominated, though with increasing threats from climate change, invasive non-native species, and wildfire. We recommend continued monitoring of biotic communities and climate in this sensitive zone, in situ physiological studies for the native matrix species, stricter non-native species biosecurity and sanitation protocols, wildfire prevention, and improved documentation of the effects of feral ungulates.
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