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The complexity of the modern way of life has meant that humankind is not simply one member of a natural ecosystem but is a user, consumer, dominator and potential destroyer of all the Earth’s ecosystems. Unfortunately nowhere is this more apparent than in the fragile ecosystems of the world’s oceanic islands.
Recent estimates of the number of flowering plant species on the world’s islands suggest that of the 50 000 or so insular endemics, some 20 000 are threatened with extinction. The same is true for other island organisms, and Johnson and Stattersfield (1990) estimate that the extinction rate among island birds in historical times is about 40 times greater than in continental species.
The diversity of island endemic floras always reminds us of the importance of these enclaves in understanding the origins and evolution of life on our planet. Islands represent roughly 5% of the Earth’s land surface, but their plant endemics have unique characteristics which have arisen (mainly) through isolation, and make up about one-quarter of all extant terrestrial plant species. Island floras are thus not only distinctive, but also strikingly prolific.
Despite centuries of botanical exploration, constant new findings remind us how much we still have to learn about plant biodiversity on islands. In some archipelagos, palaeo-botanical data convincingly show that the vegetation makeup may have been radically different barely a few thousand years ago, new insular species are frequently discovered, and some others that were feared extinct reappear.
Oceanic islands offer biologists unparalleled opportunities to study evolutionary processes and ecological phenomena. However, human activity threatens to alter or destroy many of these fragile ecosystems, with recent estimates suggesting that nearly half of the world's insular endemics are threatened with extinction. Bringing together researchers from around the world, this book illustrates how modern research methods and new concepts have challenged accepted theories and changed our understanding of island flora. Particular attention is given to the impact of molecular studies and the insights that they provide into topics such as colonisation, radiation, diversification and hybridisation. Examples are drawn from around the world, including the Hawaiian archipelago, Galapagos Islands, Madagascar and the Macronesian region. Conservation issues are also highlighted, with coverage of alien species and the role of ex situ conservation providing valuable information that will aid the formulation of management strategies and genetic rescue programmes.
Straddling the Tropic of Capricorn, New Caledonia is situated in the South Pacific Ocean between latitudes 18° 00′ and 23° 50′ S, and longitudes 154° 45′ and 176° 20′ E. It is an archipelago made up of the islands of Grande Terre, Iles Belep, d’Entrecasteaux Récifs, Île des Pins, the Loyalty Islands and several other small islands such as the Chesterfield Islands and Walpole Island (Fig. 9.1). New Caledonia is an isolated archipelago situated some 1500 km east of Australia with the nearest land further to the east at the New Hebrides Islands and Fiji. New Caledonia is one of the extant land masses of an ancient continent known as Zealandia and now almost completely submerged. The island was formerly part of Australasia but separated from it about 60–80 million years ago (Ma) and drifted to its present position by about 50 Ma. It is, therefore, one of the most important and isolated surviving fragments of Gondwanaland. In the process, much or all of the area of New Caledonia appears to have been submerged for up to 20 Ma. During this period, oceanic mantle was deposited over the original schistic rock, eventually forming a thick layer of ultrabasic substrates including peridotite, ferricrete, serpentinite and laterite. These were once widespread over the islands and still cover about 30% of the land surface.
Island plants and their habitats will be affected in the future not just by climate change but by a whole series of factors that make up the ongoing process of global change. While much of the focus in recent years has been on the impacts of climate change, these do not operate, now, nor will they in the future, in isolation but closely interact with human population changes and alterations in disturbance regimes. This inevitably leads to an impoverishment of biodiversity and loss or fragmentation of habitats.
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