Lord Howe Island is the spectacular remnant of a large shield volcano that was active 7 million years ago in an isolated part of the southwestern Pacific Ocean between Australia and New Zealand. The high proportion of rare and endemic plants and animals, the rugged natural beauty of the landscape, and the occurrence of the southernmost coral reef in the world contribute to its status as a UNESCO World Heritage Site. The Permanent Park Preserve encompasses 75% of the island. Scientific studies dating from the 1850s have provided an unusually detailed documentation of natural history phenomena, making Lord Howe one of the most intensively studied sites in Australia. Because it is one of the last island biodiversity hotspots on the planet to be discovered and colonized by humans, the original composition of the biota is relatively well known. Successful management efforts to eliminate introduced species and site-based initiatives for conserving native habitats and threatened species place Lord Howe at the forefront of island conservation practice.
Lord Howe Island is the largest emergent feature on the western flank of the Lord Howe Rise, at the southern end of a north–south chain of seamounts and guyots extending from southwest of New Caledonia to the Challenger Plateau, west of New Zealand. The island is 702 km northeast of Sydney, Australia, at a latitude of 31° S. The Lord Howe Rise is bounded by the Tasman Sea on the west and the New Caledonia Basin on the east. The rise is no more than 2000 m below sea level, whereas depths in the Tas- man Sea between the rise and Australia exceed 4000 m. The rise is underlain by continental crust that separated from eastern Australia during the Cretaceous, moving eastward to its current position during the 30-million- year-old opening of the Tasman Basin. The Lord Howe World Heritage Site includes offshore islands, islets, and rocks: the Admiralty group to the northeast, Mutton Bird and Sail Rock to the east, Rabbit Island within the lagoon of the Lord Howe reef, Gower Island off the southern end, and Ball's Pyramid 25 km south of the island. The main island is crescent shaped, measuring 10 km from north to south and approximately 2 km in width.
Topographically, Lord Howe is dominated by the southern basalt peaks of Mount Lidgbird (777 m) and Mount Gower (875 m), which rise nearly vertically out of the sea forming steep cliffs and slopes covered with dense subtropical rain forest (Fig. 1A). A narrow lowland isthmus separates the southern peaks from an older northern highland that forms the shear cliffs of the northern coastline. Only the lowland isthmus is habitable.
The two major rock types exposed on Lord Howe are basalt and calcarenite. The majority of the exposed rock is layered basalt, with individual flows ranging in thickness from a few centimeters to more than 30 m (Fig. 1B). The nearly horizontal basalt layers of Mount Lidgbird are part of a sequence that formed near the close of volcanic activity, filling an immense caldera that resulted from collapse of the summit of the original volcano. In addition to basalt, the older sequences of volcanic rock at the north end of the island and in the Admiralty Islands include tuff and volcanic breccia, consolidated fragmental deposits from a more explosive earlier phase of volcanism.
The basalt layers on Lord Howe are extensively crosscut by dikes. These features formed when younger basalt was intruded into fissures cutting obliquely across the older basalt layers (Fig. 1C).
The low-lying coastal strip of Lord Howe is dominated by calcarenite, a sedimentary rock that normally does not occur on high volcanic islands. Calcarenite consists of calcium carbonate sand, formed by mechanical breakdown of the skeletons of coral, calcareous algae, and shells. The calcarenites of Lord Howe represent major episodes of erosion of the coral reef during ice-age fluctuations of sea level and subsequent formation of beach sands and windblown dunes around the flanks of the old volcano. Cementatation of the deposits and their subsequent erosion has formed many interesting sedimentary features (Fig. 2A).
The calcarenite is also notable for its fossil content, which includes both marine and terrestrial biota. Fragments of the bones of seabirds are common (Fig. 2B) along with shells of endemic land snails and large quantities of bone of the extinct giant horned turtle Meiolania platyceps. The British Museum of Natural History and the Australian Museum both contain hundreds of specimens resulting from collections as early as the i880s. The skull of a new species of extinct endemic bat, an extinct species of penguin, and bird eggs are included in the interesting fossil discoveries. Some of the best-preserved fossil invertebrates are in beach rock exposed at sea level when storms wash away the overlying beach sand (Fig. 2C).
When the emergent portion of Lord Howe Island formed, 7 million years ago during the Miocene epoch, its sub- aerial extent was 40 times greater than it is today. The subaerial phase of eruption and building of the shield volcano culminated in a collapse of a caldera estimated to be 900 m deep and 5 km by 2 km. Rapid filling of the caldera with horizontal basalt layers ended the volcanic phase of island history 6.4 million years ago.
The modern landscape is predominantly a consequence of erosion of the original edifice. Very little is known of the larger submarine portion of the island, which is more than 25 km in diameter at its base. The Admiralty Islands and small rocks and islands adjacent to Lord Howe are part of the original shield volcano. Ball's Pyramid, the dramatic 551-m pinnacle located 25 km southeast of Lord Howe Island, is the remnant of a different shield volcano. It is separated from Lord Howe by depths of approximately 500 m, and the two were never connected by land.
Beach sand units and windblown dune units include fossil soil layers. The history and ages of the Lord Howe calcar- enites have been studied in detail using five different dating techniques. The cyclical pattern of formation can be linked to periods of sea-level change during successive ice ages.
Lord Howe Island has a humid subtropical climate, with mean summer temperatures of 23 °C and mean winter temperatures of 16 °C. Mean annual rainfall is approximately 165 cm, with higher rainfall during the winter. The peaks of Mt. Lidgbird and Mt. Gower must receive significantly higher precipitation throughout the year.
The marine climate is notable for its mix of temperate and tropical water. The tropical East Australia Current flows south along the Great Barrier Reef and into the northern Tasman Sea, but in some years there are strong incursions of cold subantarctic currents from the south.
There are no large terrestrial vertebrates in the native fauna, which is restricted to a skink, a gecko, and a small bat. Of the 15 native land bird species at the time of discovery of Lord Howe, nine are now extinct. Two were eaten to extinction by sailors (white gallinule, white- throated pigeon) and a third was eliminated by early settlers because it was a crop pest (red-fronted parakeet). Five additional species were eliminated when the black rat reached the island in 1918. Two of the seven remaining native landbirds are endemic (Lord Howe woodhen, Lord Howe island silvereye). The most conspicuous members of the avifauna are seabirds (Fig. 3A). Fourteen species nest on Lord Howe and adjacent islets, including huge colonies of tens of thousands of individuals of flesh-footed shearwaters, sooty terns, and providence petrels.
The terrestrial invertebrate fauna is rich in unusual, rare, and endemic species. There are at least 85 endemic species of land snails and a remarkable evolutionary radiation of freshwater hydrobiid snails. More than i00 species of spiders have been identified, and 50% of these are believed to be endemic to the island (Fig. 3B). There is an endemic freshwater shrimp, an endemic freshwater crab, an endemic leech, ten endemic earthworm species, an endemic amphipod, i2 endemic species and one endemic genus of terrestrial isopod, and an endemic cicada. Genuslevel endemism in the insects includes the hemipterin bug Howeria and the cricket Howeta.
One of the most unusual insects is the Lord Howe Island phasmid, Dryococelus australis, a giant stick insect reaching lengths of 15 cm. It was common until the arrival of the black rat in 1918 and extinct by 1920. Rediscovery of a small population of the "extinct" phasmid on Ball's Pyramid in 2001 is an example of the "Lazarus phenomenon." It has triggered a vigorous debate about conservation options for reappearing species.
The marine fauna of Lord Howe is remarkable for its mix of tropical and temperate species. The reef has attracted attention not only as the most southerly coral reef in the Pacific, but also because it has unusually high coral cover and high algal biomass. The 83 reported species of coral form some unique associations of tropical species. More than 400 species of fish have been reported. As with the rich marine invertebrate fauna, the fish are a unique mix of tropical and temperate species.
There are 241 native vascular plant species in the Lord Howe Island group, and 105 (44%) are endemic. The richness of the flora can be attributed in part to the variety of habitats. Twenty-five vegetation associations have been recognized. It is unusual for an island as small as Lord Howe to have altitudes supporting a true cloud forest (Fig. 3C). The moss forests at the summits of Mt. Gower and Mt. Lidgbird are rich in orchids as well as mosses.
The endemics are not all rare, high-elevation species. There are four endemic species of palm in three endemic genera. Howea forsteriana is the most notable, forming dense lowland forests.
Exotic species pose one of the greatest threats to the native flora. There are 230 introduced species, including i7 that are considered noxious weeds. Most of these are restricted to the settlement area, and most have not invaded the indigenous plant communities.
The Lord Howe Island biota is a composite of organisms with different geographic affinities. Many endemic elements in the flora have their closest affinities with New Zealand, but there is a mix of tropical and temperate components. Insects show many different patterns. There are beetles whose closest relatives are on New Caledonia and Norfolk Island. The endemic species and genera of Lord Howe crickets also have their closest affinities with crickets on New Caledonia and Norfolk. Four species of caddis flies endemic to Lord Howe are in a genus endemic to Australia, and the endemic muscid flies of both Lord Howe and Norfolk have an Australian origin. The Lord Howe stick insect is closely related to a genus in New Guinea. The land snails also show several different biogeographic patterns. In one family there is a close affinity with Norfolk Island, whereas the Lord Howe Placostylus is closest to a species in New Zealand.
Reconstructing the deep history of island biotas of the western Pacific requires understanding 100 million years of plate tectonics events that both created and destroyed islands. These events were set in motion with separation of the immense continental crustal block containing the modern emergent islands of New Zealand, Lord Howe, New Caledonia, and Norfolk from Antarctica and Australia. The two main ridges on the block, the western Lord Howe Rise and the eastern Norfolk Ridge, separated 65 million years ago with the opening of the New Caledonia Basin. The probability of preexisting islands, connections, and extinct island biotas is strong, but it lacks preserved geologic evidence.
There is no evidence of prehistoric habitation of Lord Howe Island. The earliest recorded sighting of the island was by Henry Lidgbird Ball, in command of HMS Supplybound from Sydney to Norfolk Island in 1788. He landed on his return trip to Sydney, claiming the island for Great Britain and naming several prominent features (Mt. Lidgbird, Ball's Pyramid) for himself. The island itself he named for the first lord of the British Admiralty, Lord Howe. Although ships in search of food and freshwater visited the island, it was not settled until 45 years after its discovery. Sparse early settlement in 1833 and 1844 was restricted to the lowland and supported by subsistence farming and supplying passing ships. The only "industry" in the latter part of the nineteenth century was the marketing of seeds of the Howea palm, an adaptable and hearty indoor plant that achieved great popularity during the Victorian era.
Tourism has been the only other "industry," initially by steamship service and small rustic guesthouses. Today the number of tourist beds on the island is controlled, and the natural history, beauty, and tranquility are the major attractions.
The island is under jurisdiction of the New South Wales Government and is administered locally by the Lord Howe Island Board. There is no private land ownership. Leaseholders must reside on the island, under a management plan for the settlement. The board also manages the Permanent Park Preserve, which encompasses 75% of the land on the island and has its own management plan. Listing of the island group as a world heritage property included 1455 hectares of the main island, offshore islets, and Ball's Pyramid. In 1988, the New South Wales government created the marine park that expanded the area to 145,000 hectares.
Although Lord Howe Island has not been drastically modified relative to most Pacific islands, the most obvious steps in conservation have focused on eradicating introduced feral animals. Feral pigs were eliminated in 1995. Feral cats have been eliminated, and goats may be totally eliminated. Rodent eradication assessments have been made, and eliminating rats appears feasible if external funding can be obtained to meet the relatively high costs.
Intensive efforts have been made on behalf of a number of endemic species listed as threatened or endangered. The Lord Howe Island woodhen, Tricholimnas sylvistris, had been reduced to three adult pairs by 1980. They were transferred to a captive breeding facility on the island. By the end of three breeding seasons, 57 individuals had been released on the island. By 1992, the population was estimated at 250–300 birds. Eradication of pigs and cats has been critical to the success of the captive breeding program.
There is a recovery plan for the Lord Howe Placostylus, a large, critically endangered land snail. It occurs in the fossil calcarenites of the island and is most often encountered today as empty shells (Fig. 4). The recovery plan emphasizes community involvement in conserving suitable habitat for the species.
Although Lord Howe Island has not been drastically modified relative to most Pacific islands, the "people pressure" is a constant threat. An Australian voluntary conservation movement views Lord Howe as "a paradise in peril," and has generated a "management strategy" to afford better protection to its world heritage values.
The Australian Commonwealth includes several island territories in addition to the islands such as Lord Howe that are under the jurisdiction of mainland territories. Off the east coast there are two island territories. The Coral Sea Islands Territory is a vast complex of uninhabited reefs and atolls northeast of Queensland and the Great Barrier Reef. Norfolk Island is a small, subtropical, volcanic island territory on the Norfolk Ridge, midway between New Zealand and New Caledonia, twice as far from Sydney as Lord Howe. The territory comprises three islands: Norfolk and the small adjacent Phillip and Nepean Islands. Norfolk Island is the only Australian territory with self-governance. Like Lord Howe, Norfolk is the remnant of a submarine volcano, but it differs from Lord Howe in its low topographic relief and considerably younger age (2–3 million years). In contrast to Lord Howe, there is archaeological evidence of late prehistoric Polynesian occupation, although there was no indigenous population at the time of its discovery in 1774 by Captain James Cook. It was more heavily colonized and disturbed following European discovery, and only 5% of the native forest remains intact. The origins of its endemic plants and animals have been of considerable interest to biogeographers.
Endemism / Extinction / Fossil Birds / Island Formation / Land Snails / Spiders
- Quaternary calcarenite stratigraphy on Lord Howe Island, southwestern Pacific Ocean and the record of coastal carbonate deposition. Quaternary Science Reviews 22: 859-880. , , , , and . 2003.
- Checklist of the coastal fishes of Lord Howe, Norfolk, and Kermadec Islands, southwest Pacific Ocean. Pacific Science 47: 136-170. 1993.
- The coral communities of Lord Howe Island. Marine and Freshwater Research 46: 457-465. , , and . 1995.
- Lord Howe Island. Australian Capital Territory: Conservation Press. 1986.
- Reassembling island ecosystems: the case of Lord Howe Island. Animal Conservation 10: 22-29. , , and . 2007.
- Origin and evolution of Lord Howe Island, southwest Pacific Ocean. Journal of the Geological Society of Australia 28: 155-176. , , and . 1981.
- Rehabilitation of an endangered Australian bird: the Lord Howe Island woodhen Tricholimnas sylvestris (schlater). Biological Conservation 34: 55-95. , and . 1985.
- Vegetation of Lord Howe Island. Cunninghamia 1: 133-266. 1983.
- Rediscovery of the 'extinct' Lord Howe Island stick-insect (Dryo- cocelus australis (montrouzier)) (Phasmatoidea) and recommendations for its conservation. Biodiversity and Conservation 12: 1391-1403. , , , , and . 2003.
- Geology of Lord Howe Island. Proceedings of the Royal Society of New South Wales 96: 107-121. 1963.