East Rennell, Solomon Islands

Published: July 22, 2008, 6:34 pm

Topics:

Marine Ecology (main) Ecology (main) Geography (main)

Geographical Location

East Rennell (11°39'-11°43' S, 160°18'-160°20' E) is a World Heritage Site located on Rennell Island, which is the southernmost island in the Solomons, and covers portions of the Rennell and Bellona Province. Rennell Island is located approximately 180 kilometers (km) to the south of Guadalcanal and to the south-west of San Cristobal.

Date and History of Establishment

There is currently no legislation specifically protecting the natural and cultural features of East Rennell.

Area

East Rennell has an area of 37,000 hectares (ha) and includes Lake Tegano (15,500 ha).

Land Tenure

Rennell Island Reef, Solomon Islands. (Source: Creative Commons)

Customary. Lake Tegano is regarded as property common to the people from four lakeside villages.

Altitude

From sea level to 1,000 meters (m) below sea level.

Physical Features

The Solomon Islands is a group of islands of volcanic origin with basement rocks formed along a spreading mid-ocean ridge some time between the late Cretaceous and early Eocene. Around the early Eocene, a convergent plate boundary formed in the vicinity of Rennell and Bellona, to the south of the main Solomon chain. Near the end of the Pleistocene, tectonic movements raised the seabed sufficiently to allow coral building on Bellona, Rennell and Indispensable Reefs. Rennell and Bellona are geologically younger than most of the rest of the Solomon Islands and they have experienced different forces of emergence. Both islands are well away from the crusted plate collision zone and have a very low degree of seismic activity. The structure and geomorphology of Rennell and Bellona indicate that Rennell Ridge on which they are situated is presently situated in a phase of active uplift following a long history of subsidence. The whole Rennell area is thought to have been initially deposited as coralline algal limestone and then dolotomized. This dolomitic reef complex is overlain by younger undolotomized reef limestone.

Lake Tegano is contained in the central basin which was the old lagoon. It is 29 km long and 10 km wide and occupies 17.6% of the total area of Rennell Island. It is also the largest body of enclosed water in the insular Pacific. Its central part forms a nearly unbroken plain with a depth rarely exceeding 40 m. The hard bottom is covered by several meters of suspended mud. The lake is brackish with the elevated salt concentration being kept by a subterranean duct system which connects it with the sea. There are no streams or rivers on Rennell Island although there are freshwater (Freshwater biomes) springs around the lake edge and they emerge in various places from the cliffs at the coast. Sub-surface water flow is likely to be directed along the lower central axis of the island from the highest western and eastward until it enters the lake.

Soils are derived from weathered coral limestone and are present as small scattered pockets. There has been no soil enrichment by volcanic dust or sea-borne river sediment because of the great distance from the larger islands and the direction of the prevailing wind and sea currents. High grade phosphates of alumina and iron oxides are found in Bellona soils and high grade (low silica) bauxite deposits are found on Rennell. Soils have a pH range from 6 at 1 centimeter (cm) depth to 8.5 at 6 cm depth.

Climate

Rennell and Bellona experience a typical tropical climate characterized by high and rather uniform temperatures (between 22.7°C and 32.2°C) and humidity. Rennell annual rainfall ranges between 3,000 millimeters (mm) and 4,000mm. There may be a marked dry period from May to June. This can extend from May to August with a very dry month in July. Southeast trade winds prevail from April to the end of November. The island is also located within the band of known cyclone paths and is subject to cyclone (Tropical weather and hurricanes)s at relatively frequent intervals. The latest major cyclone to hit Rennell was Nina in 1993 which caused extensive damage to the forests and villages.

Vegetation

There are three major vegetation types on Rennell Island: (i) low mature forest of the karst ridge on the island perimeter; (ii) tall forest of the island interior; and (iii) beach flora of the Lake Tekano margins. There are also small patches of mangrove vegetation on the lake margin. The differences in species and structural attributes between the karst ridge and island interior forests are the result of different physical conditions on the exposed island margins and the relatively sheltered island interior where deeper [[soil]s] occur.

The Solomon Islands constitute a major transition point in the sequence of decreasing floral diversity eastward into the tropical Pacific from Papua New Guinea. The sequence involves a decline in phanerogam genera from c.1,400 in Papua New Guinea to c. 260 in both Tonga and Niue. The Solomon group contains almost 650 species of phanerogam with 162, or 25% of the total not occurring on any other island to the east.

To date, no endemic tree species have been found on Rennell Island but ten endemic plants have been recorded so far. The endemic orchid Dendrobium rennellii occurs on the small islands of Lake Tegano. There are also two endemic species of Pandanus (P. lacustris and P. rennellensis).

Fauna

There are 11 species of bats in the area including Rennell flying-fox Pteropus rennelli which is endemic to the island. Other species present are bare-backed fruit-bat Dobsonia inermis, Pacific flying-fox Pteropus tonganus, spurred horseshoe-bat Hipposideros calcaratus and large Melanesian bent-wing bat Miniopterus propitristis. Some 43 species of breeding land and water birds have been identified. Four species and nine subspecies are endemic to Rennell, and seven are subspecies endemic to Rennell and Bellona. Australian dab-chick Tachybaptushas novaehollandiae and little pied cormorant Phalacrocorax melanoleucus are common at Lake Tegano. Pink-spotted fruit dove Ptilinopus richardsii cyanopterus is endemic to Rennell and Bellona and is found mainly in the canopy but comes lower in second growth. Endemic species include Rennell fantail Rhipidura rennelliana and Rennell shrike-bill Clytorynchus hamlinii (NT).

Lake Tegano is the only known location for the endemic sea krait Laticauda crockeri (VU). The other species of sea snake in the lake is Laticauda colubrina which often tends to come on land when not foraging and hides in rock crevices and holes. There are five species of geckos, four skinks, one monitor lizard (Varanus sp.) and three snakes, all of which are species with widespread distributions and are typical of the region.

No amphibians have been recorded for Rennell Island so far. This is unusual as the rest of the Solomon archipelago has a rich and peculiar frog and toad fauna. This absence is probably explained by the topography and the lack of surface water except for Lake Tegano. Rennell has 27 species of land snails, seven of which are endemic to the island. Coconut crab Birgus latro (DD) and two other species of land hermit crabs (Coenobita sp.) occur on the island. A total 731 insects have been identified from collections made at Rennell and Bellona. Moths (Lepidoptera) have the greatest number of species (246, in total) with 35 species and 25 subspecies exclusive to Rennell and Bellona.

Cultural Heritage

Between 2000 and 1600 BC, people belonging to the Lapita Culture made their appearance. Over a millennium, through long-range canoe voyages, their distinctive pottery was distributed throughout the Pacific at sites from the Bismarck Archipelago in eastern Papua New Guinea to Samoa. Bellona Island was briefly occupied by Lapita people in about 1000 BC. The next settlement occurred on both Rennell and Bellona around 130 BC, with another major occupation in about 1000 AD. The present-day inhabitants say their ancestors landed on Bellona around 26 generations ago in about 1400 AD and came from Uvea, or Wallis in the Wallis and Futuna group.

It is thought that the two islands were officially discovered in 1793 by Captain Boid in the merchant ship Bellona. Traders, whalers and recruiters for the Queensland cane fields called there during the Nineteenth Century, but lack of safe anchorage, the isolation and infertility of the island and shortage of easily obtainable freshwater prevented European settlement and establishment of trading stations.

Local Human Population

Dugout Canoe in the Rennell Island lagoon, Solomon Islands. (Source: Mediawiki Commons)

The population on Rennell has never been large, partly because there are only a few small, scattered areas of soil suitable for gardens and because there are limited freshwater sources. Current population is around 1,500 people and this is declining through emigration to Honiara and the plantations of the Russell Islands. About third of the population of East Rennell (approximately 500 people) live in four villages surrounding Lake Tegano.

Most villages claim areas of around 57 square kilometers (km²) and hunting areas, which could be shared with other villages, of around 60 km². Most of the land cleared for gardens has secondary growth rather than primary forest on it. Traditional garden areas are cultivated for around nine months before being left fallow. The fallow period is around four years when the land is cleared and replanted. Gardens provide a large proportion of the villager's subsistence food and are cash crop as well. The main crops are root vegetables such as kumara, taro and pana. Slippery cabbage and paw-paw are also grown. Most villages produce coconut for sale.

Up to thirteen species of birds are taken regularly for food. All villages harvest marine animals including clams, turtles and sharks. A smaller number of villages take crayfish, dolphin and octopus and a species of seaweed. In East Rennell fish is a regular part of the diet but it is mostly Tilapia mozambica which is harvested from the lake. The government introduced this species around 1957 as an additional protein source for the villagers.

There has been no commercial logging on Rennell but local people have been using portable mills to produce timber for local use. Most villages have an average of two chainsaws. There are no fixed sawmills and three villages make charcoal. The forest is a storehouse for the villages providing timber, poles and posts, ropes and canes, firewood, food, medicine, bark for tapa cloth, canoe wood, carving wood and materials for tools, fishing and crafts.

Orchids, butterflies and small animals are occasionally taken from the forest and sold. More commonly, coconut crabs are harvested as well as coral and shells. There are no reports of live birds being sold.

Rennell Island is unusual in the Solomon group as it does not have any river or stream. The brackish water of Lake Tegano is used for bathing, laundry and cooking. Drinking water traditionally came from caves, springs and rock pools. All villages now have some rainwater tanks but these often run out in dry season .

Visitors and Visitor Facilities

There are opportunities for bird-watchers, botanists, photographers and other people who like to visit isolated areas or view World War II relics. The outstanding natural beauty of the lake and the island, snorkeling, bush walks, cultural activities and trips by canoe are only a few of the attractions available.

A road linking Lavagu and Lake Tegano was completed in 1995. Small planes fly to Rennell three times a week and can take 18 passengers. A cargo ship that also takes passengers sails approximately once a month. Otherwise, there are no facilities for visitors on the island.

Scientific Research and Facilities

Rennell has been studied as part of eight major scientific expeditions. A comprehensive list of scientific papers regarding the fauna and flora of the island is provided in Wingham (1997). There are no scientific facilities on the island.

Conservation Value

The fauna of the Solomon Islands is of considerable international importance. With the exception of Papua New Guinea, the Solomon Islands have a greater diversity of animal species and higher level of endemism than any other Pacific island nation. Within the Solomon Islands, Rennell has the highest occurrence of endemism for an island of its size. Rennell is famous for having developed many unique species and races of birds because of its isolation. East Rennell is important because it includes all the habitats found on Rennell and contains a viable representation in natural conditions of most endemic bird species.

Rennell is the world's largest raised coral atoll. Throughout the Pacific there are about 25 such atolls, most of which have been significantly modified by human activity (except for Henderson Island World Heritage site which is one-tenth the size of Rennell but is more pristine). Lake Tegano is the largest lake in the insular pacific and contains a number of endemic species (although not as many as the lakes in Palau). The forests of the nominated area are mostly undisturbed by humans and display a number of adaptations to the effects of frequent cyclonic storms. For its size, Rennell Island has a high number of endemic species, particularly birds. Along with 29 other Islands in the Pacific, Rennell is listed as an endemic bird area by Birdlife International (though it is ranked third level in terms of priorities). Within the pacific, most oceanic islands have been much modified by human activity. On Rennell, these impacts have been relatively light and invasive (Invasion fact sheet) predators such as rats and alien land snails which have decimated the faunas of other islands are absent.

In conclusion, East Rennell has a number of marine, [[coast]al] and forest values that are better displayed in other Pacific locations. The fact, however, that East Rennell combines them in one place and in a relatively undisturbed state makes the island a special place in the Papuan Biogeographical Province.

Conservation Management

The people of East Rennell have helped to prepare a draft resource management plan with input from the Tegano Management Conservation Committee, the provincial members, the Council of Chiefs and the Paramount Chief. This is in preparation and will be circulated and revised to form the East Rennell Resource Management Plan. The local peoples' understanding of environmental matters and desire to generate income through ecotourism are all factors that work together to give protection to the area. The Ministry of Forests, Environment and Conservation of the Solomon Islands will be responsible for reviewing the Resource Management Plan.

Management Constraints

Rennell Island is isolated geographically from Guadalcanal. It is sparsely populated and is characterized by pristine rain forest. Very few areas have been modified by logging and shifting cultivation. With the extension of the road in 1995 from Lavagu to the lake end, timber trees were removed from both sides of the road. Much of this timber has been used for rebuilding houses after cyclone (Tropical weather and hurricanes) Nina.

Following cyclone Nina many mature trees were blown down creating gaps in the forest canopy. This has led to increased growth of the vine Meremia peltata which appears to be degrading the forest.

Terrestrial mammals have been introduced to the island and some have become feral, e.g. pigs and goats. They do not appear to be in large numbers. Some households have cats and education is needed so that they do not become a problem.

Staff

No information.

Budget

No information.

IUCN Management Category

Natural World Heritage Site - Criteria (i), (ii), (iii), (iv)

Further Reading

Some of the principle references listed in Wingham (1997) included as follows:

• Cogger, H., Heatwole, H., Ishikawa, Y., McCoy, M., Tamiya, N. and Teruuchi, T. (1987). The status and natural history of the Rennell Island sea krait, Laticauda crockeri (Serpentes: Laticauda). Journal of Herpetology 21: 255-266.
• Diamond, J.M. (1984). The avifauna of Rennell and Bellona Islands. In Wolff, T. (ed.) The Natural History of Rennel Island, British Solomon Islands. University of Copenhagen, Danish Science Press. Pp. 127-168.
• Flannery, T.F. (1995). Mammals of the south-west Pacific and Moluccan Islands. Imago Productions. Singapore. ISBN: 0801431506.
• Grover, J.C. (1960). The geology of Rennell and Bellona Atolls: the great uplifted atolls on the edge of the Coral Sea. In Wolff, T. (ed.) The Natural History of Rennell Island, British Solomon Islands. University of Copenhagen, Danish Science Press. Pp. 103-119.
• Pegler, J.M. (1996). A bird study at Rennell Island, Solomon Islands. Unpublished.
• Wingham, E.J. (1997). Nomination of East Rennell, Solomon Islands for inclusion in the World Heritage List - Natural sites. New Zealand Official Development Assistance Programme, Ministry of Foreign Affairs and Trade. 47 pp.

Disclaimer: This article is taken wholly from, or contains information that was originally published by, the United Nations Environment Programme-World Conservation Monitoring Centre (UNEP-WCMC). Topic editors and authors for the Encyclopedia of Earth may have edited its content or added new information. The use of information from the United Nations Environment Programme-World Conservation Monitoring Centre (UNEP-WCMC) should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.

Citation

M, U. (2008). East Rennell, Solomon Islands. Retrieved from http://editors.eol.org/eoearth/wiki/East_Rennell,_Solomon_Islands