Rapa Nui and Sala Y Gómez Subtropical Broadleaf Forests

Rapa Nui, also known as the Easter Island, was once covered in tall Jubaea palm, Triumfetta sp., and Sophoro toromiro tree forests. This extremely isolated volcanic island in the eastern Pacific supported a simple, but unique, ecosystem until Polynesians arrived thousands of years ago and transformed it over time to grass savannas. Sala-y-Gomez is a small reef 415 km to the northeast of Rapa Nui. It is only 300 m long at low tide, and shrinks to a mere 70 m at high tide. Four species of terrestrial plants occur.

The island experiences a tropical rainforest, humid subtropical climate, with minimum and maximum temperature ranging from 15ºC in July to 28ºC in February. The annual average precipitation is 1,118 mm, with the heaviest rainfall occurring usually in May. The current number of native plant species is around 46 with nine endemic species. Many species are thought to have been lost with the destruction of the forest. Four of 15 known ferns are endemic. Triumfetta semitriloba, a woody shrub, persists, but only four individuals were found in 1988. 

The steep inner slopes of the Rano Rakau crater offer some of the last refuge from fire and grazing to remnant native plant populations. Original forests were made up of the now-extinct palm, related to the Chilean palm, Jubaea chilensis, toromiro (Sophora toromiro), hau hau (Triumfetta semitriloba), still extant, and Coprosoma spp., now gone. The bottom of Rano Rakau crater is covered with thick stands of tall bulrushes, Scirpus tautara, though it may have been introduced by visiting canoes from South America long ago. The extinct fauna of Rapa Nui included two parrots, a rail, a crake, and a heron. Before people arrived, millions of seabirds likely nested in the original forests as there were no predators. 

There are two lizards, the gecko Lepidodactylus lugubris and the skink Ablepharus boutoui poecilopleurus, though both could have arrived with people. Although most of the native biota has been decimated since human settlement, several endemic micro-moths, pillbugs, and springtail invertebrates are still extant on the islands; it is likely that other unique invertebrates disappeared with the forests.

Heavy grazing, invasive plants and animals, and frequent fires continue to diminish populations of the last remaining species. Any restoration efforts will have to deal with all three of these threats. Rapa Nui National Park (68 km²) has inadequate management and support. 

The priority conservation actions for the next decade are to: 1) support further efforts to grow and restore toromiro trees to steep slopes inaccessible to grazers and fires; 2) protect several caves from that still retain populations of native invertebrates (tourists trample the fragile fern beds); and 3) eradicate rats and goats from offshore islets to conserve native invertebrates and seabirds.

Citations

1. Aldén B. 1990. Wild and introduced plants on Easter Island: A report on some species noted in February 1998. Pages 209-216 in HM Esen-Baur, editor. State and Perspectives of Scientific Research in Easter Island Culture. Courier Forschungsinstitut Senckenberg, Frankfurt, Germany.
2. Arnold M, M Orliac, H Valladas. 1990. Données nouvelles sur la disparition du palmier (cf. Jubaea) de l’Ile de Pâques. Pages 217-219 in HM Esen-Baur, editor. State and Perspectives of Scientific Research in Easter Island Culture. Courier Forschungsinstitut Senckenberg, Frankfurt am Main, Germany.
3. CEPF. 2007. Ecosystem Profile: Polynesia/Micronesia Biodiversity Hotspot. Critical Ecosystem Partnership Fund, Washington, DC.