Tahiti:  The Physical Environment

The lush, green volcanic island of Tahiti rises from the South Pacific and is the biggest island with the tallest mountain—the more than two-kilometer high Mount Orohena—in French Polynesia. The landmass of Tahiti is mountainous with ridges that rise steeply around calm inlets in the flat coastal plain, where much of the development is located. The physical structure of Tahiti plays a major role in the unique environments and abundant endemism, features that do not exist to the same extent anywhere else in French Polynesia.

The geomorphology of Tahiti is an important aspect of the island's physical environment because it provides the substrate which climate then shapes. The large size of the island primarily has to do with its age. Tahiti is a volcanic island that emerged approximately 1.4 million years ago, slowly rising over hundreds of thousands of years from the sea floor some 4000 meters deep.[1]  Initially emerging as two islands, Tahiti Iti and Tahiti Nui, these two constituent parts were later connected by the isthmus  of Taravao. Given its volcanic origins, the rocks in Tahiti are basalts, alkali basalts, transition atlotholeiites, basanites, picrites, and evolved lavas.[2]

Hot spot volcanoes, the kind responsible for forming most of the Polynesian Archipelago, are the result of consistent convection plumes of molten mantle material that eventually rise to the surface.[4] In comparison to the tectonic plate above, a hot spot is a stationary feature of the mantle below and will generate volcanic islands in a chain above its plume of heated lava as it penetrates the oceanic plate when it moves across the hot spot. It is this geologic process that formed Tahiti and the other islands in the Society Archipelago, with Tahiti being the youngest of the chain. Volcanic activity ended 380,000 years ago on Tahiti Iti and 200,000 years ago on Tahiti Nui,[5] and a new island called Mehetia is currently forming above the hot spot some 125 km from Tahiti Nui.[6]

Tahiti is classified as a basaltic shield volcano, and as such formed from the accumulation of large amounts of entirely fluid lava flows [7] [8].  They are also much larger compared to other volcanoes because of the enormous and relatively constant release of fluid lava. While today Tahiti is the tallest of French Polynesia’s islands, the persistent processes of cooling, isostatic sinking and erosion will, over a span of millions of years, reduce Tahiti to an atoll as coral reef growth gradually overtakes the continually eroding landmass.[9]

As already mentioned, Tahiti is the largest of the islands of French Polynesia measuring 1,042 square kilometers in area.[10]  Tahiti is home to ten mountain summits that are over 1,500 meters high, and three that are over 2,000 meters high.[11] It is host to French Polynesia’s highest peak, Mont Orohena, which reaches 2,241 meters above sea level.[12] From these summits descend thousands of intricate indentations caused by erosion.

The climate of Tahiti is a result of both the island’s physical features and its physical location, 17 degrees south of the equator. Because of the relatively constant temperatures associated with the tropics, seasons are differentiated as being wet or dry rather than hot or cold. The dry period extends from May to October with an average temperature of 25-26 degrees Celsius. The wet season is from November to April and is accompanied by a rise in humidity, more cloud cover and an increase in rainfall. The average temperature during the wet period is 26 to 27 degrees Celsius.[13] While the average annual temperature is 26 degrees Celsius, it decreases 0.6 degrees for every 100m of altitude.[14]

Importantly, there are climatic variations between the leeward and windward sides of Tahiti due to such factors as differing sunlight exposures, trade winds, humidity and altitude all creating unique ecosystem niches on the island. The wet, southeast trade winds that occur from November to March create a distinctively different climate and growing environment on the windward sides of the island. In contrast, the leeward coast is drier, receiving 2 meters rainfall per year compared with an average rainfall of 3-4 meters per year on the windward coast.[15] Mount Orohena is nearly always enveloped in heavy cloud cover and rainfall increases rapidly with elevation, reaching up to 10m per year in the center of the island.[16] Brief and turbulent storms frequently occur during the wet season, and cyclones, which are less common in French Polynesia, can sometimes occur.[17] Traditionally cyclones are rare, yet in 2010 Cyclone Olly caused significant damage in Tahiti.[18] Prior to this example of extreme weather, it had been 28 years since the last substantial cyclone.[19]

The components of Tahiti’s tropical climate and volcanic soils provide ideal growing conditions. Volcanic soil is very fertile and the amount of sunlight available to plants is considerable because of the island’s location in relation to the equator. The above-mentioned processes that keep temperature moderate and the rainfall  ample are excellent for a large number of plants, but one drawback to this growing environment is that it is as good for many introduced species as it is for endemic ones.

The biodiversity of Tahiti is a direct effect of the physical nature of the island. Looking at French Polynesia as a whole, though there are relatively low total numbers of species, there are high amounts of endemism on the islands.[20] French Polynesia has nearly 900 indigenous plant species and 31 different species of terrestrial birds.[21] While these numbers are comparatively low to other areas of the world, 58% of the plant species and 22 of the bird species are endemic to the French Polynesia. Tahiti itself boasts 467 different species of plants, with 212 being endemic, which gives the island a very high rate of 45% endemism for plants.[22] The principal reason for this high rate of endemism on these islands is their pronounced isolation.  Also contributing  is the variance of habitats that high islands like Tahiti present along their altitudinal gradient.[23] Because Tahiti rises from sea level to the 2241-meter summit of Mount Orohena, many different habitats exist in accordance with the change of temperature and rainfall. As temperature in Tahiti drops 0.6ºC for every 100m of altitude, the habitats at the top of the mountains could be anywhere from 15-20ºC cooler than the 26ºC that is common at sea level.[24]

Related to the altitude gradient, Tahiti has several different types of plant communities. These include the coastal and low-to-mid altitude regions where agriculture is centered, higher and wetter zones that include rain and cloud forests, and even a sub-alpine area and plant community at the highest elevations.[25] The most important of these habitats to biodiversity and endemism are the montane cloud forests and the sup-alpine zones because these two areas are where a majority of the endemic plants on the island are found.[26] The cloud forest in Tahiti contains a wide array of trees, shrubs, orchids, ferns, and mosses and is the largest, undisturbed montane rainforest of any Pacific island.[27] The sub-alpine zone is perhaps the most remarkable habitat on the island as it is the only example of such an environment existing in the South Pacific.[28]Accordingly, these high regions are characterized by small, scrubby, plant species that tolerate limited rainfall and cooler temperatures. The sub-alpine zones are found on three of Tahiti’s mountains that reach over 2,000 meters, and occupy no more than 1.25 square kilometers of space.[29] While these high altitude habitats are only small portion of Tahiti, they are a distinguishing feature that separates the island from other islands in the South Pacific.

Another explanation of the situation of low overall diversity yet high endemism is the relative geographic isolation of the Pacific islands, with Tahiti being some 6000km away from the nearest continent (Australia), and the resulting processes of colonization and adaptive radiation. Adaptive radiation, as it occurred in French Polynesia, is the progression of certain families of species colonizing an isolated area and then, over the course of millions of years, species evolving from that initial gene pool to fill out the unoccupied ecological niches.[30] As this occurs in relative seclusion, any species that is an offshoot of the initial colonizer is unique, or endemic, to that area and consequently not found anywhere else in the world.

The flora and fauna colonization of the Polynesian islands before human arrival came from the all directions around the Pacific, with the biota coming from Malaysia, Southeast Asia, Australia, New Caledonia, New Zealand, and even to some extent the Americas via long distance dispersion.[31] [32]  While the physical environment and location of Tahiti dictate the level of diversity, humans also play a major role in contributing to the makeup of that diversity. When the Polynesian people arrived in Tahiti they brought some thirty different domestic species of plants including taro, breadfruit, coconuts, and bamboo, which in large part replaced much of the native vegetation of the coastal and low valley zones.[33]

Although Polynesians undoubtedly altered Tahiti’s natural environment, Europeans are responsible for a much greater degree of destruction and modifications, being accountable for some 1500 introduced plant species.[34] However, as dramatically altered as the coastal areas of Tahiti have been by the presence of humans, the upper reaches of Tahiti were mostly spared.[35]What kept the montane cloud forest and sub-alpine forest of Tahiti relatively safe from the introduced species was the temperature variation associated with altitude. Unfortunately, since its 1937 introduction, the vascular plant Miconia calvescens  has been the exception to this rule and now covers nearly two-thirds of Tahiti.[36] Miconia is a threat to almost 100 native plant species, including roughly 45 of the endemics, and it is also a danger to endemic birds by reducing areas for brooding and eliminating natural food sources.[37] Moreover, miconia has a shallow root system, which offers a poor replacement to native plants in regards to soil integrity.[38] Given the steepness of much of the island, landslides are a dangerous and destructive consequence of the plant’s domination. [39] Luckily, the sub-alpine habitat has so far been secure due to its relative harshness and general inaccessibility.[40]

The Factors that have largely dictated the amount of biodiversity and endemism on Tahiti are climate, geological processes, and the physical geography of the island. These aspects have influenced which species can exist and has dictated the number of habitats present. However, this is only the first layer of biodiversity. Human impacts of both the Polynesians and Europeans have greatly affected the physical layout and species diversity of the island. Humans are responsible for many introduced species, some such as coconut palm and taro have been relatively benign and others like miconia have been very destructive. In the future human impacts, in the forms of urbanization and climate change, will continue to compromise Tahiti’s physical and natural environment potentially destroying the features that make Tahiti unique in both a global and regional context.

Nicholas Costantino, Hamilton College
Emily Leshner, Wheaton College



[1]  K. Ye, et al., "Modeling the erosion of tropical volcanic ocean islands: The Tahiti island case (French Polynesia)," Fall Meeting 2009, American Geophysical Union, 9 Dec, 2009.

[2]  Ye, et al.

[3]  G. Schubert, M. McNutt, and D.W. Caress, "Seismology and the Structure of the Earth," Treatise on geophysics. Amsterdam: Elsevier B.V., 2007, 445-478.

[4]  Douglas A. Segar and Elaine Stamman Segar, Introduction to ocean sciences, 2nd ed., New York: W.W. Norton & Co., 2007.

[5]  Ye, et al.

[6]  Douglas A. Craig, "Geomorphology, Development of Running Water Habitats, and Evolution of Black Flies on Polynesian Islands," BioScience 53.11 (2003): 1079-093, BioOne, Web, <www.bioone.org>.

[7]  Robert A. Duncan, et al., "Tahiti: Geochemical Evolution of a French Polynesian Volcano," Journal of Geophysical Research 99.B12 (1994): 24341-4357.

[8]  "CVO Website - Shield Volcanoes," USGS Cascades Volcano Observatory (CVO), Web, 30 Jan, 2011, <http://vulcan.wr.usgs.gov/Glossary/ShieldVolcano/description_shield_volcano.htm>.

[9]  Craig, “Geomorphology.”

[10]  Brij V. Lal and Kate Fortune, The Pacific islands: an encyclopedia / Honolulu: University of Hawai'i Press, 2000.

[11]  SPREP, “French Polynesia,” Secretariat of the Pacific Regional Environment Programme, SPREP.org.

[12]  SPREP, “French Polynesia.”

[13]  Weather Base, “Papeete, French Polynesia,” 2011, <http://www.weatherbase.com/weather/weather.php3?s=173919&refer=>.

[14]  J. Pasturel, "La climatologie des iles,” Atlas de la Polynesie francaise, 42-43. l'ORSTOM, Paris, 1993.

[15]  SPREP, “French Polynesia.”

[16]  SPREP, “French Polynesia.”

[17]  Encyclopædia Britannica, “Tropical Cyclone,”Encyclopædia Britannica Online <http://www.britannica.com/EBchecked/topic/606551/tropical-cyclone>.

[18]  Tahiti Sun Travel, "About Tahiti and Her Capital City Papeete: Tahiti Sun Travel,"Complete Guide to Tahiti and Her Capital City, Papeete - Tahiti Sun Travel Network & Dream-Islands.com, Web, <http://www.papeete.com/about.html>.

[19]  Tahiti Sun Travel.

[20]  SPREP, “French Polynesia.”

[21]  SPREP, “French Polynesia.”

[22]  Jean-Yves Meyer and Jacques Florence, “Tahiti’s native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae),” Journal of Biogeography 23.6 (Nov., 1996): 775-781, JSTOR, Web, p.775.

[23]  Meyer and Florence, 775.

[24]  Meyer and Florence, 775.

[25]  Meyer and Florence, 776.

[26]  Meyer and Florence, 776.

[27]  Meyer and Florence, 776.

[29]  SPREP, “French Polynesia.”

[30]  Jérôme Petit and Guillaume Prudent, "Climate Change and Biodiversity in the European Union Overseas Entities,"SPREP, IUCN, 11 July 2008, Web, <http://www.sprep.org/att/IRC/eCOPIES/Global/525.pdf>.

[31]  Gunnar Keppel, Andrew J. Lowe, and Huge P. Possingham, “Changing perspectives on the biogeography of the tropical Southern Pacific: influences of dispersal, vicariance and extinction,” Journal of Biogeography 36 (2009): 1035-1054, JSTOR, Web.

[32]  Keppel et al., 1045.

[33]  Meyer and Florence, 777.

[34]  Meyer and Florence, 777.

[35]  Meyer and Florence, 777.

[36]  Meyer and Florence, 777.

[37]  Meyer and Florence, 778.

[38]  Susan McGarth, “Attack of the Alien Invaders,” National Geographic, Article republished online from National Geographic magazine, Web, <http://environment.nationalgeographic.com/environment/habitats/attack-alien-invaders.html#page=1>.

[39]  McGarth

[40]  SPREP, “French Polynesia.”



“Adaptive Radiation." Biology Online. Web. 30 Jan. 2011. <http://www.biology-online.org/2/15_adaptive_radiation.htm>.

Craig, Douglas A. "Geomorphology, Development of Running Water Habitats, and Evolution of Black Flies on Polynesian Islands." BioScience 53.11 (2003): 1079-093. BioOne. Web. <www.bioone.org>.

“Climate Change." Encyclopædia Britannica Online. 2011. Web. 30 Jan. 2011 <http://www.britannica.com/EBchecked/topic/121632/climate-change>.

"CVO Website - Shield Volcanoes." USGS Cascades Volcano Observatory (CVO). Web. 30 Jan. 2011 <http://vulcan.wr.usgs.gov/Glossary/ShieldVolcano/description_shield_volcano.htm>.

Duncan, Robert A., Martin R. Fisk, William M. White, and Roger L. Nielsen. "Tahiti: Geochemical Evolution of a French Polynesian Volcano." Journal of Geophysical Research 99.B12 (1994): 24341-4357.

Fontaine, Yolande. "French Polynesia." A Directory of Wetlands in Oceania. Ed. Derek A. Scott. Slimbridge, U.K: Wetlands International, 1993. 

Keppel, Gunnar, Andrew J. Lowe, and Huge P. Possingham. “Changing perspectives on the biogeography of the tropical Southern Pacific: influences of dispersal, vicariance and extinction.” Journal of Biogeography 36 (2009): 1035-1054. 

Lal, Brij Vilash, and Kate Fortune. The Pacific islands: An Encyclopedia, Honolulu: University of Hawai'i Press, 2000.

Meyer, Jean-Yves and Jacques Florence. “Tahiti’s native flora endangered by the invasion of Miconia calvescens DC. (Melastomataceae).” Journal of Biogeography 23.6 (Nov., 1996): 775-781. 

McGarth, Susan. “Attack of the Alien Invaders,” National Geographic, Article republished online from National Geographic Magazine, Web, 26 Jan. 2011 <http://environment.nationalgeographic.com/environment/habitats/attack-alien-invaders.html#page=1>.

Mueller-Dombois, Dieter. "Forest Vegetation across the Tropical Pacific: A Biogeographically Complex Region with Many Analogous Environments." Plant Ecology 163 (2002): 155-76. Springer. Web. 29 Jan. 2011. <http://www.jstor.org/stable/20051320>.

National Weather Service “Tropical Weather,” USA.gov, Jan 5, 2010 <http://www.srh.noaa.gov/jetstream/tropics/tropics_intro.htm>.

Oliver, Douglas Polynesia In Early Historic Times. Honolulu: The Bess Press, 2002.

Parkes, Annette, James T. Teller, and John R. Flenley. “Environmental history of the Lake Vaihiria drainage basin, Tahiti, French Polynesia.” Journal of Biogeography 19.4 (Jul., 1992): 431-447. 

Pasturel, J. "La climatologie des iles.” Atlas de la Polynesie francaise, 42-43.  l'ORSTOM, Paris, 1993.

Petit, Jérôme and Guillaume Prudent. "Climate Change and Biodiversity in the European Union Overseas Entities."SPREP. IUCN, 11 July 2008. Web. 29 Jan. 2011. <http://www.sprep.org/att/IRC/eCOPIES/Global/525.pdf>.

Segar, Douglas A., and Elaine Stamman Segar. Introduction to ocean sciences. 2nd ed. New York: W.W. Norton & Co., 2007. 

Schubert, G., M. McNutt, and D.W. Caress. "Seismology and the Structure of the Earth." Treatise on geophysics. Amsterdam: Elsevier B.V., 2007. 445-478.

SPREP. “French Polynesia,” Secretariat of the Pacific Regional Environment Programme, SPREP.org, Web, Online PDF p.105, 26 Jan., 2011.

"Tahiti." Encyclopædia Britannica Online. Web. 10 Jan. 2011 <http://www.britannica.com/EBchecked/topic/580410/Tahiti>.

Tahiti Sun Travel. "About Tahiti and Her Capital City Papeete : Tahiti Sun Travel." Complete Guide to Tahiti and Her Capital City, Papeete. Web. 30 Jan. 2011 <http://www.papeete.com/about.html>.

“Tropical Cyclone." Encyclopædia Britannica Online. Web. 30 Jan. 2011 <http://www.britannica.com/EBchecked/topic/606551/tropical-cyclone>.

Weather Base. “Papeete, French Polynesia.” 2011 <http://www.weatherbase.com/weather/weather.php3?s=173919&refer=>.

Ye, K., F. Sichoix, L. Barriot, and J. Dampas. "Modeling the erosion of tropical volcanic ocean islands: The Tahiti island case (French Polynesia)." Fall Meeting 2009. American Geophysical Union. 9 Dec. 2009.