Last week I visited the Pacific island of Moorea, which sits just next to Tahiti in the Society Islands, in French Polynesia, an array of islands widely scattered across the Central Pacific. The islands form a progression of volcanic seamounts, with youngest in the south-east peaking in the 2100 m peaks of Tahiti, and the oldest in the north-west subsiding into perfect coral atolls. My host was Neil Davies, Director of the Gump Research Station in Moorea, and I am here to discover a little more about the forests of Polynesia, to find ways of supporting and devleoping some of the forest research here, and to bring in some of the ecosystem process studies that we do elsewhere across the tropics, with the potential of bring some of these forests into our Global Ecosystems Monitoring Network. Moorea is the focus of the IDEA Digital Avatar project, and effort to digitise an entire island ecosystem from 'genes to satellites'. There is an article about this project in Nature. As a result the biodiversity of the land and marine ecosystems in Moorea is particularly well catalogued.
The landscapes of Tahiti and Moorea (and many other Pacific volcano islands) are truly breath-taking, with the basalt volcanoes eroding way into almost vertical-sided mountains and towers, some of the most astounding topography I have seen anywhere. As Darwin noted when stopping at Tahiti after his explorations of South America: “in the Cordillera, I have seen mountains on a far grander scale, but for abruptness, nothing at all comparable with this". The high mountains hold on to native cloud forest and rocky scrub, but the lower levels are a lush green mosaic of invasive species, farms and light green fernlands. The islands are surrounded by a skirt of coral reef holding in a lagoon of perfect turquoise waters.
In between meetings and visiting the forest and lagoon, I tried and absorb all I could about this mesmerising land I found myself in and knew so little about. My sources on the geology and vegetation history were “Vegetation of the Tropical Pacific Islands” by Dieter Mueller-Dombois and Raymond Fosberg. I also borrowed off Neil an excellent biography of James Cook by Frank McLynn, and read particularly closely the descriptions of Cook’s several contacts with Tahiti and the societies he found there, and how both reacted to the “other” in this collision of worlds. A highly recommended book that highlights how astonishing both Cook and the Polynesian societies were, and captures the astonishing nature of the first contacts.
We visit the Opunohu valley, a lush mosaics of forests, farmlands, archaeological remains. This area was densely populated and farmed at the time of European contact, and suffered a population crash and almost complete depopulation over the 18th and 19th centuries. Feral chickens, first brought over by the Polynesians, run wild over the landscape, itself almost entirely free of predators. The mapae are rectangular stone enclosures that were used for religious ceremonies, and are now groves of Tahitian chestnut trees (Inocarpus fagifer) with wonderful fluted buttress roots.
Some of the key trees that may have been brought by the Polynesians or that may be native include Hibiscus tiliaceus, Pandanus tectonis, Casuarina equisetifolia. As in many islands, the main environmental story is one of biological invasion, Big invasive species here include Tecoma stands, Psidium cattleianum (strawberry guava) and most recently, the all-smothering Miconia calvescens.
The view from Moorea is of an ocean planet. Polynesia sits in the middle of a hemisphere that is probably over 95% ocean, with what continental area there is is ringing its fringes, and scattered throughout this planet-sized ocean are small islands that are legacies of volcanic hotspots. Every wave of “discovery” of these is an astounding tale. First the various species of plant, bird and insect that manage to make it across thousands of miles, often by accident, to stumble on an island refuge. There they slowly specialise and diverge and take advantage of this new ecosystem that they build. Then the human discovery, an amazing tale of Polynesian adventures reading the stars, winds and swells to cross vast distances and create unique cultures. Then the Europeans, with adventurers such as Cook and his sailors expanding the known world with their exploration of a new ocean world and civilization. Each "discovery" has been accompanied by ecosystem disruption and loss, as well as the creation of something new.
Yadvinder Malhi is an ecosytem ecologist and Professor of Ecosystem Science at Oxford University