Forest monitoring in the South Pacific – Blog #4
We are regularly asked – ‘Why are you studying forests on Tetiaroa? It’s just all coconuts trees isn’t it?’, and it’s easy to understand why people are surprised!
Polynesians originally introduced coconut trees to Tetiaroa, possibly at the time of their arrival in what is now French Polynesia, some 1000 years ago. The atoll used to be place of retreat and relaxation for Tahitian royalty and was planted with several introduced food crops for visitors to indulge in.
In the early 1900s a dentist was given the atoll as a gift and planted up seemingly every square inch with Cocos nucifera – not for it’s sweet water or juicy flesh, but for the copra that surrounds the hard coconut shell. Copra harvesting was abandoned in the mid-1900s but coconut trees remain plentiful (the periodic thuds as a coconut falls are a constant reminder!)
Despite the fact there is evidence of coconuts having been planted on all the twelve motu/islets which make up Tetiaroa, there are actually many different native vegetation types growing on the motu. We have selected monitoring sites to provide a picture of this diversity, and I’ll introduce some of them now.
Cabbage tree forests
I introduced the fragile but determined Pisonia grandis tree (cabbage tree or pu’atea) in last week’s blog – home to boobies, terns and frigate birds in the treetops and enormous electric blue coconut crabs (kaveu) between the large, buttress roots. They grow all over Tetiaroa but these guys rule on Reiono, creating an airy forest that is unique amongst the motu. In our ¼ ha monitoring plot they make up 73% of the tree species, with only coconuts, vestiges of an old planted area, making up the remainder.
Fara, the Tahitian name for Pandanus tectorius is also a boy’s name in Tahitian. The wood is extremely hard (I bent over 30 aluminium nails yesterday trying to attach tree tags to grizzled old fara trees!) It is a monocot, like the coconut tree, so it grows mainly from the tips of branches, which are formed at the base of a swirl of leaf bracts. This is how it gets the name ‘screwpine’. Stilt-like aerial roots add to the strange appearance and give it another bizarre name, ‘walking tree’.
Again, fara are often found bordering the shore, but they are also dominant in a few places. Rimatu has a freshwater lake in the interior, and on the north western edge of the motu, it opens up into an arid landscape dotted with clumps of fara trees, scraggly Scaevola taccada (‘apata) bushes and soils covered by a black crust of cyanobacteria. When the sun’s out it is hot and raw – reminding me of the Australian bush.
Calophyllum inophyllum is not just a fun scientific name, it’s also a large tree found along shorelines and occasionally forming dense stands in the interior of the motu. (Island species can’t afford to be too picky about their locations, many species are generalists in one way or another.) Known as tamanu, it is used for its wood, is often planted in gardens, and has medicinal properties. Mosquitos love tamanu forests…
A merger of the French word for large and the Tahitian for Pemphis acidula, grands mikimiki seems an appropriate title for another important habitat for nesting birds. Particularly abundant on the northern edge of Tetiaroa and on tiny motu A’ie, these hardy bushes are home to brown and red footed boobies, frigate birds and terns. A popular spot for Tetiaroa Society guides to take guests on the a bird tour is the ‘hoa’ or shallow channel between motus Tiaraunu and Tauvini, where mikimiki are abundant. It is stunning.
I’ve only just scratched the surface here but even amongst the areas once solely planted with coconut trees, there are many other species coexisting in different combinations and playing important ecological roles. Take our plot on northern Tiaraunu for example, the forest floor is carpeted with beautiful birds nest ferns (Asplenium nidus, or ’o’aha) and cabbage trees, kahaia (Guettarda speciosa, with its fragrant flowers) and noni trees (Morinda citrifolia).
Most of the plant species on Tetiaroa are native or were Polynesian introductions which have become naturalised, forming a strong base for future restoration efforts. To assist these species, and the animals that depend on them, there are plans to remove the coconut trees and to eliminate rats.
These are enormous tasks and no simple solutions exist. Aerial baiting using specially designed pellets is one option for the rats, and on-site mulching of coconut trunks, or dumping out at sea may also be feasible at this scale.
Our long-term monitoring plots and Xenia Jost’s vegetation transects on Onetahi and Tiaraunu will provide baselines for comparing future vegetation changes on Tetiaroa, in areas where coconuts and rats are removed.
It’s definitely not just all coconuts here!
Merci Heipoe pour tes modifications!