Moa in Central Otago?

Jenny Nicholls Waiheke-based writer specialising in science commentary



Stuff NZ Newspapers

Opinion | Mainlander

It is spring in Central Otago, and vast groves of ko¯ whai trees are lit by the soft glow of a sinking sun. Moa, adorned with fallen seed pods and yellow blossoms, plough through a deep litter on the ko¯ whai forest floor, disturbing insects, and birds as they browse. Forests of ko¯ whai in Central Otago? This sci-fi vision comes to us courtesy of a remarkable new peerreviewed study in the January issue of the science journal Palaeontologia Electronica .It argues that large stands of ko¯ whai cloaked the lower slopes and gorges of Central Otago, in a type of forest now unknown in New Zealand. This ‘‘vanished ecosystem’’ was revealed after decades of arduous, self-funded work by the Dunedinborn palaeobotanist Mike Pole. ‘‘Central Otago may be unique as having been the last relatively dry place on Earth to remain human-free. ‘‘It has much to teach us about what kind of vegetation can exist in such environments,’’ the study concludes. ‘‘This is fascinating,’’ tweeted zoologist and Wikipedia editor Mike Dickison, in response to the paper’s publication. ‘‘It suggests that the Central Otago landscapes, romanticised for their tussock-covered hills and threatened by wilding pines, should actually be being restored as ko¯ whai/lancewood forest.’’ Rolling Central Otago hills and gorges filled with golden trees and sculptural lancewoods – I cannot remember when a science paper has been quite so surprising or evocative. The lovely but, let’s be honest, arid hills of modern Central result from fire, says Pole, and introduced animals such as sheep and rabbits. New plants have also wreaked havoc. Ma¯ ori introduced around a dozen plants to Aotearoa, a number swamped by the tidal wave that arrived thanks to European colonisation – some 25,000 new species. Today’s landscape is so different that ‘‘it is difficult to understand what the ‘original’ vegetation was’’, Pole says. Difficult, but not impossible – he began searching for the answer more than 40 years ago. ‘‘I first collected moa remains from the Cromwell Gorge in the late 1970s, as work for the Clyde Dam began. Then, at Otago University in 1982, I started on a broader project of trying to document some of the sediment layers in the gorge, before it flooded. ‘‘That was put on hold when I focused on the much older plant fossils at Bannockburn and Cromwell. I picked up the gorge work again in about 1999 …’’ Pole visited rock overhangs and small caves – shelters – throughout Otago before selecting 115 suitable candidates in the Kawarau, Cromwell, and upper Roxburgh gorges. He was looking for undisturbed accumulations of ancient, dried vegetation. Some of it, he says, seemed to be moa roosting material, the moa poo still scattered through it. The vegetation he used in his study dated to between 4000 and 1000 years old. ‘‘It required an awful lot of hard walking, even chartering a jet boat to get me down the Roxburgh Gorge, around 2001. I took to cycling into the Cromwell Gorge with a blow-up dinghy, and rowing across.’’ Based on the ‘‘nearly ubiquitous’’ presence of their leaves in the shelters, Pole concluded that the most important plant in the area during this era was Sophora microphylla [a species of ko¯ whai]. ‘‘It likely formed a forest with a continuous but low – perhaps 14m – open canopy over the study area.’’ Other trees common then, but entirely missing from the area now, include Pittosporum tenuifolium (ko¯ hu¯ hu¯ or black matipo) and Pseudopanax ferox (toothed lancewood or horoeka), although these were subordinate to the ko¯ whai, he says. The existence of ko¯ whai, horoeka and black matipo was also documented here in a pioneering study by University of Otago researcher Jamie Wood and Susan Walker from Landcare Research. Pole also found signs of Carmichaelia (native broom), Rubus and Hebe, shrubs suggestive of open vegetation among the forests of ko¯ whai. Some species of moa, he explains, were forest or forestmargin dwellers, and ‘‘treebrowse’’ was a big part of their diet. Scientists know this by analysing their poo. ‘‘There is no sign of a conifer component or of ‘wetter’ forest trees like beech or kapuka’’ in the shelters, he says. Another clue, says Pole, comes from a comprehensive study led by Trevor Worthy, a palaeozoologist from New Zealand now based in Australia. This showed that some of the birds who lived here thousands of years ago typically lived in forest or dense shrubland. If the best science is one which asks the right questions, Pole has a few for researchers following in his footsteps, cycle trail and inflatable dinghy route. ‘‘There is plenty of scope for researchers to work on what existed in Central Otago before humans arrived,’’ he says. ‘‘What were the reptiles? The insects? How did the whole system work? We are so used to seeing this bleak landscape – and I grew up in it, so I understand its charm. ‘‘But it’s time we also understood that it’s one more example of a human-trashed habitat.’’ Near the end of my own street at the other end of the country, on Waiheke Island, is a tall and peculiar-looking tree, as fulsome and blowsy as an emerald green crinoline: underneath the foliage a second underskirt peeks out, with different leaves of a lighter green. It took me until yesterday to understand that the tree is actually a ko¯ whai, struggling under a massive wisteria overcoat. Wisteria is an introduced cottage garden creeper, with pretty, pendulous flowers as long as a ruler, of purple, violet, pink or white. Here it is, I thought. The perfect symbol of what we’ve lost.