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Accueil du site → Doctorat → Australie → Pre-settlement paleoecology of Central Otago’s semi-arid lowlands, with emphasis on the pre-settlement role of avian herbivory in South Island dryland ecosystems, New Zealand

University of Otago (2007)

Pre-settlement paleoecology of Central Otago’s semi-arid lowlands, with emphasis on the pre-settlement role of avian herbivory in South Island dryland ecosystems, New Zealand

Wood, Jamie Russell

Titre : Pre-settlement paleoecology of Central Otago’s semi-arid lowlands, with emphasis on the pre-settlement role of avian herbivory in South Island dryland ecosystems, New Zealand

Auteur : Wood, Jamie Russell

Université de soutenance : University of Otago

Grade : Doctor of Philosophy PhD 2008

Résumé
The vegetation communities that existed in the semi-arid intermontane basins and gorges of Central Otago prior to human settlement -750 years B.P. are poorly understood. This is because of a lack of fossil evidence and complex restructuring by anthropogenic factors, especially increased fire frequency, and more recently mammalian grazing. There is also little information regarding the effect of the lost fauna on maintaining and structuring presettlement communities, both in Central Otago and throughout the eastern South Island dryland zone. This study aims to provide a clearer understanding of the functioning of pre-settlement ecosystems in dry land Central Otago, particularly the role of the largest vertebrate herbivores, the moa (Aves : Dinornithiformes), and to explore the implications of the extinct fauna for dryland conservation management across New Zealand. Late Pleistocene and Holocene vegetation communities of the Central Otago lowlands were reconstructed from plant macrofossils, including seeds, leaves, and wood, excavated from rockshelter, cave, and swamp deposits throughout the region. The macrofossils represent three main vegetation types : late Pleistocene to mid (late ?) Holocene basin floor wetland herb associations, Olearia-shrublands surrounding these wetlands, and mid to late Holocene open scrubland and woodland in gorges and on low altitude slopes, dominated by filiramulate Olearia, Coprosma, and Corokia, with abundant lianes (Muehlenbeckia spp. and Rubus spp.) and understorey herbs. Many native tree and shrub species that are presently widespread in the Central Otago lowlands were rare or absent prior to apthropogenic fires (e.g. Discaria toumatou, Kunzea ericoides, Leptospermum scoparium). Other tree and shrub species once present are now extinct in the region (e.g. Coprosma obconica, Plagianthus regius, Pseudopanaxferox). The loss ofthese indigenous woody vegetation communities was a major factor contributing to the extirpation of many small bird species, and undoubtedly also reptile and invertebrate species, from the region. Plant macrofossils from rockshelters included remains of bird nests, identifiable by desiccated feathers and eggshell amongst them. These macrofossils include the first described plant remains from the nests of moa, which were constructed from a shallow bed of twigs of locally available shrubs and lianes. Many of the twigs are 25-30 mm in length and show evidence of having been clipped by moa bills. Abstract 11 Desiccated coprolites, mostly of moa, but also specimens attributed to Finsch’s duck (Chenonetta finschi) and red-crowned parakeet (Cyanoramphus novaezelandiae), were recovered from rockshelter excavations. Moa species associated with a sample of coprolites were identified using ancient DNA analysis, and plant macrofossils from these were examined, together with previously unexamined moa gizzard content samples ·excavated from mires in the eastern South Island dryland zone. The results indicate that, in addition to previously reported browsing, upland moa (Megalapteryx didinus) and heavy-footed moa (Pachyornis elephantopus) also functioned as grazers, and seeds in their coprolites are dominantly of low shrubs and ground-cover herbs. Of particular interest was the higher than expected frequency of seeds from the currently rare and threatened ’spring annual’ herbs ; Ceratocephala pungens and Myosurus minimus subsp. novae-zelandiae (Ranunculaceae), suggesting further research on potential ecological relationships between moa and these plants would be worthwhile. The results of this study have provided a baseline for future conservation and restoration projects in the Central Otago lowlands.

Présentation

Page publiée le 10 octobre 2008, mise à jour le 16 juillet 2017