Donna D'Costa

Plant remains in coprolites: diet of a subalpine moa (Dinornithiformes) from southern New Zealand

Abstract Analysis of plant macrofossils and pollen in putative coprolites (2538 ± 95 14C years ago) of Megalapteryx didinus, a southern subalpine species of the extinct moa, indicates that this bird browsed branchlets of forest trees (mainly Nothofagus), and grazed on tussockland and lake edge herbs (Poaceae, Cyperaceae, Isoetes). The data provide the first direct evidence of diet of an upland moa.

Holocene vegetation and environmental reconstructions from swamp deposits in the Dargaville region of the North Island, New Zealand: implications for the history of kauri (Agathis australis).

Multiproxy analysis of two swamps, representative of numerous sites in the Dargaville area, provide a Holocene record of a transition from flooded marine valleys to freshwater swamp-forests. Dendrochronology of subfossil wood from these and other associated sites provide a record of kauri ( Agathis) growth and demise over 3600 calendar years. A discrepancy between the abundance of kauri pollen and the timing of maximum kauri forest development, as revealed by dendrochronology, suggests that kauri pollen abundance at our sites is determined by the wetness of the substrate rather than by proximity of source trees. This finding has implications for the palaeoclimatic interpretation of late Quaternary Agathis pollen curves. Kauri has been present in the Dargaville area for more than 7000 14C yr BP with suitable conditions for the preservation of wood leading to an apparent expansion in Agathis population after ~3600 cal. yr BP rather than representing a southerly migration of this species.

A Late Quaternary Record of Natural Change and Human Impact from Rangihoua Bay, Bay of Islands, Northern New Zealand

Abstract A multiproxy analysis of back-dune sediment cores from Rangihoua Bay, northern New Zealand, provides an environmental history of the Late Quaternary, placing human impacts on the site into a geomorphological and ecological context. The inferred paleoecological significance of the trends is generally coeval between proxies. The history commences with a Late Pleistocene deposit that formed part of a river terrace during lower sea level. The dryland vegetation at that time was dominated by Fuscospora forest. The record recommences at ca. 7400 YBP, by which time Fuscospora had been replaced by podocarp-hardwood forest, comprising mainly Dacrydium and Prumnopitys taxifolia emerging through a Metrosideros canopy. One of the core sites was a lagoon fringed with mainly Cyperaceae, Leptospermum, and Dodonaea. Redox-sensitive elements reflect phases of anoxia related to variation in lagoon depth. Transition from lagoon to peat swamp, due to natural infilling and/or climate change, occurred after ca. 5500 YBP. Human impacts were of high magnitude and include deforestation of the catchment and drainage of the wetland by early Polynesians. Errors in the radiocarbon and tephra chronologies preclude an accurate date for this. Microfossils of introduced Polynesian plants and a thick gravel bed in one of the cores suggest that parts of the wetland were used for prehistoric horticulture.

Palaeoenvironment and human impact in modifying vegetation at Mt St John, Auckland Isthmus, New Zealand

Abstract A 2.34 m sediment profile from the base of the crater of Mt St John volcano (a small basaltic cone on Auckland Isthmus) provides a partial environmental record of the Late Quaternary. The record highlights potential age control problems with sediment cores taken directly from archaeological sites. Two distal tephras were recorded: 9.5 ka Rotoma and 7 ka Tuhua. A date of 16 309 ± 90 14C yr BP from the basal scoria of the profile provides a minimum date for the eruption of Mt St John. Pollen was present only in the upper 0.33 m of the profile, in a layer of peat and soil which caps highly weathered silts and clays eroded from the crater walls. In early Polynesian times (most likely after c. 800 14C yr BP), vegetation of the crater swamp was dominated by Cyperaceae sedges and Paesia ground fern. Dacrycarpus trees were also present. Podocarp‐hardwood forest, dominated by Metrosideros, grew on the rim and inner slopes of the crater. Elaeocarpus, Griselinia, and Cyathea were also present. A decline in Dacrycarpus pollen and an accelerated erosion rate mark Polynesian forest clearance within the crater. Typha became a major component of the swamp vegetation during the Late Polynesian‐European era.

An MIS 5a/b to MIS 3 bog sequence from Henderson Bay, northern New Zealand

Abstract A discontinuous Late Pleistocene pollen record from an eroding coastal cliff section at Henderson Bay on the east coast of Northland, New Zealand, reveals changes in vegetation composition and associated palaeosol development under both stadial and interstadial climatic conditions ascribed to the last interglacial–glacial cycle, probably MIS (Marine Isotope Stage) 5a/b to early MIS 3. An increase in charcoal towards the top of the sequence is believed to be due to natural rather than anthropogenic ignition sources which resulted in the development of scrub rather than forest vegetation. The sequence is capped by gravel previously inferred to have been emplaced by tsunami event(s) some time after early MIS 3. A lack of Agathis pollen in our sequence despite unequivocal evidence for the parent trees (gum) strengthens a call for caution when inferring climatic conditions from the abundance of Agathis pollen in New Zealand pollen records.