A Holocene pollen and sediment record of Whangape Harbour, far northern New Zealand

Aims To quantify pollen-vegetation relationships from saline to freshwater in an estuarine gradient from surface samples of the modern pollen rain, to allow more accurate interpretations of the stratigraphic palynological record.Location Whangapoua Estuary, Great Barrier Island, northern New Zealand.Methods Six transects were laid out along a vegetation sequence running from estuarine mud to freshwater swamp. Along these transect lines, 108 plots were sampled for vegetation and surface sediments from wet sand, mud, plant litter or moss (sand and mud sites are inundated by most tides, other sites less frequently). All sediment samples were analysed for pollen. The relationships between plant species frequency and pollen representation were examined at a community scale using twinspan and ordination analyses, and for individual species using fidelity and dispersibility indices, regression and box-plot analyses. ResultsThe quantitative relationships between source taxon vegetation frequency and its pollen representation varied between species due to differential pollen production and dispersal. twinspan of the surface pollen samples suggests five vegetation types: (A) mangrove (Avicennia marina); (C) Leptocarpus similis salt meadow; (D) Baumea sedges; (E) Leptospermum shrubland; and (F) Typha/Cordyline swamp forest. The (B) Juncus kraussii community is not represented palynologically owing to the destruction of its delicate pollen grains during acetolysis of samples. Detrended correspondence analysis places these communities on an estuarine-to-freshwater gradient. However, pollen assemblages at the seaward end of the salinity gradient are less clearly representative of the associated vegetation than those at the landward end, probably because the open vegetation at the former allows the influx of wind-and water-dispersed pollen from surrounding vegetation. Main conclusionsThe vegetation pattern (zonation) at Whangapoua is reflected in the pollen rain. When the long-distance and over-represented pollen types are excluded, five out of six of the broad vegetation communities can be identified by their pollen spectra. Species with high fidelity and lowto-moderate dispersibility indices can be used to identify the vegetation types in the sedimentary sequences. The more open vegetation types at the 'marine end' of the sequence tend to be 'overwhelmed' by regional pollen, but the nature of the sediments and the presence of discriminatory species (e.g. A. marina, Plagianthus divaricatus, Cordyline australis), even in small amounts, will allow correct identification of the local vegetation represented in sedimentary palynological sequences. A box-plot analysis indicates that the pollen and spore types A. marina (mangroves), Sarcocornia quinqueflora (salt meadow), P. divaricatus (sedges), Gleichenia (shrubland) and C. australis (swamp forest) are highly discriminatory in relation to vegetation type. These discriminatory palynomorphs help with the

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“…, 1999, 2000a,b; Ogden et al. , 2006) and Whangape Harbour in northern New Zealand (Horrocks et al. , 2001).…”

Section: Discussionmentioning

confidence: 99%

Modern pollen–vegetation relationships along transects on the Whangapoua Estuary, Great Barrier Island, northern New Zealand

Deng

Horrocks

Ogden

et al. 2006

Journal of Biogeography

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“…Previous far northern pollen studies (e.g. Elliot et al, 1997;Horrocks et al, 2001;Newnham et al, 2004) suggest that regional Polynesian deforestation occurred at a similar time to that of much of New Zealand generally, ca. 800-600 yr BP (McGlone, 1983;McGlone and Wilmshurst, 1999).…”

Section: Late Quaternary Environments In Northern New Zealand 275mentioning

confidence: 99%

“…Agathis also expanded after this time. Other pollen records from the southern part of the region, notably from the Bay of Islands and Whangape Harbour (Elliot et al, 1997Horrocks et al, 2001Horrocks et al, , 2007 (Fig. 1), together cover much of the Holocene, showing Dacrydium-dominated conifer-hardwood forest undergoing large-scale destruction by Polynesian fires during the last millennium.…”

Section: Introductionmentioning

confidence: 99%

Late Quaternary environments, vegetation and agriculture in northern New Zealand

Horrocks

Nichol

Augustinus

et al. 2007

J Quaternary Science

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A sedimentological and plant microfossil history of the Late Quaternary is preserved in two sediment cores from early Polynesian ditch systems on southern Aupouri Peninsula. The study places human activities into a geomorphological and ecological context and allows comparison of natural and anthropogenic effects on two different geological settings: a floodplain and a relatively closed peat swamp. The data fill part of the current gap in the environmental record from northern New Zealand, namely MIS 3 (57k-26k yr BP). There is evidence for an increase in fire frequency in the region after 40k 14 C yr BP, suggesting a shift to drier (and cooler) conditions. Pollen records show that conifer-hardwood forest dominated by podocarps (especially Dacrydium) prevailed prior to Polynesian arrival and deforestation within the last millennium, with Fuscopsora insignificant throughout. Both cores show sections with gaps in deposition or preservation, possible flood-stripping of peat during the pre-Holocene and mechanical disturbance by early Polynesians. The identification of prehistoric starch grains and other microremains of introduced Colocasia esculenta (taro) in both cores supports indirect evidence that the ditch systems of far northern New Zealand were used for the extensive cultivation of this crop.

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“…Previous palaeo-environmental research on Te Aupouri Peninsula includes studies of coastal sediment types and sources (Schofield 1970;Ricketts 1979), geomorphic mapping of dune systems and palaeosols (Hicks 1983) and shallow stratigraphic studies of wetlands to document regional vegetation history Enright et al 1988;Ogden et al 1993;Elliot et al 1995Elliot et al ,1998Horrocks et al 2001Horrocks et al ,2007. These works established the Late Quaternary age for much of the surface and near-surface depositional sequences on the peninsula.…”

Section: The Study Areamentioning

confidence: 99%

A marine to freshwater sediment succession from Kowhai Beach wetland, Northland: Implications for Holocene sea level

Hicks

Nichol²

2007

Journal of the Royal Society of New Zealand

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An infilled wetland located behind coastal dunes in north-east Northland is used to reconstruct a local history of environmental change spanning early Holocene (c. 7000 yr BP) to modern time. Proxy indicators (sediment texture, diatoms and pollen) provide evidence for a transition from marginal marine-to brackish-to freshwaterconditions in the wetland. Radiocarbon ages constrain the chronology of this succession to 7880-7430 cal. yr BP for the early period of marine conditions, 3570-3210 cal. yr BP for the latter brackish phase and 1060-800 cal. yr BP for the change to freshwater conditions. Within this succession, the diatom record preserves a strong brackish signal at core depths above the limit of the modern tidal range. This is presented as preliminary evidence for a mid-Holocene sea level highstand for northern New Zealand of approximately 1.2 m above present mean sea level. Keywords diatoms;14 C dating; highstand; palynology; sea level; sediments; stratigraphy INTRODUCTIONThe characteristics of sedimentary successions that constitute the coastal depositional record are controlled by the interplay between sea level, sediment supply and accommodation space. Studies of the facies that comprise these sedimentary successions traditionally focus on shoreface, beach and dune environments and associated marine-dominated processes (e.g., Curray 1964;Kraft 1971; Thorn 1983;Davis & Clifton 1987;Roy et al. 1994). In general, these particular environments do not always preserve a detailed record of environmental change in adjacent terrestrial systems. In contrast, back-barrier environments (wetlands, swamps, marshes and lagoons) do have the potential to record details of environmental change in both coastal and terrestrial systems, particularly responses to sea-level change .For the New Zealand coast, there has been little effort to use back-barrier environments to study environmental change, nor to resolve Holocene sea-level history beyond that established by Gibb (1986). Noticeably absent has been any attempt to establish evidence for a midHolocene highstand in sea level, a phenomenon now well documented for other coasts in the SW Pacific (e.g., Woodroffe et al. 1995;Baker & Haworth 1997Nunn 1998; Sloss et al. in press). This paper addresses these matters via a case study of a back-barrier wetland in northern New Zealand. The study objectives are to investigate the sensitivity of the wetland to marine and terrestrial influences, and to test for evidence of a sea-level highstand using a multiproxy analysis of the sediment record.

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A Holocene pollen and sediment record of Whangape Harbour, far northern New Zealand

Cited by 12 publications

References 24 publications

Modern pollen–vegetation relationships along transects on the Whangapoua Estuary, Great Barrier Island, northern New Zealand

Modern pollen–vegetation relationships along transects on the Whangapoua Estuary, Great Barrier Island, northern New Zealand

Late Quaternary environments, vegetation and agriculture in northern New Zealand

A marine to freshwater sediment succession from Kowhai Beach wetland, Northland: Implications for Holocene sea level

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