Late Quaternary environments, vegetation and agriculture in northern New Zealand

Abstract

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.

Examining plant physiological responses to climate change through an evolutionary lens

“…in our study, glacial Agathis spp. experienced warmer and wetter conditions during the last glacial period compared with modern climates (Elliot et al, 2005;Horrocks et al, 2007;D'Costa et al, 2008). We examined the effects of increasing [CO 2 ] in controlled locations in both study systems; the full Juniperus spp.…”

Low-resolution Australasian palaeoclimate records of the last 2000 years

“…Humans have likely impacted Australian wetland ecosystems for the entire duration of the Holocene (Fletcher and Thomas, 2010b;Black et al, 2007), and an impact has been recognised in New Zealand during the last millennium (Horrocks et al, 2007;McGlone and Wilmshurst, 1999b). This anthropogenic influence has intensified across Australasia since the arrival of European settlers Bickford and Gell, 2005;McGlone and Wilmshurst, 1999a), which may lead to palaeolimnological signals unrelated to climate.…”

Stratigraphy, pollen and 14C dating of Johnston's Gum Hole, a late Quaternary fossil kauri (Agathis australis) site, Northland, New Zealand

“…If this is the case, then the MIS 3 forest may be coeval with the forest represented by the plunging branch and peg roots in unit 2 of Johnston's Gum Hole. Horrocks et al (2007) have also recently reported evidence for Agathis forest early in MIS 3 from nearby Motutangi Swamp. Late glacial records from Kaitaia Bog and nearby Lake Tangonge indicate that Fuscospora forest, similar to that reported here for MIS 4, occurred during MIS 2 in the Far North (Elliot, 1998;Elliot et al, 2005).…”

“…The Gum Hole, and similar alternating sand/peat sequences on coastal dunes in Northland Horrocks et al, 2007), represent an important repository of proxy-climatic information for the late Quaternary. The shallow seas on both sides of the Aupouri Peninsula imply major shifts in hydrology and sediment supply with relatively slight changes of sea level.…”