Holocene vegetation, climate and history of a raised bog complex, northern New Zealand based on palynology, plant macrofossils and tephrochronology

Abstract

A Holocene history of vegetation, climate, and ombrogenous mire development is presented from pollen and plant macrofossil analyses of sediments at Kopouatai Bog, a large, raised, restiad bog in northern New Zealand. Tephra layers of established ages, supplemented by numerous radiocarbon dates, provide a secure chronology. The earliest peats, overlying last glacial sediments, and dated at c. 11700 radiocarbon years BP, with extensive accumulation after c. 10360 BP, are dominated by pollen of warm temperate podocarp-angiosperm forest, indicating a moist, mild early-Holocene climate. The bog began as a series of small soligenous mires within lowland podocarp-dominated swamp forest but was mostly oligotrophic by c. 8500 BP. Peat accumulation rates have varied spatially and temporally, averaging 0.9 mm yr -1 in central and southern areas. The deposition of deltaic muds in the northern part of the bog accompanied a marine transgression c. 6500-5000 BP, while elsewhere an associated groundwater table rise resulted in a temporary return to mesotrophic conditions. As the marine influence subsequently receded, the northern areas remained subject to regular flooding, but underwent rapid peat growth at a mean rate of 1.7 mm yr -1 , while oligotrophic conditions returned to other parts of the bog. Regional vegetation developments indicate a change, c. 6000 BP, to drier, frostier conditions during the late Holocene. Ascarina lucida and Agathis australis may be used as regional pollenstratigraphic markers for the early Holocene and late Holocene, respectively. The loss of tall trees and expansion of subcanopy species and seral vegetation in forests near Kopouatai Bog, just before the deposition of Kaharoa Tephra (c. 700 BP), are likely evidence for human activity dating from at least this time.

Stratigraphy and chronology of a 15 ka sequence of multi‐sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand

“…It has a unique ferromagnesian mineralogical assemblage dominated by sodic phases, especially aegirine (Table 1), and a distinctive peralkaline (molar [Na 2 O + K2O]/ Al O3 >1) major element composition (anal. 17, Table 2), consistent with previous mineralogical and glass compositional analyses of this tephra (Lowe 1988a, b;Stokes & Lowe 1988;Froggatt & Lowe 1990;Newnham & Lowe 1991;Pillans & Wright 1992;Newnham et al 1995b). The glass, although silicic, has relatively low amounts of AI2O3 (9.5%) and CaO (0.3%) but characteristically high amounts of FeO totai (5.5%) and Na 2 O (5.3%).…”

“…The average sedimentation rate (on a tephra-free basis and i.sing radiocarbon years) for the entire Kaipo sequence is ('.19 mm/yr, comparable with similar rates for a bog at Holdens Bay, Rotorua (McGlone 1983) and peat lakes in lae lowland Waikato region (Lowe 1988b; 989) (see also Froggatt & Rogers 1990), but considerably slower than mean rates of c. 1 mm/yr at Rukuhia and Kopouatai Bogs in the Waikato region (Green & Lowe 1985;Newnham et al 1995b) and at Lake Poukawa, Hawke's Bay (Howorth et al 1980). However, the rates of accumulation at Kaipo have varied with three distinct phases evident ( Green & Lowe 1985;Hogget al 1987).…”

“…1; Lowe 1988b;Newnham & Lowe 1991), was clearly distributed in a southeasterly direction as well (see also Kennedy & Froggatt 1984). With its distinctive composition, Tuhua Tephra forms an important regional marker of mid-Holocene age (Newnham et al 1995b).…”

Vegetation recovery following fire in two Waikato peatlands at Whangamarino and Moanatuatua, New Zealand

“…Stratigraphic studies of Waikato peat bogs indicate a fire every one hundred to several hundred years in pre-human times, i.e., up to about 700 years ago (Newnham et al 1995). Since then the frequency has increased dramatically owing to land clearance first by Polynesian and then, more widely, by European settlers.…”

Ecology and vegetative morphology of the carnivorous plantUtricularia dichotorna(Lentibulariaceae) in New Zealand

“…The role of fires in the Kopouatai Peat Dome vegetation was recently discussed by Newnham et al (1995), while the detailed results of fire successive patterns at Kopouatai and Moanatuatua, in relation to Sporodanthus communities, are given by de Lange et al (1999). In peat bogs of the Waikato, U. dichotoma grows abundantly in the permanent "bum pools" where past fires have bumed down to the water table.…”