Modern pollen rain, central-western North Island, New Zealand

The composition and structure of three small areas of west Taupo forest, blasted down and buried during the c. AD 130 Taupo tephra eruption, are revealed by analysis of plant macrofossils, including leaves, seeds and wood. Data from these three sites and from the recently described Pureora buried forest were then used to interpret the pre-eruption vegetation along a 20 kilometre transect, from Pureora westward to Benneydale. All the stands were on flat or undulating terrain and dominated by podocarps, ranging from rimu (Dacrydium cupressinum)-tanekaha (Phyllocladus trichomanoides) at Pureora to rimu at Benneydale. Broadleaved trees increased westward; on lower hillslopes in the Benneydale buried forest, northern rata (Metrosideros robusta) was an important canopy component. An amelioration of climate with decreasing altitude westward was indicated by a gradual change from prominence of horopito (Pseudowintera colorata) at Pureora to P. axillaris at Benneydale, and the presence of rewarewa (Knightia excelsa) and Metrosideros perforata only at the Benneydale site. In the extant forests adjacent to the sites, the broadleaved tree species, tawa (Beilschmiedia tawa), kamahi (Weinmannia racemosa) and mahoe (Melicytus ramiflorus ssp. ramiflorus) are common, but these were not recorded in any buried forest. Classification and ordination techniques were applied to data from three buried forest sites, approximately 10 km apart along the transect. These arranged the plots and species in a spatial sequence from Pureora to Benneydale, and also reflect a gradient from very poor to comparatively better drainage. The volcanic succession hypothesis of McKelvey (1963McKelvey ( , 1986) is discussed in light of the macrofossil data. Our evidence suggests that broadleaved, notably tawa, forest is not the endpoint of the forest succcession on flat to undulating sites, and that forests may not converge to the extent suggested by McKelvey. We postulate that, under the present climate regime, and in the absence of volcanic eruptions and logging, the podocarp species which were widespread in the buried forests will eventually dominate terrain of gentle relief in the Pureora-Benneydale district.Keywords: buriedforest, plant macrofossils, Taupopumice, Dacrydium cupressinum, Phyllocladus trichomanoides, Metrosideros robusta, radiocarbondating, volcanic succession hypothesis INTRODUCTIONMacrofossils preserved among the remains of forest near Pureora which was overwhelmed and buried during the c. AD 130 (Froggatt, 1981) Taupo eruption were described by Clarkson, Patel and Clarkson (1988). We also made additional studies of three other buried forests in the district. Our aim was to determine the pre-Taupo forest pattern over a wider area. and to use these data to further refine hypotheses presented in our earlier paper. We also appreciated the opportunity to examine the composition of forests pre-dating humans and introduced animals.

Section: Discussionmentioning

confidence: 64%

The pre-Taupo eruption (c.AD 130) forest of the Benneydale-Pureora district, central North Island, New Zealand

Clarkson

Clarkson²,

Patel³

1992

“…Studies in New Zealand on the representation of pollen in relation to source vegetation (summarised in Macphail & McQueen 1983;McGlone 1988;Bussell 1988) and observations on flower structure and pollen presentation, have generally confirmed the importance of these factors. Taxa can be placed into several groups according to their dispersal characteristics, as follows.…”

Section: Representation Of Buried Forest Taxa In the C 1850 Yr Bp Pomentioning

confidence: 93%

“…Taxa can be placed into several groups according to their dispersal characteristics, as follows. Dacrycarpus dacrydioides has been reported as being both under-represented (Pocknall 1978;Macphail & McQueen 1983) and over-represented, because it is capable of longdistance dispersal (Bussell 1988). It is one of the tallest trees in the New Zealand flora, and is wind pollinated.…”

Section: Representation Of Buried Forest Taxa In the C 1850 Yr Bp Pomentioning

confidence: 99%

Macrofossils and pollen representing forests of the pre‐Taupo volcanic eruption (c. 1850 yr BP) era at Pureora and Benneydale, central North Island, New Zealand

Clarkson

McGlone

Lowe

et al. 1995

Micro-and macrofossil data from the remains of forests overwhelmed and huried at Pureora and Benneydale during the Taupo eruption (c. 1850 conventional radiocarbon yr BP) were compared. Classification of relative abundance data separated the techniques, rather than the locations, because the two primary clusters comprised pollen and litter/ wood. This indicates that the pollen:litter/wood within-site comparisons (Pureora and Benneydale are 20 km apart) are not reliable. Plant macrofossils represented mainly local vegetation, while pollen assemblages represented a combination of local and regional vegetation. However, using ranked abundance and presence/absence data, both macrofossils and pollen at Pureora and Benneydale indicated conifer/broadleaved forest, of similar forest type and species composition at each site. This suggests that the forests destroyed by the eruption were typical of mid-altitude west Taupo forests, and that either data set (pollen or macrofossils) would have been adequate for regional forest interpretation.The representation of c. 1850 yr BP pollen from the known buried forest taxa was generally consistent with trends determined by modern comparisons between pollen and their source vegetation, but with a few exceptions.A pollen profile from between the Mamaku Tephra (c. 7250 yr BP) and the Taupo Ignimbrite indicated that the Benneydale forest had been markedly different in species dominance compared with the forest that was destroyed during the Taupo eruption. These differences probably reflect changes in drainage, and improvements in climate and/or soil fertility over the middle Holocene.

“…Interpretation of the pollen assemblages is based partly on modern pollen studies from the region (McGlone, 1982;Bussell, l 988b) and partly on comparison of the assemblages with those from the Holocene and last glaciation in the area (Mcintyre, 1963(Mcintyre, , 1970McGlone, 1980;Bussell, 1988c). Norton et al (1986) have shown that selected modern pollen spectra in New Zealand correlate with modern vegetation associations, and that the abundance of certain pollen taxa correlates well with some climatic parameters.…”

Section: Palynology Methodsmentioning

confidence: 99%

A late Pleistocene vegetational and climatic history of part oxygen isotope stage 5, Ararata, south Taranaki, New Zealand

Bussell¹

1993

Self Cite

A late Pleistocene palynological record of vegetation and climate is investigated from a 5m lignite section within terrestrial cover beds of the Ngarino Marine Terrace on Ararata Road, near Hawera, south Taranaki, New Zealand.The pollen assemblages are dominated throughout by high levels of pollen derived from gymnosperm trees. A lower zone (ARI) is characterised by high levels of pollen of Prumnopitys taxifolia, Libocedrus, shrubs and grass, interpreted to represent a stadia! phase with climate cooler and drier compared with present. A middle zone (AR2) is characterised by high levels of pollen of P. taxifolia, Dacrydium cupressinum, Metrosideros and spores of Cyathea dealbata-type and of the bryophyte Bryosporis anisopolaris Mildenhall and Bussell. Pollen values for Libocedrus and grass are low. These assemblages are similar to Holocene pollen spectra in the region but differ in containing high levels of Dracophyllum-type and Restionaceae pollen, and Gleichenia spores. The zone also lacks any significant levels of Ascarina lucida pollen, typical of interglacial maxima in this region, and is considered to represent an interstadial phase with climate approaching that of the present. The third zone (AR3) is characterised by high values for P. taxifolia, Nothofagus, shrub, and grass pollen with decreases in abundance of D. cupressinum and Metrosideros pollen, and C. dealbata-type spores in particular. This zone is considered to represent a transitional cooling phase leading into a stadia! period. Climate was initially cooler and drier than present but may have become wetter later.The Ngarino Terrace marine deposits that underlie the section provide a maximum age constraint of c. 210,000 yr, while tephra within the lignite are estimated to age 70,000-110,000 yr, and amino acid racemisation dating of a wood sample in the lignite provides an age estimate of c. 80,000 ± 20,000 yr. The lower pollen zone (ARI) is correlated with stadial oxygen isotope substage 5d, the middle zone (AR2) is correlated with interstadial substage 5c, and the upper zone (AR3) is correlated with early stadia! substage 5b. Climate during oxygen isotope substage 5c is inferred closely to have approached interglacial conditions similar to those of the present day.Libocedrus, Nothofagus menziesii, Halocarpus, Dracophyllum-type, and Gleichenia are some taxa which were growing near the Ararata Road Site at various times during oxygen isotope stage 5, but which are either not found in Taranaki today or are mainly restricted to higher altitudes or local areas in Taranaki.