John Flenley

Pollen texture identification using neural networks

The importance of research leading to the automation of pollen identification is briefly outlined. A new technique, neural network analysis, is briefly introduced, and then applied to the determination of light microscope images of pollen grains. The results are compared with some previously published statistical classifiers. Although both types of classifiers may work, the neural network is apparently superior to the statistical methods in three ways: high success rates (100% in this case), small number of samples needed for training, and simplicity of features.

Palynological and sedimentological evidence for a radiocarbon chronology of environmental change and Polynesian deforestation from Lake Taumatawhana, Northland, New Zealand.

We present pollen diagrams and sedimentological analyses from a lake site within an extensive dune system on the Aupouri Peninsula, Northland. Five thousand years ago, a regional Agathis australis -- podocarp-broadleaf forest dominated the vegetation, which manifested an increasing preponderance of conifer species. Climate was cooler and drier than at present. From ca. 3400 BP, warmth-loving species such as A. australis and drought-intolerant species, Dacrydium cupressinum and Ascarina lucida, became common, implying a warm and moist climate. The pollen record also suggests a windier climate. The most significant event in the record, however, occurred after ca. 900 BP (800 cal BP) when anthropogenic deforestation commenced. A dramatic decline in forest taxa followed, accompanied by the establishment of a Pteridium-esculentum-dominated community. Fire almost certainly caused this, evidenced by a dramatic increase of charcoal. Sedimentological evidence for this site indicates a relatively stable environment before humans arrived and an increasingly unstable environment with frequent erosional events after human contact.

Anomalous radiocarbon dates from Easter Island.

The largest volcanic crater on Easter Island in the South Pacific contains a lake 1 km in diameter with large floating mats of vegetation, mainly Scirpus californicus. A core taken through a mat near the center produced anomalous dates, with older dates above younger ones. The possibility that the mat had become inverted was considered, but palynolog- ical evidence refutes this idea because it shows a progressive upward decline of forest pollen, which is well known from other swamp cores on the island. A new series of radiocarbon dates made directly on pollen concentrates was obtained. These dates also produced inconsistencies, particularly when pollen concentrate ages were compared with 14C ages on plant fragments from the same depth. This series of 14C ages seems to indicate that both old and young organic components in the sediment are deposited contiguously and that the depositional history of these cores is more complex than previously known. Previous age determinations on bulk sediments from Easter Island, which also show anomalous dates, may be too simplistic. This paper provides a warning to other researchers dating sediments from Easter Island. We suggest that sample selection and dating pro- cedures be carefully considered for these sediments.

A late Holocene pollen record of deforestation and environmental change from the Lake Tauanui catchment, Northland, New Zealand

Late Holocene pollen and sediment records from the Lake Tauanui catchment, northern New Zealand, indicate that the lake formed about 5500 years ago following a series of volcanic events in the Tauanui Volcanic Centre. These volcanic events initiated a volcanosere resulting in a mixed conifer-hardwood forest. Dacrydium cupressinum was the dominant tree. Agathis australis was always present. Changes similar to those registered in other Northland pollen diagrams are apparent. At ca 4000 yr B.P., when the climate became cooler and drier than before, a fire occurred in the catchment area causing erosion of the surrounding slopes and some destruction of forest. Fluctuations in abundance of many forest species, including Ascarina lucida, A. australis and D. cupressinum, from ca 3500 yr B.P. indicate repeated disturbance, increasingly so after 1600 yr B.P. Summer droughts and increased frequency of cyclonic winds are suggested as the cause. Major anthropogenic deforestation events defined by palynology occurred across many parts of the New Zealand landscape at ca 700 yr B.P. At Lake Tauanui anthropogenic forest disturbance, radiocarbon dated to ca 1000 yr B.P., is indicated by significant decline in all tree and shrub elements with concomitant increase in pteridophytes, especially Pteridium esculentum. Charcoal concentration increases steadily from the onset of disturbance, and in the final phase after the arrival of Europeans, major clearance of vegetation is indicated. Herbs increase markedly in this period, in diversity and abundance.

A 4300 year palynological and sedimentological record of environmental change and human impact from Wharau Road Swamp, Northland, New Zealand

The palynology and sedimentology of the late Holocene Wharau Road Swamp, Northland, are described Organic sediment began accumulating ca 4300 yr B P ma valley as a result of damming by a basaltic lava flow from nearby Mount Te Puke Mixed conifer‐hardwood forest dominated the region until major anthropogenic forest clearance dated by radiocarbon at ca 600 yr B P Dacrydium cupressinum was the dominant taxon Agathis austrahs was always present until European clearance, with peaks in the pollen record at inferred ages of ca 3700 yr B P and ca 1800 yr B P Climate changes similar to those registered in other pollen diagrams from northern New Zealand are evident, and suggest that climate was wetter and warmer than at present before 4000 yr B P From about 2600 yr B P climate became drier and cooler, indicated by a decline in Ascanna lucida and D cupressinum A period of milder and wetter climate from ca 2000 yr B P is suggested by increases m D cupressinum A lucida and Cvathea Major forest disturbance at ca 600 yr...

The Quaternary history of far eastern rainforests

This region differs from those supporting tropical rainforest in other parts of the world in that it is less continental and geologically much more dynamic. It incorporates some major pieces of continental plate, but its center—the so-called ‘‘Maritime Continent’’ (Ramage, 1968)—is largely a complex interaction zone between the Asian and Australian Plates resulting from the continued movement of the Australian Plate into Southeast Asia (Metcalfe, 2002). The effects of tectonic and volcanic activity have resulted in mountain uplift, particularly in New Guinea, and formation of the volcanic island chain of Indonesia. Vulcanicity also occurs out into the Pacific beyond the ‘‘andesite line’’ where most ‘‘high’’ islands are volcanic and most ‘‘low’’ islands are coral islands developed on sunken volcanoes.

Microfossils of Polynesian cultigens in lake sediment cores from Rano Kau, Easter Island

Previous wetland vegetation records from Easter Island showing deforestation and Polynesian agriculture are limited to cores that rely on pollen, with a single cultigen pollen type identified: Urticaceae/Moraceae, possibly Broussonetiapayrifera (paper mulberry). Here we redress this by also using phytolith and starch analyses on four lake sediment cores on a ~350-m transect along the southwest edge of Rano Kau, focusing on in-washed basal clayey layers. We also use a new method, Fourier transform infrared spectroscopy, to positively identify degraded starch collected from sedimentary deposits. The cores are the first samples recovered from an area in the lake that (a) lies below the relict village of Orongo, (b) is near a section of the crater believed to be most accessible from the Pacific coast, and (c) is far from the northern crater rim and receives high solar radiation, a likely benefit for crops of tropical origin. Pollen and phytoliths are abundant in the clayey layers and sparse in overlying layers of organic lake detritus and living rhizomes. Mixing of core deposits as a result of human activity has disordered the radiocarbon sequence, precluding development of an reliable chronology. Containing microfossils of several introduced cultigens, the clayey layers represent gardened terraces that have slumped into the lake. The data indicate large-scale deforestation and a mixed-crop production system including Broussonetiapapyrifera, Colocasiaesculenta (taro), Dioscoreaalata (greater yam), Ipomoeabatatas (sweet potato), Lagenariasiceraria (bottle gourd) and Musa (banana) sp. The data show (a) the potential for using the combined analyses to provide direct evidence of Polynesian horticulture on Easter Island and (b) that the island’s wetlands potentially hold extensive horticultural records. The study highlights the concept of ‘transported landscapes,’ whereby colonising people replace indigenous forests with artificial, imported agricultural landscapes.

Vegetation changes and their climatic implication for the late Pleistocene at Lake Poukawa, Hawkes Bay, New Zealand

A detailed vegetation history extending back to the Last Interglacial (Marine Isotope Substage 5e) is presented for Lake Poukawa, Hawkes Bay, New Zealand. This history is based on palynological analyses of a 198-m core record, age secured by uranium/thorium (U/Th) and optically stimulated luminescence (OSL) dates as well as tephrochronology. Vegetation of the penultimate glacial (Isotope Stage 6) probably consisted of a very sparse shrubby herbland of stunted podocarps (Phlyllocladus sp.), daisies, grasses and sedges. Similar floras existed in each of the succeeding cool periods. Four interglacial/interstadial floras are preserved. The peak of the Last Interglacial (Substage 5e) was dominated by extensive lowland forest of tall forest podocarps (Podocarpus/Prumnopitys), most probably matai (Prumnopitys taxifolia) with red beech (Nothofagus fusca), secondary forest trees (Coprosma spp., Myrsine spp.) and tree ferns (Cyathea spp.). In the Poukawa basin itself, a swamp forest of the podocarp (Dacrycarpus dacrydioides) with the true palm (Rhopalostylis sapida) expanded. Substage 5e was significantly warmer and/or moister than the present day. Substage 5c/5a was marked by montane forest of red and silver beeches (N. fusca and N. menziesii), Phyllocladus spp. and secondary trees. A reduced representation of Podocarpus/Prumnopitys possibly consists of montane podocarp (Podocarpus hallii). We infer the temperature of Substage 5c/5a to have been 3.5-5 degreesC lower than the present day. Although Stage 3 flora are superficially similar to those of Substage 5c/5a, the beeches are relatively less dominant. The regional flora during Stage 1 is very similar to those of Substage 5e, but the density is lower with no swamp forest during the present interglaciation. This may represent a change in evapotranspiration balance around Poukawa, but may also be controlled by hydrological conditions within the basin

Some prospects for lake sediment analysis in the 21st century

Abstract This paper reviews the following recent and possible future developments in lake sediment analysis: pollen extraction for radiocarbon dating, automated palynology, ancient DNA extraction palyno-richness and palyno-diversity, palaeo-population biology, pollen pore number.

Late Glacial beech forest: an 18,000–5000-BP pollen record from Auckland, New Zealand

Australia, New Zealand and South America are the main sources of terrestrial climate change records for midlatitudes in the Southern Hemisphere. The advantage of studying the New Zealand record is that its vegetation has been subject to human influence for only the last thousand years. Vegetation records for Auckland are important because earlier work indicates that during the Last Glacial Maximum, the boundary between scrubland and forest lay in the Auckland region. Auckland is situated in a volcanic field and the coring site was in the crater of a small extinct volcano (Crater Hill, formed about 29 ka BP). The 4-m long core contained sediment dating from c. 5 to c. 18 ka BP. We present pollen and diatom records from this core. The pollen records from basal clays indicate southern beech forest (mainly Nothofagus menziesii) was present in the region around Crater Hill from 18 to 14.5 ka BP. At this time, there were areas of scrub in the crater surrounding a hardwater lake. The southern forest limit could well have been close to the site. Records from overlying peat indicate beech forest was replaced by Podocarp broadleaf forest as the Last Glacial ended. Metrosideros spp. (coastal forest trees) peak in the early Holocene. This coincides with an impoverished diatom flora which indicates drier conditions in the basin. When the lake reformed in the Holocene on peat its water was more acidic.