194 results for Lowe, David J.

  • Assessing drivers of plantation forest productivity on eroded and non-eroded soils in hilly land, eastern North Island, New Zealand

    Heaphy, Marie; Lowe, David J.; Palmer, David John; Jones, Hayden S.; Gielen, Gerty J. H. P.; Oliver, Graeme R.; Pearce, Stephen H. (2014-07-02)

    Journal article
    University of Waikato

    Methods: The impact of soil erosion by mass movement on forest productivity was investigated in a paired plot trial in a planted forest in a mainly hilly to steepland catchment (Pakuratahi) near Napier, eastern North Island, New Zealand. Tree growth and form were measured and soil properties analysed to compare productivity and productivity drivers in adjacent non-eroded and eroded plots. Background: The effect of soil erosion on New Zealand production forestry is not well known and there has been no research prior to our study into the relationship between soil nutrient status and planted forests growing in eroded soils in steeplands. Results: Regression analysis showed that the decreased soil total nitrogen, total carbon, total phosphorus, and soil organic matter content in eroded plots had a negative impact on tree volume, resulting in a 10% decrease in measured tree volume. Based on an assessment of log quality, trees in the eroded plots were forecast to produce 16% less volume from high-quality pruned logs (with associated reduction in revenue of around $4000 per hectare), than trees in non-eroded plots. The total recoverable volume (TRV), estimated (for a 25-year rotation) from the measured Pinus radiata D. Don trees growing on the eroded sites, was valued at $68,500, about 9% less than the estimated TRV from trees measured on non-eroded plots ($76,000). Tree form and mean tree height in eroded and non-eroded plots were not significantly different. Conclusions: Soil erosion impacts production in planted forests. Afforestation of erodible land provides a valuable ecosystem service through land and soil stabilisation but this service is currently not reflected in the market prices for timber in New Zealand. Maintaining the productive capacity of erodible soils through practices such as fertilisation or continuous-cover forestry can add further costs to production forestry. To ensure that sustainable forest practices are carried out to protect the productivity of soils, financial incentives may be justified.

    View record details
  • Intra-conference and Post-conference Tour Guides, International Inter-INQUA Field Conference and Workshop on Tephrochronology, Loess, and Paleopedology

    Lowe, David J. (1994-02-01)

    Book
    University of Waikato

    New Zealand consists of a cluster of islands, the three largest being North, South, and Stewart, in the southwest Pacific Ocean. They have a total land area of about 270 000 km2 (similar to that of the British Isles or Japan). The islands are the small emergent parts of a much larger submarine continental mass (Fig. 0.1) that was rafted away from Australia and Antarctica by sea-floor spreading in the proto-Tasman Sea between 85 and 60 Ma. Much of this New Zealand subcontinent is a remnant of the former eastern margin of Gondwanaland, the ancient southern supercontinent. The mainland islands form a long, narrow, NE-SW trending archipelago bisected by an active, obliquely converging, boundary between the Australian and Pacific lithospheric plates (Fig. 0.2), which has evolved over the last 25 million years (Kamp 1992). The plate boundary is marked by active seismicity and volcanic arcs, illustrating New Zealand's position as part of the Circum-Pacific Mobile Belt -the so-called "Pacific Ring of Fire". The NE-SW trend of the modem plate boundary cuts across mainly NW-SE oriented structural features inherited from earlier (mid-Cretaceous) rifting events.

    View record details
  • Guidebook for ‘Land and Lakes’ field trip, New Zealand Society of Soil Science Biennial Conference, Rotorua

    Lowe, David J. (2006-11-01)

    Book
    University of Waikato

    Welcome to Rotorua. The trip today (28th November, 2006) has twin themes: “Land and soil in the making” and “Land and soil management for cleaner water”. It offers an opportunity for participants to ‘peep behind the scenes’ at the wonderful volcanic landscapes, ash layers, soils, and waters of the Lake Rotorua−Lake Okaro−Lake Rerewhakaaitu areas in the Rotorua region. We hope the trip will be an informative, interesting and enjoyable day out with something for everyone. We will look at the linkages between soils and water and show how science and society are working together to understand and reduce the impacts of municipal, farming and forestry activities on our environment. Multiple layers of tephras, clear examples of buried soil horizons, and three remarkable soil profiles will be seen. Soil and environmental scientists, foresters, tephrochronologists (volcanic ash specialists), and volcanologists will join forces with local farmers and others to give us their perspectives at various stops during the trip.

    View record details
  • Guidebook for Pre-conference North Island Field Trip A1 ‘Ashes to Issues’, 28-30 November, 2008

    Lowe, David J. (2008-11-01)

    Book
    University of Waikato

    Welcome to New Zealand or Aotearoa – „Land of the long lingering day [twilight]‟ – and to our three-day pre-conference North Island field trip „Ashes and Issues‟. We trust your stay in New Zealand is both informative and friendly and there is something for everyone on the trip. The itinerary in brief and a map of the North Island showing the main scientific stops are shown above. At the time of guidebook preparation, we have a group of 23, including four students, on the tour with participants from Japan, Taiwan, USA, UK, Australia and New Zealand. The tour leaders are Prof David Lowe (Univ. of Waikato, Hamilton) and Dr Haydon Jones (Scion Research, Rotorua). Assistant leader is Prof Paul McDaniel (Univ. of Idaho, Moscow), on leave at the Univ. of Waikato July-December, 2008. We offer a warm welcome to you all. Because we have considerable distances to travel (especially Day 3), as well as a range of stops planned, we will need to leave the hotel at 8.00 am each day.

    View record details
  • INTREPID Tephra-II: - 1307F

    Lowe, David J. (2013)

    Journal article
    University of Waikato

    The INTREPID Tephra project, “Enhancing tephrochronology as a global research tool through improved fingerprinting and correlation techniques and uncertainty modelling”, was an overarching project of the international community of tephrochronologists of the International Focus Group on Tephrochronology and Volcanism (INTAV), which in turn lies under the auspices of INQUA’s Stratigraphy and Chronology Commission (SACCOM). INTREPID’s main aim has been to advance our understanding and efficacy in fingerprinting, correlating, and dating techniques, and to evaluate and quantify uncertainty in tephrochronology, and thus enhance our ability to provide the best possible linking, dating and synchronising tool for a wide range of Quaternary research projects around the world. A second aim has been to re-build the global capability of tephrochronology for future research endeavours through mentoring and encouragement of emerging researchers in the discipline.

    View record details
  • Stop 2 Kainui silt loam and Naike clay, Gordonton Rd

    Lowe, David J. (2008)

    Conference item
    University of Waikato

    At this stop are several remarkable features both stratigraphic and pedological, and a “two-storied” soil, the Kainui silt loam alongside (in just a few places) the Naike clay. Both soils are Ultisols. The sequence of tephra beds and buried soil horizons spanning about 1 million years was exposed in 2007 by road works.

    View record details
  • "New Zealand Soil Classification” by A.E. Hewitt [Book review]

    Lowe, David J. (1992)

    Journal article
    University of Waikato

    The publication of `New Zealand Soil Classification' by Dr Alan Hewitt this year (Hewitt 1992a) represents a major milestone in New Zealand soil science. That it was one of the final publications of the now defunct DSIR is somehow appropriate because, as classification systems should, it provides (in a mere 133 pages) a synthesis of much of what has been learnt about the soils of New Zealand over the past 60 years or more, The new classification was officially launched at the New Zealand Society of Soil Science Conference in Rotorua on 16 November, 1992.

    View record details
  • Guidebook for Pre-conference North Island Field Trip ‘Ashes and Issues’, 28-30 November, 2008

    Lowe, David J.

    Book
    University of Waikato

    Guidebook for Pre-conference North Island, New Zealand Field Trip ‘Ashes and Issues’, 28-30 November, 2008. The route goes progressively towards the locus of the most recently active volcanic centres in central North Island. Concepts of upbuilding pedogenesis in tephra-mantled terrains will be discussed. Topical issues relating to soil and water quality and land management of intensive horticulture, pastoral farming (especially dairying), plantation forestry and C budgeting and modelling, and municipal effluent disposal by land treatment, will be considered as well. The declining quality of water in lakes in the Rotorua region and in Lake Taupo (mainly as a result of increasing N and P), and large-scale land-use conversions from plantation forestry to dairy farming in the Taupo area, and implications, are examined on days 2 and 3 of the trip.

    View record details
  • Preface: Enhancing tephrochronology and its application (INTREPID project): Hiroshi Machida commemorative volume

    Lowe, David J.; Davies, Siwan M.; Moriwaki, Hiroshi; Pearce, Nicholas J.G.; Suzuki, Takehiko (2011)

    Journal article
    University of Waikato

    Tephrochronology is the characterization and use of tephras – the explosively-erupted, unconsolidated, pyroclastic products of volcanic eruptions – or cryptotephras (glass-shard and/or crystal concentrations not visible as layers) as a unique stratigraphic linking, synchronizing, and dating tool. The word ‘tephra’ is derived directly from the Greek word tephra meaning ‘ashes’. Although the method is founded in stratigraphy, tephrochronology relies also on characterizing or ‘fingerprinting’ inherent tephra-derived components using laboratory-based analysis to complement field-based evidence. Such analysis includes the petrographic identification of mineral assemblages and the geochemical assay of glass shards, melt inclusions, or crystals (minerals including plagioclase, olivine, pyroxenes, amphiboles, biotite, or Fe–Ti oxides such as titanomagnetite) using the electron microprobe and other instruments including laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) ( [Lowe, 2011] and [1] ). These data are supported by the derivation of numerical ages on tephras/cryptotephras using a range of techniques including radiometric (e.g., radiocarbon, fission track, luminescence), incremental (e.g., layering in ice cores, varves, dendrochronology), age-equivalence (e.g., orbital tuning, magnetopolarity, palynostratigraphy), relative dating (e.g., obsidan hydration), and historical observation. Ages are also obtained using Bayesian-based flexible depositional modelling and wiggle matching (e.g., [Lowe et al., 2007] and Lowe et al., 2008 D.J. Lowe, P.A.R. Shane, B.V. Alloway and R.M. Newnham, Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 years ago: a framework for NZ-INTIMATE.. Quaternary Science Reviews, 27 (2008), pp. 95–126. [Lowe et al., 2008] ).

    View record details
  • Colin George Vucetich (1918–2007)—pioneering New Zealand tephrochronologist

    Lowe, David J.; Tonkin, Philip J.; Neall, Vincent E.; Palmer, Alan S.; Alloway, Brent V.; Froggatt, Paul C. (2008)

    Journal article
    University of Waikato

    Many Quaternarists, tephrochronologists, and soil scientists mourned the passing in New Zealand of Colin Vucetich—gentle mentor, pedologist, and pioneering tephrochronologist—on 25 April (Anzac Day), 2007. Colin was in his 89th year. As well as forming a 25-year partnership with W.A. “Alan” Pullar, with whom he published three classic papers on tephrostratigraphy based on field work undertaken by the pair largely in their own time, Colin inspired and mentored numerous postgraduates in his later career as an academic at Victoria University of Wellington. There he taught pedology, soil stratigraphy, and tephrochronology until his retirement as Reader (Associate Professor) in 1982. In retirement he was an honorary lecturer and supervisor at Massey University (Palmerston North) until 1991 (Fig. 1, Fig. 2 and Fig. 3).

    View record details
  • Volcano-meteorological tsunamis, thec. AD 200 Taupo eruption (New Zealand) and the possibility of a global tsunami

    Lowe, David J.; de Lange, Willem P. (2000)

    Journal article
    University of Waikato

    Meteorological tsunamis are long-period waves that result from meteorologically driven disturbances. They are also generated by phase coupling with atmospheric gravity waves arising through powerful volcanic activity. The AD 1883 Krakatau eruption generated volcano-meteorological tsunamis that were recorded globally. Because of its extreme violence and energy release (≥150±50 megatons explosive yield), and by analogy with the Krakatau event, it is highly possible that the ignimbrite-emplacement phase of the c. ad 200 Taupo eruption of North Island, New Zealand, generated a similar volcano-meteorological tsunami that may have reached coastal areas worldwide. Tsunami deposits of identical age to the Taupo eruption occur in central coastal New Zealand and probably relate to that event; definitive evidence elsewhere has not yet been found. In theory, volcano-meteorological tsunamis are likely to be produced during comparable eruptive events at other explosive volcanoes, and thus represent an additional volcanic hazard at coastal sites far from source. We suggest that evidence for such tsunamis, both for marine and lacustrine environments, may be preserved in geological records, and that further work searching for this evidence using a facies approach is timely.

    View record details
  • Mapping and explaining the productivity of Pinus radiata in New Zealand

    Palmer, Jonathan G.; Watt, Michael S.; Kimberley, Mark O.; Hock, Barbara K.; Payn, Tim W.; Lowe, David J. (2010)

    Journal article
    University of Waikato

    Mapping Pinus radiata productivity for New Zealand not only provides useful information for forest owners, industry stakeholders and policy managers, but also enables current and future plantations to be visualised, quantified, and planned. Using an extensive set of permanent sample plots, split into fitting (n = 1,146) and validation (n = 618) datasets, models of P. radiata 300 Index (an index of volume mean annual increment) and Site Index (an index of height growth) were developed using a regression kriging technique. Spatial predictions were accurate and accounted for 61% and 70% of the variance for 300 Index and Site Index, respectively. Productivity predicted from these surfaces for the entire plantation estate averaged 27.4 m³ ha⁻¹ yr⁻¹ for the 300 Index and 30.4 m for Site Index. Surfaces showed wide regional variation in this productivity, which was attributable mainly to variation in air temperature and root-zone water storage from site to site.

    View record details
  • A discontinuous ca. 80 ka record of Late Quaternary environmental change from Lake Omapere, Northland, New Zealand

    Newnham, Rewi M.; Lowe, David J.; Green, John D.; Turner, Gillian M.; Harper, Margaret A.; McGlone, Matt S.; Stout, Stephen L.; Horie, Shoji; Froggatt, Paul C. (2004)

    Journal article
    University of Waikato

    We present an integrated record of environmental change from Lake Omapere, Northland, New Zealand, based on palaeolimnological analysis of a 7-m-long core and eight adjunct cores spanning part of the last 80 calendar (cal.) ka. The chronology was developed using tephrochronology, palaeomagnetism and radiocarbon dating together with climato- and palyno-stratigraphy. Two of 14 tephra layers in the cores provide markers for correlating the record with other New Zealand climato-stratigraphic sequences, deep-sea cores and the global marine isotope record. Pollen, diatom, palaeomagnetic, sedimentologic and pigment analyses show that Lake Omapere, currently 2 m deep, has had a discontinuous history. Occupying a shallow basin perched partly within old basalt lavas, the initial (alkaline) lake formed towards the end of MIS 5a at ca. 80 cal. ka, presumably because of blockage of local drainage of a swampy alluvial floodplain, inundating peat deposits and forest trees, including kauri (Agathis australis). The lake filled rapidly to a level 1–2 m above that at present. Such filling was probably unrelated to climate but a subsequent phase of variable but generally falling lake levels and increasing dystrophy may have been climatically controlled, commencing during MIS 4 and culminating in periods early in MIS 3 when the lake became swampy or dry. Conditions of non-deposition (or non-preservation) obtained for most of the period after ca. 55 cal. ka (Rotoehu Ash) until formation of the modern lake approximately 600–700 cal. years ago or soon after, as indicated by the presence of Tephra-1, identified in part as Kaharoa Tephra (AD 1314), near the top of the core. The modern lake originated possibly through damming of the western outlet as a consequence of accelerated erosion accompanying earliest Polynesian deforestation, an interpretation supported by Maori oral tradition. The pollen record indicates that beech Nothofagus (presumably N. truncata) was much more common in Northland during the Last Glacial, and that for this region the relative abundance of Nothofagus vs. Agathis pollen serves as a better indicator of cooler versus warmer intervals during the Quaternary than the ratio of tree to non-tree pollen. However, it seems likely that moisture balance was a more critical factor than temperature in vegetation composition and distribution, particularly during the LGM, and the long periods of hiatus may also be linked to a drier climate than present. Correlation coefficients between the pollen curves confirm that several tree species (Halocarpus bidwillii, H. biformis and Phyllocladus alpinus), previously palynologically concealed within generic taxonomic groups, occurred about two degrees latitude further north and at a much lower altitude than their current limits during cooler or drier phases of the Last Glacial. A temperature depression in Northland of 4 °C at various times during the Last Glacial is inferred from these range expansions. Nevertheless, the persistence of widespread forest cover suggests that the late Pleistocene climate of Northland was less severe than for most of the rest of New Zealand and strengthens the argument for a heightened temperature gradient across northern New Zealand during the Last Glacial.

    View record details
  • Impact of tephra fall and environmental change: a 1000 year record from Matakana Island, Bay of Plenty, North Island, New Zealand.

    Giles, Teresa M.; Newnham, Rewi M.; Lowe, David J.; Munro, Adam J. (1999-01-01)

    Journal article
    University of Waikato

    Palynological evidence was used to determine the development of vegetation communities on Matakana Island, North Island, New Zealand, over the last 1000 radiocarbon years. The pollen record indicates that changes occurred in the vegetation immediately following fallout deposition of the Kaharoa Tephra approximately 100 km from source at c. 665 years BP. Such changes may be a direct response to the impact of tephra fall, although the possibility of anthropogenic disturbance cannot be discounted. As a result of the eruption some taxa (Leucopogon fasciculatus and Tupeia antarctica) became at least temporarily extinct from the area. Two phases of anthropogenic influence on the environment are recorded in the pollen record: Polynesian, followed by European inhabitation of the island, giving a detailed history of human influence in the area for the millennium.

    View record details
  • Globalization of tephrochronology: new views from Australasia

    Lowe, David J. (2008)

    Journal article
    University of Waikato

    Tephra (or volcanic ash) studies, once confined largely to volcanic lands, have become increasingly practised in countries far removed from areas of active or recent volcanism – and Australia is no exception. At the International Union for Quaternary Research (INQUA) conference in Cairns in July/August 2007, Sarah E. Coulter (née Davies), now a postdoctoral ice-core tephrochronologist at Queen’s University Belfast, reportedthe first occurrence of an exotic tephra in Australia in a core from Lynch’s Crater, Atherton Tableland, Queensland (Figure 1). The distal tephra, manifest as a tiny concentration of glass shards, was probably derived from a Papua New Guinean eruption around 75,000–80,000 years ago (S.E. Davies et al., 2007). Its value lies in providing a precise chronostratigraphic marker that potentially allows correlation of other long palaeoenvironmental sequences over wide distances. Davies’ study is but one of a revolutionary development in tephrochronology now focused on detecting diminutive, distal tephras that are invisible in the field and referred to as cryptotephras. From the Greek word kryptein, meaning ‘to hide’ (Hunt, 1999a; Hunt and Hill, 2001; Lowe and Hunt, 2001), cryptotephras typically comprise fine-ashsized (< ~100 μm) glass shards sparsely preserved and ‘hidden’ in peats or in lake, marine or aeolian sediments, or in ice cores (Figure 2). The cryptotephra theme is continued in section III, but beforehand nomenclature associated with the term ‘tephra’, which can be confusing and which sometimes is used incorrectly, is outlined.

    View record details
  • Towards rapid assay of cryptotephra in peat cores: review and evaluation of selected methods

    Gehrels, Maria J.; Newnham, Rewi M.; Lowe, David J.; Wynne, Shirley; Hazell, Zoë J.; Caseldine, Chris (2008-02)

    Journal article
    University of Waikato

    Peat bogs are highly effective archives for the preservation and detection of cryptotephra but the conventional methods used to detect these hidden, diminutive layers are destructive and can be time consuming. We briefly review methods that have been used for cryptotephra detection and evaluate the potential of a range of alternative reconnaissance methods, both non-destructive and destructive, to provide for more rapid examination of continuous cryptotephra content in peat cores. The techniques evaluated—magnetic susceptibility (MS), spectrophotometry, and X-ray fluorescence—are used to pick out compositional contrasts between tephra deposits and peat. Measurements of organic content are also evaluated as a potential guide to tephra content based on an inverse relationship. Although we find limitations to each method, particularly where deployed at the distal-most end of tephra dispersal, there is potential for all methods to be used in the detection of cryptotephra where time or material is limited. These methods can also provide additional sedimentological and stratigraphic information for studies of peat cores. However, where a reliable cryptotephra profile is required, we conclude that there is no quick or easy substitute for the conventional extraction-microscopy method.

    View record details
  • Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 years ago: a framework for NZ-INTIMATE

    Lowe, David J.; Shane, Phil A.R.; Alloway, Brent V.; Newnham, Rewi M. (2008-01)

    Journal article
    University of Waikato

    The role of tephras in the NZ-INTIMATE project is a critical one because most high-resolution palaeoclimatic records are linked and dated by one or more tephra layers. In this review, first we document eruptive, distributional, and compositional fingerprinting data, both mineralogical and geochemical, for 22 key marker tephras erupted since 30,000 years ago to facilitate their identification and correlation. We include new glass compositional data. The selected marker tephras comprise 10 from Taupo and nine from Okataina volcanoes (rhyolitic), one from Tuhua volcano (peralkaline rhyolitic), and one each from Tongariro and Egmont volcanoes (andesitic). Second, we use four approaches to develop 2σ-age models for the tephras (youngest to oldest): (1) calendar ages for Kaharoa and Taupo/Y were obtained by wiggle-matching log-derived tree-ring sequences dated by 14C; (2) Whakaipo/V was dated using an age–depth model from peat; (3) 14 tephras in the montane Kaipo peat sequence (Waimihia/S, Unit K, Whakatane, Tuhua, Mamaku, Rotoma, Opepe/E, Poronui/C, Karapiti/B, Okupata, Konini, Waiohau, Rotorua, Rerewhakaaitu) were dated by simultaneously wiggle-matching stratigraphic position and 51 independent 14C-age points against IntCal04 using Bayesian probability methods via both OxCal and Bpeat; and (4) the five oldest tephras, erupted before ca 18,000 cal. yr BP, were dated by calibrating limited numbers of 14C ages using IntCal04 (Okareka) or comparison curves of the expanded Cariaco Basin sequence (Te Rere, Kawakawa/Oruanui, Poihipi, Okaia). Kawakawa/Oruanui tephra, the most widely distributed marker tephra, was erupted probably ca 27,097±957 cal. yr BP. Potential dating approaches for the older tephras include their identification in Antarctic ice cores (if present) or annually laminated sediments for which robust calendar-age models have been constructed, high-precision AMS 14C dating on appropriate material from environmentally stable sites, systematic luminescence dating, or new radiometric techniques (e.g. U–Th/He) if suitable minerals are available and errors markedly reduced. Further application of Bayesian age-modelling to stratigraphic sequences of 14C ages, possibly augmented with luminescence ages, may help refine age models for pre-Holocene tephras with the largest errors. Finally, we discuss the critical role these marker tephras play in the ongoing construction of an event stratigraphy for the New Zealand region, which is a key objective of Australasian and Southern Hemisphere INTIMATE projects.

    View record details
  • Test of AMS 14C dating of pollen concentrates using tephrochronology

    Newnham, Rewi M.; Vandergoes, Marcus J.; Garnett, Mark H.; Lowe, David J.; Prior, Christine; Almond, Peter C. (2007-01)

    Journal article
    University of Waikato

    Previous attempts to radiocarbon date sediments >10 kyr from the high rainfall region of Westland, New Zealand, a critical location for investigation of interhemispheric patterns of climate change, have been problematic. This study, building on recent work by Vandergoes and Prior (2003), shows that AMS 14C dating of pollen concentrates has potential to provide more reliable ages than other sediment constituents, including plant macrofossils. The method was applied to sediments from three sites containing the 22.6k 14C yr Kawakawa Tephra, which provided an independent test of the 14C ages. Although some minor laboratory contamination was detected in tests on background standards, the modelled relationship between sample mass and measured 14C content permitted an appropriate correction to be determined. Improved pollen concentrations derived by density separation between 1.4 and 1.2 specific gravity and sieving in the range 10-50 m provided either older ages than other fractions of the same sample or, where in situ contamination was not evident, equivalent ages. Differences in degree of in situ contamination between depositional environments indicated that, in Westland, lake sites may be less susceptible to contamination by younger carbon than peat sites, where this process may be facilitated by root penetration into underlying sediments.

    View record details
  • Comparison of spatial prediction techniques for developing Pinus radiata productivity surfaces across New Zealand

    Palmer, David John; Hock, Barbara K.; Kimberley, Mark O.; Watt, Michael S.; Lowe, David J.; Payn, Tim W. (2009)

    Journal article
    University of Waikato

    Spatial interpolation is frequently used to predict values across a landscape enabling the spatial variation and patterns of a property to be quantified. Inverse distance weighting (IDW), ordinary kriging (OK), regression kriging (RK), and partial least squares (PLS) regression are interpolation techniques typically used where the region of interest's spatial extent is relatively small and observations are numerous and regularly spaced. In the current era of data ‘mining’ and utilisation of sparse data, the above criteria are not always fully met, increasing model uncertainties. Furthermore, regression modelling and kriging techniques require good judgement, experience, and expertise by the practitioner compared with IDW with its more rudimentary approach. In this study we compared spatial predictions derived from IDW, PLS, RK, and OK for Pinus radiata volume mean annual increment (referred to as 300 Index) and mean top height at age twenty (referred to as Site Index) across New Zealand using cross-validation techniques. Validation statistics (RMSE, ME, and R2) show that RK, OK, and IDW provided predictions that were less biased and of greater accuracy than PLS predictions. Standard deviation of rank (SDR) and mean rank (MR) validation statistics showed similar results with OK the most consistent (SDR) predictor, whereas RK had the lowest mean rank (MR), closely followed by IDW. However, the mean performance rankings for validation observations classified according to their distance to the nearest model data point indicate that although PLS provided the poorest predictions at relatively close separation distances (<2 km), in the medium range ( 4–8 km) performance was of similar ranking to that of the other techniques, and at greater separation distances PLS outperformed the other techniques. Maps illustrating the spatial variation of P. radiata forest productivity are provided.

    View record details
  • Stratigraphy and chronology of a 15ka sequence of multi-sourced silicic tephras in a montane peat bog, eastern North Island, New Zealand.

    Lowe, David J.; Newnham, Rewi M.; Ward, Chris M. (1999-12-01)

    Journal article
    University of Waikato

    We document the stratigraphy, composition, and chronology of a succession of 16 distal, silicic tephra layers interbedded with lateglacial and Holocene peats and muds up to c. 15 000 radiocarbon years (c. 18 000 calendar years) old at a montane site (Kaipo Bog) in eastern North Island, New Zealand. Aged from 665 +/- 15 to 14 700 +/- 95 14C yr BP, the tephras are derived from six volcanic centres in North Island, three of which are rhyolitic (Okataina, Taupo, Maroa), one peralkaline (Tuhua), and two andesitic (Tongariro, Egmont). Correlations are based on multiple criteria: field properties and stratigraphic interrelationships, ferromagnesian silicate mineral assemblages, glass-shard major element composition (from electron microprobe analysis), and radiocarbon dating. We extend the known distribution of tephras in eastern North Island and provide compositional data that add to their potential usefulness as isochronous markers. The chronostratigraphic framework established for the Kaipo sequence, based on both site-specific and independently derived tephra-based radiocarbon ages, provides the basis for fine-resolution paleoenvironmental studies at a climatically sensitive terrestrial site from the mid latitudes of the Southern Hemisphere. Tephras identified as especially useful paleoenvironmental markers include Rerewhakaaitu and Waiohau (lateglacial), Konini (lateglacial-early Holocene), Tuhua (middle Holocene), and Taupo and Kaharoa (late Holocene).

    View record details