Agathis Research Articles

Dissolved and particulate carbon and nitrogen fluxes along a Phytophthora agathidicida infection gradient in a kauri (Agathis australis) dominated forest

Abstract Kauri dieback, caused by Phytophthora agathidicida, is an emergent threat to the ecologically unique and carbon-rich kauri (Agathis australis) forests in New Zealand. Our main aim was to assess the effect of kauri dieback on canopy and forest floor dissolved and particulate carbon (C) and nitrogen (N) fluxes. Throughfall and stemflow collectors and free-draining lysimeters were deployed underneath the canopy of ten kauri trees differing in their soil P. agathidicida DNA concentration and visual health status and sampled weekly to monthly over 1 y. Throughfall and forest floor dissolved C and N fluxes decreased significantly with increasing soil P. agathidicida DNA concentration which may be related to changes in leaf chemistry, leachable kauri leaf surface area and uptake of N by the understory vegetation. The observed alteration in dissolved and particulate C and N fluxes under P. agathidicida infected kauri trees could lead to long-term changes in biogeochemical processes (e.g. mineralization, nutrient availability) in these ecologically unique kauri forests.

IDENTIFYING AND QUANTIFYING TREE-RING CHRONOLOGY VARIANCE ARTEFACTS RELATED TO CO-OCCURRING CHANGES IN GROWTH RATE

Expectations that a warming world will be associated with more hydro-climatological extremes has motivated research exploring if an associated signal is evident in paleoclimate archives. Tree-ring chronologies are central to this work because of their high temporal resolution, but they are also potentially compromised by variance artefacts associated with the evolving composition of the chronology and with data processing. Here we present two empirical methods to identify and quantify potential artefacts related specifically to temporally varying growth rate (local level, LL): LL-based partitioning analysis and LL-based chronology stripping. The two methods were developed and tested using a multi-site New Zealand kauri (Agathis australis) living-tree data set. Our results show that the methods are complementary in terms of artefact identification and quantification, and that they can provide useful insight into causal processes when used conjointly. Our results also indicate that data pre-processing to remove LL-related artefacts may be sub-optimal, that there may be an optimal standardization that minimizes bias, and that the evolving variance of kauri master chronologies over the last 500 years is not significantly affected by LL-related artefacts.

Hydraulic Coupling of a Leafless Kauri Tree Remnant to Conspecific Hosts.

SummaryTrees are commonly regarded as distinct entities, but the roots of many species fuse to form natural root grafts allowing the exchange of water, carbon, mineral nutrients, and microorganisms between individuals. Exploiting the phenomenon of leafless (photosynthetically inactive) tree remnants being kept alive by conspecifics, we show tight physiological coupling of a living kauri (Agathis australis) stump to conspecific neighbors. The trunk remnant displayed greatly reduced, inverted daily sap flow patterns compared with intact kauri trees. Its stem water potential showed strong diel variation with minima during daytime and maxima at night, coinciding with peak and minimal sap flow rates in neighbors, respectively. Sudden atmospherically driven changes in water relations in adjacent kauri trees were very rapidly and inversely mirrored in the living stump's water status. Such intimate hydrological coupling suggests a “communal physiology” among (conspecific) trees with far-reaching implications for our understanding of forest functioning, particularly under water shortage.

Dendroprovenancing: A preliminary assessment of potential to geo-locate kauri timbers in northern New Zealand

After 1840, New Zealand kauri (Agathis australis) became the focus of a large-scale timber industry in the upper North Island, which converted trees into timber that was then used in construction. Cities such as Auckland and Wellington relied on importing kauri to meet local demand for construction and other uses. Kauri timbers from buildings and in-ground features, mostly in Auckland city, have been collected for tree-dating and master chronology development. Although the use of timber at archaeological sites is understood, the geographic origin of the timber from within the natural range of kauri (north of 38 °S) is largely unknown. This limits interpretation of archaeological wood and constrains use of the tree-ring data in dendroclimatology. In this paper, we consider the potential to provenance kauri timbers used in 19th and early 20th century New Zealand buildings, using a combination of documentary sources, t-value mapping, and refined statistical matching using spatial patterns of correlations. Analysis of documentary sources for a test period of 1861–1865 CE indicates that there is sufficient information about the kauri timber industry to provide a geographic context for provenancing kauri in the upper North Island. The use of t-values for provenancing may be confounded by the relatively small size of the kauri growth region and a lack of sufficient spatial differentiation in growth patterns between the sub-regions. However, a new approach of using indexed residual chronologies and field correlations has promise for geo-locating timber in a relatively small region. The research highlights the value of establishing kauri provenance to New Zealand dendroclimatology, dendroarchaeology and environmental history.

Land‐use changes influence the sporulation and survival of Phytophthora agathidicida, a lethal pathogen of New Zealand kauri (Agathis australis)

AbstractPhytophthora agathidicida is the accepted causal agent of dieback in remnant stands of long‐lived indigenous New Zealand kauri (Agathis australis) and poses a significant threat to the long‐term survival of this species. Little is known about the effect of key soil physicochemical characteristics on the growth of P. agathidicida. In this study, we investigated the growth of P. agathidicida in soils collected from adjacent areas under original kauri forest, short rotation pine (Pinus radiata) plantation forest and grazed pastures. A growth response assay was used to quantify asexual (sporangia) and sexual (oospore) spore counts over 8 days in soils sampled from each land‐use. Significantly higher numbers of sporangia (p < 0.001) and oospores (p < 0.01) were found in pasture and pine forest soil within 2 days of the growth assay trials, suggesting these soils may favour asexual/sexual reproduction in the early stages of P. agathidicida establishment compared to kauri forest soils. Additionally, oospore production significantly increased over 8 days in pine forest soil, suggesting that with an increase in inoculum loads, these soils potentially act as pathogen reservoirs. The soil physicochemical properties (e.g., pH, C and N, phosphorus content and electrical conductivity) investigated in this study did not significantly correspond to spore count data between land‐uses, suggesting that differences in growth response are driven by other edaphic factors not explored in the present study.

Stem water storage of New Zealand kauri (Agathis australis)

The southern conifer Agathis australis (kauri) is one of the largest trees in the world. Due to their large sapwood volume, we expect that some transpired water originates from storage. The discharge of stored water can buffer daily fluctuations of xylem tension and decrease the risk of hydraulic failure, providing hydraulic safety in times of low soil moisture. To examine the amount and diurnal patterns of stored water use, we measured sap flow at the base and the top of the stem simultaneously. The withdrawal of stored water was calculated by comparing integrated flows. We also installed point dendrometers at the same positions and on smaller branches within the canopy. Time lags of flows and radius changes were investigated by cross correlation analysis. On average 10 to 13% of transpiration was withdrawn from stem water storage during well-watered conditions. We observed time lags of up to 60 min between the base and top of the stem and up to 90 min between base and smaller branches of the spreading crown, indicating that branches also serve as water storage compartments. Analysis of radius changes over five months showed evidence for stem water storage maintaining hydraulic integrity under dryer conditions, as the stem of one tree showed greater relative depletion/shrinkage than the top of the stem or the branches.

Holocene temperature, humidity and seasonality in northern New Zealand linked to Southern Hemisphere summer insolation

The Holocene thermal maximum (HTM) is a spatio-temporally variable period of generally warmer conditions during the early and middle Holocene that is often used as an analogue for future climate change. Global scale climate reconstructions and models tend to smooth out the variations and complexity of the HTM and inconsistencies between reconstructions from different locations and proxies are often attributed to bias arising from different locations or proxies. We use these differences as a source of information about seasonality and precipitation during the Holocene in a multi-proxy investigation of the sediments of Lake Pupuke, northern New Zealand. The sediments, spanning the last 16 kyr, were analysed for pollen, from which mean annual air temperatures (MAAT) and effective precipitation were estimated, and chironomids, from which summer air temperature (SmT) was estimated. We found no evidence for an HTM in the MAAT reconstruction, questioning the validity of treating the early-to-mid Holocene as an analogue for future climate change in northern New Zealand. SmT increases between 10 and 3 cal kyr BP, correlating strongly with integrated local summer insolation. Early-Holocene low seasonality (from 12 to 9.3 cal kyr BP) was likely driven by low local summer insolation intensity. An early-to-mid-Holocene wet period (9.6–7.5 cal kyr BP) corresponds to relatively high southern westerly wind (SWW) strength. Mid-to-late-Holocene summers following the wet period were hot and dry, especially 4.0–2.4 cal kyr BP, allowing the tall conifer, kauri (Agathis australis) to expand throughout northern New Zealand. Low effective precipitation at this time is consistent with increased evapotranspiration due to higher SmT, although reduced precipitation due to southward displaced SWW or increased El Niño frequency may also have contributed.

Biomass and root attributes of eight of New Zealand\u2019s most common indigenous evergreen conifer and broadleaved forest species during the first 5\xa0years of establishment

BackgroundTree allometric equations are critical tools for determining tree volume, biomass and carbon stocks. However, there is a lack of species-specific biomass equations for juvenile trees of many of New Zealand’s indigenous species. The aim of this study was to provide allometric equations for total above- and below-ground biomass and total root biomass and length for eight common evergreen conifer and broadleaved species.MethodsIn a plot-based field trial, growth metrics of conifers Prumnopitys taxifolia (matai), Agathis australis (kauri), Prumnopitys ferruginea (miro), Podocarpus totara (totara), Dacrycarpus dacrydioides (kahikatea) and Dacrydium cupressinum (rimu) and broadleaved species Alectryon excelsus (titoki) and Vitex lucens (puriri) were measured annually. These species were selected based on their potential role as a long-term solution for mitigating erosion in areas of marginal land proposed for new afforestation/reforestation and as an important carbon (C) sink.ResultsRoot collar diameter (RCD) provided the best fit for tree height, total above-ground biomass (AGB) and total below-ground biomass (BGB), and all regressions were highly significant (P = 0.001). Most species showed significant increases in annual growth and, by year 5, the BGB ranged between 21 and 42% of total biomass and decreased with increasing plant age. Of the conifers, Podocarpus totara had the greatest mean maximum root spread (2.2 m) exceeded only by the broadleaved Vitex lucens (2.5 m). For all species, and in each year of the trial, 100% of the BGB remained confined to within 0.5 m of the ground surface. With the exception of Vitex lucens and Podocarpus totara, > 90% of the total root length remained within a 0.5-m radius of the root bole. The species-specific mean tree biomass of 5-year-old plants ranged from 0.32 to 4.28 kg plant−1. A mixed-species forest established at 1000 stems per hectare (spha), consisting of 200 of each of the best performed of the trialled species, would amass ~ 2.3 t ha−1 of biomass and a forest carbon stock of 3.8 t CO2 ha−1 within 5 years.ConclusionsInter-species differences in the allocation of BGB and AGB appeared to be age dependent. The root-growth metrics of these common indigenous forest species, as candidates for erosion control, have improved our understanding of their potential usefulness for stabilising marginal land. Whole-plant biomass of juvenile trees will greatly improve the accuracy of current estimates of forest carbon stocks for proposed new areas of indigenous afforestation/reforestation.

In vitro assays of Phytophthora agathidicida on kauri leaves suggest variability in pathogen virulence and host response

Phytophthora agathidicida is an aggressive soil-borne oomycete pathogen that kills New Zealand kauri trees (Agathis australis). When artificially inoculated, P. agathidicida causes lesions on leaves as well as roots, providing a non-invasive method for virulence screening. However, little is known about the extents to which the pathogen varies in virulence and kauri trees vary in disease susceptibility. Three isolates of P. agathidicida grown in culture were inoculated onto detached leaves from six kauri trees. Visible disease lesions were measured and the extent of asymptomatic leaf colonisation determined by culturing. All six trees were susceptible to P. agathidicida, but one showed higher susceptibility than the others. The pathogen also showed variability in virulence among isolates. Asymptomatic colonisation of leaf tissue was also found, suggesting a latent or biotrophic phase for the pathogen. Although further work is needed, the variability of both pathogen virulence and host susceptibility have important implications for management of kauri dieback. Furthermore, asymptomatic colonisation of kauri tissues suggests that P. agathidicida could be present outside of regions with visible disease symptoms.

The scientific value and potential of New Zealand swamp kauri

New Zealand swamp kauri (Agathis australis) are relic trees that have been buried and preserved in anoxic bog environments of northern New Zealand for centuries through to hundreds of millennia. Kauri are massive in proportion to other native New Zealand trees and they can attain ages greater than 1000 years. The export market for swamp (subfossil) kauri has recently been driven by demand for a high-value workable timber, but there are concerns about the sustainability of the remaining resource, a situation exacerbated in recent years by the rapid extraction of wood. Economic exploitation of swamp kauri presents several unique opportunities for Quaternary science, however the scientific value of this wood is not well understood by the wider research community and public. Here, we summarise the history of scientific research on swamp kauri, and explore the considerable potential of this unique resource. Swamp kauri tree-ring chronologies are temporally unique, and secondary analyses (such as radiocarbon and isotopic analyses) have value for improving our understanding of Earth's recent geologic history and pre-instrumental climate history. Swamp kauri deposits that span the last interglacial-glacial cycle show potential to yield “ultra-long” multi-millennia tree-ring chronologies, and composite records spanning large parts of MIS3 (and most of the Holocene) may be possible. High-precision radiocarbon dating of swamp kauri chronologies can improve the resolution of the global radiocarbon calibration curve, while testing age modelling and chronologic alignment of other independent long-term high-resolution proxy records. Swamp kauri also has the potential to facilitate absolute dating and verification of cosmogenic events found in long Northern Hemisphere tree-ring chronologies. Future efforts to conserve these identified values requires scientists to work closely with swamp kauri industry operators, resource consent authorities, and export regulators to mitigate potential losses to science as this precious material is progressively extracted from the ground and utilized.

Assessing the potential to calendar date Māori waka (canoes) using dendrochronology

The short (c. 750year) span of human occupation in Aotearoa New Zealand and imprecision of archaeological dating techniques available, presents particular challenges when investigating societal and technological change and continuity during the pre-European and early historic periods. Currently, radiocarbon (14C) dating is used to determine the age of archaeological artefacts and/or sites but variations in atmospheric radiocarbon can affect the precision of calibrated dates resulting in broad age ranges for artefacts. This paper assesses the potential of dendrochronology to accurately and precisely date Māori artefacts, which would securely place them in a temporal context, enhancing understanding of manufacturing, provenance, and changes in style. Two kauri (Agathis australis) canoes (waka) recovered from waterlogged deposits in the Waikato River Delta and at Muriwai Beach, west Auckland, and currently undergoing conservation, were sampled for tree-ring dating. The ring width series were too short (<40 rings) for crossdating, however, the work described here has been valuable to informing processes regarding sampling and in highlighting the potential of tree-ring analysis to contribute meaningfully to understanding of these culturally and spiritually significant taonga.

Modeling the effects of tree species and incubation temperature on soil's extracellular enzyme activity in 78-year-old tree plantations

Abstract. Forest plantations have been widely used as an effective measure for increasing soil carbon (C), and nitrogen (N) stocks and soil enzyme activities play a key role in soil C and N losses during decomposition of soil organic matter. However, few studies have been carried out to elucidate the mechanisms behind the differences in soil C and N cycling by different tree species in response to climate warming. Here, we measured the responses of soil's extracellular enzyme activity (EEA) to a gradient of temperatures using incubation methods in 78-year-old forest plantations with different tree species. Based on a soil enzyme kinetics model, we established a new statistical model to investigate the effects of temperature and tree species on soil EEA. In addition, we established a tree species–enzyme–C∕N model to investigate how temperature and tree species influence soil C∕N contents over time without considering plant C inputs. These extracellular enzymes included C acquisition enzymes (β-glucosidase, BG), N acquisition enzymes (N-acetylglucosaminidase, NAG; leucine aminopeptidase, LAP) and phosphorus acquisition enzymes (acid phosphatases). The results showed that incubation temperature and tree species significantly influenced all soil EEA and Eucalyptus had 1.01–2.86 times higher soil EEA than coniferous tree species. Modeling showed that Eucalyptus had larger soil C losses but had 0.99–2.38 times longer soil C residence time than the coniferous tree species over time. The differences in the residual soil C and N contents between Eucalyptus and coniferous tree species, as well as between slash pine (Pinus elliottii Engelm. var. elliottii) and hoop pine (Araucaria cunninghamii Ait.), increase with time. On the other hand, the modeling results help explain why exotic slash pine can grow faster, as it has 1.22–1.38 times longer residual soil N residence time for LAP, which mediate soil N cycling in the long term, than native coniferous tree species like hoop pine and kauri pine (Agathis robusta C. Moore). Our results will be helpful for understanding the mechanisms of soil C and N cycling by different tree species, which will have implications for forest management.

Rapid global ocean-atmosphere response to Southern Ocean freshening during the last glacial

Contrasting Greenland and Antarctic temperatures during the last glacial period (115,000 to 11,650 years ago) are thought to have been driven by imbalances in the rates of formation of North Atlantic and Antarctic Deep Water (the ‘bipolar seesaw’). Here we exploit a bidecadally resolved 14C data set obtained from New Zealand kauri (Agathis australis) to undertake high-precision alignment of key climate data sets spanning iceberg-rafted debris event Heinrich 3 and Greenland Interstadial (GI) 5.1 in the North Atlantic (~30,400 to 28,400 years ago). We observe no divergence between the kauri and Atlantic marine sediment 14C data sets, implying limited changes in deep water formation. However, a Southern Ocean (Atlantic-sector) iceberg rafted debris event appears to have occurred synchronously with GI-5.1 warming and decreased precipitation over the western equatorial Pacific and Atlantic. An ensemble of transient meltwater simulations shows that Antarctic-sourced salinity anomalies can generate climate changes that are propagated globally via an atmospheric Rossby wave train.

Vertical distribution of soil extractable organic C and N contents and total C and N stocks in 78-year-old tree plantations in subtropical Australia.

Few studies have focused on the effects of long-term forest plantations on the soil profile of carbon (C) and nitrogen (N) stocks. In this study, we selected 78-year-old tree plantations that included three coniferous tree species (i.e., slash pine, hoop pine and kauri pine) and a Eucalyptus species in subtropical Australia. We measured soil extractable organic C (EOC) and N (EON) contents and total C and N stocks under different tree species on the forest floor and along a soil profile to 100cm depth. The results showed that Eucalyptus had significantly higher soil EOC contents (3.3Mgha-1) than the other tree species (EOC of 1.9-2.3Mgha-1) and had significantly higher EON (156kgha-1) contents than slash pine (107kgha-1). Eucalyptus had significantly higher soil C (58.9Mgha-1) and N (2.03Mgha-1) stocks than the other tree species (22.3-27.6MgCha-1 and 0.71-1.23MgNha-1) at 0-100cm depth. There were no differences in soil C stocks at the 0-100cm depth among the coniferous tree species. Forest floor C stocks had stronger effects on mineral soil total N stocks than fine root biomass, whereas fine root biomass exerted stronger effects on soil total C stocks at the 0-100cm depth than forest floor C and N stocks. Our results addressed large differences in soil C and N stocks under different tree species, which can provide useful information for local forest management practices in this region.

Identification of selected CITES-protected Araucariaceae using DART TOFMS

Determining the species source of logs and planks suspected of being Araucaria araucana (Molina) K.Koch (CITES Appendix I) using traditional wood anatomy has been difficult, because its anatomical features are not diagnostic. Additionally, anatomical studies of Araucaria angustifolia (Bertol.) Kuntze, Araucaria heterophylla (Salisb.) Franco, Agathis australis (D.Don) Lindl., and Wollemia nobilis W.G.Jones, K.D.Hill &amp; J.M.Allen have reported that these taxa have similar and indistinguishable anatomical characters from A. araucana. Transnational shipments of illegal timber obscure their geographic provenance, and therefore identification using wood anatomy alone is insufficient in a criminal proceeding. In this study we examine the macroscopic appearance of selected members of the Araucariaceae and investigate whether analysis of heartwood chemotypes using Direct Analysis in Real Time (DART) Time-of-Flight Mass Spectrometry (TOFMS) is useful for making species determinations. DART TOFMS data were collected from 5 species (n =75 spectra). The spectra were analyzsed statistically using supervised and unsupervised classification algorithms. Results indicate that A. araucana can be distinguished from the look-alike taxa. Another statistical inference of the data suggests that Wollemia nobilis is more similar and within the same clade as Agathis australis. We conclude that DART TOFMS spectra can help in making species determination of the Araucariaceae even when the geographic provenance is unknown.

Soil microbial community structure and diversity are largely influenced by soil pH and nutrient quality in 78-year-old tree plantations

Abstract. Forest plantations have been recognised as a key strategy management tool for stocking carbon (C) in soils, thereby contributing to climate warming mitigation. However, long-term ecological consequences of anthropogenic forest plantations on the community structure and diversity of soil microorganisms and the underlying mechanisms in determining these patterns are poorly understood. In this study, we selected 78-year-old tree plantations that included three coniferous tree species (i.e. slash pine, hoop pine and kauri pine) and a eucalypt species in subtropical Australia. We investigated the patterns of community structure, and the diversity of soil bacteria and eukaryotes by using high-throughput sequencing of 16S rRNA and 18S rRNA genes. We also measured the potential methane oxidation capacity under different tree species. The results showed that slash pine and Eucalyptus significantly increased the dominant taxa of bacterial Acidobacteria and the dominant taxa of eukaryotic Ascomycota, and formed clusters of soil bacterial and eukaryotic communities, which were clearly different from the clusters under hoop pine and kauri pine. Soil pH and nutrient quality indicators such as C : nitrogen (N) and extractable organic C : extractable organic N were key factors in determining the patterns of soil bacterial and eukaryotic communities between the different tree species treatments. Slash pine and Eucalyptus had significantly lower soil bacterial and eukaryotic operational taxonomical unit numbers and lower diversity indices than kauri pine and hoop pine. A key factor limitation hypothesis was introduced, which gives a reasonable explanation for lower diversity indices under slash pine and Eucalyptus. In addition, slash pine and Eucalyptus had a higher soil methane oxidation capacity than the other tree species. These results suggest that significant changes in soil microbial communities may occur in response to chronic disturbance by tree plantations, and highlight the importance of soil pH and physiochemical characteristics in microbially mediated ecological processes in forested soils.

Sustained carbon uptake in a mixed age southern conifer forest

Larger trees accumulate more carbon but have lower growth rates per unit biomass. Nevertheless, large trees are a vital part of the carbon cycle of this mixed age forest. Globally, there is a strong need for detailed information on carbon (C) budgets of native forests, yet New Zealand forests are underrepresented in C inventories. Stem growth and CO2 efflux are two of the major components of forest C budgets, especially in forests with long-lived, large trees. In this paper, we present a breakdown of tree-level C accumulation rates for 26 trees [9.7–176 cm diameter at breast height (DBH)] of one of the world’s largest tree species: the endemic conifer kauri (Agathis australis) over 3 years (2010–2013) in west Auckland. We examined the relationship between C accumulation, tree size, and canopy class (dominant, co-dominant, and intermediate). The total amount of C accumulated was 2.7, 3.5, and 4.2 Mg C ha−2 year−1 in 2011, 2012, and 2013, respectively. Large trees (>70 cm DBH) had the fastest absolute rates of growth (basal area increment; 30–140 cm2 year−1) and C accumulation (0.01–0.048 Mg C year−1), but the lowest rates of relative growth (per unit biomass). Relative growth rates peaked at a diameter at breast height of 25 cm, and consequently, co-dominant trees had the highest annual relative growth rates (1.7–2.2% year−1). The majority of C was accumulated in co-dominant trees (62%), with smaller amounts accumulated in dominant (29%) and intermediate trees (9%). One-third of the stand’s C accumulation was accrued by the largest 6% of trees, which made up 46% of the stand’s basal area. While maintenance and growth respiration rates were higher for larger trees, C use efficiency (CUE) was consistent across tree-size classes. To extend the size of trees analysed, we included data from tree-ring analysis of 13 additional trees up to 243 cm DBH and found larger trees accumulated proportionally less C per unit biomass than smaller trees.

Kakapo habitat selection on Hauturu-o-toi in relation to plant phenology

Kakapo (Strigops habroptilus) breed only when certain gymnosperm species produce unusually abundant mast seed crops, events that can occur up to 5 years apart. Kakapo were first translocated to the offshore island refuge of Hauturu-o-toi (Little Barrier Island) in 1982. Despite the absence of known breeding triggers, several breeding attempts did occur prior to the birds’ removal in 1999. Although kakapo were reintroduced to Hauturu in 2012, the question of what triggers them to breed there remains a mystery. This paper re-examines unanalysed datasets to explore the link between kakapo habitat selection and plant phenology patterns on Hauturu during the 1990s. By comparing plant phenology with breeding attempts, we provide insights into potential breeding triggers, and the potential future of Hauturu as a sustainable refuge. We also provide an account of plant phenology patterns occurring on Hauturu. Resource selection ratios were calculated to determine habitat selection preferences using kakapo location data and a vegetation map of Hauturu. Analysis of plant phenology within preferred habitats was then undertaken to determine potential breeding triggers using a dataset of over 70 plant species collected from 1991-1995. Female kakapo that attempted to breed on Hauturu preferred Agathis australis (kauri) dominated vegetation to any other vegetation type. Phenology patterns coincided with kakapo breeding attempts, and attempted breeding years on Hauturu were years with high A. australis female cone abundance. The association between A. australis and breeding suggests that A. australis cone production could trigger kakapo breeding on Hauturu. With an increasing kakapo population and a limited number of suitable refuges, understanding the potential reproductive productivity of kakapo on Hauturu will be vital for their future management and recovery.

Changes in El Niño – Southern Oscillation (ENSO) conditions during the Greenland Stadial 1 (GS-1) chronozone revealed by New Zealand tree-rings

The warming trend at the end of the last glacial was disrupted by rapid cooling clearly identified in Greenland (Greenland Stadial 1 or GS-1) and Europe (Younger Dryas Stadial or YD). This reversal to glacial-like conditions is one of the best known examples of abrupt change but the exact timing and global spatial extent remain uncertain. Whilst the wider Atlantic region has a network of high-resolution proxy records spanning GS-1, the Pacific Ocean suffers from a scarcity of sub-decadally resolved sequences. Here we report the results from an investigation into a tree-ring chronology from northern New Zealand aimed at addressing the paucity of data. The conifer tree species kauri (Agathis australis) is known from contemporary studies to be sensitive to regional climate changes. An analysis of a ‘historic’ 452-year kauri chronology confirms a tropical-Pacific teleconnection via the El Nino – Southern Oscillation (ENSO). We then focus our study on a 1010-year sub-fossil kauri chronology that has been precisely dated by comprehensive radiocarbon dating and contains a striking ring-width downturn between ∼12,500 and 12,380 cal BP within GS-1. Wavelet analysis shows a marked increase in ENSO-like periodicities occurring after the downturn event. Comparison to low- and mid-latitude Pacific records suggests a coherency with ENSO and Southern Hemisphere atmospheric circulation change during this period. The driver(s) for this climate event remain unclear but may be related to solar changes that subsequently led to establishment and/or increased expression of ENSO across the mid-latitudes of the Pacific, seemingly independent of the Atlantic and polar regions.

Leaf age-related and diurnal variation in gas exchange of kauri (Agathis australis)

ABSTRACTNew Zealand kauri (Agathis australis) (D.Don) Lindl. is a large and long-lived tree species endemic to the species-rich forests of the north of the North Island. Agathis australis are culturally and ecologically significant, but little is known about their ecophysiology. In particular, environmental drivers of fluxes of carbon and water for A. australis trees have not been quantified. We measured leaf gas exchange to explore the effect of leaf age, tree size, foliar nitrogen concentration, photosynthetically active radiation (PAR) and vapour pressure deficit (D) on assimilation rates (A) and stomatal conductance (gs). We also measured carbon isotope discrimination of leaves and applied an optimal stomatal behaviour model. Both gs and A were highest for year one leaves (130 mmol m−2 s−1 and 5 μmol m−2 s−1, respectively) then declined with leaf age to < 80 mmol m−2 s−1 and < 3 μmol m−2 s−1, respectively, in 4–5-year-old leaves. Instantaneous water use efficiency (A/gs) was highly variable, but there was no leaf age-related pattern. Our diurnal results indicate that A. australis gs peaks early in the day (before 0900 h at 250 mmol m−2 s−1) and A is comparatively low, remaining below 9 μmol m−2 s−1 throughout the day. Overall, water use efficiency is low based on intrinsic water use efficiency and the stomatal model. Isotopic analysis indicated moderate water use efficiency over the life of leaves compared to other temperate conifers. This information is valuable for modelling carbon and water fluxes of A. australis and for improving our understanding of the threat of summer droughts to these forest giants.