Agathis Research Articles

Soil CO<sub>2</sub> efflux in an old-growth southern conifer forest (<i>Agathis australis</i>) – magnitude, components and controls

Abstract. Total soil CO2 efflux and its component fluxes, autotrophic and heterotrophic respiration, were measured in a native forest in northern Aotearoa–New Zealand. The forest is dominated by Agathis australis (kauri) and is on an acidic, clay rich soil. Soil CO2 efflux, volumetric soil water content and soil temperature were measured bi-weekly to monthly at 72 sampling points over 18 months. Trenching and regression analysis was used to partition total soil CO2 efflux into heterotrophic and autotrophic respiration. The effect of tree structure was investigated by calculating an index of local contribution (Ic, based on tree size and distance to the measurement location) followed by correlation analysis between Ic and total soil CO2 efflux, root biomass, litterfall and soil characteristics. The measured mean total soil CO2 efflux was 3.47 µmol m−2 s−1. Autotrophic respiration accounted for 25 % (trenching) or 28 % (regression analysis) of total soil CO2 efflux. Using uni- and bivariate models showed that soil temperature was a poor predictor of the temporal variation in total soil CO2 efflux (< 20 %). In contrast, a stronger temperature sensitivity was found for heterotrophic respiration (around 47 %). We found significant positive relationships between kauri tree size (Ic) and total soil CO2 efflux, root biomass and mineral soil CN ratio within 5–6 m of the sampling points. Using multiple regression analysis revealed that 97 % of the spatial variability in total soil CO2 efflux in this kauri-dominated stand was explained by root biomass and soil temperature. Our findings suggest that biotic factors such as tree structure should be investigated in soil carbon related studies.

Stable oxygen isotope signatures of early season wood in New Zealand kauri (Agathis australis) tree rings: Prospects for palaeoclimate reconstruction

One of the longest Southern Hemisphere tree ring chronologies that has potential to provide past climate reconstructions has been produced using New Zealand kauri (Agathis australis). Work to date on kauri has been limited to reconstructions from whole-ring width analysis. In this study, we present the first replicated stable oxygen isotopic composition of early season alpha-cellulose from calendar-dated kauri tree rings within the natural growth range of the species. We also use newly established kauri physiology information about stomatal conductance and a mechanistic model to place initial interpretations on kauri δ18O signatures.Kauri early season δ18O has a range from 26 to 34‰ (V-SMOW) for a site located at Lower Huia Dam in west Auckland, and the mean δ18O chronology from that site is significantly correlated (p<0.05) to October-December vapor pressure, May-December relative humidity and other associated hydroclimatic variables. The observed statistical relationships are consistent with mechanistic δ18O simulations using the forward model of Barbour et al. (2004) that incorporates a leaf temperature energy balance model to calculate transpiration as forced with local meteorological variables and a range of physiological parameters. The correlation results and mechanistic model simulations suggest kauri δ18O early season wood has the potential to provide new quantitative past climate information for northern New Zealand, and also complement whole ring-width reconstructions of past regional climate variability – a component of which is previously established as sensitive to El Niño-Southern Oscillation activity. Additional work is required to determine whether the observed relationships are consistent across the growth range of kauri and what the optimum sample depth is before long isotope-based palaeoclimate reconstructions from modern and sub-fossil kauri sites are undertaken.

The origins of New Zealand’s first government house

SUMMARY: In 1842 the former first government house located at Okiato, New Zealand, burnt to the ground and the site was abandoned. A well on the site was excavated in 1994–95, revealing a base layer of burnt timbers, a Maori digging stick and ceramic sherds with an estimated manufacture date range of 1823–41. We argue that this deposit is derived from the 1842 destruction of the Okiato government house building. An analysis of the wood identified kauri (Agathis australis) and kahikatea (Dacrycarpus dacrydioides), confirming that the building was not a prefabricated imported structure, but rather was constructed on site from locally available timber.

Punctuated Shutdown of Atlantic Meridional Overturning Circulation during Greenland Stadial 1.

The Greenland Stadial 1 (GS-1; ~12.9 to 11.65 kyr cal BP) was a period of North Atlantic cooling, thought to have been initiated by North America fresh water runoff that caused a sustained reduction of North Atlantic Meridional Overturning Circulation (AMOC), resulting in an antiphase temperature response between the hemispheres (the ‘bipolar seesaw’). Here we exploit sub-fossil New Zealand kauri trees to report the first securely dated, decadally-resolved atmospheric radiocarbon (14C) record spanning GS-1. By precisely aligning Southern and Northern Hemisphere tree-ring 14C records with marine 14C sequences we document two relatively short periods of AMOC collapse during the stadial, at ~12,920-12,640 cal BP and 12,050-11,900 cal BP. In addition, our data show that the interhemispheric atmospheric 14C offset was close to zero prior to GS-1, before reaching ‘near-modern’ values at ~12,660 cal BP, consistent with synchronous recovery of overturning in both hemispheres and increased Southern Ocean ventilation. Hence, sustained North Atlantic cooling across GS-1 was not driven by a prolonged AMOC reduction but probably due to an equatorward migration of the Polar Front, reducing the advection of southwesterly air masses to high latitudes. Our findings suggest opposing hemispheric temperature trends were driven by atmospheric teleconnections, rather than AMOC changes.

Dendrochronological dating of kauri timbers from Browne's spar station (1832–1836), Mahurangi, Auckland, New Zealand

In New Zealand, timbers and other wooden objects have been found preserved in waterlogged prehistoric and historic-era archaeological sites, but dendrochronological analysis of such material is rare. In 2010 an archaeological investigation was carried out at the site of Browne's spar station, Mahurangi, Auckland (CE 1832–1836), documented as the earliest European settlement in the Auckland region. The station supplied spars to the British Admiralty and sawn timber to the Australian colonies. Timber features, made of kauri (Agathis australis), were present on the foreshore and included relics from a possible sawpit structure and a catwalk made from offcuts. Tree-ring samples were obtained from these to determine if they were associated with the spar station or from a later phase of activity. A four-timber tree-ring chronology was calendar dated to CE 1756–1831 and felling dates were obtained from three timbers. These indicated that: (a) the possible sawpit structure was built from trees felled between May and October 1832; (b) two offcuts used in the catwalk were from trees felled in late 1832 or early 1833; and (c) the catwalk was built in or after 1833. The tree-ring dates provide independent evidence that the timbers were contemporaneous with, and complement documentary information related to, the spar station. Analysis of wood samples also provides some insight into human behaviour regarding tree selection and the use of waste material. The spar station material is only the second waterlogged assemblage of kauri timbers to be analysed using dendrochronology in New Zealand and the first to be recovered from an inter-tidal context. The results demonstrate the potential for tree-ring analysis of waterlogged wood to provide accurate and precise dates for archaeological sites in New Zealand.

Visualizing the early infection of Agathis australis by Phytophthora agathidicida, using microscopy and fluorescent in situ hybridization

SummaryPhytophthora agathidicida (PTA) causes a root rot and collar rot of New Zealand kauri (Agathis australis). This study developed techniques to visualize early infection of kauri by PTA in deliberately inoculated seedlings. Conventional light microscopy was carried out on cleared and stained roots using trypan blue to observe PTA structures. Additionally, scanning electron microscopy (SEM) was used to study the PTA root structures at a higher resolution. A fluorescent in situ hybridization assay (FISH) was developed using a PTA‐specific probe to label PTA structures in planta. Infection progression in roots of 2‐year‐old kauri inoculated with PTA at 5, 10, 16 and 20 days post‐inoculation (d.p.i.) was compared using these three approaches. Light microscopy identified no Phytophthora‐like structures in the control treatments. In PTA‐inoculated plants, lignitubers were produced 5 d.p.i. in cortical cells. Infection was localized after 5 days, but as the infection progressed (up to 20 d.p.i.), the ‘degree’ of root infection increased, as did the number of replicates in which structures were observed. SEM provided higher resolution images; again, no PTA structures were observed in the negative control material examined. The slide‐based FISH‐specificity assay successfully hybridized with PTA hyphae. Fluorescence was observed using 330–380 nm excitation and an emission filter at 420 nm (DAPI), with PTA nuclei fluorescing a bright greenish‐yellow. Cross‐reactivity was not observed when the assay was applied to six other non‐target Phytophthora species. Successful hybridization reactions occurred between the primer and PTA structures in planta. Applying this FISH assay has allowed clear differentiation of the intracellular and intercellular structures of PTA. The technique can be applied to longer term studies or analysis of ex situ inoculation studies aiming to elucidate differential host‐responses to the pathogen. Additionally, the technique could be applied to study the interactions with other fungal endophytes (e.g. mycorrhizal fungi), which could be assessed for biocontrol potential as part of the integrated management of the disease.

High-precision dating and correlation of ice, marine and terrestrial sequences spanning Heinrich Event 3: Testing mechanisms of interhemispheric change using New Zealand ancient kauri (Agathis australis)

Robustly testing hypotheses of geographic synchroneity of abrupt and extreme change during the late Pleistocene (60,000 to 11,650 years ago) requires a level of chronological precision often lacking in ice, marine and terrestrial sequences. Here we report a bidecadally-resolved New Zealand kauri (Agathis australis) tree-ring sequence spanning two millennia that preserves a record of atmospheric radiocarbon (14C) during ice-rafted debris event Heinrich Event 3 (HE3) in the North Atlantic and Antarctic Isotope Maximum 4 (AIM4) in the Southern Hemisphere. Using 14C in the marine Cariaco Basin and 10Be preserved in Greenland ice, the kauri 14C sequence allows us to precisely align sequences across this period. We observe no significant difference between atmospheric and marine 14C records during HE3, suggesting no stratification of surface waters and collapse in Atlantic Meridional Overturning Circulation (AMOC). Instead our results support recent evidence for a weakened AMOC across at least two millennia of the glacial period. Our work adds to a growing body of literature confirming that Heinrich events are not the cause of stadial cooling and suggests changes in the AMOC were not the primary driver of antiphase temperature trends between the hemispheres. Decadally-resolved 14C in ancient kauri offers a powerful new (and complementary) approach to polar ice core CH4 alignment for testing hypotheses of abrupt and extreme climate change.

The arbuscular mycorrhizal fungi colonising roots and root nodules of New Zealand kauri Agathis australis

As the only endemic member in New Zealand of the ancient conifer family, Araucariaceae, Agathis australis is an ideal species to study putatively long-evolved mycorrhizal symbioses. However, little is known about A. australis root and nodular arbuscular mycorrhizal fungi (AMF), and how mycorrhizal colonisation occurs. We used light, scanning and transmission electron microscopy to characterise colonisation, and 454-sequencing to identify the AMF associated with A. australis roots and nodules. We interpreted the results in terms of the edaphic characteristics of the A. australis-influenced ecosystem. Representatives of five families of Glomeromycota were identified via high-throughput pyrosequencing. Imaging studies showed that there is abundant, but not ubiquitous, colonisation of nodules, which suggests that nodules are mostly colonised by horizontal transmission. Roots were also found to harbour AMF. This study is the first to demonstrate the multiple Glomeromycota lineages associated with A. australis including some that may not have been previously detected.

Chemical Composition and Antibacterial Activity of the Essential Oil of Kauri Pine [ Agathis robusta (C. Moore ex F. Muell.) F.M. Bailey] from India

Agathis robusta (C. Moore ex F. Muell.) F.M. Bailey, commonly known as Queensland Kauri or smooth-barked Kauri, is a coniferous tree in the family Araucariaceae. This study aimed to investigate the chemical composition and antibacterial activity of the essential oil of A. robusta from India. The hydrodistilled resin and leaf essential oils were analyzed using GC-FID and GC-MS. Altogether, 34 constituents (forming 98.2% of the resin oil) and 43 constituents (forming 91.2% of the leaf oil composition) were identified. Major constituents of the resin oil were isobornyl acetate (37.9%), limonene (12.3%), bornyl acetate (7.4%), and myrtenol (5.8%), while the leaf oil contained β-selinene (18.1%), rimuene (14.2%), caryophyllene oxide (11.5%), spathulenol (10.5%), α-selinene (9.8%), and γ-muurolene (5.8%) as main constituents. The resin essential oil showed minimum inhibitory concentration (MIC) in the range of 250–500 μg/mL and minimum bactericidal concentration (MBC) in the range of 500 to >1000 μg/mL against pathogenic strains of eight bacteria.

Assessing the accuracy of three commonly used pith offset methods applied to Agathis australis (Kauri) incremental cores

Knowing the number of rings from the pith to the last cross-dated ring on incremental cores is important for regional curve standardisation, for constructing the best chronology by excluding rings formed when the tree was young, and for forest stand dynamics and regeneration studies. As the pith is rarely present on the samples an estimate of the distance to the pith is required. The aim of this paper is to assess the accuracy of three commonly used pith offset estimation methods for estimating pith offsets from kauri incremental cores.Literature identifies three main approaches for estimating pith offsets: Duncan’s geometric method, the concentric circles method (CCM), and the radius–length method. The accuracy of geometric and CMM were assessed using virtual cores constructed from an Agathis australis (Kauri) cross-section. Then the estimates for all three methods were applied to a subset of the kauri incremental cores database.The most accurate method for estimating the pith offset for kauri trees was found to be geometric method, followed by CCM. However, these approaches could only be used to estimate the pith offset for a few cores as they require the core to pass close enough to the pith that there is visible curvature on the cores. For most cores the radius–length method is the only method available for estimating the pith offset. This method relies on the assumption that the pith is located at the geometric centre of the tree which may not be a valid assumption for some species.

Species-level determination of closely related araucarian resins using FTIR spectroscopy and its implications for the provenance of New Zealand amber.

Some higher plants, both angiosperms and gymnosperms, can produce resins and some of these resins can polymerize and fossilize to form ambers. Various physical and chemical techniques have been used to identify and profile different plant resins and have then been applied to fossilized resins (ambers), to try to detect their parent plant affinities and understand the process of polymerization, with varying levels of success. Here we focus on resins produced from today’s most resinous conifer family, the Araucariaceae, which are thought to be the parent plants of some of the Southern Hemisphere’s fossil resin deposits. Fourier transform infrared (FTIR) spectra of the resins of closely related Araucariaceae species were examined to test whether they could be distinguished at genus and species level and whether the results could then be used to infer the parent plant of a New Zealand amber. The resin FTIR spectra are distinguishable from each other, and the three Araucaria species sampled produced similar FTIR spectra, to which Wollemia resin is most similar. Interspecific variability of the FTIR spectra is greatest in the three Agathis species tested. The New Zealand amber sample is similar in key shared features with the resin samples, but it does differ from the extant resin samples in key distinguishing features, nonetheless it is most similar to the resin of Agathis australis in this dataset. However on comparison with previously published FTIR spectra of similar aged amber and older (Eocene) resinites both found in coals from New Zealand and fresh Agathis australis resin, our amber has some features that imply a relatively immature resin, which was not expected from an amber of the Miocene age.

Concordance: A Measure of Similarity Between Matrices of Time Series with Applications in Dendroclimatology

A fundamental assumption in dendroclimatology is that the common signal produced by multiple trees of the same species, growing under similar environmental conditions within the same climate region, relates to changes in the climate within that region in the same way. However, there are concerns that the climate response of young kauri trees may differ to older kauri. As a result, the inclusion of radii from young kauri may weaken the climate signal of the composite chronology. To address this concern, a subset of the data containing tree rings formed when the trees were young was compared to those formed when the trees were old. These subsets contained time series of correlated tree rings aligned by year with start and end years differing for each series. Existing techniques for comparing subsets of time series lack reliability for ragged arrays of dependent non-stationary time series. The concordance method was developed to overcome this. Concordance is a non-parametric method based on bootstrapping that is used to test the hypothesis that two subsets of time series are similar in terms of mean, variance or both. Simulations show that concordance is effective for detecting difference in both the level and scale of two submatrices containing non-stationary and dependent time series. When applied to tree-ring data, the concordance method was able to detect evidence against the subset of young tree rings having the same mean, variance or both than older, more established trees.

A taxonomic revision of Phytophthora Clade 5 including two new species, Phytophthora agathidicida and P. cocois

Phytophthora Clade 5 is a very poorly studied group of species of oomycete chromists, consisting of only two known species P. castaneae (≡ P. katsurae, nom. illegit.) and P. heveae with most isolates from East Asia and the Pacific Islands. However, isolates of two important disease-causing chromists in Clade 5, one of kauri (Agathis australis) in New Zealand, the other of coconut (Cocos nucifera) in Hawaii, poorly match the current species descriptions. To verify whether these isolates belong to separate species a detailed morphological study and phylogenetic analysis consisting of eight genetic loci was conducted. On the basis of genetic and morphological differences and host specificity, we present the formal description of two new species in Clade 5, Phytophthora agathidicida sp. nov. and Phytophthora cocois sp. nov. To clarify the typification of the other Clade 5 species, an authentic ex-holotype culture of Phytophthora castaneae is designated and P. heveae is lectotypified and epitypified.

Progress in refining the global radiocarbon calibration curve using New Zealand kauri (Agathis australis) tree-ring series from Oxygen Isotope Stage 3

Ancient kauri (Agathis australis) buried in bogs across Northland, New Zealand, provide potential for a continuous high-precision radiocarbon calibration curve that extends to the full chronologic range of the dating method. Here we report four new tree-ring series which in addition to previous work represent some 5312 years across Oxygen Isotope Stage 3, a period during which human evolution, migration and extinction took place against a backdrop of extreme and abrupt global climate and environmental change. We compare our radiocarbon-dated series against three different calibration datasets and find considerable differences in the wiggle-matched solutions, demonstrating the difficulty in undertaking high-precision correlation between ice, marine and terrestrial sequences. One way around the apparent impasse is the use of 10Be in the Greenland and Antarctic ice cores to precisely link to kauri 14C from which a decadally/bidecadally-resolved floating ‘calibration’ dataset can be generated.

When conifers took flight: a biomechanical evaluation of an imperfect evolutionary takeoff

AbstractManifera talaris, a voltzian conifer from the late early to middle Permian (ca. 270 Ma) of Texas, is the earliest known conifer to produce winged seeds indicative of autorotating flight. In contrast to autorotating seeds and fruits of extant plants, the ones ofM. talarisare exceptional in that they have variable morphology. They bore two wings that produced a range of wing configurations, from seeds with two equal-sized wings to single-winged specimens, via various stages of underdevelopment of one of the wings. To examine the effects of various seed morphologies on aerodynamics and dispersal potential, we studied the flight performance of paper models of three morphotypes: symmetric double-winged, asymmetric double-winged, and single-winged. Using a high-speed camera we identified the mode of descent (plummeting, gliding, autorotation) and quantified descent speed, autorotation frequency, and other flight characteristics. To validate such modeling as an inferential tool, we compared descent of extant analogues (kauri;Agathis australis) with descent of similarly constructed seed models. All three seed morphotypes exhibited autorotating flight behavior. However, double-winged seeds, especially symmetric ones, failed to initiate slow autorotative descent more frequently than single-winged seeds. Even when autorotating, symmetric double-winged seeds descend faster than asymmetric double-winged ones, and descent is roughly twice as fast compared to single-winged seeds. Moreover, the relative advantage that (effectively) single-winged seeds have in slowing descent during autorotation becomes larger as seed weight increases. Hence, the range in seed wing configurations inM. talarisproduced a wide variation in potential dispersal capacity. Overall, our results indicate that the evolutionarily novel autorotating winged seeds must have improved conifer seed dispersal, in a time when animal vectors for dispersion were virtually absent. Because of the range in wing configuration, the early evolution of autorotative flight in conifers was a functionally imperfect one, which provides us insight into the evolutionary developmental biology of autorotative seeds in conifers.

Sap flow of the southern conifer, Agathis australis during wet and dry summers

Analysis of sap flux density during drought suggests that the large sapwood and rooting volumes of larger trees provide a buffer against drying soil. The southern conifer Agathis australis is amongst the largest and longest-lived trees in the world. We measured sap flux densities (F d) in kauri trees with a DBH range of 20–176 cm to explore differences in responses of trees of different sizes to seasonal conditions and summer drought. F d was consistently higher in larger trees than smaller trees. Peak F d was 20 and 8 g m−2 s−1 for trees of diameters of 176 and 20 cm, respectively, during the wet summer. Multiple regression analysis revealed photosynthetically active radiation (PAR) and vapour pressure deficit (D) were the main drivers of F d. During drought, larger trees were more responsive to D whilst smaller trees were more responsive to soil drying. Our largest tree had a sapwood area of 3,600 cm2. Preliminary analysis suggests stem water storage provides a buffer against drying soil in larger trees. Furthermore, F d of smaller trees had higher R 2 values for soil moisture at 30 and 60 cm depth than soil moisture at 10 cm depth (R 2 = 0.68–0.97 and 0.55–0.67, respectively) suggesting that deeper soil moisture is more important for these trees. Larger trees did not show a relationship between F d and soil moisture, suggesting they were accessing soil water deeper than 60 cm. These results suggest that larger trees may be better prepared for increasing frequency and intensity of summer droughts due to deeper roots and/or larger stem water storage capacity.

Rapid increase in cosmogenic 14C in AD 775 measured in New Zealand kauri trees indicates short-lived increase in 14C production spanning both hemispheres

In 2012, Miyake et al. reported a sudden and strong increase of the atmospheric radiocarbon (14C) content in Japanese cedar trees of 1.2% between AD 774 and 775. While their findings were quickly confirmed by a German oak chronology for the Northern Hemisphere (NH), the question remained if the effect was seen in both hemispheres. Here we present the first annually resolved Southern Hemisphere (SH) 14C record spanning the interval AD 760–787, using New Zealand kauri (Agathis australis) chronology wood. An almost identical distinct increase compared to Northern Hemisphere data was observed, suggesting a cosmic event with globally uniform impact as a potential cause for the increase. Deploying a carbon cycle box model a worldwide averaged net 14C production of 2.2×108 C14 atoms cm−2 was estimated, which is 3.7 times higher than the average annual 14C production. The immediate appearance of the event in tree rings on both hemispheres suggests a short duration event of significantly less than 1 yr.

Litterfall, carbon and nitrogen cycling in a southern hemisphere conifer forest dominated by kauri (Agathis australis) during drought

Under future climates, droughts will be more frequent and severe in parts of New Zealand, but the impact of drought has not been studied in New Zealand forests. Litterfall is one of the major fluxes of forest carbon. We explored seasonal and annual patterns of litterfall, carbon and nitrogen cycling in wet (2012) and dry (2013) years at Huapai Scientific Reserve, west Auckland. During 2012, rainfall was close to average with a wet summer, while the summer rainfall in the period from January to April 2013 was only 1/3 of the volume that fell during the same period in 2012, causing significant reductions in soil moisture. For the wet year, total annual litterfall was 9.00 ± 0.44 t ha−1, while during the dry year, there was a 72 % increase to 15.46 ± 0.85 t ha−1. Kauri constituted 80 % of the basal area of the plot and also contributed 80 % of the litter. The majority additional litter in the dry year was kauri leaves and twigs. Drought impacted slightly more heavily on the C cycle (with an 85 % increase during the drought year) than the N cycle (with a 69 % increase during the drought year) because concentrations of N in kauri leaves were lower during the drought period, due to nutrient reabsorption. Drought clearly enhances litterfall in this forest, stimulating the carbon and nitrogen cycles. These results have implications for forest C and N budgets as well as fire management practices due to the build-up of dry litter during drought.

Growth and productivity of New Zealand kauri (Agathis australis (D.Don) Lindl.) in planted forests

BackgroundThe establishment of even-aged planted stands of New Zealand kauri (Agathis australis (D.Don) Lindl.) for timber has been constrained by a lack of quantitative information on productivity and rotation length on which forest management and investment decisions could be made.MethodsStand-level models of height and basal area against time were developed (as well as a stand-volume function to calculate volume from height and basal area) based on planted stands that were up to 83-years old and represented planting sites both within and outside the current natural range of the species.ResultsPlanted kauri was shown to be slow to establish with little height growth for the first five years after planting. Similar trends were observed for basal area and whole-tree volume development. A Schumacher equation with local slope parameter and asymptote bounded at 45 m gave the best fit for height, while a von Bertalanffy-Richards equation in difference form with local slope parameter gave the best fit for basal area. For plantations with an average site index (20.4), height was predicted to be 22.3 m in height at age 60, with a basal area of 78.1 m2 ha-1. Whole-tree volume was predicted to be 702 m3 ha-1. Predicted volume mean annual increment was 11.7 m3 ha-1 yr-1for all stands at age 60. From age 20-60 years, stands with a higher site index had a volume mean annual increment of 18.6 m3 ha-1 yr-1. The best stand exceeded 20 m3 ha-1 yr-1.ConclusionsThis study indicates an opportunity to grow kauri in plantations on selected good-quality sites over rotations of 60-80 years or less.

Raised in the wild south: a dendrochronological and dendrochemical profile of a far-southern stand of kauri (Agathis australis) on the Taieri Plain, Otago

BackgroundKauri (Agathis au stralis (D.Don) Lindl.) is endemic to New Zealand and is the southernmost species of the tropical genus Agathis.MethodsThe growth history of the second southern-most known stand of New Zealand kauri is documented. This stand is located at Wairongoa Springs near Dunedin, approximately 8° of latitude south of the modern natural range of the species. This stand was established in the 1950s and now approximates a natural ‘ricker’ stand of juvenile kauri. Sample plot measurements of height and diameter growth taken in 2009 were compared to published 1986 data from the same stand, and were used for modelling self-thinning dynamics. An investigation was also undertaken using ring-widths from cores obtained by increment boring to generate a 52-year dendrochronological record that shows a strong common pattern of long-term and inter-annual changes in growth. Carbon isotope analysis of annual rings from 1983–2009 revealed corresponding multi-decadal chemical trends. Segmented linear regression was used to compare the ring-width record with existing kauri growth and self-thinning models.ResultsGrowth of kauri at Wairongoa Springs was fast, was comparable to other plantations of kauri without silvicultural tending, and was generally faster than that of natural stands. The growth of the stand can be considered as occurring in two apparent phases. The first was a 26-year period of relatively constant rapid growth with ring-widths averaging 3.5 mm while the second phase showed a steady decline in annual growth thought to be indicative of self-thinning due to increasing competition. This ring-width decline was matched by a gradual decline in the ratio of carbon isotope 13C to 12C.ConclusionsRing-width measurements and carbon isotope determinations compared with forestry-based modelling of self-thinning in kauri suggest that this stand is undergoing self-thinning much sooner than other kauri stands. This result highlights other possible influences beyond simple biomass accumulation triggering the onset of self-thinning. The growth rate of the plantation is comparable to others from the North Island, demonstrating that kauri can be grown, albeit in sheltered sites, throughout the length of New Zealand.