Central Volcanic Plateau Research Articles

Inferring the biogeography of New Zealand’s only endemic holoparasitic plant, the threatened Dactylanthus taylorii (Mystropetalaceae)

ABSTRACT Despite a rich history of botanical research, little is known about the distribution of genetic variation within New Zealand plant species. With a native vascular flora that consists of ∼80% endemics, nearly one-half of which are threatened, there is a dire need for a better understanding of intraspecific diversity for individual plant species and of biogeographic patterns for the wider New Zealand flora. To these ends, we have investigated population genetic structure in the endemic root holoparasite, Dactylanthus taylorii (pua o te Rēinga, Mystropetalaceae). A total of 235 individuals from 31 locations across the North Island of New Zealand (Te Ika-a-Māui, Aotearoa) were genotyped for a suite of nuclear microsatellite loci. Genotype data were analysed at the individual and population levels to assess genetic diversity within and among populations and to investigate the geographic distribution of genetic variation within the species. Population structure was assessed using Bayesian clustering, discriminant analysis of principal components, and a Neighbor-Net analysis. A hierarchical pattern of genetic diversity was revealed, with evidence for three broad geographic regional groupings (West, East, and Central Volcanic Plateau (CVP)). Upon further analysis, each of the three geographic groups further subdivide hierarchically into two or three genetic subgroups. Genetic diversity was found to be relatively high in this endangered species but varies considerably across populations. The distribution of genetic groups appears to have been influenced by past volcanic activity as the CVP group is largely coincident with a distinct tephra isopach from the 1.8 ka Taupō eruption and the West and East groups may have diverged due to recurring volcanic activity in the Central Volcanic Zone. The genetic structure resolved here provides important information for the management of D. taylorii specifically and for our understanding of New Zealand biogeography generally.

Seasonal and environmental variation in volatile emissions of the New Zealand native plant Leptospermum scoparium in weed-invaded and non-invaded sites

The New Zealand tea tree Leptospermun scoparium (mānuka) is widely known for the antimicrobial properties of its honey. Mānuka is native to New Zealand, growing in a range of environments, including the Central Volcanic Plateau of the North Island, where it is currently threatened by the spread of exotic invasive weeds such as heather (Calluna vulgaris) and Scotch broom (Cytisus scoparius). Here, we characterise for the first time the aboveground volatile organic compounds (VOCs) produced by mānuka in this area, during summer and winter seasons, in weed-invaded and non-invaded stands. We measured plant volatiles at four sites, each with a distinct combination of woody species: (1) conspecific stands of mānuka; (2) mānuka and another native species (Dracophyllum subulatum); and mānuka with one of two European invasive plants, (3) heather or (4) Scotch broom. We also quantified herbivore damage on target mānuka plants and analysed microclimatic variables (soil nutrients, air temperature and soil water content) to investigate their impact on volatile emissions. Our results reveal a strong seasonal effect on volatile emissions, but also significant differences between sites associated with biotic and abiotic changes partly driven by invasive plants. Overall, volatile emission rates from mānuka were typically lower at sites where invaders were present. We point to several factors that could contribute to the observed emission patterns and areas of interest for future research to provide a comprehensive understanding of VOC emissions in nature. Given the vital role of volatile compounds in plant communication, we also recommend future studies to be performed in multiple seasons, with larger sample sizes and more study sites to expand on these findings and explore the ecological impacts of changes in VOC emissions during plant invasion.

Biological flora of New Zealand 14: Metrosideros excelsa, pōhutukawa, New Zealand Christmas tree

We review the biology and ecology of Metrosideros excelsa (Myrtaceae), an endemic angiosperm evergreen tree. Metrosideros excelsa belongs to a conspicuous and widely distributed Pacific Basin genus, with centres of diversity in both New Zealand and New Caledonia. Metrosideros excelsa is an iconic tree species that forms a significant component of northern New Zealand's exposed coastal headland and cliff vegetation. Where conditions are more favourable, M. excelsa forms tall coastal forest, ranging from simple young high-density stands to diverse mature forest. Inland, M. excelsa stands are confined to the margins of lakes and rivers on the Central Volcanic Plateau, where some may originate from early Māori plantings. Metrosideros excelsa is reliant on stochastic disturbance events (e.g. landslides, volcanic eruptions) to create open sites necessary for regeneration. Mass flowering (December–January), followed by abundant production of wind-dispersed seed maximises chance colonisation of such sites. Since human settlement in New Zealand, the distribution of M. excelsa forest has declined by c. 90% and the southern limit of the species has retreated north. Natural regeneration on the mainland is limited by the infrequency of large-scale disturbances and increased anthropogenic and herbivore pressures. Consequently, M. excelsa forest has become rare and localised on the mainland; monitoring and active management are fundamental to the species' long-term conservation.

Morphological dynamics of upland headwater streams in the southern North Island of New Zealand

AbstractShort‐term channel dynamics of mountain stream reaches in the southern North Island of New Zealand were assessed over two successive 3‐month periods using morphological budgeting. Response to floods varies between reaches, even when the catchments were located close to each other and had similar characteristics. The reaches on the Central Volcanic Plateau experienced least morphological change, while streams with steep catchments and migrating planform in the Tararua and Ruahine Ranges showed frequent channel adjustments. Channel response is conditioned by intrinsic variables rendering reaches responsive or robust to the effects of floods, and this is likely to reflect the degree of connectivity between slopes and channels, and reaches.

Thermal springs, fumaroles and gas vents of continental Yemen: Their relation with active tectonics, regional hydrology and the country’s geothermal potential

Most thermal springs of continental Yemen (about 65 emergences at 48 sampling sites) and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free-gas phase. Whatever the emergence, all the water discharges have an isotopic signature of meteoric origin. Springs seeping out from high altitudes in the central volcanic plateau show a prevalent Na–HCO 3-composition, clearly affected by an anomalous flux of deep CO 2 deriving from active hydrothermal systems located in the Jurassic Amran Group limestone sequence and/or the Cretaceous Tawilah Group, likely underlying the 2000–3000 m thick volcanic suite. At lower elevations, CO 2 also affects the composition of some springs emerging at the borders of the central volcanic plateau. Although mixing to a limited extent with organic CO 2 infiltrating together with the meteoric recharge waters cannot be ruled out, all the CO 2-rich gas samples have a δ 13C–CO 2 signature that falls in the range of mantle CO 2 (−3 < δ 13C < −7‰ V-PDB). The relatively high 3He/ 4He (1 < R/ R a < 3.2) ratios measured in all the CO 2-rich springs and also some mixed N 2–CO 2 gas vents in the far east Hadramaut region support the presence of mantle magmas and related hydrothermal systems residing at the crust level in several areas of Yemen. This well agrees with the presence of Quaternary basaltic magmatic activity along the Gulf of Aden, as well as inside the central Yemen volcanic plateau. Presently, the thermal springs of Yemen are prevalently used for spas and/or bathing. Nevertheless, liquid- and gas-geothermometry and geological considerations suggest that there are at least three areas (Al Lisi, Al Makhaya and Damt) inside the Yemen volcanic plateau (around Dhamar) that may be promising prospects for the future development of geothermal energy in Yemen. Alternatively, they could be used as a source of energy for small-to-medium scale agriculture and/or industrial purposes. Moreover, most of the thermal water discharges have the chemical characteristics of potable waters and, in an arid country like Yemen, they have to be considered as long-term water supply resources if the country should face water shortages.

2,4‐D Movement in Allophanic Soils from Two Contrasting Climatic Regions

Allophanic top‐ and subsoils from the Mexican and Newzealand Central Volcanic Plateau, as well as a nonallophanic sandy loam soil, were sampled to study the impact of organic matter and allophane content on 2,4‐D fate. High sorption rates were found, especially in the two topsoils from Mexico and New Zealand, with distribution coefficient (K d ) obtained from displacement experiments in packed columns equal to 7.61 and 8.43 L kg−1 respectively. 2,4‐Dichlorophenoxyacetic acid transfer through the soil columns was found to be in chemical nonequilibrium and was well predicted using a two‐site sorption model. For the two allophanic top soils, K d obtained from batch was very different to the K d obtained from column experiments. Either the equilibrium could not be reached in batch or the two‐site model was not able to describe the wide range of sorption sites present in the highly reactive organic matter and allophane components.

N and P in New Zealand Soil Chronosequences and Relationships with Foliar N and P

The growth of forest species in soil development chronosequences becomes increasingly phosphorus (P)-limited with time, as P is weathered, eroded and leached from soil. Foliar nitrogen (N) concentrations also tend to decrease with soil age when vegetation may be limited in both N and P. Here we report on soil development in temperate rain forests along three New Zealand chronosequences that have minimal pollution and disturbance from human activities, at Franz Josef, Waitutu and Central Volcanic Plateau, and on factors influencing soil net N mineralization (aerobic; 56 days) and foliar N and P concentrations. Except in very young soils (<500 years), at least 85% of total-P in mineral soil (0–10 cm) was transformed to organic-P. In each chronosequence, total-P declined with time, and foliar N:P ratios (mass) generally increased from 8 to 15–18, suggesting P was more limiting than N in the oldest soils of the chronosequence. There was a negative relationship between net N mineralization and C:N ratio for mineral soil. For the FH (organic) layer, net N mineralization had the strongest relationships with total-N concentration (positively) and C:organic-P ratio (negatively); however, relationships varied with forest group, suggesting that other factors were also important. Foliar P of kamahi (Weinmannia racemosa Linn. f.), a dominant canopy species, was related to soil organic-P, suggesting mineralization was an important process for tree nutrition.Foliar N was positively related to N concentration in the FH layer, but was not significantly related to any measured property in mineral soil, possibly because of the wide range of soils. The consistent declines in both soil and foliar P across the contrasting chronosequences strongly suggest that vegetation becomes progressively P-limited during long-term ecosystem development.

Comparing past and present trophic states of seven Central Volcanic Plateau lakes, New Zealand

Data on seven lakes in the Rotorua District were examined to determine trophic state changes in these lakes. The method of data analysis was specifically designed to find small changes in the trophic state of lakes. For each variable, the P‐value from 12 monthly paired sample Student t‐test comparisons was calculated and a change of trophic state value (CTS) was assigned, based on the P‐value. The CTS values for all the variables examined for a single lake were averaged (C) with a standard error (CV). The resulting Change/ Confidence Value index (C/CV) indicated the nature of the trophic change observed and the degree of confidence that could be placed in the stated change. This study finds that in recent years Lakes Rotorua and Rotoiti have become less eutrophic; Lakes Okareka and Rotoma may have become less eutrophic; Lakes Okataina and Rotokakahi have not changed in trophic state in the last 22 years, and Lake Tikitapu may have become more eutrophic.

Human impacts on the Waikato River system, New Zealand

The Waikato River drains 13% of the North Island. It rises in the Central Volcanic Plateau; the headwaters, including the Tongariro R., drain into oligotrophic Lake Taupo, important for fishing and holidaying. The river flows north from Taupo for 450 km to the sea near Auckland. Human impacts on the river system have been extensive, primarily dating from European colonisation begun in the 1800s. Most of the catchment below L. Taupo has been altered by agricultural development (mainly sheep and cattle rearing); the original forests and swamps have been lost leading to increased nutrient levels, erosion, light intensities, and water temperatures. There is also extensive use of the water for electricity generation. The Tongarino Power Scheme involves impoundment of water, and the diversion of additional water from the Whanganui River and other catchments with consequent effects on their biota. There are 8 hydro-electric dams on the Waikato River below Taupo causing barriers to migratory animals, downstream effects due to impoundments, and alterations to water flow regimes. Impacts of geothermal power stations, and the water-cooled Huntly Power Station in the lower Waikato are more localised. Eutrophication is enhanced by sewage and stormwater discharges, but all wastes now receive some form of treatment. There are only 340,000 people in the catchment and the major industrial pollution comes from meat and dairy processing and forestry. Some natural pollution results from geothermal inputs. Water abstraction and discharges into the river are now closely regulated. Extensive introductions of exotic biota have been made, notably trout, coarse fish, and macrophytes. The native biota has been little-studied and the biological processes operating in the river are poorly understood. It is not possible to assess the relative importance of eutrophication and habitat change, nor to predict the impacts of future changes.

The frost resistance of some native plants from the Central Volcanic Plateau, North Island, New Zealand, in relation to plant succession

Abstract The frost resistance (T 50) of several key species of the tussock grasslands, tussock shrublands, and forest on the Central Volcanic Plateau was measured, using the electrical conductivity method. The frost resistance of Chionochloa rubra, Dracophyllum filifolium, Phyllocladus alpinus, Leptospermum scoparium, Nothofagus solandri var cliffortioides, and Brachyglottis bidwillii was measured in autumn, mid winter, spring, and summer. Additional species were tested in mid winter for their maximum frost resistance. In mid winter, the T 50 ranged from -4.2°C for Pseudopanax arboreus to -27.4°C for Chionochloa rubra. Phyllocladus alpinus from different areas (including the South Island) showed significant differences in T 50 (from -9.2°C up to -16.3°C). Species which were measured throughout the year showed, with the exception of Chionochloa rubra, a significant hardening from summer to winter and a significant dehardening after winter. The seasonal and midwinter frost hardiness of the different species can be related to the actual succession in the field after disturbance.

Does the chlorophyll a content of phytoplankton vary with trophic status in lakes on the New Zealand central volcanic plateau?

Does the chlorophyll <i>a</i> content of phytoplankton vary with trophic status in lakes on the New Zealand central volcanic plateau?

The Lake Okaro ecosystem 2. Production of the chironomidPolypedilum pavidusand its role as food for two fish species

Abstract Lake Okaro, a nutrient‐rich lake on the central volcanic plateau of the North Island, New Zealand, supported a maximum littoral population of the chironomid Polypedilum pavidus Hutton of 309 000 larvae m‐2 in 1983/84. This population depended for food on the shoreward drift of cyanobacteria (blue‐green algae). The larvae were an important food source for the benthic bully Gobiomorphus cotidianus McDowall from January to June. From June to December the cladoceran Ceriodaphnia dubia Richard was prominent in the diet when the fish moved towards the open water of the lake. The bully removed up to 128% of chironomid production only when population density of the larvae was low. At other times fish predation had little impact on the larvae. Most larvae were eaten by bullies during the day. Bullies caught at night were on average larger and preferred to eat small individuals of their own species. The smelt Retropinna retropinna (Richardson) played a minor predatory role in the lake. It ate P. pavidus la...

The Lake Okaro ecosystem 1. Background limnology

Abstract Lake Okaro is a eutrophic lake on the central volcanic plateau of North Island, New Zealand. Its hypolimnion has become progressively depleted of dissolved oxygen between 1955 and 1964. Since then hypolimnetic anoxia has occurred annually. Secchi disc transparency changed little since 1955. Higher values in 1977/78 and 1983/84 appeared to be caused by greater proportions of the cladoceran Ceriodaphnia dubia in the zooplankton. Despite large interannual changes in biological and chemical properties of Lake Okaro, trophic state has changed since 1955. The phyto‐plankton species composition changed from no cyanobacteria in 1955/56 to persistent cyanobac‐terial blooms in 1963 and abundant and extensive blooms of Anabaena spiroides and A. flos‐aquae in 1979/80. Elodea canadensis dominated the macro‐phyte assemblage and its abundance has changed little since 1963. Zooplankton numbers decreased between 1979/80 and 1985/86 because of a decline in the calanoid copepod population. The zooplankton assemblage, dominated by rotifers in 1979/80, was crustacean‐dominated in 1982/83. Eutrophi‐cation coincided with a higher proportion of chi‐ronomids, particularly the littoral Polypedilum pavidus, which became abundant in the presence of cyanobacterial blooms.

The effects of changes in both the abundance of nitrogen and phosphorus and their ratio on Lake Okaro phytoplankton, with comment on six other central volcanic plateau lakes

DAVID R. S. LEAN STUART F. MITCHELL FRANCES R. PICK JOHN G. RUETER MALCOLM T. DOWNES GEORGE W. PAYNE STUART E. PICKMERE EDWARD WHITE PAUL H. WOODS National Water Research Institute Box 5050, Burlington, Ontario Canada L7R 4A6 Department of Zoology University of Otago Dunedin, New Zealand Department of Biology Ottawa University Ottawa, Ontario, Canada K1N 6N5 Department of Biology Portland State University P.O. Box 751, Portland Oregon, U.S.A. 97207 Taupo Research Laboratory Department of Scientific and Industrial Research P.O. Box 415, Taupo, New Zealand

Nutrient demand and availability related to growth among natural assemblages of phytoplankton

Abstract In the summer of 1984/85 water samples from 10 Central Volcanic Plateau lakes were examined for a variety of plant nutrient components, and the plankton were subjected to three short term physiological assays which indicate nutrient demand and to a 4 d growth assay. In samples from four of the lakes plankton were exposed to a surfeit of phosphorus, for they were bathed in substantial concentrations (> 3 mg P m‐3) of dissolved reactive phosphorus and their capacity to accumulate this nutrient was low ( < 10% of initial phosphorus content in 4 h), indicating that their phosphorus stores were substantially full. In samples from all 10 lakes, plankton biomass increase (measured by change in chlorophyll a concentration) was prevented by shortage of nutrient nitrogen.

Nutrient demand and availability among planktonic communities — an attempt to assess nutrient limitation to plant growth in 12 central volcanic plateau lakes

Abstract Four assays of nitrogen demand and 3 for phosphorus were employed in 12 lakes at 4 seasons in an attempt to identify the nutrients limiting plankton growth. Orthophosphate turnover times, chlorophyll, and a range of analyses for nitrogen and phosphorus were made in support of the bioassays. Consideration was given to both statistical and biological interpretation of the assays. It was not possible to identify with certainty the limiting nutrients from this information, but criteria were developed which allowed conclusions to be drawn about plankton nutrient sufficiency. Differential storage capacity relative to subsistence cell quota for the 2 nutrients needs to be considered when interpreting the bioassays.

Nitrogen and phosphorus in the Ngongotaha Stream

Abstract This paper gives the data and methods used to calculate the nitrogen and phosphorus loads of the Ngongotaha Stream, near Rotorua, New Zealand. The variations in concentration with time and with flow rate are given in some detail, as examples of what may happen in other streams of the central volcanic plateau, and a novel way to define a flow‐concentration curve is described. Nitrate, ammonia, dissolved reactive phosphorus (DRP), total phosphorus (TP), and total Kjeldahl nitrogen (TKN) concentrations were measured, and mean concentrations in 1976 base flow were found to be 527, 25, 32, 48, and 162 mg m‐3 respectively. Nitrate concentrations showed seasonal variations, and although changes occurred during floods, they were not correlated with flow rate. DRP concentrations showed little variation, except that they dropped at the peak of the largest floods. TP was strongly correlated with flow rate during floods, and TP loads could best be calculated by allowing for a curvilinear relationship between concentration and flow rate. The logarithms of the TP load carried by a flood and the peak flow rate of the flood were highly correlated (R = 0.984). The annual loads of nitrate, ammonia, DRP, TP, and TKN were estimated to be 34, 1.3, 2.9, 6.0, and 26 tonnes in 1976.

Symposium: Fauna of the central North Island Volcanic Region

Since the Cretaceous era the effects of climatic change and intermittent vulcanism have dictated a shifting pattern for New Zealand's forests so that in any one place the mix of species comprising the forest has continually changed. The arrival of Man heralded a reduction in indigenous forest area from an estimated 18.8 million ha to the present 6.2 million ha, about 33% of the original forest estate. A discontinuous fringe of 3 types of indigenous forest now encircles the central volcanic plateau in the North Island. Podocarp forests, which were originally very extensive, are now almost entirely restricted to the eastern fall of the Hauhungaroa Range, West Taupo, and to the Whirinaki basin, adjacent to Urewera National Park. Podocarp/hardwood forests are more extensive in the same 2 localities as well as on the Mamaku Plateau. Extensive beech forests occupy much of the Kaimanawa Range, south of Lake Taupo. In the North Island only 56 000 ha of unlogged podocarp/hardwood forest, including dense podocarp f...

Limnology of Opal Lake

Abstract Opal Lake, a cold, acid lake on the central volcanic plateau of the North Island, New Zealand, had an average pH of 4.3 and was highly eutrophic. The biota was less diverse than in neighbouring near‐neutral waters. Macrophytes were rare; phytoplankton were mainly represented by the Chlorophyceae, and there were only 4 zooplankton species. The mean standing crop of macroinvertebrates was 6240 per square metre; this was higher than in other eutrophic lakes in the region and comprised more than 98% chironomid larvae represented by 4 species. Molluscs were absent. The fauna was more diverse than in more acid lakes of the .central volcanic plateau.

Distribution and Biological Availability of Reactive High Molecular Weight Phosphorus in Natural Waters in New Zealand

Eutrophic lakes and many streams on the central volcanic plateau of the North Island, New Zealand, contain dissolved chemically reactive phosphorus which is not orthophosphate. Sephadex gel (G25-150) chromatograms reveal that one reactive component is of high molecular weight (MW &gt; 5000) while a second component elutes in the same way as phosphate-phosphorus (PO4-P). The reactive high molecular weight phosphorus (RHMW-P) in streams generally forms only a small proportion of the dissolved reactive phosphorus (DRP). In some eutrophic lakes the proportion of RHMW-P in the DRP is high (70–80%). Each lake may have a characteristic distribution of the two forms of reactive phosphorus. In summer where DRP concentrations are low (&lt;2 mg∙m−3) in lake surface waters, PO4-P seems to dominate over RHMW-P which is consistent with long 32PO4 turnover times which are found in many of the central volcanic plateau lakes. Algal growth responses to phosphorus uptake were similar for PO4-P and RHMW-P, but not all of the RHMW-P was taken up by Chlorella in bioassays. The proportion of the RHMW-P taken up by Chlorella was different for each lake examined, posing problems in relating DRP concentrations to algal growth responses in lakes.Key words: reactive phosphorus, phosphate-phosphorus, algae, Chlorella, growth, bioassay, freshwater analysis, molybdenum blue method, Sephadex gel chromatography