Hydraulic architecture and water relations of several species at diverse sites around Sydney

Seasonal comparisons of leaf water potential, root biomass, hydraulic architecture, xylem embolism and xylem dimensions were made for eight woody species in four diverse habitats (mangroves, coastal heathland, ridge-top woodland and river-flat woodland). In most comparisons, pre-dawn and minimum leaf water potentials were lower in winter than in summer, a result attributed to lower rainfall and a smaller root biomass in winter than in summer. Branch hydraulic conductivities (per unit transverse area, sapwood area or leaf area) were generally larger in summer than in winter across all species in all habitats. An inverse relationship between Huber value and conductivity was observed across all four habitats. Increased solar radiation and evaporative demand in the summer was associated with an increased percentage loss of xylem conductance arising from embolism, compared with winter. These results are discussed in the context of patterns and relationships among water relations, microclimate and hydraulic architecture

Applying a SPA model to examine the impact of climate change on GPP of open woodlands and the potential for woody thickening

Woody thickening is a global phenomenon that influences landscape C density, regional ecohydrology and biogeochemical cycling. The aim of the work described here is to test the hypothesis that increased atmospheric CO2 concentration, with or without photosynthetic acclimation, can increase gross primary production (GPP) and that this can explain woody thickening. We examine mechanisms underlying the response of GPP and highlight the importance of changes in soil water content by applying a detailed soil-plant-atmosphere model. Through this model, we show that CO2 enrichment with decreased or increased D and photosynthetic acclimation results in decreased canopy water use because of reduced gs. The decline in water use coupled with increased photosynthesis resulted in increased GPP, water-use efficiency and soil moisture content. This study shows that this is a valid mechanism for GPP increase because of CO2 enrichment coupled with either a decrease or an increase in D, in water-limited environments. We also show that a large increase in leaf area index could be sustained in the future as a result of the increased soil moisture content arising from CO2 enrichment and this increase was larger if D decreases rather than increases in the future. Large-scale predictions arising from this simple conceptual model are discussed and found to be supported in the literature. We conclude that woody thickening in Australia and probably globally can be explained by the changes in landscape GPP and soil moisture balance arising principally from the increased atmospheric CO2 concentration. © 2010 John Wiley & Sons, Ltd

Comparing the Penman-Monteith equation and a modified Jarvis-Stewart model with an artificial neural network to estimate stand-scale transpiration and canopy conductance

The responses of canopy conductance to variation in solar radiation, vapour pressure deficit and soil moisture have been extensively modelled using a Jarvis-Stewart (JS) model. Modelled canopy conductance has then often been used to predict transpiration using the Penman-Monteith (PM) model. We previously suggested an alternative approach in which the JS model is modified to directly estimate transpiration rather than canopy conductance. In the present study we used this alternative approach to model tree water fluxes from an Australian native forest over an annual cycle. For comparative purposes we also modelled canopy conductance and estimated transpiration via the PM model. Finally we applied an artificial neural network as a statistical benchmark to compare the performance of both models. Both the PM and modified JS models were parameterised using solar radiation, vapour pressure deficit and soil moisture as inputs with results that compare well with previous studies. Both models performed comparably well during the summer period. However, during winter the PM model was found to fail during periods of high rates of transpiration. In contrast, the modified JS model was able to replicate observed sapflow measurements throughout the year although it too tended to underestimate rates of transpiration in winter under conditions of high rates of transpiration. Both approaches to modelling transpiration gave good agreement with hourly, daily and total sums of sapflow measurements with the modified JS and PM models explaining 87% and 86% of the variance, respectively. We conclude that these three approaches have merit at different time-scales. © 2009 Elsevier B.V. All rights reserved

Rates of nocturnal transpiration in two evergreen temperate woodland species with differing water-use strategies

Nocturnal fluxes may be a significant factor in the annual water budget of forested ecosystems. Here, we assessed sap flow in two co-occurring evergreen species (Eucalyptus parramattensis and Angophora bakeri) in a temperate woodland for 2 years in order to quantify the magnitude of seasonal nocturnal sap flow (En) under different environmental conditions. The two species showed different diurnal water relations, demonstrated by different diurnal curves of stomatal conductance, sap flow and leaf water potential. The relative influence of several microclimatic variables, including wind speed (U), vapour pressure deficit (D), the product of U and D (UD) and soil moisture content, were quantified. D exerted the strongest influence on En (r2 = 0.59-0.86), soil moisture content influenced En when D was constant, but U and UD did not generally influence En. In both species, cuticular conductance (Gc) was a small proportion of total leaf conductance (Gs) and was not a major pathway for En. We found that En was primarily a function of transpiration from the canopy rather than refilling of stem storage, with canopy transpiration accounting for 50-70% of nocturnal flows. Mean En was 6-8% of the 24-h flux across seasons (spring, summer and winter), but was up to 19% of the 24-h flux on some days in both species. Despite different daytime strategies in water use of the two species, both species demonstrated low night-time water loss, suggesting similar controls on water loss at night. In order to account for the impact of En on pre-dawn leaf water potential arising from the influence of disequilibria between root zone and leaf water potential, we also developed a simple model to more accurately predict soil water potential (ψs). © The Author 2010. Published by Oxford University Press. All rights reserved

A modified Jarvis-Stewart model for predicting stand-scale transpiration of an Australian native forest

Rates of water uptake by individual trees in a native Australian forest were measured on the Liverpool Plains, New South Wales, Australia, using sapflow sensors. These rates were up-scaled to stand transpiration rate (expressed per unit ground area) using sapwood area as the scalar, and these estimates were compared with modelled stand transpiration. A modified Jarvis-Stewart modelling approach (Jarvis 1976), previously used to calculate canopy conductance, was used to calculate stand transpiration rate. Three environmental variables, namely solar radiation, vapour pressure deficit and soil moisture content, plus leaf area index, were used to calculate stand transpiration, using measured rates of tree water use to parameterise the model. Functional forms for the model were derived by use of a weighted non-linear least squares fitting procedure. The model was able to give comparable estimates of stand transpiration to those derived from a second set of sapflow measurements. It is suggested that short-term, intensive field campaigns where sapflow, weather and soil water content variables are measured could be used to estimate annual patterns of stand transpiration using daily variation in these three environmental variables. Such a methodology will find application in the forestry, mining and water resource management industries where long-term intensive data sets are frequently unavailable. © 2007 Springer Science+Business Media B.V

Climate change impacts on Aotearoa New Zealand: A horizon scan approach

Many of the implications of climate change for Aotearoa (New Zealand) remain unclear. To identify so-far unseen or understudied threats and opportunities related to climate change we applied a horizon-scanning process. First, we collated 171 threats and opportunities across our diverse fields of research. We then scored each item for novelty and potential impact and finally reduced the list to ten threats and ten opportunities through a prioritisation process. Within the 20 items presented in this paper, we uncover a range of climate-related costs and benefits. Unexpected opportunities evolve from economic reorganisation and changes to perspectives. The threats we highlight include the overall failure to interconnect siloed policy responses, as well as those relating to extreme events and feedbacks, as well as pressures that undermine the coherence of society. A major theme of our work is that climate change effects in Aotearoa are likely to transgress the boundaries of research disciplines, industry sectors and policy systems, emphasising the importance of developing transdisciplinary methods and approaches. We use this insight to connect potential responses to climate change with Aotearoa’s culture and geography

Climate change adaptation through an integrative lens in Aotearoa New Zealand

Climate change is being felt across all human and natural systems in Aotearoa New Zealand and is projected to worsen this decade as impacts compound and cascade through natural system and sectoral dependencies. The effectiveness of adaptation is constrained by how fast greenhouse gas emissions are reduced globally, the pace of change, the frequency and progression of impacts, and the capacity of our natural, societal and political systems to respond. We explore how these systems and sectors interact with existing and projected climate change stressors by categorising climate change impacts (Trends and Events) and consequential thresholds (Thresholds), and by grouping systems and sectors by types (Typologies). This approach has identified commonalities and differences between the typologies which are illustrated with examples. Critical constraints and opportunities for adaptation have been identified to guide sector adaptation decision-making and for ongoing adaptation progress and effectiveness monitoring. Constraints are found across all sectors, and opportunities exist to address them through modelling and projections, monitoring frameworks, decision tools and measures, governance coordination and integration of the Māori worldview of the relationship between humans and nature. However, limits to adaptation exist and will increase over time unless all sectors and all nations urgently reduce their emissions

Piezo-deformable mirrors for active mode matching in advanced LIGO

The detectors of the laser interferometer gravitational-wave observatory (LIGO) are broadly limited by the quantum noise and rely on the injection of squeezed states of light to achieve their full sensitivity. Squeezing improvement is limited by mode mismatch between the elements of the squeezer and the interferometer. In the current LIGO detectors, there is no way to actively mitigate this mode mismatch. This paper presents a new deformable mirror for wavefront control that meets the active mode matching requirements of advanced LIGO. The active element is a piezo-electric transducer, which actuates on the radius of curvature of a 5 mm thick mirror via an axisymmetric flexure. The operating range of the deformable mirror is 120±8 mD in vacuum and an additional 200 mD adjustment range accessible out of vacuum. Combining the operating range and the adjustable static offset, it is possible to deform a flat mirror from −65 mD to −385 mD. The measured bandwidth of the actuator and driver electronics is 6.8 Hz. The scattering into higher-order modes is measured to be <0.2% over the nominal beam radius. These piezo-deformable mirrors meet the stringent noise and vacuum requirements of advanced LIGO and will be used for the next observing run (O4) to control the mode-matching between the squeezer and the interferometer.Varun Srivastava, Georgia Mansell, Camille Makarem, Minkyun Noh, Richard Abbott, Stefan Ballmer, GariLynn Billingsley, Aidan Brooks, Huy Tuong Cao, Peter Fritschel, Don Griffith, Wenxuan Jia, Marie Kasprzack, Myron MacInnis, Sebastian Ng, Luis Sanchez, Calum Torrie, Peter Veitch, and Fabrice Matichar

First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto- noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far

Australasia

Observed changes and impacts Ongoing climate trends have exacerbated many extreme events (very high confidence). The Australian trends include further warming and sea level rise sea level rise (SLR), with more hot days and heatwaves, less snow, more rainfall in the north, less April–October rainfall in the southwest and southeast and more extreme fire weather days in the south and east. The New Zealand trends include further warming and sea level rise (SLR), more hot days and heatwaves, less snow, more rainfall in the south, less rainfall in the north and more extreme fire weather in the east. There have been fewer tropical cyclones and cold days in the region. Extreme events include Australia’s hottest and driest year in 2019 with a record-breaking number of days over 39°C, New Zealand’s hottest year in 2016, three widespread marine heatwaves during 2016–2020, Category 4 Cyclone Debbie in 2017, seven major hailstorms over eastern Australia and two over New Zealand from 2014–2020, three major floods in eastern Australia and three over New Zealand during 2019–2021 and major fires in southern and eastern Australia during 2019–2020