Describing and classifying a landscape for environmental impact and risk assessment purposes is a non-trivial challenge because this requires region-specific landscape classifications that cater for region-specific impacts. Assessing impacts on ecosystems from the extraction of water resources across large regions requires a causal link between landscape features and their water requirements. We present the rationale and implementation of an ecohydrological classification for regions where coal mine and coal seam gas developments may impact on water. Our classification provides the essential framework for modelling the potential impact of hydrological changes from future coal resource developments at the landscape level. We develop an attribute-based system that provides representations of the ecohydrological entities and their connection to landscape features and make use of existing broad-level classification schemes into an attribute-based system. We incorporate a rule set with prioritisation, which underpins risk modelling and makes the scheme resource efficient, where spatial landscape or ecosystem classification schemes, developed for other purposes, already exist. A consistent rule set and conceptualised landscape processes and functions allow for the combination of diverse data with existing classification schemes. This makes the classification transparent, repeatable and adjustable, should new data become available. We apply the approach in three geographically different regions, with widely disparate information sources, for the classification, and provide a detailed example of its application. We propose that it is widely applicable around the world for linking ecohydrology to environmental impacts.

The El Nino o Southern Oscillation (ENSO) significantly influences wheat yield variability in Australia. Tailoring crop agronomic managements to ENSO phases can effectively manage climate variability and reduce crop yield variability. Previous studies have mostly been conducted at a site scale, whose results are hardly extrapolated to a large heterogeneous area. Here, the CERES-Wheat model was calibrated at 5-minute grid scale and applied to simulate wheat yield and adaptation measures under different ENSO phases across wheat cultivation areas in Australia. The results show that the calibrated gridded model can capture wheat phenology and yield variations reasonably. Wheat yields are significantly affected by ENSO-induced changes in precipitation and maximum temperature. During El Nino o phase, more dry days, hot days, frost days, water stress, and lower LAI (Leaf Area Index) and ET (Evapotranspiration) lead to an obvious yield decline, especially in southeastern Australia. Wheat sown in the mid-season (Day of Year, DOY of 144) increase yield by 433.5 + 25.6 kg/ha (27.9 + 1.6%) during El Nino, o, while late-season sowing is more suitable for Neutral (DOY of 153.4) and La Nina a phases (DOY of 147.5). A higher nitrogen rate is needed during La Nina a (106 kg/ha) and Neutral (106.5 kg/ha) compared to El Nino o (94.5 kg/ha) phase. Optimizing varieties is the most effective option and may increase yield by 624+20.9 +20.9 kg/ha, 562.9 + 21.5 kg/ha, and 614.3 + 21 kg/ha for Neutral, El Nino, o, and La Nina a phases, respectively, over traditional farming practices, respectively. The wheat varieties with a larger photoperiod sensitivity and shorter grain-filling duration are favorable during El Nino. o. Our findings demonstrate a powerful model-based decision support system in tailoring agronomic management practices to ENSO phases and local environments at a high resolution.

Stomatal conductance schemes that optimize with respect to photosynthetic and hydraulic functions have been proposed to address biases in land‐surface model (LSM) simulations during drought. However, systematic evaluations of both optimality‐based and alternative empirical formulations for coupling carbon and water fluxes are lacking. Here, we embed 12 empirical and optimization approaches within a LSM framework. We use theoretical model experiments to explore parameter identifiability and understand how model behaviors differ in response to abiotic changes. We also evaluate the models against leaf‐level observations of gas‐exchange and hydraulic variables, from xeric to wet forest/woody species spanning a mean annual precipitation range of 361–3,286 mm yr−1. We find that models differ in how easily parameterized they are, due to: (a) poorly constrained optimality criteria (i.e., resulting in multiple solutions), (b) low influence parameters, (c) sensitivities to environmental drivers. In both the idealized experiments and compared to observations, sensitivities to variability in environmental drivers do not agree among models. Marked differences arise in sensitivities to soil moisture (soil water potential) and vapor pressure deficit. For example, stomatal closure rates at high vapor pressure deficit range between −45% and +70% of those observed. Although over half the new generation of stomatal schemes perform to a similar standard compared to observations of leaf‐gas exchange, two models do so through large biases in simulated leaf water potential (up to 11 MPa). Our results provide guidance for LSM development, by highlighting key areas in need for additional experimentation and theory, and by constraining currently viable stomatal hypotheses.

Background and Aims Hydraulic failure is considered a main cause of drought-induced forest mortality. Yet, we have a limited understanding of how the varying intensities and long time scales of natural droughts induce and propagate embolism within the xylem. Methods X-ray computed tomography (microCT) images were obtained from different aged branch xylem to study the number, size and spatial distribution of in situ embolized conduits among three dominant tree species growing in a woodland community. Key Results Among the three studied tree species, those with a higher xylem vulnerability to embolism (higher water potential at 50 % loss of hydraulic conductance; P-50) were more embolized than species with lower P-50. Within individual stems, the probability of embolism was independent of conduit diameter but associated with conduit position. Rather than the occurrence of random or radial embolism, we observed circumferential clustering of high and low embolism density, suggesting that embolism spreads preferentially among conduits of the same age. Older xylem also appeared more likely to accumulate embolisms than young xylem, but there was no pattern suggesting that branch tips were more vulnerable to cavitation than basal regions. Conclusions The spatial analysis of embolism occurrence in field-grown trees suggests that embolism under natural drought probably propagates by air spreading from embolized into neighbouring conduits in a circumferential pattern. This pattern offers the possibility to understand the temporal aspects of embolism occurrence by examining stem cross-sections.

ABSTRACT Drought is a regular feature of Australian landscapes, and its intensity and frequency are likely to increase in a changing climate. Land managers are grappling with managing the impacts of drought, with large-scale die-offs occurring more frequently in forests globally. Drought-induced tree mortality has caused major impacts in Pinus radiata plantations in New South Wales, Australia, with extended drought, heatwaves and pest and disease attacks all recognised as predisposing, inciting or contributing factors. The extent and severity of drought-induced tree mortality has been mapped across the Pinus plantation estate in New South Wales annually since 1996. In this study, we used this long-term empirical data to develop a model of drought risk for P. radiata plantations. Using random forest, we identified site index, annual temperature, annual rainfall, elevation and increasing number of hot days (above 20°C and 35°C) as the influencing variables associated with drought-induced tree mortality. We then used this model to look at the risk of drought-induced tree mortality under climate-change scenarios in 2050 and 2070. Although forest managers already understand the drought risk in their estates, we developed an empirical model and produced GIS layers at high resolution (100 m) to assist in more accurately and effectively managing drought. The accuracy and precision of our model (overall accuracy 89.2%, kappa 0.75) enables forest managers to include it in their decision-making in the management of the potential impacts of drought on the current plantation estate (e.g. via modified silvicultural regimes) as well as in the future (e.g. modified silvicultural regimes or planting drought-tolerant genotypes).

National and regional yield forecasts can provide important insights into agribusiness beyond the farm gate. The incorporation of dynamical climate models into these forecasting systems strengthen their predictive performance in many cases but may contribute inherent biases to the final yield estimates. Downscaling the native climate model output so that is suitable for crop simulation modelling can also present challenges in representing realistic conditions for plant growth from a climate model. This study evaluated the performance of an operational national wheat yield forecast system for the Australian wheatbelt using climatology and seasonal climate model-based input data, and introduces an alternative approach using a data fusion method. The crop forecasting system uses the APSIM wheat model to estimate water-limited potential yield. The climatology-based forecast tended to over predict national yield (high yield bias; 1.5 to 7% across forecast months), while the model-based method (using ACCESS-S1 dynamical model) tended to under predict yield (low yield bias; -5.9 to -0.5% across forecast months) and had a lower spread than climatology (10 to 50% lower across forecast months). The model-based forecast had skill in terms of accuracy and reliability during the second half of the season. The newly developed data fusion method used a weighting method calibrated for separate forecast locations (stations) to remove bias in the mean forecast yield and reduce ensemble spread. This resulted in improvements in the Australia-wide yield forecasts across all forecast start dates. This study provides a demonstration of how a data-driven approach can be applied to a crop forecast to improve accuracy and resolution of crop yield forecasts without the need for more computationally intensive downscaling approaches.

Plant transpiration links physiological responses of vegetation to water supply and demand with hydrological, energy, and carbon budgets at the land–atmosphere interface. However, despite being the main land evaporative flux at the global scale, transpiration and its response to environmental drivers are currently not well constrained by observations. Here we introduce the first global compilation of whole-plant transpiration data from sap flow measurements (SAPFLUXNET, https://sapfluxnet.creaf.cat/, last access: 8 June 2021). We harmonized and quality-controlled individual datasets supplied by contributors worldwide in a semi-automatic data workflow implemented in the R programming language. Datasets include sub-daily time series of sap flow and hydrometeorological drivers for one or more growing seasons, as well as metadata on the stand characteristics, plant attributes, and technical details of the measurements. SAPFLUXNET contains 202 globally distributed datasets with sap flow time series for 2714 plants, mostly trees, of 174 species. SAPFLUXNET has a broad bioclimatic coverage, with woodland/shrubland and temperate forest biomes especially well represented (80 % of the datasets). The measurements cover a wide variety of stand structural characteristics and plant sizes. The datasets encompass the period between 1995 and 2018, with 50 % of the datasets being at least 3 years long. Accompanying radiation and vapour pressure deficit data are available for most of the datasets, while on-site soil water content is available for 56 % of the datasets. Many datasets contain data for species that make up 90 % or more of the total stand basal area, allowing the estimation of stand transpiration in diverse ecological settings. SAPFLUXNET adds to existing plant trait datasets, ecosystem flux networks, and remote sensing products to help increase our understanding of plant water use, plant responses to drought, and ecohydrological processes. SAPFLUXNET version 0.1.5 is freely available from the Zenodo repository (https://doi.org/10.5281/zenodo.3971689; Poyatos et al., 2020a). The “sapfluxnetr” R package – designed to access, visualize, and process SAPFLUXNET data – is available from CRAN.

Riparian forests in floodplains are occasionally or regularly submerged by flooding. However, controversy exists regarding the effects of flooding on water use in riparian forests, and this controversy severely restricts our ability to better utilize limited water resources to restore damaged riparian forests in arid regions.The evapotranspiration (Et) and transpiration (T) of riparian P. euphratica forests in the arid regions of northwestern China were determined using eddy covariance and sap flow technology across a 3-year period. Fortunately, the flooding introduced by ecological water diversion was occurred in 2014 and 2016 but not in 2015. Our results showed that the magnitude and seasonal pattern of Et across 3 years was comparable (approximately 900 mm), but the T was higher in 2015 (431 mm) than in the other two years (288 mm in 2014 and 290 mm in 2016). The interannual patterns in the transpiration were consistent with the net ecosystem productivity at the site. Given the similar meteorological conditions (e.g. net radiation, temperature, relative humidity, and vapor pressure deficit) among the 3 years, two aspects may contributed to the suppressed tree water use and productivity under flooding: 1) the increased soil salinity reduce the roots water uptake from soil by increasing root water potential via osmotic adjustment; and 2) the depressed tree growth (e.g. the leaf area) via suspended water upward transport along soil-plant-atmosphere continuum. Although flooding is widely known beneficial for the regeneration, we suggest that it is not appropriate for the rejuvenation of phreatophyte (e.g., Populus spp.) in arid regions. Our results were drawn from only three years of measurement and therefore longer time series are needed to confirm or refine those conclusions.

Agriculture faces increasing sustainability pressures. Land intensification and degradation, energy use and inputs, complex environmental management, social issues facing farming communities and climate change are just some of the headline sustainability concerns threatening the viability of farming. Simultaneously, there is a need to increase food and fibre production and resource use efficiency. For many of these sustainability issues, increasing the number of trees planted in agricultural systems, or agroforestry, can improve the productivity and sustainability of future rural agricultural landscapes. In many parts of the world, the benefits of agroforestry remain under-realised. To understand the reasons behind this, interviews were conducted with 44 predominantly mixed enterprise farmers and farm advisors in Tasmania, Australia. Discourse analysis identified three groups of values driving perceptions and behaviours relating to agroforestry, trees as an economic proposition, trees as uneconomic and trees as essential regardless of economics. Previous work has identified many complex factors contributing to the lack of tree planting on farms including failures of past reforestation schemes, lack of awareness of the benefits of trees, perceptions of market volatility and risk, or simply a lack of time and money. This is one of the first times the underlying social norms and values creating perceptions of agroforestry have been identified. These new insights allow extension programs to tailor recommendations to identified groups based on perceptions of agroforestry. Evaluating these perceptions also allows new perspectives on opportunities for agroforestry adoption to be created, both in Tasmania and more broadly.

Comparing juvenile and adult shoots of Eucalyptus globulus reveals that juvenile leaves are more vulnerable to hydraulic failure than adults while stems show no significant differences. Understanding variation in the susceptibility for xylem tissue to cavitate and lose its function during water stress exposure is critical for predicting plant mortality during drought. An increasing number of studies examine variation in xylem vulnerability to water-stress-induced damage among species, but very few studies explore variation associated with ontogeny and development. Here, we assess stem and leaf vulnerability to cavitation in the heteroblastic tree species Eucalyptus globulus using a non-invasive optical technique to measure the accumulation of air embolisms during dehydration. No significant difference between the vulnerability of stem xylem was found between juvenile and adult stems, but the xylem of juvenile leaves was more susceptible to cavitation during dehydration than adult leaves. Analysis of vessel diameters indicates differences in maximum vessel diameter but little differences in hydraulically weighted mean vessel diameter. The results are discussed in context of similar studies that compare juvenile and adult plants, as well as potential anatomical and functional trade-offs associated with phase change and growth in E. globulus, which presents a complex relationship across its broad distribution.

Extreme disturbance events, such as wildfire and drought, have large impacts on carbon storage and sequestration of forests and woodlands globally. Here, we present a modelling approach that assesses the relative impact of disturbances on carbon storage and sequestration, and how this will alter under climate change. Our case study is semi-arid Australia where large areas of land are managed to offset over 122 million tonnes of anthropogenic carbon emissions over a 100-year period. These carbon offsets include mature vegetation that has been protected from clearing and regenerating vegetation on degraded agricultural land. We use a Bayesian Network model to combine multiple probabilistic models of the risk posed by fire, drought, grazing and recruitment failure to carbon dynamics. The model is parameterised from a review of relevant literature and additional quantitative analyses presented here. We found that the risk of vegetation becoming a net source of carbon due to a mortality event, or failing to realise maximum sequestration potential, through recruitment failure in regenerating vegetation, was primarily a function of rainfall in this semi-arid environment. However, the relative size of an emissions event varied across vegetation communities depending on plant attributes, specifically resprouting capacity. Modelled climate change effects were variable, depending on the climate change projection used. Under 'best-case' or 'most-likely' climate scenarios for 2050, similar or increased projections of mean annual precipitation, associated with a build-up of fuel, were expected to drive an increase in fire activity (a 40-160% increase), but a decrease in drought (a 20-35% decrease). Under a 'worst-case' climate scenario, fire activity was expected to decline (a 37% decrease), but drought conditions remain similar (a 5% decrease). These projected changes to the frequency of drought and fire increase the risk that vegetation used for carbon offsetting will fail to provide anticipated amounts of carbon abatement over their lifetime.

In the version of this Perspective originally published, affiliations 1 and 4 ware incorrect, and should have read: “ 1 Antarctic Climate & Ecosystems CRC, University of Tasmania, Hobart, Tasmania, Australia” and “ 4 Centre for Water, Climate and Land (CWCL), University of Newcastle, Callaghan, NSW, Australia”. These have been corrected in the online versions of this Perspective.

AbstractDuring the night, plant water loss can occur either through the roots, as hydraulic redistribution (HR), or through the leaves via the stoma, as nocturnal transpiration (En), which was methodologically difficult to separate from stem refilling (Re). While HR and En have been reported across a range of species, ecosystem, and climate zone, there is little understanding on the interactions between En and/or Re and HR. As water movement at night occurs via gradients of water potential, it is expected that during periods of high atmospheric vapor pressure deficit (VPD), water loss via En will override water loss via HR. To test this hypothesis, sap flow in stems and roots of Populus euphratica Oliv. trees, growing in a riparian zone in a hyperarid climate, was measured once in a year. Nocturnal stem sap flow was separated into En and Re using the “forecasted refilling” method. Substantial nocturnal sap flow (38% of 24‐hr flux on average) was observed and positively correlated with VPD; however, the strength of the correlation was lower (R2 = .55) than diurnal sap flow (Ed) (R2 = .72), suggesting that nocturnal stem sap flow was attributed to both water loss through the canopy and replenishment of water in stem tissues. Partitioning of nocturnal sap flow shows that Re constituted approximately 80%, and En ~20%, of nocturnal sap flow. The amount of root sap flow attributed to redistribution was negatively related to Ed (R2 = .69) and the amount of acropetally sap flow in stems, Re (R2 = .41) and En (R2 = .14). It was suggested that the magnitude of HR is more strongly depressed by Re that was recharge to the water loss via Ed than by En. It was consistent with whole‐tree water balance theory, that the nighttime upward sap flow to xylem, stem refilling and transpiration, may depress hydraulic redistribution of roots.

Reforestation schemes, which encompass environmental plantings and natural regeneration of vegetation on cleared land, are increasingly being established for the purposes of mitigating anthropogenic carbon emissions. However, these schemes are themselves at risk from climate change and associated changes in disturbance regimes. Simultaneously, there is increasing pressure on reforested areas to achieve multiple co-benefits, e.g. maximizing carbon storage, ameliorating environmental degradation and promoting biodiversity objectives, all while not adversely affecting community values, such as agricultural production. Here, we review the myriad of biophysical risks posed by climate change to reforested areas while documenting management actions and policies that can enhance both the resistance and resilience of reforested areas to such risks. While it is difficult to buffer vegetation against the direct effects of climate change, such as elevated temperature and changed precipitation patterns, it is possible to manage some of the indirect effects, such as wildfire, drought and insect defoliation. Methods for reducing the vulnerability of reforested areas range from site-specific management actions, particularly around design and location, through to regional and national scale initiatives, such as vulnerability assessments and decision support tools. The complexity of objectives and risks posed to reforested areas means that it is vitally important to evaluate outcomes from across the current estate of reforested areas. However, there is currently no national protocol in place in Australia to track, monitor or evaluate the outcomes of reforestation. Thus, we recommend the establishment of a national framework for analyzing and supporting the growing range of reforestation activities.

"Surgeons and the Model Calibration method of trial interpretation." British Journal of Neurosurgery, 32(2), pp. 125–126

Heat waves have profoundly impacted biota globally over the past decade, especially where their ecological impacts are rapid, diverse, and broad-scale. Although usually considered in isolation for either terrestrial or marine ecosystems, heat waves can straddle ecosystems of both types at subcontinental scales, potentially impacting larger areas and taxonomic breadth than previously envisioned. Using climatic and multi-species demographic data collected in Western Australia, we show that a massive heat wave event straddling terrestrial and maritime ecosystems triggered abrupt, synchronous, and multi-trophic ecological disruptions, including mortality, demographic shifts and altered species distributions. Tree die-off and coral bleaching occurred concurrently in response to the heat wave, and were accompanied by terrestrial plant mortality, seagrass and kelp loss, population crash of an endangered terrestrial bird species, plummeting breeding success in marine penguins, and outbreaks of terrestrial wood-boring insects. These multiple taxa and trophic-level impacts spanned >300,000 km2-comparable to the size of California-encompassing one terrestrial Global Biodiversity Hotspot and two marine World Heritage Areas. The subcontinental multi-taxa context documented here reveals that terrestrial and marine biotic responses to heat waves do not occur in isolation, implying that the extent of ecological vulnerability to projected increases in heat waves is underestimated.

Understanding intraspecific variation in the vulnerability of the xylem to hydraulic failure during drought is critical in predicting the response of forest tree species to climate change. However, few studies have assessed intraspecific variation in this trait, and a likely limitation is the large number of measurements required to generate the standard 'vulnerability curve' used to assess hydraulic failure. Here we explore an alternative approach that requires fewer measurements, and assess within species variation in leaf xylem vulnerability in Eucalyptus globulus Labill., an ecologically and economically important species with known genetic variation in drought tolerance. Using this approach we demonstrate significant phenotypic differences and evidence of plasticity among two provenances with contrasting drought tolerance.

Substantial uncertainty surrounds our knowledge of tree stem growth, with some of the most basic questions, such as when stem radial growth occurs through the daily cycle, still unanswered.We employed high-resolution point dendrometers, sap flow sensors, and developed theory and statistical approaches, to devise a novel method separating irreversible radial growth from elastic tension-driven and elastic osmotically driven changes in bark water content. We tested this method using data from five case study species. Experimental manipulations, namely a field irrigation experiment on Scots pine and a stem girdling experiment on red forest gum trees, were used to validate the theory.Time courses of stem radial growth following irrigation and stem girdling were consistent with a-priori predictions. Patterns of stem radial growth varied across case studies, with growth occurring during the day and/or night, consistent with the available literature. Importantly, our approach provides a valuable alternative to existing methods, as it can be approximated by a simple empirical interpolation routine that derives irreversible radial growth using standard regression techniques. Our novel method provides an improved understanding of the relative source-sink carbon dynamics of tree stems at a sub-daily time scale.

Drought can cause major damage to plant communities, but species damage thresholds and postdrought recovery of forest productivity are not yet predictable. We used an El Niño drought event as a natural experiment to test whether postdrought recovery of gas exchange could be predicted by properties of the water transport system, or if metabolism, primarily high abscisic acid concentration, might delay recovery. We monitored detailed physiological responses, including shoot sapflow, leaf gas exchange, leaf water potential and foliar abscisic acid (ABA), during drought and through the subsequent rehydration period for a sample of eight canopy and understory species. Severe drought caused major declines in leaf water potential, elevated foliar ABA concentrations and reduced stomatal conductance and assimilation rates in our eight sample species. Leaf water potential surpassed levels associated with incipient loss of leaf hydraulic conductance in four species. Following heavy rainfall gas exchange in all species, except those trees predicted to have suffered hydraulic impairment, recovered to prestressed rates within 1 d. Recovery of plant gas exchange was rapid and could be predicted by the hydraulic safety margin, providing strong support for leaf vulnerability to water deficit as an index of damage under natural drought conditions.