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Describing and classifying a landscape for environmental impact and risk assessment purposes is a non-trivial challenge, as standard landscape classifications that cater for region specific impacts do not exist. Assessing impacts on ecosystems from extraction of water resources across large regions requires linking of landscape features to 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 underpin risk modelling and make 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 combining 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.

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; P50) were more embolized than species with lower P50. 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.

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.

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.

During 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 (E n), which was methodologically difficult to separate from stem refilling (R e). While HR and E n have been reported across a range of species, ecosystem, and climate zone, there is little understanding on the interactions between E n and/or R e 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 E n 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 E n and R e 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 (R 2 = .55) than diurnal sap flow (E d) (R 2 = .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 R e constituted approximately 80%, and E n ~20%, of nocturnal sap flow. The amount of root sap flow attributed to redistribution was negatively related to E d (R 2 = .69) and the amount of acropetally sap flow in stems, R e (R 2 = .41) and E n (R 2 = .14). It was suggested that the magnitude of HR is more strongly depressed by R e that was recharge to the water loss via E d than by E n. 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.

Summary 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 Nino 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.

A 27-year-old active-duty male sailor directly accessed physical therapy for deep left anterior shoulder pain. The patient sustained his injury the previous day, when he threw a left hook into the body of his sparring partner, creating a sudden high-energy external rotation force. Based on the patient's complaint, mechanism of injury, and internal rotation weakness, the examining physical therapist ordered magnetic resonance imaging. The images revealed a large partial tear, with retraction of the subscapularis tendon at the lesser tuberosity, a labral tear, and an intratendon biceps tendon tear with subluxation. J Orthop Sports Phys Ther 2018;48(12):983. doi:10.2519/jospt.2018.8221.

International audience; AbstractAgriculture 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.

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.

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.

© 2015 Elsevier B.V. The objective of this study was to estimate the recovery trajectory of evapotranspiration (Et) and streamflow (Q) in resprouting forested catchments following wildfire. Recovery dynamics were assessed in mixed species eucalypt forests in south-eastern Australia which recover from disturbance largely via vegetative resprouting, and to a lesser degree, via seedling recruitment. Changes in Et were evaluated in two ways. Firstly, we developed semi-empirical models of post-fire Et following moderate and high severity wildfire. These models were based on datasets of plot-scale Et, measured within five years post-fire, and published literature on post-fire changes in vegetation structure. Secondly, we analysed long-term Q records (25years) from a mixed species catchment, including a 1-5year period following a predominately moderate severity wildfire. We found that the overall length of recovery time for Et and Q following wildfire was 8-12years, which is much less than for eucalypt forests recovering via seedlings only. This emphasises the importance of functional responses to fire in forest ecosystems as a key driver of the hydrologic resilience of catchments, with resprouting forest types conferring relatively rapid recovery following disturbance. We also found that the recovery trajectory of post-fire Et was dependent on fire severity. Increased Et and consequent declines in Q occurred following moderate severity fire. In contrast, there was no evidence of increased Et following high severity fire. Based on patterns of long-term Q and rainfall observed in a small mixed species catchment, declines in Q due to increased Et following moderate severity wildfire were of similar magnitude to Q declines driven by a drought that coincided with the fire. We conclude that the coincidence of wildfire with drought exacerbates reductions in Q under moderate severity fire, resulting in greater Q declines. This is due to the enhanced rates of Et, primarily driven by regenerating seedlings and higher rates of transpiration from surviving trees.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Widespread tree mortality associated with drought has been observed on all forested continents and global change is expected to exacerbate vegetation vulnerability. Forest mortality has implications for future biosphere–atmosphere interactions of carbon, water and energy balance, and is poorly represented in dynamic vegetation models. Reducing uncertainty requires improved mortality projections founded on robust physiological processes. However, the proposed mechanisms of drought-induced mortality, including hydraulic failure and carbon starvation, are unresolved. A growing number of empirical studies have investigated these mechanisms, but data have not been consistently analysed across species and biomes using a standardized physiological framework. Here, we show that xylem hydraulic failure was ubiquitous across multiple tree taxa at drought-induced mortality. All species assessed had 60% or higher loss of xylem hydraulic conductivity, consistent with proposed theoretical and modelled survival thresholds. We found diverse responses in non-structural carbohydrate reserves at mortality, indicating that evidence supporting carbon starvation was not universal. Reduced non-structural carbohydrates were more common for gymnosperms than angiosperms, associated with xylem hydraulic vulnerability, and may have a role in reducing hydraulic function. Our finding that hydraulic failure at drought-induced mortality was persistent across species indicates that substantial improvement in vegetation modelling can be achieved using thresholds in hydraulic function

Increases in drought and temperature stress in forest and woodland ecosystems are thought to be responsible for the rise in episodic mortality events observed globally. However, key climatic drivers common to mortality events and the impacts of future extreme droughts on tree survival have not been evaluated. Here, we characterize climatic drivers associated with documented tree die-off events across Australia using standardized climatic indices to represent the key dimensions of drought stress for a range of vegetation types. We identify a common probabilistic threshold associated with an increased risk of die-off across all the sites that we examined. We show that observed die-off events occur when water deficits and maximum temperatures are high and exist outside 98% of the observed range in drought intensity; this threshold was evident at all sites regardless of vegetation type and climate. The observed die-off events also coincided with at least one heat wave (three consecutive days above the 90th percentile for maximum temperature), emphasizing a pivotal role of heat stress in amplifying tree die-off and mortality processes. The joint drought intensity and maximum temperature distributions were modeled for each site to describe the co-occurrence of both hot and dry conditions and evaluate future shifts in climatic thresholds associated with the die-off events. Under a relatively dry and moderate warming scenario, the frequency of droughts capable of inducing significant tree die-off across Australia could increase from 1 in 24 years to 1 in 15 years by 2050, accompanied by a doubling in the occurrence of associated heat waves. By defining commonalities in drought conditions capable of inducing tree die-off, we show a strong interactive effect of water and high temperature stress and provide a consistent approach for assessing changes in the exposure of ecosystems to extreme drought events.

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.

Summary Plant survival during drought requires adequate hydration in living tissues and carbohydrate reserves for maintenance and recovery. We hypothesized that tree growth and hydraulic strategy determines the intensity and duration of the ‘physiological drought’, thereby affecting the relative contributions of loss of hydraulic function and carbohydrate depletion during mortality. We compared patterns in growth rate, water relations, gas exchange and carbohydrate dynamics in three tree species subjected to prolonged drought. Two Eucalyptus species (E. globulus, E. smithii) exhibited high growth rates and water-use resulting in rapid declines in water status and hydraulic conductance. In contrast, conservative growth and water relations in Pinus radiata resulted in longer periods of negative carbon balance and significant depletion of stored carbohydrates in all organs. The ongoing demand for carbohydrates from sustained respiration highlighted the role that duration of drought plays in facilitating carbohydrate consumption. Two drought strategies were revealed, differentiated by plant regulation of water status: plants maximized gas exchange, but were exposed to low water potentials and rapid hydraulic dysfunction; and tight regulation of gas exchange at the cost of carbohydrate depletion. These findings provide evidence for a relationship between hydraulic regulation of water status and carbohydrate depletion during terminal drought.

The complex regulatory system controlling stomata involves physical and chemical signals that affect guard cell turgor to bring about changes in stomatal conductance (gs). Abscisic acid (ABA) closes stomata, yet the mechanisms controlling foliar ABA status in tree species remain unclear. The importance of foliage-derived ABA in regulating gas exchange was evaluated under treatments that affected phloem export through girdling and reduced water availability in the tree species, Pinus radiata (D. Don). Branch- and whole-plant girdling increased foliar ABA levels leading to declines in gs, despite no change in plant water status. Changes in gs were largely independent of the more transient increases in foliar non-structural carbohydrates (NSC), suggesting that gradual accumulation of foliar ABA was the primary mechanism for reductions in gs and assimilation. Whole-plant girdling eventually reduced root NSC, hindering root water uptake and decreasing foliar water potential, causing a dramatic increase in ABA level in leaves and concentrations in the xylem sap of shoots (4032 ng ml-1), while root xylem sap concentrations remained low (43 ng ml-1). Contrastingly, the drought treatment caused similar increases in xylem sap ABA in both roots and shoots, suggesting that declines in water potential result in relatively consistent changes in ABA along the hydraulic pathway. ABA levels in plant canopies can be regulated independently of changes in root water status triggered by changes by both phloem export and foliar water status.

* The evolution of lignified xylem allowed for the efficient transport of water under tension, but also exposed the vascular network to the risk of gas emboli and the spread of gas between xylem conduits, thus impeding sap transport to the leaves. A well-known hypothesis proposes that the safety of xylem (its ability to resist embolism formation and spread) should trade off against xylem efficiency (its capacity to transport water). * We tested this safety–efficiency hypothesis in branch xylem across 335 angiosperm and 89 gymnosperm species. Safety was considered at three levels: the xylem water potentials where 12%, 50% and 88% of maximal conductivity are lost. * Although correlations between safety and efficiency were weak (r2 < 0.086), no species had high efficiency and high safety, supporting the idea for a safety–efficiency tradeoff. However, many species had low efficiency and low safety. Species with low efficiency and low safety were weakly associated (r2 < 0.02 in most cases) with higher wood density, lower leaf- to sapwood-area and shorter stature. * There appears to be no persuasive explanation for the considerable number of species with both low efficiency and low safety. These species represent a real challenge for understanding the evolution of xylem. Fil: Gleason, Sean M.. Macquarie University. Department of Biological Sciences ; Australia. USDA-ARS. Water Management Research; Estados Unidos Fil: Westoby, Mark. Macquarie University. Department of Biological Sciences; Australia Fil: Jansen, Steven. Ulm University. Institute of Systematic Botany and Ecology; Alemania Fil: Choat, Brendan. Western Sydney University. Hawkesbury Institute for the Environment; Australia Fil: Hacke, Uwe G.. University of Alberta. Department of Renewable Resources; Canadá Fil: Pratt, Robert B.. California State University. Department of Biology; Estados Unidos Fil: Bhaskar, Radika. Haverford College. Department of Biology; Estados Unidos Fil: Brodibb, Tim J.. University of Tasmania. School of Biological Sciences; Australia Fil: Bucci, Sandra Janet. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia Golfo San Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia Golfo San Jorge. Universidad Nacional de la Patagonia "san Juan Bosco". Centro de Investigaciones y Transferencia Golfo San Jorge; Argentina Fil: Cao, Kun-Fang. Guangxi University. College of Forestry. Utilization of Subtropical Agro-Bioresources ; China Fil: Cochard, Hervé. Clermont Université. Université Blaise Pascal. UMR547 PIAF; Francia. Institut National de la Recherche Agronomique; Francia Fil: Delzon, Sylvain. Institut National de la Recherche Agronomique; Francia Fil: Domec, Jean-Christophe. Duke University, Durham. Nicholas School of the Environment; Estados Unidos. Institut National de la Recherche Agronomique; Francia Fil: Fan, Ze-Xin. Chinese Academy of Sciences. Xishuangbanna Tropical Botanical Garden. Key Laboratory of Tropical Forest Ecology; China Fil: Feild, Taylor S.. James Cook University. School of Marine and Tropical Biology; Australia Fil: Jacobsen, Anna L.. California State University. Department of Biology; Estados Unidos Fil: Johnson, Daniel M.. University of Idaho. Rangeland and Fire Sciences. Department of Forest; Estados Unidos Fil: Lens, Frederic. Leiden University. Naturalis Biodiversity Center; Países Bajos Fil: Maherali, Hafiz. University of Guelph. Department of Integrative Biology; Canadá Fil: Martínez-Viralta, Jordi. CREAF; España. Institució Catalana de Recerca i Estudis Avancats; España Fil: Mayr, Stefan. University of Innsbruck. Department of Botany; Austria Fil: McCulloh, Katherine A.. University of Wisconsin-Madison. Department of Botany; Estados Unidos Fil: Mencuccini, Maurizio. University of Edinburgh. School of GeoSciences; Reino Unido. Institució Catalana de Recerca i Estudis Avancats; España Fil: Mitchell, Patrick J.. CSIRO Land and Water Flagship; Australia Fil: Morris, Hugh. Ulm University. Institute of Systematic Botany and Ecology ; Alemania Fil: Nardini, Andrea. Università Trieste. Dipartimento Scienze della Vita ; Italia Fil: Pittermann, Jarmila. University of California. Department of Ecology and Evolutionary Biology; Estados Unidos Fil: Plavcová, Lenka. Ulm University. Institute of Systematic Botany and Ecology; Alemania. University of Alberta. Department of Renewable Resources; Canadá Fil: Schreiber, Stefan G.. University of Alberta. Department of Renewable Resources; Canadá Fil: Sperry, John S.. University of Utah. Department of Biology; Estados Unidos Fil: Wright, Ian J.. Macquarie University. Department of Biological Sciences; Australia Fil: Zanne, Ami E.. George Washington University. Department of Biological Sciences; Estados Unidos

Forest water use estimates derived from sap flow measurements in three contrasting regions of south-eastern Australia were compared. In each region, annual evapotranspiration was highly spatially variable, influenced by water availability, potential evapotranspiration, soil depth and texture, groundwater depth and salinity and at one site by species. In a low rainfall region (mean precipitation -400 mm year -1 ), ET in five irrigated eucalypt plantations ranged from 415 mm year -1 by Eucalyptus grandis W.Hill ex Maiden at a site with deep clayey soil and high salinity groundwater to 1277 mm year -1 by Corymbia maculate (Hook.) K.D.Hill & L.A.S. Johnson, at a site with loamy soil and low saline groundwater. On the same site, ET in a plantation of E. grandis was only 928 mm year -1 . In a medium rainfall region (mean precipitation 657 mm year -1 ), in gently undulating terrain containing large-scale plantations of Pinus radiata D. Don and Eucalyptus globulus Labill., fresh groundwater (EC -1 ) was often present but at depths varying from less than 2 m to greater than 20 m. Among 22 study sites, rainfall varied spatially from 362 to 800 mm year -1 but ET varied from 560 to 1414 mm year -1 . About 94% of this variation was explained by water availability from rainfall and groundwater and by potential evapotranspiration. In the highest rainfall region (precipitation ~1200 mm year -1 ) within a 1.2 km 2 catchment covered by native eucalypt forest in steep, mountainous terrain, annual ET varied by up to 63% between four study sites. In all three regions, only sapflow measurements would have revealed the high spatial variability in mean annual transpiration and ET that occurred over distances of

Across southern Australia, a large proportion of urban water supply is sourced from mountainous catchments forested with native eucalypts. Mixed species eucalypt forest (MSEF) is the most common forest type in this region and occurs on relatively dry, fire prone sites, yet factors controlling forest water use and stream flow in response to topography, disturbance and drought are poorly understood. This study investigated the patterns and drivers of water balance over a 4 year period in a 1.36 km2, MSEF catchment by: quantifying spatial and temporal variability in evapotranspiration (Et) and its components; evaluating the abiotic, structural and physiological factors controlling water use across the catchment; and testing the effects of antecedent soil water conditions on water fluxes after drought. This was done using a ‘bottom up’ measurement approach that included stream flow and Et (sap flow, interception troughs and evaporation dome) and a simple empirical model of Et to track catchment response to drought. Spatial variability was considerable, with 40% lower rates of Et at an up slope plot compared to mid and bottom slope plots. Tree transpiration was the dominant flux annually and was correlated to reference Et (r2 = 0.35–0.80), implying strong limitation by atmospheric demand across the catchment. Annual Et totals were relatively consistent between years (841 ± 34 mm) despite large variation in rainfall (463–1179 mm y−1). Annual stream flow represented a very small proportion of the water budget (

SUMMARY Patterns in forest structure and function are tightly coupled to variation in energy and soil water gradients and disturbance history across the landscape. In eucalypt forests of southern Australia, changes in forest structure may account for the majority of variation in the evapotranspiration (Et) signal across a single forest type. In this study, the potential for using light detection and ranging (LiDAR)-derived canopy height profiles to predict key components of Et; transpiration (Esap), interception loss (Ei) and forest floor evapotranspiration (Efloor) was assessed in a mixed-species eucalypt forest in south-eastern Australia. Step-wise regression was used to select suitable LiDAR canopy height indices to predict stand structural attributes at all grid points within the catchment using field plot inventory data (r2 = 0.76–0.88). Similar rates of sap velocity were observed among trees at different landscape positions and during all seasons, irrespective of tree size and stature, enabling scaling of stand-level Esap. The revised Gash interception model was successfully used to model Ei across the catchment using stand-level variation in canopy cover (derived from LiDAR). Similarly, Efloor was quantified spatially using variation in leaf area index and a two-bucket numeric model to interpolate field measurements. Our results show that variation in forest structure arising from changes in elevation in these south-facing catchments is a major determinant of forest water use and shows a threefold change in annual Et across the elevation gradient. The merging of detailed forest structural data and field-validated Et fluxes offers promise in advancing our understanding and prediction of key ecohydrologic processes in forested catchments. Copyright © 2011 John Wiley & Sons, Ltd.

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

In semi-arid ecosystems, evapotranspiration ( E t ) generally represents the greatest flux of water out of an ecosystem and is sensitive to changes in vegetation cover. In southern Australia, removal of native, deep-rooted perennials to make way for annual crops and pastures with shallower roots and less annual transpiration has led to rising, saline groundwater. Steps to redress this hydrological imbalance require knowledge of the ecohydrology of native systems such as eucalypt woodlands, which grow on deeper soils low in the landscape, and, unlike annual crops, sustain growth and water use during summer months. We assessed the partitioning of E t in a common woodland type in south-western Australia ( Eucalyptus capillosa subsp. capillosa Brooker and Hopper) and the response of tree transpiration ( E sap ) to both atmospheric and soil water conditions. Overall, the total woodland evapotranspiration ( E total ) exceeded present-year rainfall (359 mm vs. 265 mm) but was equal to average rainfall of the preceding 10 years, suggesting long-term balance in water supply and E total in this system. The contribution of E sap to E total was surprisingly small (53 and 22% of E total in summer and winter, respectively) while woodland floor evapotranspiration ( E floor ) contributed 38 and 64% during the same periods. Rates of E sap increased in response to summer rainfall, due primarily to reduced sensitivity in summer to vapour pressure deficit when soil water potentials increased. Additionally, night-time tree transpiration contributed appreciably to the overall water budget (2–8% of seasonal E total ), being similar in magnitude to interception losses, and therefore should be included in water budgets. Partitioning of E total in this woodland type also demonstrated that trees provide a more stable water flux out of the system than E floor , most likely because they access soil water from a large volume of soil.

We measured leaf water relations and leaf structural traits of 20 species from three communities growing along a topographical gradient. Our aim was to assess variation in seasonal responses in leaf water status and leaf tissue physiology between sites and among species in response to summer water deficit. Species from a ridge-top heath community showed the greatest reductions in pre-dawn leaf water potentials (Psi(leaf)) and stomatal conductance during summer; species from a valley-floor woodland and a midslope mallee community showed less reductions in these parameters. Heath species also displayed greater seasonal reduction in turgor-loss point (Psi(TLP)) than species from woodland or mallee communities. In general, species that had larger reductions in Psi(leaf) during summer showed significant shifts in either their osmotic potential at full turgor (Psi(pi 100); osmotic adjustment) or in tissue elasticity (epsilon(max)). Psi(pi 100) and epsilon(max) were negatively correlated, during both spring and summer, suggesting a trade-off between these different mechanisms to cope with water stress. Specific leaf area varied greatly among species, and was significantly correlated with seasonal changes in Psi(TLP) and pre-dawn Psi(leaf). These correlations suggest that leaf structure is a prerequisite for cellular mechanisms to be effective in adjusting to water deficit.

The surge in global efforts to understand the causes and consequences of drought on forest ecosystems has tended to focus on specific impacts such as mortality. We propose an ecoclimatic framework that takes a broader view of the ecological relevance of water deficits, linking elements of exposure and resilience to cumulative impacts on a range of ecosystem processes. This ecoclimatic framework is underpinned by two hypotheses: (i) exposure to water deficit can be represented probabilistically and used to estimate exposure thresholds across different vegetation types or ecosystems; and (ii) the cumulative impact of a series of water deficit events is defined by attributes governing the resistance and recovery of the affected processes. We present case studies comprising Pinus edulis and Eucalyptus globulus, tree species with contrasting ecological strategies, which demonstrate how links between exposure and resilience can be examined within our proposed framework. These examples reveal how climatic thresholds can be defined along a continuum of vegetation functional responses to water deficit regimes. The strength of this framework lies in identifying climatic thresholds on vegetation function in the absence of more complete mechanistic understanding, thereby guiding the formulation, application and benchmarking of more detailed modelling.

Yan-Shih Lin [et al.].- Received 16 August 2014, Accepted 16 January 2015, Published online 02 March 2015, Stomatal conductance (gs) is a key land-surface attribute as it links transpiration, the dominant component of global land evapotranspiration, and photosynthesis, the driving force of the global carbon cycle. Despite the pivotal role of gs in predictions of global water and carbon cycle changes, a global-scale database and an associated globally applicable model of gs that allow predictions of stomatal behaviour are lacking. Here, we present a database of globally distributed gs obtained in the field for a wide range of plant functional types (PFTs) and biomes. We find that stomatal behaviour differs among PFTs according to their marginal carbon cost of water use, as predicted by the theory underpinning the optimal stomatal model1 and the leaf and wood economics spectrum2, 3. We also demonstrate a global relationship with climate. These findings provide a robust theoretical framework for understanding and predicting the behaviour of gs across biomes and across PFTs that can be applied to regional, continental and global-scale modelling of ecosystem productivity, energy balance and ecohydrological processes in a future changing climate.

Understanding the water relations of Eucalyptus trees plays an important role in finding solutions to dryland salinity in southern Australia. A model for studying structure-function relationships in isolated tree crowns (radiation absorption, transpiration and photosynthesis, RATP) was parameterized to permit the seasonal transpiration course of a Eucalyptus salmonophloia tree to be quantified. Model responses to different parameterizations were tested in a sensitivity analysis. Predictive quality was mostly affected by the accuracy of information about leaf area density and stomatal responses to air vapor pressure deficit, and to a lesser extend by foliage dispersion. Assuming simple, non-synergistic influences of changes in photosynthetic active radiation and air vapor pressure deficit on stomatal transpiration control, the model was able to simulate the daily water uptake of E. salmonophloia trees with reasonable predictive quality during an entire season. In order to more precisely simulate short-term (i.e. diurnal) water use dynamics, the model must be extended to account for hydraulic and chemical controls of stomatal regulation of crown energy balance.

Tree species are exposed to single and combined forms of stress capable of inducing severe changes in plant functioning and survival. Climate change and other human disturbance continue to introduce novel combinations of stressors in forest ecosystems that make predicting their impact exceedingly difficult. In this chapter, we examine the causes and consequences of combined stresses in forest ecosystems. We discuss the significance of a range of abiotic and biotic factors responsible for various impacts on forest ecosystems, including long-term decline and episodic forest collapse. A generalized framework is presented that helps elucidate the contributions of primary, secondary, conditioning, and anthropogenic factors in determining levels of physiological stress in trees. The intensity, frequency, and duration of the constitutive stressors can determine the effect of other stress factors, thereby mediating the importance of singular and multiple factors in defining physiological distress and recovery. The importance of understanding the mechanistic basis for observed stress responses is discussed in light of the challenges associated with predicting impacts from multiple stressors.

Gas exchange, growth, water transport and carbon (C) metabolism diminish during drought according to their respective sensitivities to declining water status. The timing of this sequence of declining physiological functions may determine how water and C relations compromise plant survival. In this paper, we test the hypothesis that the degree of asynchrony between declining C supply (photosynthesis) and C demand (growth and respiration) determines the rate and magnitude of changes in whole-plant non-structural carbohydrates (NSC) during drought. Two complementary experiments using two tree species (Eucalyptus globulus Labill. and Pinus radiata D. Don) with contrasting drought response strategies were performed to (i) assess changes in radial stem growth, transpiration, leaf water potential and gas exchange in response to chronic drought, and (ii) evaluate the concomitant impacts of these drought responses on the temporal patterns of NSC during terminal drought. The three distinct phases of water stress were delineated by thresholds of growth cessation and stomatal closure that defined the 'carbon safety margin' (i.e., the difference between leaf water potential when growth is zero and leaf water potential when net photosynthesis is zero). A wider C safety margin in E. globulus was defined by an earlier cessation of growth relative to photosynthesis that reduced the demand for NSC while maintaining C acquisition. By contrast, the narrower C safety margin in P. radiata was characterized by a synchronous decline in growth and photosynthesis, whereby growth continued under a declining supply of NSC from photosynthesis. The narrower C safety margin in P. radiata was associated with declines in starch concentrations after ∼ 90 days of chronic drought and significant depletion of starch in all organs at mortality. The observed divergence in the sensitivity of drought responses is indicative of a potential trade-off between maintaining hydraulic safety and adequate C availability.

Following disturbance many woody species are capable of resprouting new foliage, resulting in a reduced leaf-to-sapwood area ratio and altered canopy structure. We hypothesized that such changes would promote adjustments in leaf physiology, resulting in higher rates of transpiration per unit leaf area, consistent with the mechanistic framework proposed by Whitehead et al. (Whitehead D, Jarvis PG, Waring RH (1984) Stomatal conductance, transpiration and resistance to water uptake in a Pinus sylvestris spacing experiment. Can J For Res 14:692–700). We tested this in Eucalyptus obliqua L’Her following a wildfire by comparing trees with unburnt canopies with trees that had been subject to 100% canopy scorch and were recovering their leaf area via resprouting. In resprouting trees, foliage was distributed along the trunk and on lateral branches, resulting in shorter hydraulic path lengths. We evaluated measurements of whole-tree transpiration and structural and physiological traits expected to drive any changes in transpiration. We used these structural and physiological measurements to parameterize the Whitehead et al. equation, and found that the expected ratio of transpiration per unit leaf area between resprouting and unburnt trees was 3.41. This is similar to the observed ratio of transpiration per unit leaf area, measured from sapflow observations, which was 2.89 (i.e., resprouting trees had 188% higher transpiration per unit leaf area). Foliage at low heights (

Forests that recover from disturbance predominately via vegetative resprouting may be expected to have different catchment water balance dynamics following wildfire than forests recovering from seed. However, the impacts of wildfire on forest water use are largely unknown in resprouting forest types. This is despite their dominance across the majority of southern Australia's forested catchments and the large areas burnt in recent years. We hypothesized that postfire changes in evapotranspiration (E t ) would be a function of fire severity and topography and that partitioning of E t would change after fire because of altered stand structure. We tested these hypotheses by monitoring E t and component fluxes across different topographic positions and fire severities in a mixed eucalypt species forest located in water supply catchments for the city of Melbourne. For this forest type, wildfire triggers vegetative resprouting from lignotubers and epicormic shoots on the bole and branches of the overstorey trees, in addition to prolific seedling germination. Monitoring was undertaken over 1-3 years following the 2009 Black Saturday wildfires. We found that E t was on average 41% lower in forest burnt at high severity compared with unburnt forest, whereas E t from forest burnt at moderate severity was only 3% lower than unburnt forest over 1-2years postfire but on average 9% higher over 2-3 years postfire. E t losses were driven by tree and shrub mortality in conjunction with lower transpiration in surviving trees. Lower E t was partially offset by regenerating seedlings that drove increases in forest floor E t and interception loss. Finally, we found that topography, through its effects on evaporative demand and forest structure, was a strong determinant of total E t but did not affect the nature of postfire recovery.

Research into the mechanisms driving drought-related plant mortality has seen a focussed effort in recent years. Drought and water availability are pervasive factors influencing the distribution of forests and woodlands globally, particularly in water-limited environments, where evaporation exceeds rainfall and is therefore a major constraint on productivity. However, the lack of a predictive framework for forest mortality remains an important knowledge gap in ecosystem and biogeochemical models (Roxburgh et al., 2004). The paper by Hartmann et al. (pp. 340–349) in the Feature on drought-related mortality in this issue of New Phytologist provides some novel insights into the relative contributions of hydraulic failure and carbon (C) starvation in trees. In conjunction with recent activity focussed on unravelling the relative importance of the putative mechanisms of plant mortality, our goal should be to improve our understanding of C, water and nutrient dynamics in ecosystems and improve our capacity to predict conditions under which mortality is likely to occur.

Describing a recent drought-related forest dieback event in south-western Australia in 2011 (Matusick 2012), a colleague remarked upon the distinctive sounds of wood boring beetles feeding on weakened eucalypt trees during one of the most severe droughts on record (K. Ruthrof, personal communication). For this insect population, normally scarce and benign, drought stress had most likely triggered a surge in their abundance, thereby amplifying declines in forest health during an already stressful event. Observations of an apparent coincidence of stressors such as drought and pests are of course common across many ecosystems (Mattson and Haack 1987, Ayres and Lombardero 2000). The subsequent impacts on forest function and structure from stressors such as drought and herbivory represent complex interactions between abiotic and biotic factors (Raffa et al. 2008).

Assessing the hydrological imbalance and associated land degradation issues facing much of southern Australia and other parts of the world requires a better understanding of the defining features of ecosystem water use and the design of sustainable agroecosystems. Thus, by grouping species with similar water-use strategies into ‘hydraulic functional types’ (HFTs), we investigated the characteristics of water use in species-rich plant communities of south-western Australia. HFTs were determined using multiple-trait associations between morphological and physiological traits relating to water transport, water-use efficiency and response to water deficit. Sixteen traits were assessed from a subset of 21 species from three plant communities located along a topographically determined soil- and water-availability gradient. Multivariate analyses showed that trait variation was least at sites with shallower soils and putatively lower water availability, suggesting a convergence of water-use strategies at sites where plants are exposed to large seasonal water deficits. Stem hydraulic parameters, including stem-specific hydraulic conductivity, conduit diameter and maximum percentage embolism, were positively correlated, indicating the generality that larger conduit diameter permits greater hydraulic efficiency and is associated with greater seasonal reductions in hydraulic conductivity in this ecosystem. Wood density was not correlated with these traits, but closely associated with species’ ability to withstand more negative water potentials during summer. Long-term integrated water-use efficiency was lower in shallow-rooted species that exhibited more negative summer water potentials. Specific leaf area and minimum leaf water potential were correlated with a number of separate traits, and appear to represent key axes of trait variation that describe the water-use strategies of different HFTs along the topographic gradient. Five HFTs were classified using a resemblance analysis according to combinations of traits that pertain to different water-use strategies among species; year-round active tree, year-round active shrub, hemiparasite, drought-suppressed broad-leaved shrub and drought-suppressed narrow-leaved shrub.

Growth responses to water deficit translate into discernible changes in the structure of woody tissues and provide an integrated record of historical water availability throughout the life of the individual. The highly dynamic nature of woody growth can impart adaptive changes in physiological performance through changes in xylem elements that regulate water transport. Here, we present a case study of how sapwood anatomical properties can be mapped using point dendrometers, in a diffuse porous, Eucalyptus spp. to reveal plasticity in hydraulic architecture under water deficit. Reductions in stem growth in response to water deficit coincided with marked changes sapwood vessel anatomy that could be matched to the commencement of large fluctuations in stem radius. These changes included: a reduction in hydraulically-weighted vessel diameter, increases in vessel density, sapwood lumen fraction and density and increase in wall strength. However, no changes in estimated stem conductivity were observed during the water deficit. This approach emphasises the responsiveness of species such as Eucalyptus to changes in water supply and provides an illustration of how we might detect short-term and rapid changes in stem hydraulic architecture in response to water availability and other environmental controls.