Mass forest die-offs will proliferate and expand. The trend toward more extreme heat waves and droughts is lethal for forests.

At the current pace of warming, much of the world will be inhospitable to forests as we know them within decades. The extinction of some tree species by direct or indirect action of drought and high temperatures is certain. And some recent research suggests that, in 40 years, none of the trees alive today will be able to survive the projected climate, Brodribb said.

“Nobody predicted the coral bleaching scenario. If a similar thing evolves with forests, that is pretty catastrophic,” he said. “We’re at a point where we can see the process, we can predict it. It’s time to start making some noise about it. We can’t afford to sit on our hands.”

An emerging megadrought has already weakened and killed hundreds of millions of trees, including Rocky Mountain lodgepole and piñon pines, as well as aspens.

On an article from April 17 in the journal Science. Following article from Inside Climate News, by Bob Berwyn, April 25, 2020 ‘We Need to Hear These Poor Trees Scream’: Unchecked Global Warming Means Big Trouble for Forests

In Eastern California, the U.S. Forest Service is using controlled fires in Jeffrey pine forests to try and make them more resilient to climate change. Credit: Bob Berwyn

Tim Brodribb has been measuring all the different ways global warming kills trees for the past 20 years. With a microphone, he says, you can hear them take their last labored breaths. During blistering heat waves and droughts, air bubbles invade their delicate, watery veins, cracking them open with an audible pop. And special cameras can film the moment their drying leaves split open in a lightning bolt pattern, disrupting photosynthesis.

“We really need to be able to hear these poor trees scream. These are living things that are suffering. We need to listen to them,” said Brodribb, a plant physiologist at the University of Tasmania who led a recent study that helps identify exactly when, where and how trees succumb to heat and dryness.

The study, published April 17 in the journal Science, reviewed the last 10 years of research on tree mortality, concluding that forests are in big trouble if global warming continues at the present pace. Most trees alive today won’t be able to survive in the climate expected in 40 years, Brodribb said. The negative impacts of warming and drying are already outpacing the fertilization benefits of increased carbon dioxide.

Trees and forests can be compared with corals and reefs, he said. Both are slow-growing and long-lived systems that can’t easily move or adapt in a short time to rapid warming and both have relatively inflexible damage thresholds. For corals, a global tipping point was reached from 2014 to 2016. In record-warm oceans, reefs around the world bleached and died.

The detailed new information and modeling on how water stress kills trees suggests there is a similar drought threshold for tree mortality, beyond which forests could also perish on a global scale, he said.

“Nobody predicted the coral bleaching scenario. If a similar thing evolves with forests, that is pretty catastrophic,” he said. “We’re at a point where we can see the process, we can predict it. It’s time to start making some noise about it. We can’t afford to sit on our hands.”

No CO2 Greening

The new paper shows that the hope that rising carbon dioxide would green the planet is probably misplaced. Studies have shown that increased carbon dioxide in the atmosphere boosts photosynthesis, spurring plant growth by chemically combining the carbon with water and ground nutrients.

But there will “probably be more browning than greening,” said University of Arizona forest scientist Dave Breshears, who was not involved in the new research.

“The review ends on a hard note, with high confidence that we’re going to have a lot of impacts with hotter droughts in the future,” he said. Mass forest die-offs will proliferate and expand. The trend toward more extreme heat waves and droughts is lethal for forests. But despite the grim outlook, it’s important not to paint an entirely desperate picture, he said.

“It’s our choice of how much worse we want it to get. Every little bit of reduction of warming can have a positive effect. We can reduce the tree die-off. Are we going to make the choices to try and minimize that?“

Breshears has used tree mortality data to try and make near real-time projections for tree die-offs in the Southwest. This would help adapt forest management, including firefighting, to rapidly changing conditions in a region where an emerging megadrought has already weakened and killed hundreds of millions of trees, including Rocky Mountain lodgepole and piñon pines, as well as aspens.

Piñon pines in Colorado's Mesa Verde National Park have been killed by beetles and wildfires and in many areas it's become too warm and dry for new trees to sprout from seed and grow. Credit: Bob Berwyn — Piñon pines in Colorado’s Mesa Verde National Park have been killed by beetles and wildfires and in many areas it’s become too warm and dry for new trees to sprout from seed and grow. Credit: Bob Berwyn

Elsewhere, African cedars and acacias are dying, South America’s Amazon rainforest is struggling, and junipers are declining in the Middle East. In Spain and Greece, global warming is shriveling oaks, and even in moist, temperate northern Europe, unusual droughts have stressed vast stands of beech forests.

“That’s one of the potential scenarios, and we need to know if that’s right. We have to establish the consequences of rising temperatures unequivocally for policy makers,” he said.

The stakes are high, since trees are the foundation for terrestrial biodiversity and because they capture and store about one-third of human-caused CO2 emissions within their dense wood frames. A global loss of forests could lead to a surge in heat-trapping carbon dioxide, causing more warming, and would also eliminate habitat for countless other animals, plants and fungi, with a rippling effect that reaches humans.

“The closer people are to the land and living at subsistence level, it’s going to hit those people hardest,” Breshears said.

Shifting Forests

Forests in warm and semi-arid regions may suffer the most in the decades ahead, but there may also be big changes in store for cooler, wetter regions. Some forests that need a lot of moisture could dry up with just a small decline in precipitation because rapid warming magnifies the loss of moisture from soils.

Even if forests don’t die, they will fundamentally change. A recent study published in the journal Global Change Biology zoomed in on the evergreen forests in the Stubai Valley in Tirol, Austria. At 3.6 degrees Fahrenheit (2 degrees Celsius) of global warming, which will be reached during the last few decades of this century, the dense stands of spruce and fir will change to a mix of oaks and pines, more like forests on the drier southern fringes of the Alps in Italy, the projections showed.

“We found that at warming levels above 2 degrees Celsius a threshold was crossed, with the system tipping into an alternative state,” the researchers wrote. Even warming that corresponds with the current policy goals of the Paris climate agreement could “result in critical transitions of forest ecosystems. Overshooting the climate targets could be dangerous, because “ecological impacts can be irreversible at millennial time scales once a tipping point has been crossed.”

Forests on a Knife Edge

The new paper reinforces the observational evidence that global warming has pushed many of the world’s forests to a knife edge, said University of Utah forest researcher Bill Anderegg. In the West, you can’t drive on a mountain highway without seeing how global warming affects forests, from wildfires to die-offs caused by beetles or other pathogens, he said.

In some areas, researchers have documented how forests are struggling to grow back. For example, in parts of the Four Corners region, hardly any new piñon pines have sprouted to replace trees killed by beetles in the early 2000s because it’s too warm for seeds to take hold and grow.

And older trees conserve their energy to survive drought and fend off beetles rather than producing seeds. As result, there were almost no piñon pine nuts to be harvested last fall on the Navajo Nation, where the nutritious nuts have been part of cultural tradition for centuries.

“The risks of climate change to forests are substantial and going up faster than we thought,” Anderegg said. The new physiological models of trees and ecosystems helps pinpoint exactly when and where forests are vulnerable, with the aim of making credible forecasts for forests in this century, giving landowners and policymakers more useful tools, he added.

Accurate new information is also valuable for climate policy, because many national carbon-reduction targets based on the Paris climate agreement include tree planting as a key tool to reduce emissions. But rapid forest change and catastrophic die-offs could put a monkey wrench in those plans. And in addition to the direct tree-killing effects of heat and drought, interactions with other disturbances like insects and other pathogens will magnify forest die-offs, he said.

Restoration and Resilience?

University of Montana forest ecologist Diana Six said the conclusions in the new research weren’t surprising because she’s always been skeptical of the projected beneficial effects of carbon dioxide triggering photosynthesis in plants.

“I was always amazed by the early predictions for enhanced growth of forests, especially in the West,” she said. Many of the models only included warmer temperatures or higher CO2 effects. The projections were made mainly by economists who assumed that only temperatures and CO2 affect tree growth, she added.

“No one seemed to consider water. With warmer temperatures and a longer growing season comes greater demand for water and we are getting less, not more, in most cases. That should have been a big red flag,” she said.

Six’s research focuses on tree-killing bugs, and she said it’s clear how global warming and insect devastation fit together. Heat causes drought-weakened trees to release different chemicals from healthy trees, and the bugs “are incredibly good at finding them,” she said.

And global warming has weakened a lot of trees in the West.

“Even with average rainfall it’s still a drought for trees now much of the time because of increased temperatures. Trees are tough, but they can only take so much. Some of the forests look like they’re fine, but they’re not, they are already near thresholds,” she said.

Some mature trees can survive conditions that aren’t supportive for them anymore. They have deep roots and can hunker down in survival mode for decades in dry conditions, but that doesn’t mean conditions exist for new growth. And not all old trees can survive.

“Some recent research shows that a lot of our forests may be genetically maladapted to the changing climate. We’re losing big trees faster and regeneration is not keeping up. This is not a sustainable pattern that we’re seeing,” she said.

But there is also critical information to be gleaned from the trees that aren’t killed.

“The trees that survive are very different genetically and chemically, and they also grow very differently. In some cases it’s the slower-growing trees that survive,” she said. That’s important information for forest restoration and resilience planning, she added.

“There are ways we can help our forests adapt, with space, sizing and composition. But eventually, you really have to get at adaptation. You have to get trees on the landscape that can survive in new conditions,” she said.

That would include leaving the few trees that survived massive beetle outbreaks, rather than cutting them down during the salvage logging of beetle-killed trees. Often, the loggers are eager to harvest the remaining live trees because they are worth more, but Six said it’s exactly those survivors that could help seed a new forest that’s more resistant to insects and warming.

The survivors may hold some of the secrets to ensuring that at least some forests will survive human-caused global warming. And they show that there is already some natural adaptation under way. The die-offs are natural selection working on a large scale, and for some trees, that might be enough to trigger an evolutionarily adaptive response, she said. After all, conifers have a huge amount of genetic diversity and have survived drastic climate change on a geological time scale over millions of years.

“Some of the things we are seeing are dreadful and devastating, but there are studies showing trees can adapt quite rapidly on an evolutionary level. But if we keep cranking up the temperature, there is never going to be enough adaptation possible,” she said.

PUBLISHED UNDER:CLIMATE SCIENCE BIODIVERSITY CONSERVATION FORESTS DEFORESTATION CLIMATE CHANGE

Regents’ Professor Dr. David Breshears discusses tree die-off …www.youtube.com › watch▶ 3:52 Meet Dr. David Breshears, a Regents Professor at the University of … and hear about his career studying how …Feb 20, 2019 – Uploaded by School of Natural Resources and the Environment

https://scholar.google.com/citations?user=JQOZ4cUAAAAJ&hl=en&oi=aoOffice Location: ENR2 N227Mailing Address: 1064 E. Lowell St.Tucson, AZ 85721

520-621-7259 daveb@email.arizona.edu

His research focuses on ecology-hydrology interrelationships, gradients from grassland to forest, transport and erosion of sediment by water and wind, and drought-induced tree die-off, all to aide in addressing climate change, land use, and pollutionTeaching: Classes taught include Dryland Ecohydrology & Vegetation Dynamics (WSM/RNR/EEB/HWRS 452/552), Leadership & Communication Skills for Environmental Scientists (RNR 596L), & National Climate Assessment (RNR 496G/596G) as well as frequent guest lectures.Research Topics: Climate Adaptation and SustainabilityEcohydrology and BiogeochemistryEcosystem ServicesPlant and Soil EcologyWatershed Management

Climate Adaptation and Sustainability

Natural resource managers in the Southwest are beginning to respond to the profound and rapid observed impacts of climate variability, and the anticipated impacts of projected environmental changes. We have observed wide-ranging changes, such as forest mortality, changes in species’ life cycles, massive wildfires, and dwindling surface water flows.

David D. Breshears | Institute of the Environmentwww.environment.arizona.edu › profile › david-d-bres…

PhD, Colorado State University, 1993. David D. Breshears is a Professor of Natural Resources in the School of Natural … A global overview of drought and heat–induced tree mortality reveals emerging climate change risks for forests.
A global overview of drought and heat-induced tree mortality …www.researchgate.net › publication › 222062857_A_gl…

Nov 11, 2017 – David D. Breshears. i. , E.H. (Ted) … Examples of recent climate-induced forest mortality … Increased tree mortality linked to drought and heat.
A global overview of drought and heat-induced tree mortality …hal.archives-ouvertes.fr › hal-00457602 › document

PDFFeb 17, 2010 – of drought and heat–induced tree mortality reveals emerging climate change risks for forests. Forest … Michel Vennetier f, Thomas Kitzberger g, Andreas Rigling h, David D. Breshears i, E.H. (Ted) Hogg j, … 22 USA (Colorado).by CD Allen – ‎2010 – ‎Cited by 4525 – ‎Related articles
On underestimation of global vulnerability to tree mortality and …esajournals.onlinelibrary.wiley.com › doi › fullAug 7, 2015 – David D. Breshears … 2010); and broad‐scale forest die‐off events (Breshears et al. … Locations of substantial drought‐ and heat‐induced tree mortality … and Colorado) highlight the effects of hotter drought on forest stress, …by CD Allen – ‎2015 – ‎Cited by 873 – ‎Related articles
A global overview of drought and heat-induced tree mortality …www.patrickgonzalez.net › images › Allen_et_al_2010

PDFA global overview of drought and heat–induced tree mortality reveals … Michel Vennetier f, Thomas Kitzberger g, Andreas Rigling h, David D. Breshears i, E.H. (Ted) Hogg j, … Rapid mortality of Populus tremuloides in southwestern Colorado,.by CD Allen – ‎2010 – ‎Cited by 4519 – ‎Related articles
A Dirty Dozen Ways to Die: Metrics and Modifiers of … – Frontierswww.frontiersin.org › articles › ffgc.2018.00004 › full

Oct 26, 2018 – Tree mortality events driven by drought and warmer temperature, often … species globally for drought–induced tree mortality is piñon pine, Pinus edulis. … ³Department of Forest and Rangeland Stewardship, Colorado State … drought in the Southwestern US (Breshears et al., 2005) and may be overly tied …by DD Breshears – ‎2018 – ‎Cited by 7 – ‎Related articles
Temperature response surfaces for mortality risk of tree …iopscience.iop.org › articleNov 17, 2017 – The temperature sensitivity of drought–induced mortality of tree … al 2014 2015) and observational (Breshears et al 2005) studies of drought have … In some regions where elevated tree mortality has been reported, drought and heat … two species (P. edulis and P. ponderosa) from the Colorado State Forest …by HD Adams – ‎2017 – ‎Cited by 18 – ‎Related articles
Precipitation thresholds and drought-induced tree die-off …www.fs.fed.us › pubs_other › rmrs_2013_clifford_m001

PDFJun 17, 2013 – Michael J. Clifford1, Patrick D. Royer2,3, Neil S. Cobb4, David D. Breshears5 and Paulette … focused on resolving mechanisms of drought–induced tree mortality, an evaluation of how … triggered by a combination of drought and heat – previously referred to as ‘global-change-type drought‘ (Breshears et al.,.by MJ Clifford – ‎2013 – ‎Cited by 68 – ‎Related articles
A Great Aridness: Climate Change and the Future of the …books.google.com › books“Temperature sensitivity of drought–induced tree mortality portends increased regional die-off under … Allen, Craig D., and David D. Breshears. “Drought, tree …William DeBuys – 2013 – ‎History

Timothy J. Brodribb, 23 September 2019

https://doi.org/10.1111/nph.16097 SECTIONS PDF TOOLSSHARE

What inspired your interest in plant science?

When I was 11 years old we moved from a grey industrial city near Manchester in the UK to the leafy paradise of Tasmania; I think after that baptism of greenery I really fell in love with trees. At university I realized that we did not know much about these magnificent organisms that so cleverly soak up the sunshine to power life on earth. Questions about how plants live, what makes them thrive and what makes them suffer and die seemed (seem) like the most important questions on Earth to answer. In my last year as an undergraduate at university I took a course with Professor Bob Hill who inspired me with tales of Australia’s transformation from rainforest to desert over millions of years of climate change: these evolutionary processes continue to fascinate me and are more relevant today than ever. I ended up doing a PhD with Bob, working on the physiological evolution of conifers.

Why did you decide to pursue a career in research?

I have enjoyed the freedom of not being much of a capitalist. This has allowed me to make decisions largely based upon interest rather than remuneration. Figuring out how plants work is the thing that interested me most, so when faced with choices I always chose research (rarely the most lucrative option). Thus, I am incredibly fortunate that research ultimately became my career, but it was more of a gravitational process than a career decision. I have benefitted enormously from fabulous fellowship programmes in the United States and Australia that continue to enable young researchers to manage their own research projects and follow their own passion and intuition. I believe that in an increasingly commercial world it is critically important to maintain an unencumbered pathway for ‘blue sky’ research.

What motivates you on a day‐to‐day basis?

The thrill of discovery is a great motivator for me. Plants guard their secrets well, so it is very exciting when you find a way into their world. It is easy to get carried away sometimes when you think you are on the brink of something new; I have to force myself to go home for dinner, or to go the beach for a surf and think about nothing for a while. I also get a tremendous amount of satisfaction when my students or postdoctoral students discover new things. I spend a lot of time peering over their shoulders in the laboratory. I like to think I am a motivating force, but I am sure that sometimes I may provide more advice than is desired.

Box 1.

I completed my undergraduate studies in Plant Science at the University of Tasmania (Australia) (UTAS). Staying put, I received my PhD at UTAS in 1997. After a year postdoctoral study with my supervisor (Professor Bob Hill), I spent 3 years working as a postdoctoral student with Missy Holbrook at Harvard University (Cambridge, MA, USA). I won a Putnam Fellowship at the Arnold Arboretum (Boston, MA, USA) for a further 2 years. After this I returned to Tasmania in 2005 and was awarded two successive fellowships funded by the Australian Research Council. I was awarded a permanent position at the University of Tasmania in 2017. My current interests include all aspects of plant hydraulics, plant mortality, and links between hydraulic and photosynthetic function including stomatal physiology and anatomical associations. I continue to look into evolutionary patterns in water relations and gas exchange physiology through the different vascular plant lineages.

Tim has been an Associate Editor of New Phytologist since 2019, and was previously a Co‐editor of New Phytologist from 2010.

For more information on Tim, visit http://www.brodribblab.org.au/ or www.utas.edu.au/profiles/staff/plant-science/Tim-Brodribb

ORCID: Timothy J. Brodribb https://orcid.org/0000-0002-4964-6107.

Is there anyone that you consider to be a role model?

Creativity is an important part of scientific discovery, and I admire those who are able to combine lateral thinking, imagination and experimental design to reveal new concepts. I remember reading a paper by John Sperry and Mel Tyree during my PhD and being so impressed that these scientists could imagine that cavitation in the transpiration stream was a limiter of plant survival: it seemed such a lateral concept at the time. I have always greatly admired Graham Farquhar (Australian National University, Canberra), his ability to come up with so many good ideas over his 40+ year career is inspirational, and he is still as keen as ever. The passion for discovery in science that I see among my colleagues is something I respect deeply. The dedication of people like Missy Holbrook (my first postdoctoral supervisor at Harvard University, Cambridge, MA, USA) and Jennifer Powers (the queen of dry tropical forest ecology), who successfully combine scientific discovery and motherhood, provides a tremendous role model for women in science.

What are your favourite New Phytologist papers of recent years, and why?

I just finished writing a New Phytologist Editorial with Nate McDowell and Andrea Nardini about hydraulics (McDowell et al., 2019). During this process it was impressive to see how many critical hydraulics papers have appeared in New Phytologist since the dawn of hydraulic science (c. 40 years ago). So it is hard to pick a favourite, but I really like all Taylor Feild’s papers about early angiosperm evolution (see for example the Tansley review Feild & Arens, 2005). The paper on pit anatomy by Frederik Lens and colleagues is a corker (Lens et al., 2011), and Max Larter’s paper on the evolution of drought tolerance in the conifer Callitris is great (Larter et al., 2017); they are such amazing plants.

What is your favourite plant, and why?

This is a tricky question, there are so many plants that I love. Among the conifers, I think that the Fijian Acmopyle sahniana is my favourite. This extraordinary ghost of a conifer (its leaves are totally white due to epicuticular wax) is nearly extinct. In order to find this species during my PhD, I had to find an old village chief in Fiji who knew where the plants were, then walk 13 hours through the jungle to discover them hidden on a high ridge in cloud forest. I think we were among the first people to see them in cone. Callitris is another favourite conifer because it has unbelievably bulletproof xylem, and Parasitaxus because it is such a freak of a red parasitic conifer hidden in the hills of New Caledonia. I am very fond of the moss Dawsonia, a giant of a plant that can grow up to 1 m tall in Papua New Guinea; it is the Sequoia of mosses. The lycophyte Selaginella pallescens is very cool. It covers the forest floor in parts of Costa Rica, invisible during the dry season, until it rains, then 5 minutes later it transforms the entire forest floor from grey to verdant green. Among the angiosperms, I really like Nothofagus, not only because it is beautiful genus of trees, containing Australia’s only winter deciduous species, but also because it links together the ancient biogeography of the southern continents.

WHOLE PLANT AND ECOPHYSIOLOGYYou have access

Stomatal Closure during Leaf Dehydration, Correlation with Other Leaf Physiological Traits

Tim J. Brodribb, N. Michele Holbrook

Published August 2003. DOI: https://doi.org/10.1104/pp.103.023879

Abstract

The question as to what triggers stomatal closure during leaf desiccation remains controversial. This paper examines characteristics of the vascular and photosynthetic functions of the leaf to determine which responds most similarly to stomata during desiccation. Leaf hydraulic conductance (K_leaf) was measured from the relaxation kinetics of leaf water potential (Ψ_l), and a novel application of this technique allowed the response of K_leaf to Ψ_l to be determined. These “vulnerability curves” show that K_leaf is highly sensitive to Ψ_l and that the response of stomatal conductance to Ψ_l is closely correlated with the response of K_leaf to Ψ_l. The turgor loss point of leaves was also correlated with K_leaf and stomatal closure, whereas the decline in PSII quantum yield during leaf drying occurred at a lower Ψ_l than stomatal closure. These results indicate that stomatal closure is primarily coordinated with K_leaf. However, the close proximity of Ψ_l at initial stomatal closure and initial loss of K_leaf suggest that partial loss of K_leaf might occur regularly, presumably necessitating repair of embolisms.

Stomata appear in the fossil record approximately 400 million years ago (Edwards et al., 1998) at approximately the same time as the evolution of an internal water conducting system in plants. Stomatal evolution is believed to be a response to selective pressure to optimize the ratio of CO₂ uptake to water lost during photosynthesis (Raven, 2002). The evolution of internal conduits for water transport added a level of complexity to optimizing gas exchange during photosynthesis, because of the dependence of water supply capacity upon the water potential in the plant (Sperry et al., 2002). This complexity is evidenced by the variable effects of leaf water potential (Ψ_l) and vapor pressure deficit on stomatal movements among species. Although stomatal aperture responds predictably to guard cell turgor (Franks et al., 1995), the relationships between guard cell turgor and either transpiration (E) or mesophyll turgor are still hypothetical (Buckley and Mott, 2002). Amid mechanistic debate as to the process of stomatal closure, the fundamental question of why stomata close remains unanswered. Given that stomata may predate the evolution of xylem (Edwards et al., 1998; Raven, 2002), it is appropriate to question whether it is vascular or other tissues that provide the trigger for stomatal closure.

We focus here on the question of what sets the point of stomatal closure in leaves. That is to say which aspect of a plant’s physiology is sufficiently sensitive to decreasing Ψ_l that it requires stomata to be closed and photosynthesis sacrificed to protect from loss of function and damage. A key assumption here is that traits responsible for determining the stomatal response to leaf desiccation are coordinated with physiological characters dictating the sensitivity of the metabolic or transport machinery of the plant to water stress. Candidates for these coordinated traits are likely be located in or near the leaf, because transduction of signals from far upstream of the leaves is generally slow relative to the half-time for stomatal responses to perturbations in leaf water balance (Tardieu and Davies, 1993). Additionally, it would be expected that among these traits, adaptation to sustain lower Ψ_l would come at a significant cost. Features such as the vulnerability of leaf xylem to cavitation and the resistance of leaf cells to collapse fulfill these criteria in that they are prone to failure (either structural or functional) under conditions of low water content and are both costly to augment. However, it is clear that photosynthesis in most species becomes irreversibly depressed when leaf relative water content (RWC) falls to around 70% (Lawlor and Cornic, 2002), and thus the resistance of the photosynthetic apparatus to desiccation is also a potential trigger for stomatal closure.

In this paper, we examine the vascular and photosynthetic apparatus of the leaf to test whether stomatal closure is correlated with the water-stress tolerance of different leaf tissues or functions. This work follows a number of studies that have demonstrated similarity between the response of both stomatal conductance (g_s) and stem xylem cavitation to decreasing Ψ_l (Salleo et al., 2000; Hubbard et al., 2001; Cochard et al., 2002). It is likely that this correlation between stomatal closure and xylem cavitation will be most prominent in the leaf, given that leaf minor veins appear more prone to cavitation than stems (Nardini et al., 2001), and that leaves represent a large proportion of the whole plant hydraulic resistance (Nardini, 2001; Brodribb et al., 2002). Surprisingly there have been few studies that have quantified the effect of Ψ_l on leaf hydraulic conductance (K_leaf) in woody plants (Nardini et al., 2001), probably due to technical difficulties in measuring the hydraulic conductance of the leaf.

Here, we quantify the relationship between Ψ_l on K_leaf by examining the kinetics of Ψ_l relaxation in rehydrating leaves. A number of studies have examined the dynamics of pressure equilibration in leaves to estimate components of their hydraulic resistance. For example, Cruiziat et al. (1980) and Tyree et al. (1981) estimated K_leaf from the kinetics of water flow into dehydrated sunflower leaves, whereas Nobel and Jordan (1983) used the time constant for water potential equilibration following overpressurization to estimate leaf mesophyll transfer resistance. In this study, we measured the rate of relaxation of Ψ_l during the rehydration of leaves desiccated to different water potentials, enabling the quantitative determination of leaf vulnerability to cavitation…

Tim Brodribb

Plants can only function on land by virtue of beautifully efficient systems that regulate water transport and evaporation. My research focuses on how water transport and water use have evolved together in plants. The fundamental questions my research addresses are

How do characteristics of the plant vascular system limit productivity?
How does xylem and stomatal behaviour limit survival and distribution of plant species?
How have the performance of hydraulic and stomatal systems changed through evolutionary time?
How do hydraulic characteristics determine species ecology?

** Developing answers to these questions provides critical knowledge for diverse applications, ranging from understanding the impacts of past and future climate change, to developing more productive crop varieties.

Current Publications

Triggers of tree mortality under drought Download
Mesophyll cells are the main site of abscisic acid biosynthesis in water-stressed leaves Download
Leaves, not roots or floral tissue, are the main site of rapid, external pressure-induced ABA biosynthesis in angiospermsFeng-Ping Zhang, Frances Sussmilch, David S Nichols, Amanda A Cardoso, Timothy J Brodribb, Scott A M McAdam; Leaves, not roots or floral tissue, are the main site of rapid, external pressure-induced ABA biosynthesis in angiosperms, Journal of Experimental Botany, Volume 69, Issue 5, 23 February 2018, Pages 1261–1267, https://doi.org/10.1093/jxb/erx480Download
Guard cells in fern stomata are connected by plasmodesmata, but control cytosolic Ca2+ levels autonomouslyVoss, L. J., McAdam, S. A., Knoblauch, M. , Rathje, J. M., Brodribb, T. , Hedrich, R. and Roelfsema, M. R. (2018), Guard cells in fern stomata are connected by plasmodesmata, but control cytosolic Ca2+ levels autonomously. New Phytol, 219: 206-215. doi:10.1111/nph.15153Download
Mapping xylem failure in disparate organs of whole plants reveals extreme resistance in olive rootsRodriguez‐Dominguez, C. M., Carins Murphy, M. R., Lucani, C. and Brodribb, T. J. (2018), Mapping xylem failure in disparate organs of whole plants reveals extreme resistance in olive roots. New Phytol, 218: 1025-1035. doi:10.1111/nph.15079Download

View All Publications by Tim Brodribb

Room 111 , Life Sciences Building

+61 3 6226 1707 (phone)

+61 3 6226 2698 (fax)

timothyb@utas.edu.au

Tim Brodribb is an Associate Professor of plant physiology and an ARC Future Fellow. His research is focused on how plants transport and use water, which is one of the most important factors in determining the survival or extinction of plant species in different environments. Associate Professor Brodribb was awarded a Putnam Fellowship in 2007 from the Arnold Arboretum at Harvard University, the Grady L. Webster Structural Botany Prize in 2009 from the American Journal of Botany, and the W.S. Cooper Award from the Ecological Society of America in 2012 and a Thomson Reuters Citation and Innovation Award in 2015.

Biography

1999-2000: Post-doctoral Fellow (University of Tasmania).
2000-2004: Post-doctoral Fellow (Harvard University, Organismic Evolutionary Biology)
2005: Putnam Fellow (Arnold Arboretum, Harvard University)
2006-2010: Australian Research Fellow (University of Adelaide/ University of Tasmania)
2010- 2014: Future Fellow (UTAS A/Professor)
2015: Senior Research Fellow (UTAS)

Career summary

Qualifications

Degree	University	Country	Date of award
PhD	University of Tasmania	Australia	1997
BSc (1^st Class Hons)	University of Tasmania	Australia	1992

Languages (other than English)

Spanish, French

Teaching

Environmental Stress, Stomatal Responses, Vascular Plants, Water Stress, Leaf Hydraulics